Still running hot, any advice?

[circa1968]

5 hours ago, 93 venture said:

what about coolant temp, have you used your temp gun to check it. i wonder if the coolant system could have a air pocket causing a hot spot ? the manual says it hold 3.7 qt. Or  possible water pumps isn't moving coolant. even if it had a lean cylinder being a water cooled engine one would think it could take the extra heat  away except what comes off of the header pipe. what did your plugs look like did you take any pictures of them?

 

I wondered about that too.  I have been checking top & bottom of radiator, I don't have the #'s off the top of my head, but did not seem out of the ordinary.  In the range of 200 deg, IIRC.   I just put in iridium plugs and will get a pic of the old plugs.

[circa1968]

2 hours ago, BlueSky said:

Well now,  I went for a ride on my 07 RSV today and checked the exhaust temps afterwards.  #1 and 2 checked mid-200s.  #3 checked almost 400 and #4 checked less than 200.  So,  syncing the carbs is on my "to do" list now?  

My sync gauges showed up at the end of the day today, a day late.  So much for Amazon Prime.  I will be doing my very first carb sync tomorrow.   Sorry to hear you are having same issue, but I feel a bit better now knowing this may be a more common, & easily solvable issue, than I thought.

Still hoping this is the root cause of my heat issue (my heat issue being me boiling in short order). 

[BlueSky]

My 07 is similar to yours. It only has about 24k miles on it so it's been sitting a lot too.  I don't ride it that often and one cylinder seems dead on initial startup and starts firing after warming.  I suspect that cyl is #4 that is running a little low in temp.  I bought the same sync gauge set but I stupidly paid for the K&L brand which is also made in Taiwan I found out after it arrived.  I suspect it's the very same set you bought for half as much.  I'm changing the spark plugs too and I'm not buying the NGK brand.  

When I bought the ZN700 in 2009, it only had 1k miles on it.  One spark plug was dead.  I replaced them with NGK and recently with 6k miles on the bike one of those was causing the low temp in cyl #1.  So, I'm getting a low opinion of NGK plugs.  

[CaseyJ955]

1 hour ago, BlueSky said:

I bought the same sync gauge set but I stupidly paid for the K&L brand which is also made in Taiwan I found out after it arrived.  I suspect it's the very same set you bought for half as much. 

I thought K&L was Japanese, I got K&L parts for the carbs that were all Japanese. I hope it's just the gauge that we have not lost a valuable source for non-Chinese parts.  I hold Taiwan in very high regard,  but sadly the quality control in Taiwan is about on par with China. I've been using the UK made Carbtune Pro that seems quite popular here and on the Vmax site. It was less than $100 and took no time at all to arrive.  Carb balance is pretty delicate stuff. One way I would test gauges of unknown descent is to plug them in on a bike and get it all balanced, then swap the vac ports on the gauge and see if it's still about even.  I found some sync gauges I had to straight up toss for this reason, some weren't even close.

Also, I recall some discussion, I think I read it on the Vmax forum but not sure, it's been a while.  Did Yamaha use different jet sizing between front and rear banks, or maybe one rear cyl, to address the temp inconsistencies? Maybe just for a year or two?  This did not turn out to be true on my Gen1 Vmax or Gen1 Venture but I'm pretty sure it was in regards to Gen2.  I've never owned or wrenched a Gen2 so I have no personal experience with specific jetting, just throwing it out there in case it's a possible factor. I thought it was odd so this much of it stuck in my head.

 

[BlueSky]

After my sad experience with the Motion Pro manometers, I decided I didn't want that type of gauge.  Using tees I connected all four gauges to my hand held mityvac and checked. All 4 gauges read the same.  So, I'm happy with the gauge set.  

[circa1968]

So, after syncing the carbs, both back exhaust (#1 & 3) are now running 200 deg hotter than the front.  wth?  Normal?  I'm going to buy a small hand vacuum pump to test the gauges and verify they are all consistent.  Idle is bouncing around within a 100-150 rpm range.  Normal?

Also, the bike still runs hot, its like riding a weber bbq grill.  I checked the tank temp, right where my legs touch and it was 105 degrees - with a nearly full tank of gas.   I've been thinking of ways to check the whole system to verify coolant is working its way all the way through.  I suspect either blockage or an air gap somewhere, although I did "bleed" it when changing coolant.

[BlueSky]

You can also test the gauges by teeing the lines together and hooking the last line to one carb vacuum connection.   Although I love my mityvac!

[circa1968]

Quick update.  I think (hope) good news on the running hot issue!  I took it out for a short run today and it subjectively felt much better, so when I pulled back in, took a few quick measurements while it was still running.  The radiator was measuring 178F top & bottom.  I went back through some notes and found I had measured 220F a few weeks ago!  For what its worth, it was in the 90's first reading and in the 60's today.  Here's what I did yesterday:

1) Drained coolant.

2) Removed fins & emptied the cyclinder cooling jackets.

3) Refilled w/ distilled water & bled all the air out of the system.

4) Repeated steps 1-3.  Yes, two flushes w/ distilled water.

5) After completely draining the system of water, I used some red-neck engineering to apply air pressure @ the radiator cap with one cylinder jacket plug removed at a time.  This blew out more than what was simply drained.

6) Removed the water pump cover.  A bit more water drained out and I did not see any thing abnormal there, so buttoned it back up.

7) Refilled w/ 50/50 mix, bled out all air pockets and wrapped it all up.

During this process, there were small bits of black gunk, maybe slime or degraded rubber.  I'm not sure what it was, but not a lot and very small bits.  Also saw 2-3 small white pcs of what looked like calcium buildup, but not much of that either and they were quite small.

The one thing that surprised me was behind cylinder plug #3, I saw a small pc of something with a tan color.  Using a pick and tweezers was able to retrieve a small pce of what looked like thin plastic.  It was a bit chewed up and deformed (see attached).  I have no idea what this is, but its no longer in my cooling system!

I can't say if this unidentified object, an air pocket in the system or something else was causing the heat issue, but it seems to be behind me now (hopefully)!

I synced the carbs and still getting a high temp reading on exhaust #1.  Also, idle is all over the place but that could also just be the cheap ebay tach I'm using.  It does idle rough/low until thoroughly warmed up.

I will be changing the fuel filter next,  and then completely drain the gas tank, make sure it is clean and go down to home depot to buy an insanely expensive gallon of REAL gasoline, with no ethanol.  The latter is just to start with a baseline of ruling out crappy gas.

Question for the gurus here:  @ 21k miles & 13 years old, should I take it in for a valve adjustment?  I know it can't hurt, but in your opinions is it worth it? 

Thank you all again for your ideas, support and encouragement!

[BlueSky]

When you synced the carbs, did you try adjusting the idle mixture screws?  

I'm in the process of valve adjustment on my Kawasaki ZN700 four.  It only has 6k plus miles on it and the valves are too tight to meet spec on 3 of the 4 cyl and the 4th is at the lower edge of spec.   I have revved the crap out of that engine though and a few times over revved it when I missed a shift.  It will not shift quickly when it's revved tight. (10,000 rpm redline) The Yamaha V4s may be entirely different though.  Cowpuc says he ran his 5  XVZ1200s over 200k miles and never adjusted the valves!  

[circa1968]

I did not adjust the mixture screws.  Are those the ones behind the plug that has to be drilled out?  I will wait to see if a clean filter and clean tank with fresh gas helps before jumping into that.

[BlueSky]

1 hour ago, circa1968 said:

I did not adjust the mixture screws.  Are those the ones behind the plug that has to be drilled out?  I will wait to see if a clean filter and clean tank with fresh gas helps before jumping into that.

Yep, those are the ones.  I think the standard advice is to start with them 2 1/2 turns from bottom.  When you check bottom, be gentle.  Some fine tuning of the idle mixtures may help.  

[ragtop69gs]

Did the valve shims at 60k miles and found 1 exhaust valve only slightly tight. There was still lots of life left if I'd have left it alone.

[Patch]

On 11/7/2020 at 7:50 PM, circa1968 said:

I synced the carbs and still getting a high temp reading on exhaust #1.  Also, idle is all over the place but that could also just be the cheap ebay tach I'm using.  It does idle rough/low until thoroughly warmed up.

So there's a lot to cover: Yes @BlueSky sync time. Yes @CaseyJ955 you are right regarding the jets.

Some time back I think in February when I came back to the forum we laid out some theory on carb syncing and some of the common miss conceptions that rookies tend to make, worth looking back to find that (I believe it was with regards to carb sync gauges)

I am going to forget much of what I have floating around my head as I write, maybe I'll add a couple of posts.

The UFO looks to me to be sealant that came loose?

The one thing I would have done differently with regards to flush is to use a chemical flush, not just water.

But that is not what I see as the problem, @cowpuc / Grasshopper was leading you in the right direction early in the thread. He also took his big clumsy foot off the peddle to soon as he I think was not wanting to push you past your comfort zone! I on the other hand am Canadian and there colder and more direct.

Between 230 and 250 f is a good place, 400 @ idle is just not acceptable and is my opinion that running it at that will only shorten #1 life span.

Somebody F*** with #1 and one is the first I would focus on. Having said that, it is possible that this has lead to some carbon buildup above the valve face (the bell shape area) this will reduce flow volume especially at higher rpm which will cause the mass to sync more heat then then natural coolent flow can absorb! Is why that mechanic mentioned it.

Again I don't think that is the problem yet either.If it were me I would start with a "bench sync" you can do this with the carbs installed.

Pull the side covers off the slides, 4 crews per

There is a spring behind them, it is not going to fly just be aware they are there and be gentle with them,

Eash cap gets its 4 screws and spring place together,

then gently pull the diagram out placing it by the cap to each carb,

Each set will go back t o the same carb it came from!

Go to the hardware and purchase the longest 1/4 or 3/16 th inch drill bit, often you find the longest one have the carbide tip used for tile.

Withe the air box removed and the slides out of the way:

Set the # screw so that the throttle plate is just touching the shank of the bit, not resting enough to restrict it but just enough to let the bit slide smoothly!

Repeat that for each carb, this is easy stuff and you will not get mixed up in parts order!

You will likely find that each time you set one to the bit the other will change some and the "gap" between the carb bore and throttle plate will tighten or loosen, if so then you are winning! This may take 3 or for rounds before you are satisfied with the results.

Once you are then we will walk you through the next very simple steps.

YOU CAN DO THIS   

[Patch]

I for one would like the chance to read the plugs in a way that mention which cylinder they come from.

[circa1968]

Thank you Patch.  I understood your procedure perfectly and will follow it.  Unfortunately, I did not track the plugs when I removed them, but have a few miles on the new plugs, so will pull them & get pics to see if that is of any use.  I will also take pics of the old plugs, for what that's worth.

I'm pretty mechanically inclined and have an engineering degree and a quick study of most things that come along.  I like challenges, just have zero experience working on engines or carbs and don't want to screw anything up.  But that said, I've learned a lot already and each new step leaves me wanting to learn/do more.  Fascinating stuff.

I did get out for a ride yesterday.  the cooling issue seems to be much better.  I noticed it getting warm a couple times when in traffic, but out on the twisty road had no issues.  Of course it was also in the 60's vs. 90's when I first got the bike and noticed the heat.

At the end of my ride, the radiator was reading ~200F, a little warm, but seems mostly normal.  #1 & #3 (two back) were reading 400+ on the exhaust pipe (#3 was not this high previously).  #2 & 4 were reading ~200ish but I can only check those on the mounting flange, not the pipe itself. 

For what its worth, when I check the mounting flange on #1 & #3, instead of the exhaust pipe, they are also 200ish.

Again, I sincerely appreciate the help and information!

 

[Patch]

36 minutes ago, circa1968 said:

Thank you Patch.  I understood your procedure perfectly and will follow it.  Unfortunately, I did not track the plugs when I removed them, but have a few miles on the new plugs, so will pull them & get pics to see if that is of any use.  I will also take pics of the old plugs, for what that's worth.

That would be very be very helpful to the boys:

I'm pretty mechanically inclined and have an engineering degree and a quick study of most things that come along.  I like challenges, just have zero experience working on engines or carbs and don't want to screw anything up.  But that said, I've learned a lot already and each new step leaves me wanting to learn/do more.  Fascinating stuff.

This is good to know, so expect that the boys here have made enough mistakes to walk blindfolded thru traffic on the 401, just ask Carl  

I did get out for a ride yesterday.  the cooling issue seems to be much better.  I noticed it getting warm a couple times when in traffic, but out on the twisty road had no issues.  Of course it was also in the 60's vs. 90's when I first got the bike and noticed the heat.

The rad temps work on a different scale it will at first spike as a result of the Tsat opening then down from there. Later on as you live in a warm climate consider adding some bite to the rad flush. I would be more inclined to add a 1/2 can of seafoam to the crankcase the the fuel tank as well.

At the end of my ride, the radiator was reading ~200F, a little warm, but seems mostly normal.  #1 & #3 (two back) were reading 400+ on the exhaust pipe (#3 was not this high previously).  #2 & 4 were reading ~200ish but I can only check those on the mounting flange, not the pipe itself. 

RIGHT RIGHT ON, as I was expecting, very good feed back! So answer yourself this question, what changed that could make that difference?

For what its worth, when I check the mounting flange on #1 & #3, instead of the exhaust pipe, they are also 200ish.

Again, I sincerely appreciate the help and information!   As do we for bringing the challenge forward!

 

Take a look at the quoted area its how I work best over the net:

[cowpuc]

Seeing I got summons here (thanks @Patch) I thought I better join in on the fun and share some more, maybe it will help - maybe it won't back yard wrench spinning free advice.. 

Noting now @circa1968 that you have been taking your temp reading off different spots on both the front and rear jugs changes the dynamics a lot IMHO. Taking the reading right off the header itself on the rears and off the clamps on the front should actually read about what you are describing.. The headers are way thinner than the clamps and are also in direct line of fire for exhaust flames,, to me what you are saying makes sense.  Also, those front jugs are directly exposed to air flow with the rear jugs getting no where near the exposure. I ran/rebuilt/tuned/modded numerous HD air cooled over the years and being air cooled - one of the things I did was ran dual carbs (or later injected with a race tuner was even easier to do this) and then run fatter on the rear jug to keep it cooler.. Lean = hot IMHO.

I always found the following advice a little easier to do on a single, or even a twin cylinder scoot but with a little focus on my part I can usually adjust by ear a multi jug, multi carb in the following way too.  Another way besides the following is with either a sniffer or a Color Tune (so you can actually look into the combustion chamber and adjust for the blue flame) but again, I have found following to work well. 

If lean does equal heat than it may be possible that you are seeing a lean condition.. That would not surprise me because it seems like for many years bike manufacturers have been actually outputting scoots that run extremely lean since new, maybe due to EPA regs,, maybe not.. Maybe I am even wayyyy off base with that comment but it seems that way to me..  I have noticed lean idle circuits also causing erratic idle and also stumble right off the bottom when you crack the throttle,, a bog so to speak.. The way an idle circuit works, at least in my pea brain, is that with the throttle plates closed meaning your throttle is twisted at all and your throttle cable has slack in it, vacuum forms behind the throttle plate and fuel/air mix is drawn into the throat of the carb thru that set of little holes you will see back there.  One of the ways I always used, right or wrong it worked for me, to know that my low speed jets were correct size and that I used for setting my air screws with NO sniffer or carb tune was by ear tuning.  Simply run your air screws down to bottom lightly and back them out a turn, start your bike and let it warm up so it is no longer needing choke, set your idle at 1000 rpm, now adjust the air screw and adjust it out till it reaches top r's - there should be a point where it reaches top rpms and if you keep unscrewing it will falls off again,  then screw it back in till it reaches top r's again, now screw it in farther and it will fall off again. The "sweet spot" of top R's on the air screw is where I always found the perfect idle circuitry tune.  Now if you run the screw back to bottom and note the turns it takes to get to a soft bottom - if the turns equal between 1 and 3 turns out you have the correct idle/low speed jet in that carb. If the top r's are below 1 turn your low speed jet is to small, higher than 3 turns out and your low speed jet is to high. Make since?

If so, and I have used this method for years in tuning, than you can now see where you could use that logic in diagnosing whether you are dealing with a lean low speed circuitry caused by crud buildup in one of your carbs or not simply by tuning them. 

Right off idle and up to WOT (wide open throttle) and the tapered metering rod hanging off the slide into the emulsion tube and the main jet at the bottom of the tube take over.  I spent a couple years doing final tune on small 1 pot Hondas at a Honda dealership and 90% of the final tune work on those brand new bikes right out of the crate was moving the E clip on that jet needle hanging from the slide to get em to run right.. Most of the time this meant fattening em up so they didnt bog when I wacked the throttle.  Because our V-4's carbs do not have E-clips I am running shimmed metering rods in mine right now.  Shimming them out gives you a fatter off idle/mid range/WOT,, lowering them will lean er down.. Why do I mention this? Because,, IMHO, you could - for very little money - fatten up a jug or two and see if your temps drop..  If they did, again IMHO, this could indicate a partially blocked main.. Make since?  

I know,, getting long winded,, dont blame me, blame @Patch lol

[cowpuc]

On 11/7/2020 at 11:15 PM, BlueSky said:

When you synced the carbs, did you try adjusting the idle mixture screws?  

I'm in the process of valve adjustment on my Kawasaki ZN700 four.  It only has 6k plus miles on it and the valves are too tight to meet spec on 3 of the 4 cyl and the 4th is at the lower edge of spec.   I have revved the crap out of that engine though and a few times over revved it when I missed a shift.  It will not shift quickly when it's revved tight. (10,000 rpm redline) The Yamaha V4s may be entirely different though.  Cowpuc says he ran his 5  XVZ1200s over 200k miles and never adjusted the valves!  

Yep,, that is a fact @BlueSky,,, out of my 6 xvz1200's, 5 of which were/are 83's and 1 84 I have never ever opened one up and did the valves.. I have also never ever ran synthetic oils to accomplish that BUT I always have kept clean oil in em,, cheap stuff, usually 20/50 (ran Walmart Supertech for many years and then when wally world stopped carrying that cheap stuff I jumped over to Family Dollar 20/50). Of those 6 bikes, all ran out well over 200k, I know for certain that 3 of them were never opened up from new.. 2 of them I am uncertain about whether or not a previous owner had the valves checked cause I did not know enough of their history BUT, even those were low mileage, blown 2nd gear bikes with under 35k on em so I doubt it.. Now get this - you should find this interesting Sky cause I sure do, the last one, Tweeksis, the one we ride now, had her valves adjusted SEVERAL times (may have 10 or 12 times, cant remember) in her early life,, I know this because Carbon One gave me her complete maintenance and repair work history schedule records that "DenDen" kept on her and those adjustments are recorded right there in black and white. I have no doubt of the honesty of those records as even @Squidley, a really good friend of mine - straight shooter that Squid, has stated he knew DenDen (correct me if I am wrong on this Brad and am thinking of someone else) and DenDen was a gearhead.  Ironically, Tweeksis's valves are some of the loudest valves I have ever heard on any of my 1st Gens.. I keep thinking that maybe DenDen set them on the high side for break in purposes,, not sure.  DenDen also did repair the 2nd gear in Tweeksis too,, thats right,, she is my ONLY complete trannied 1st Gen scoot out of all those miles and miles and miles LOL. 

On a side note,, do I advise just runnin em till she drops,,, nahhhh.. I only did that because back in the day, blown 2nd gear Ventures were all over the place CHEAP and after the first one proved reliable well past 200k with no 2nd gear, I just ran em till they dropped and then grabbed another for a few bucks - it was never worth the time to open one up and fool with the valves or tranny or crank or whatever else IMHO - I always had TONS of other bikes to work on around the shop - these Yams were my go to bike for just riding em out.  Another of my IMHO's, I have a hunch that something changed in Mom Yams quality control in the newer V-4's or something.. I have heard of many many more valves going tight on the new ones for some reason,, it just seems like that. This may sound crazy but that also goes for fuel pumps and rear shocks too.. I also have noticed, what seems to me anyway, more Regulators failing too.  Just some thoughts.. Maybe folks who have owned both for years could share thoughts on that either way. Be an interesting thread maybe,, maybe not..

Puc

[bpate4home]

OK b4 y'all run me down I did do a text search on all the posts. Before I joined I had an '06 that started running hot on me. I went through a lot of stuff and spent a couple hundred on parts and the bike kept running hot. I'm on a ride with a group, get stuck in traffic, the temp light goes on and have basically given up thinking out loud of selling the bike. I open the manuals on my laptop as soon as we get to the Hotel and Pour through the electrical first. No reason just did.  Then it hit me The radiator fan must not be coming on. I start looking for a replacement. The that light bulb moment, the fuse for the fan. Finally find it and replace it.  It did not look blown but that did the trick.  Just a thought. 

[circa1968]

Hi Puc, Up until this last ride, and maybe one other time, the two back pipes did not read the same.  I am able to take the exact same reading (directly on the pip, same angle, etc) on both of them.  #1 is always ~400+ and #3 was reading the same (~200) as I got on the #1 & #2 flanges. 

I guess I made a bad assumption there on those readings (pipe vs. flange).  Part of my learning/education process.   I guess I see now the difference in thermal mass, but not sure why I was seeing such a difference, directly on the #1 & #3 pipes before.

And for what its worth, #1 gets to that temperature within minutes.  From what I'm learning from all you zen masters, that sounds like it is running lean and now maybe the same for #3.  

I'm going to follow Patch's bench sync advice and see what comes next.

@bpate4home Yeah, I hear you and having an EE background that was my first instinct also.  I hooked up 12 v to the fan connector and confirmed it came on and then also got her warm & let it sit until the fan kicked on to confirm all the other sensor & control circuitry works. 

If it makes small sparks, I understand it.  Its all this big, controlled explosion stuff that's outside of my wheelhouse!

[Squidley]

10 hours ago, cowpuc said:

Yep,, that is a fact @BlueSky,,, out of my 6 xvz1200's, 5 of which were/are 83's and 1 84 I have never ever opened one up and did the valves.. I have also never ever ran synthetic oils to accomplish that BUT I always have kept clean oil in em,, cheap stuff, usually 20/50 (ran Walmart Supertech for many years and then when wally world stopped carrying that cheap stuff I jumped over to Family Dollar 20/50). Of those 6 bikes, all ran out well over 200k, I know for certain that 3 of them were never opened up from new.. 2 of them I am uncertain about whether or not a previous owner had the valves checked cause I did not know enough of their history BUT, even those were low mileage, blown 2nd gear bikes with under 35k on em so I doubt it.. Now get this - you should find this interesting Sky cause I sure do, the last one, Tweeksis, the one we ride now, had her valves adjusted SEVERAL times (may have 10 or 12 times, cant remember) in her early life,, I know this because Carbon One gave me her complete maintenance and repair work history schedule records that "DenDen" kept on her and those adjustments are recorded right there in black and white. I have no doubt of the honesty of those records as even @Squidley, a really good friend of mine - straight shooter that Squid, has stated he knew DenDen (correct me if I am wrong on this Brad and am thinking of someone else) and DenDen was a gearhead.  Ironically, Tweeksis's valves are some of the loudest valves I have ever heard on any of my 1st Gens.. I keep thinking that maybe DenDen set them on the high side for break in purposes,, not sure.  DenDen also did repair the 2nd gear in Tweeksis too,, thats right,, she is my ONLY complete trannied 1st Gen scoot out of all those miles and miles and miles LOL. 

On a side note,, do I advise just runnin em till she drops,,, nahhhh.. I only did that because back in the day, blown 2nd gear Ventures were all over the place CHEAP and after the first one proved reliable well past 200k with no 2nd gear, I just ran em till they dropped and then grabbed another for a few bucks - it was never worth the time to open one up and fool with the valves or tranny or crank or whatever else IMHO - I always had TONS of other bikes to work on around the shop - these Yams were my go to bike for just riding em out.  Another of my IMHO's, I have a hunch that something changed in Mom Yams quality control in the newer V-4's or something.. I have heard of many many more valves going tight on the new ones for some reason,, it just seems like that. This may sound crazy but that also goes for fuel pumps and rear shocks too.. I also have noticed, what seems to me anyway, more Regulators failing too.  Just some thoughts.. Maybe folks who have owned both for years could share thoughts on that either way. Be an interesting thread maybe,, maybe not..

Puc

You are correct, Dennis was a serious gearhead. Very meticulous with any maintenance he did on any machine. If he did the work, it was done correct to perfection.

[Patch]

Lets see if I can confuse Puc and maybe connects some dots

B4 what you describe is an overheating issue that is simple to understand in that a component essential to the design is simply not Qing in . So the Tsat stays open and the cooling cycle is absent, the btus continue to accumulate. That make the fix simple.

When I troubleshoot I easily build mental working models and I check the boxes. If the theories I build off of are correct then I can fallow the logic, assume to understand the why's that lead to the what's. The what's are for me the results.

First find the common threads, to me that is the practical. In this case what I see I have brought forward before, and those of us that have the experience challenged the my gathering of thoughts (really what I enjoy most about this school)! 

In this case we have 4 jugs all connected to the crank, why bring the crank into the discussion ? How many have run a biggish 4 stroke Thumper? Well all 4 strokes driven by one combustion cycle. The energy of that 1 cycle spins the crank freely till the next thump, simple right. All associa ted drag is simply x(1) x being 4 strokes to deliver that one next thump. Each piston we add to the crank also adds to the cranks effort to share each jug energy input.

I am purposely skipping past any timing outside of know there will be a next - intake cycle, compression, combustion, and exhaust cycle or 4(4).

Heat is a result of effeminacy and is what OP has brought to the table as a question. His logic is suggesting that there must be an issue. 

Ask the question then, why if I have greater combustion heat on 1 jug is that a problem? Why can I not see it as a benefit as it should mean that jug is producing more energy? And that is where the crank comes in.

The total engine is out of sync, why is due to the set of components/carbs being off sync. Breaking this down: 3 carbs are performing well enough to force the crank to rotate @ a  predictable speed; now lets say #1 turn to fire and it delivers a unexpected force or a higher pressure output to the crank that is already rotating: that say on a scope would show up as a blip/spike! That in turn changes the speed at which the next inline travels. That in real terms is a misfire.  Injection system here in place of a carb would be much more easy to diagnose, right, ECM spits out a 300, general misfire, or unexpected rotation speed off the crank or how about describing it as unequal pressure/force. True it is cause by heat, true the rad has to deal with it, but that is calibration issue so treat that instead of the symptom.

Next: understand by dividing the component into segments: the carb design (singular) is one air 2 gas for a stochiometeric and that is another word for achieving heat efficiency. It is much easier to figure out a rich problem than a lean problem as it is much easier to figure a  thumper carb issue then a linked crank one such as in these 4 cylinders.

Final: the bench marks are important when working or tuning carbs, we know that drill so I'll skip over, but in this case and now @BlueSky 700 we have a mix of hotter and colder combustion cycles, for me as they in these two cases are changing suggest that the throttle plates are not synced. There is more air volume on one or 2 of them that also means that those that have that now have to deal with the drag of those that don't!! How we know this is by monitoring the exhaust heat and, the rpms as we try a sync. How we correct the tail chasing is by starting back at the bench marks. In this case for OP we set the plate to Idle but feeler gauge/bit then sync to jug breath, which should be as close to spec as possible or within a couple PSI.

Hope that helps

after you sync the plates then we'll look at the rest like mixing/low speed circuits

 

[circa1968]

Thank you for that Patch.  I mostly followed you on that explanation.  Not to toot my own horn, but back in my day I was very good and well known for my troubleshooting skills of computer/electronic systems (I worked in both Mfg & Development).   I like challenges and, when faced with a new one, I always try to first obtain some basic knowledge of how the thing is supposed to work before I can figure out why the thing does not currently work.  Hence my frustration here and grasping at straws (definitely not my normal approach).  I think I was hoping to get lucky with a quick and simple action.

Thanks for getting me on track and the education.  I think I'm on day 2 of school here but loving the learning. 

I'm slowly getting over my fear of screwing something up too.   And we're heading into cooler/wetter weather so I guess even if I do, I have more time to unscrew it.  haha

Attached is a pic of the plugs I removed, but failed to track from which cylinder.

[circa1968]

16 hours ago, cowpuc said:

Seeing I got summons here (thanks @Patch) I thought I better join in on the fun and share some more, maybe it will help - maybe it won't back yard wrench spinning free advice.. 

Noting now @circa1968 that you have been taking your temp reading off different spots on both the front and rear jugs changes the dynamics a lot IMHO. Taking the reading right off the header itself on the rears and off the clamps on the front should actually read about what you are describing.. The headers are way thinner than the clamps and are also in direct line of fire for exhaust flames,, to me what you are saying makes sense.  Also, those front jugs are directly exposed to air flow with the rear jugs getting no where near the exposure. I ran/rebuilt/tuned/modded numerous HD air cooled over the years and being air cooled - one of the things I did was ran dual carbs (or later injected with a race tuner was even easier to do this) and then run fatter on the rear jug to keep it cooler.. Lean = hot IMHO.

I always found the following advice a little easier to do on a single, or even a twin cylinder scoot but with a little focus on my part I can usually adjust by ear a multi jug, multi carb in the following way too.  Another way besides the following is with either a sniffer or a Color Tune (so you can actually look into the combustion chamber and adjust for the blue flame) but again, I have found following to work well. 

If lean does equal heat than it may be possible that you are seeing a lean condition.. That would not surprise me because it seems like for many years bike manufacturers have been actually outputting scoots that run extremely lean since new, maybe due to EPA regs,, maybe not.. Maybe I am even wayyyy off base with that comment but it seems that way to me..  I have noticed lean idle circuits also causing erratic idle and also stumble right off the bottom when you crack the throttle,, a bog so to speak.. The way an idle circuit works, at least in my pea brain, is that with the throttle plates closed meaning your throttle is twisted at all and your throttle cable has slack in it, vacuum forms behind the throttle plate and fuel/air mix is drawn into the throat of the carb thru that set of little holes you will see back there.  One of the ways I always used, right or wrong it worked for me, to know that my low speed jets were correct size and that I used for setting my air screws with NO sniffer or carb tune was by ear tuning.  Simply run your air screws down to bottom lightly and back them out a turn, start your bike and let it warm up so it is no longer needing choke, set your idle at 1000 rpm, now adjust the air screw and adjust it out till it reaches top r's - there should be a point where it reaches top rpms and if you keep unscrewing it will falls off again,  then screw it back in till it reaches top r's again, now screw it in farther and it will fall off again. The "sweet spot" of top R's on the air screw is where I always found the perfect idle circuitry tune.  Now if you run the screw back to bottom and note the turns it takes to get to a soft bottom - if the turns equal between 1 and 3 turns out you have the correct idle/low speed jet in that carb. If the top r's are below 1 turn your low speed jet is to small, higher than 3 turns out and your low speed jet is to high. Make since?

If so, and I have used this method for years in tuning, than you can now see where you could use that logic in diagnosing whether you are dealing with a lean low speed circuitry caused by crud buildup in one of your carbs or not simply by tuning them. 

Right off idle and up to WOT (wide open throttle) and the tapered metering rod hanging off the slide into the emulsion tube and the main jet at the bottom of the tube take over.  I spent a couple years doing final tune on small 1 pot Hondas at a Honda dealership and 90% of the final tune work on those brand new bikes right out of the crate was moving the E clip on that jet needle hanging from the slide to get em to run right.. Most of the time this meant fattening em up so they didnt bog when I wacked the throttle.  Because our V-4's carbs do not have E-clips I am running shimmed metering rods in mine right now.  Shimming them out gives you a fatter off idle/mid range/WOT,, lowering them will lean er down.. Why do I mention this? Because,, IMHO, you could - for very little money - fatten up a jug or two and see if your temps drop..  If they did, again IMHO, this could indicate a partially blocked main.. Make since?  

I know,, getting long winded,, dont blame me, blame @Patch lol

Thank you Puc!  I'm looking forward to digging into the carbs more and learning how they work.  I looked on ebay for a used set, just to play around with and explore how they work.  Oh my, that's an expensive toy, $300+ for a set of used carbs!

[Patch]

those plugs look too me as low mileage yet the top one way lean, bottom lean ish, the second and third down are better but the third looks spot on.

Will be interesting to see the ones in there now.

remember after you set the plates, do not reassemble the slides, we'll go a bit further before doing that.