Air Mix Screw Setting

[.45Cole]

What's the best way to get the air/fuel adjustment from scratch, or is there an accepted setting from the factory? Completely went through them and figured I'd just reset the mix via vacuum but I didn't figure on the carbs being out of sync, 2 equations and 2 variables so I've got a problem. I think I found the sync setting with the manometers but the idle really takes off, is there an idle adjust somewhere? 87 VR

[cowpuc]

.45, at exactly 14:42 in this little video the idle adjustment screw is right above my index finger. I was getting ready to reach in and turn it but the motor was hot and I had to default to a screw driver to do so (not shown in vid). The screw is a knob with a phillips screwdriver head in the center of it and is located low/under and between the drain hoses on the left side of your bike (left as when you are sitting on the bike,,,,,,,,,,,,,, same side as the shift lever).

For air/screw setting,,,, aside from having/using an actual exhaust sniffer - using the tool I am showing you in the ebay link is probably one of the most accurate ways in my untrained opinion. It gives you a window into the combustion chamber so you can adjust per flame color (blue burn being best). Other than that, it's a matter of ear and finding the lean setting that creates the fastest idle = delicate job.

 

Heres the ebay link: https://www.ebay.com/itm/Gunson-COLORTUNE-Carburetor-Adjustment-Tool-12mm-SHIPS-FROM-USA/232813706940?epid=13020431292&hash=item3634c73ebc:g:J~IAAOSwHNxaL~W2

 

and tthe vid:

[Marcarl]

In addition to what Puc said: highest idle on the sync is not necessarily what you are looking for. All carb butterflies need to be set at the same opening setting, and that is what is done by doing a sync, during the process the idle may increase or decrease, and yes adjustment will be required to keep it in the idle circuit, somewhere between 900 to 1000rpm.

I don't have a colortune so do mine the old school way for the mixture screws. Start out at 2.5 turns out from seated. Don't turn tight at seating it, just so it gets there, tight will damage the tapered end of the screw and render it useless. Hook up the carb tune or a vacuum gauge to the cylinder in question and adjust the screw until you get the highest attainable vacuum. Don't rush things and turn slowly. Once that is done check the sync. If you get no reaction by turning the screw the passage will most likely be plugged, so will need to be cleaned. If you need to clean, keep in mind that there are to ports in the passage, one goes straight through and one comes from the side (which you can't see) and is hard to clean unless you can get your finger inside the carb to block the straight through hole.

[Patch]

The correct process is to ALWAYS start with a compression test - when setting CV carbs.

 

Then you bench sync if they are off the bike. If not then you quick sink - then you tune match to each jug by rpm, then if you are looking to exceed this, by heat at the exhaust port.

Then dial it richer by 1/4 turn.

Now you are ready for final sync.

 

Patch

Edited June 29, 2018 by Patch

[.45Cole]

. Start out at 2.5 turns out from seated.

 

Got it! For anybody that hits this on a search:

 

I started at 2.5 turns out on the air/fuel screws (A/F) from closed (prev owner lived down the street so I knew it was properly jetted for my altitude, 6,500') and let it warm up. Take off the choke and adjust idle speed to keep it running initially, then once I progressed I targeted 1050+/- 100rpm. Once warm I started syncing each bank (ie left side and right side) using the sync screws to itself while adjusting the idle speed, I have a 4x manometer setup and an inductive rpm from the timing gun. Rev the bike a couple times after a turn on the sync screws (throttle setting). The motor will tell you what's going on. Mine hesitated and then surged, running better and giving better response once revs were up, pipes pop on decel. Needs leaned out so I turn the A/F screws in 1/4 turn and keep going about the syncing (adjusting all carbs each setting, I'll go back later and sniffer the different banks to a better adjustment once I get a sniffer). Once at a decent setting, I synced the two banks to eachother, not perfectly but close. The engine speed is constantly changing and so I keep it dialed in. Once everything seems synced, rev it up again and adjust the air/fuel mix. Took two iterations but I have great response, no popping, and as I was syncing (and going in the right direction) the vacuum steadily rose and it started acting like it should. As just about anything is changed, the idle speed will change so I kept up with it keeping it ~1050rpm.

 

 

I took the carbs off the bike and completely disassembled/cleaned them and replaced the #3 throttle cable then the carbs went back in so I was in for the full treatment: A/F settings, sync each carb to it's partner in its bank, sync the banks, idle speed, tension on the throttle cable at the carb. Took about 10 min so it's definately mechanically easy, just took attention to detail.

 

Now on to the brakes.

[Patch]

[quote=.45Cole;1042273

 

"Mine hesitated and then surged, running better and giving better response once revs were up, "

 

First congratulations on your first sync! Just focused on the above, this is the 2nd time you mention surging. If you are experiencing surging when the engine is warm/hot, and - it isn't throttle cable related.

Let us know and we can help you pin that issue down.

 

If she tends to surge I wouldn't take it out riding.

 

Patch

[bongobobny]

There are two ways to PROPERLY set your mixture screws so that they are all correct. The best and most accurate way is to use a CO sniffer on each exhaust pipe via the 4 removable caps on the pipes. In order to get that perfect 14:1 mixture, you need to set the CO reading for about 5.1. The problem being CO sniffers are expensive, around $500 or more, and shops that have them want a pretty penny to do this service. The other alternative is to use a colortune plug and adjust each cylinder to the perfect color of the explosion. Although not quite as accurate as a CO sniffer, it is pretty darn close! Colortune plugs can be had for about a tenth of the price of a CO sniffer. The only downside is you need to put a hood over yourself and be in a somewhat dark room to properly see the explosions...

[Patch]

Hi Bongo,

 

Not sure how this ties to surging unless we (in general) have a different interpretation of the term.

 

For the sniffer, here's my problem with to days shortcuts of tuning. 1st we know we need to know what the high pressure is per jug so, we can understand what to expect from the fuel circuit. These days we seem ready to tare down carbs which is pretty technical, expecting that by doing so we somehow have bonded to the bike thus correcting all things within.

 

I know you know that CV carbs need solid constant low pressure to work as expected. But what if the bike has been sitting around for x years? That's 4 piston on a V. Also springs have been compressed for usually the same amount of time, and those that have been, the seats have been exposed!

 

Now there's lots of us that know exactly what I am getting at. We know what we need for efficient combustion which might not be 14:1. So if we don't know the bench marks as is - verses what we expect then we can't tune from our keyboards any better then they can tune from what ever tools the OPs are using!

 

I am fortunate because and there's a story about me kicking around which I'll skip past; that I have an ear and a feel for combustion. I don't always get it right and can't claim I get it better than others but, I do get it pretty close. I stick to basics and, I spoiled myself by investing in a Vac Mate! I have become so use to using this tool I can almost see it playing out before hooking it up, it has really refined my carb circuit trouble shooting across rpm ranges.

 

So here's something, above OP mentions 1050 and lets say you and I might tune or sync at 1200. Lets keep in mind air pressure's and resistance to flows.

Now if we aren't looking for a problem and we are running touring bikes, where do we need or want the best "overall" performance? We know because we have many thousands of miles in touring saddles. We need passing power, we need engine braking, we need range, inertia and momentum to not get knock back flying past or opposing truck traffic. So what if we because we run touring bikes tune and sync for that scale.

 

My point is that tools that tune low down for regs don't really tune, they pass a test.

 

I really should stop here but, without compression numbers how do we troubleshoot tuning problems?

 

well just an opinion

[.45Cole]

Mine hesitated and then surged, running better and giving better response once revs were up, "If you are experiencing surging when the engine is warm/hot, and - it isn't throttle cable related."

Patch

 

I guess "surging" isn't quite the right term then. If I popped the throttle (quickly open it) she would rev up, and then keep revving. A pop from idle to say 2500 would keep creeping to say 3500 before I had to physically turn the throttle back or push the throttle linkage on the carb. Adjusting the tension on the #3 throttle cable (I replaced the cable during the carb rebuild so the adjustment was already suspect) solved the issue and she revs and comes down quite well.

 

The spring back on the throttle is a little weak, is the adjustment/spring controlled in the linkage with the cruise control?

[Patch]

I guess "surging" isn't quite the right term then. If I popped the throttle (quickly open it) she would rev up, and then keep revving. A pop from idle to say 2500 would keep creeping to say 3500 before I had to physically turn the throttle back or push the throttle linkage on the carb. Adjusting the tension on the #3 throttle cable (I replaced the cable during the carb rebuild so the adjustment was already suspect) solved the issue and she revs and comes down quite well.

 

The spring back on the throttle is a little weak, is the adjustment/spring controlled in the linkage with the cruise control?

 

 

" A pop from idle to say 2500 would keep creeping to say 3500" That is surging

 

Of course there can be more than one reason, three come to mind at the moment, air, un metered gas, and linkage.

 

For the throttle return, I would first check the cable rooting and the throttle for binding through its rotation. Could be that it was removed and incorrectly installed or have dirt and other restrictions. They might be old or ill fitting knockoffs?

[.45Cole]

I had fixed the surging, it was the #3 throttle cable tension. Once backed off, I can pop the throttle and she comes back down nicely. The new adjustment on the #3 throttle cable also really allows the idle speed screw to dial in the idle.

[Patch]

Yep quite the learning curve.

They can be sensitive to balance when any one component is incorrectly set, kind of like chasing your tail. After the 5th or 6th time around the bike its time to reach out.

So we can put this one in the win column for you, have a safe season.

Patch

[bongobobny]

Hi Bongo,

 

Not sure how this ties to surging unless we (in general) have a different interpretation of the term.

 

For the sniffer, here's my problem with to days shortcuts of tuning. 1st we know we need to know what the high pressure is per jug so, we can understand what to expect from the fuel circuit. These days we seem ready to tare down carbs which is pretty technical, expecting that by doing so we somehow have bonded to the bike thus correcting all things within.

 

I know you know that CV carbs need solid constant low pressure to work as expected. But what if the bike has been sitting around for x years? That's 4 piston on a V. Also springs have been compressed for usually the same amount of time, and those that have been, the seats have been exposed!

 

Now there's lots of us that know exactly what I am getting at. We know what we need for efficient combustion which might not be 14:1. So if we don't know the bench marks as is - verses what we expect then we can't tune from our keyboards any better then they can tune from what ever tools the OPs are using!

 

I am fortunate because and there's a story about me kicking around which I'll skip past; that I have an ear and a feel for combustion. I don't always get it right and can't claim I get it better than others but, I do get it pretty close. I stick to basics and, I spoiled myself by investing in a Vac Mate! I have become so use to using this tool I can almost see it playing out before hooking it up, it has really refined my carb circuit trouble shooting across rpm ranges.

 

So here's something, above OP mentions 1050 and lets say you and I might tune or sync at 1200. Lets keep in mind air pressure's and resistance to flows.

Now if we aren't looking for a problem and we are running touring bikes, where do we need or want the best "overall" performance? We know because we have many thousands of miles in touring saddles. We need passing power, we need engine braking, we need range, inertia and momentum to not get knock back flying past or opposing truck traffic. So what if we because we run touring bikes tune and sync for that scale.

 

My point is that tools that tune low down for regs don't really tune, they pass a test.

 

I really should stop here but, without compression numbers how do we troubleshoot tuning problems?

 

well just an opinion

Howdy Steven!

 

Well, I was addressing the original title of this thread, which is asking what is the PROPER way to adjust the air/fuel mixture. As far as just turning all 4 screws out a specific amount of turns, all that will do is give you a course adjustment. In manufacturing, to even come close to say 50 to 75 millionths of an inch tolerance is quite the feat as is holding an angle to within a second or two, so the likelihood of all four adjusters being exactly the same is pretty much impossible. Add that to the fact that actually bottoming out all four screws at exactly the same point is very difficult to achieve leads to the likelihood that all 4 screws could end up being maybe 1/8 turn off from each other give or take.

 

Tweaking each screw for a particular idle point or vacuum point may help to fine tune to a degree but the PROPER way to ensure a balanced air/fuel mixture is by monitoring exactly what is happening in each cylinder. Now as far as the 14:1 ratio I got that from the Damon Ferillo (sp?) video where he uses charts and graphs to prove why that ratio is the right one (Myself I originally thought it was supposed to be more like 12:1 or 13:1 from my old hot rodding days of long ago) and how it equates to a CO output of 5.1. If you haven't watched the video yet I strongly encourage anybody who is contemplating working on their Venture carburetors to spend the 2 hours watching it as it is a wealth of information on them!!! Hey, anybody that uses a VMax engine to bench test every set of carbs and fine tune them suggests this guy is very serious about what he is doing!!!

 

As far as surging goes I was not addressing that, I was addressing post number 1. There is a multitude of things that can cause surging and I feel that exactly balancing the air/fuel mixture will play a very minor and somewhat insignificant part in that. Proper airflow balance would most likely play a more significant role as can a plugged orifice, sticky linkage, sticky slides, etc, etc, etc...

[BlueSky]

For maximum power an air/fuel ratio needs to be about 12/1. For maximum fuel mileage, the ratio can be as high as 18/1. Excess oxygen shows up in the exhaust at 14.7/1. So cars with oxygen sensors detect oxygen at 14.7/1 and that is the control point. An engine will produce CO below 14.7/1 which is considered a pollutant and it will produce more and more NO above 14.7/1 So that is a compromise setting with cars that will produce a reasonably clean exhaust and a fuel efficient engine. Engines are designed to go rich for best acceleration and lean when cruising for better fuel efficiency/economy.

[Patch]

Howdy Steven!

 

Well, I was addressing the original title of this thread, which is asking what is the PROPER way to adjust the air/fuel mixture. As far as just turning all 4 screws out a specific amount of turns, all that will do is give you a course adjustment. In manufacturing, to even come close to say 50 to 75 millionths of an inch tolerance is quite the feat as is holding an angle to within a second or two, so the likelihood of all four adjusters being exactly the same is pretty much impossible. Add that to the fact that actually bottoming out all four screws at exactly the same point is very difficult to achieve leads to the likelihood that all 4 screws could end up being maybe 1/8 turn off from each other give or take.

 

Tweaking each screw for a particular idle point or vacuum point may help to fine tune to a degree but the PROPER way to ensure a balanced air/fuel mixture is by monitoring exactly what is happening in each cylinder. Now as far as the 14:1 ratio I got that from the Damon Ferillo (sp?) video where he uses charts and graphs to prove why that ratio is the right one (Myself I originally thought it was supposed to be more like 12:1 or 13:1 from my old hot rodding days of long ago) and how it equates to a CO output of 5.1. If you haven't watched the video yet I strongly encourage anybody who is contemplating working on their Venture carburetors to spend the 2 hours watching it as it is a wealth of information on them!!! Hey, anybody that uses a VMax engine to bench test every set of carbs and fine tune them suggests this guy is very serious about what he is doing!!!

 

As far as surging goes I was not addressing that, I was addressing post number 1. There is a multitude of things that can cause surging and I feel that exactly balancing the air/fuel mixture will play a very minor and somewhat insignificant part in that. Proper airflow balance would most likely play a more significant role as can a plugged orifice, sticky linkage, sticky slides, etc, etc, etc...

 

It's all good Bongo.

The most difficult regardless of engine is helping others that "with the best of intentions" want to NASA tune an old jug with old carbs.

 

The ratios for me at least are secret not just to me, and truth is even if we know, we don't say;)

 

If I recall you are or were looking at an injection system for one of your projects? You can get a lot closer to ideal and maintain but not with carbs. The best we do is dial in to suit that one circuit at the time of,, and for a short time.

[bongobobny]

Yup, all good Steven!

 

Yes, a couple of years ago there was this guy manufacturing fuel injectors that went into the stock carbs where the sliders go, but he went out of business. Flying Fool acquired the blueprints but never did anything with them. Now there is a member down in Florida that had a performance company working on a more proper FI system that added sensors for proper timing and advance for proper acceleration, but I'm not sure how that project is going. So, for now, I guess I'll stick with the stock carburation but I may be on the lookout for a set of VMax carbs which supposedly have even larger throats, but I also sometimes wonder just how much of a difference a 1mm larger diameter really makes...

[Patch]

Yup, all good Steven!

 

Yes, a couple of years ago there was this guy manufacturing fuel injectors that went into the stock carbs where the sliders go, but he went out of business. Flying Fool acquired the blueprints but never did anything with them. Now there is a member down in Florida that had a performance company working on a more proper FI system that added sensors for proper timing and advance for proper acceleration, but I'm not sure how that project is going. So, for now, I guess I'll stick with the stock carburation but I may be on the lookout for a set of VMax carbs which supposedly have even larger throats, but I also sometimes wonder just how much of a difference a 1mm larger diameter really makes...

 

Wow I remember that now that you mention it. The problem is the compromise of dragging the mix down!

 

CVs are close enough for the level of design our bikes have.

 

2mm maybe 4 mm for sure but it has to flow through meaning porting..