Fuel flow question

[SpencerPJ]

Been riding 50-60 miles a day, and recently I seem to have a fuel flow issue. Once hot, bike tends to starve for fuel at higher rpms, (getting on it). I let gas run low, filled at different station, premium of course, and still same issue. Not as bad, but higher gas head pressure I'm thinking. I looked at my clear filter, and it has a small amount of grit, and one small rust chunk. I was thinking that maybe I had a rust clog at my petcock, but pulled the fuel line by the fuel pump, and it flowed nicely through the line and filter (made a great mess). The filter is newer with 5k miles. So, I have observed that after a ride, my fuel filter is almost empty of gas. Today after ride, I let idle in garage and watched. Gas dribbles into the filter, and then fuel pump cycles on, clears the filter, and seems to cycle off. (I'm thinking this is normal) So my question is: Should the filter stay filled with gas at all times since it is a gravity fed system? I've loosened my gas cap wondering if it's not a vapor lock of sorts? Any suggestions? I did replace the fuel pump earlier this year with another used 83 off ebay. Thanks...

[cowpuc]

Been riding 50-60 miles a day, and recently I seem to have a fuel flow issue. Once hot, bike tends to starve for fuel at higher rpms, (getting on it). I let gas run low, filled at different station, premium of course, and still same issue. Not as bad, but higher gas head pressure I'm thinking. I looked at my clear filter, and it has a small amount of grit, and one small rust chunk. I was thinking that maybe I had a rust clog at my petcock, but pulled the fuel line by the fuel pump, and it flowed nicely through the line and filter (made a great mess). The filter is newer with 5k miles. So, I have observed that after a ride, my fuel filter is almost empty of gas. Today after ride, I let idle in garage and watched. Gas dribbles into the filter, and then fuel pump cycles on, clears the filter, and seems to cycle off. (I'm thinking this is normal) So my question is: Should the filter stay filled with gas at all times since it is a gravity fed system? I've loosened my gas cap wondering if it's not a vapor lock of sorts? Any suggestions? I did replace the fuel pump earlier this year with another used 83 off ebay. Thanks...

 

IMHO, while it is possible you do indeed have a fuel issue, something else popped into my pea brain when I read your post Spence. When was the last time you checked your carb diaphrams?

The reason I ask is if 1 or 2 or even three of puppys have a whole or two in them the scoot can act just as your speaking in my experience. I am far from a guru on these things like many around here but I theorize that with a hole in a diaphram, the slide is not being pulled into its normal opening position resulting in the metering rod not being slid out of the main resulting in less fuel being drawn in. Make sense? Probably not but personally, I would still check those diaphrams and redo the sync when I patched em up.

On another note, I really do not think in normal operation that the fuel filter needs to appear full - just because it has an air bubble in it does not mean your scoot isnt getting ample fuel supply (again, not one of our guru's here but I got fooled by that trick before, replaced parts I didnt have to on a snowmobile when I was a kid) - thinking the best way to check the pump is to pull the output and see if she;s spurtin fuel. These are not injected motors so I am thinking even 3 pounds of pressure at output. I do know from experience that, in a bad situation a person can pull the vent hose on the the tank and put pressure in the tank by blowing in the vent with your mouth and maintain enough pressure on the tank to fill the carbs and get out of the mountains.. I know,, sounds like a corny idea but worked for me once and I know I cant push no more then a couple pounds of air with my lungs..

I know LOTS of folks here have had pump issues but honestly, in wearing out 5 of these 1st gens and doing an average of 225k miles on each of those I can count on one hand = twice = that I had a fuel pump issue.. Both of those were points related (making the pump actually die and make no clickin noise. Unlike a lot of folks, I have found these pumps to be very very durable and would be extremely intriqued to hear about a pump failure outside of the points if thats what your problem ends up being. Holes in diaphrams = completely other way around!! I have patched more diaphrams then there are Hot Dogs at a Pucs MGnEM!!!

Puc

[cowpuc]

Just thinkin,, another thing you could do is disconnect the input line at the pump. Pressurize the tank by blowing in the vent and see what kind of flow you get thru the petcock and tank? Maybe ya got a small blockage upstream from the pump.. You can pull the seat, pull the sending unit out and look in the tank very easily if ya need to.. I dropped a small wadded up paper bag in my fill tube one time on the road and used that opening to fish it out.. Be crazy if something fell into yours and it found its way to plug off the tank output.. Sounds like an adventure that would happen to your truly

[SpencerPJ]

I really don't think it's a carb issue, seems to be a lack of fuel delivery, based on the filter running pretty low. Maybe 5k miles ago, I put a smaller filter (supposed high flow), maybe something acting up. Filter seems cheap enough, and no harm done replacing with larger one. I don't feel comfortable tackling carbs, give me an old Mopar that's another story. I plan to start with fuel filter replacement, and hoses, ride, then look inside tank. Looks spotless from top, lol. I just took for 30 min ride, ran great. I just put some seafoam in yesterday I just don't understand why a gravity fed system, through the filter at least, why it wouldn't keep full?

[djh3]

Check the The tank is vented thru a small hose that connects up by the cap. After a ride if you stop and open the tank do you hear a "swoosh" kind of sound? You will have to take the surround off the tank there and find the vent hose. Blow some air thru it and make sure its clear. Otherwise it is vacuum locked. Just like a bottle if you turn it upside down it will flow for a bit, then it has to get some air in.

[SpencerPJ]

I will check on vent, but I did loosen the gas cap last ride. Bike rode nice last ride, not as long, more city tooling. I'll try some of above next week and report back. It does act just like a bottle that doesn't vent well enough.

[mralex714]

Been riding 50-60 miles a day, and recently I seem to have a fuel flow issue. Once hot, bike tends to starve for fuel at higher rpms, (getting on it). I let gas run low, filled at different station, premium of course, and still same issue. Not as bad, but higher gas head pressure I'm thinking. I looked at my clear filter, and it has a small amount of grit, and one small rust chunk. I was thinking that maybe I had a rust clog at my petcock, but pulled the fuel line by the fuel pump, and it flowed nicely through the line and filter (made a great mess). The filter is newer with 5k miles. So, I have observed that after a ride, my fuel filter is almost empty of gas. Today after ride, I let idle in garage and watched. Gas dribbles into the filter, and then fuel pump cycles on, clears the filter, and seems to cycle off. (I'm thinking this is normal) So my question is: Should the filter stay filled with gas at all times since it is a gravity fed system? I've loosened my gas cap wondering if it's not a vapor lock of sorts? Any suggestions? I did replace the fuel pump earlier this year with another used 83 off ebay. Thanks...

 

Sounds like the fuel petcock screen might be clogged, BTW bike was designed to run on 87 octane and no gains from premium on a stock bike. I would also check the fuel lines after 30 plus years there maybe some deterioration.

[SpencerPJ]

I plan to start with fuel line and fuel filter. Then look in tank for rust / plugged petcock. Thanks for advise on 87 octane. I thought I read, possibly even in manual that it needed higher octane than 87. Hate spending the extra if not necessary.

[BlueSky]

You can check the diaphragms by removing the air filter and looking down the carbs while the engine is running. Blip the throttle and watch to see if the diaphragms are all working in unison. Expect a little popping back because these engines are really sensitive to air flow. Easy Peasy!

[cowpuc]

I had one of my 1st Gens once that was kind of tricky in diagnosing its diaphram issues.. The thing sounded great, performed just fine to about half throttle, slide functions looked good, synced good too but it just didnt goooooooo like it should've - felt like it was running out of gas.. I finally ripped the diaphrams out of it and found small wear thru areas on the diaphrams right where the diaphrams met the carb bodys.. It was really crazy because the rubber was still covering the wear thru spots and you had to lift up on the flap of rubber to see the wear thru's.. I "reglued" the loose rubber over the thin spots with YamaBond 5 and BINGO,, came right back to life..

[SpencerPJ]

I will look into diaphram if filter doesn't cure , and pre-carb checks out. I will need help, as that would be uncharted territory. Thanks for the input, once I get the chance, (and it might be a week), I will update. (bought a camper and the MRS wants it ready to go for fall camping)

[SpencerPJ]

I changed out fuel filter with a nice clear glass one from O'Reilly (with replaceable cartridge inserts). Wow, much improvement. I still suspect rust in my tank that might need addressed. I had great throttle response yesterday after good ride. It was a nice cool day and she always runs better. I would like to look into my diaphragms as suggested above, might be the final straw to getting this baby running near perfect. She only has 35k on her.

[GaryZ]

My 1968 Honda 350 would run pretty normal up to around 4000 rpm before choking out; Found small holes in the diaphragms.

 

My 1993 ZX11D Ninja would run wide open (WOT) until shifting to 3rd gear. It then shut down completely until the fuel pump re-filled the floats.

The pressure balance tube from the ram-air was blocked and the floats were held closed by the pressure difference.

 

My '92 Venture seems to be intermittently dropping a cylinder at WOT in all gears.

I have not figured out the Venture problem yet, but, it could be a clogged high-speed jet.

 

[cowpuc]

My 1968 Honda 350 would run pretty normal up to around 4000 rpm before choking out; Found small holes in the diaphragms.

 

My 1993 ZX11D Ninja would run wide open (WOT) until shifting to 3rd gear. It then shut down completely until the fuel pump re-filled the floats.

The pressure balance tube from the ram-air was blocked and the floats were held closed by the pressure difference.

 

My '92 Venture seems to be intermittently dropping a cylinder at WOT in all gears.

I have not figured out the Venture problem yet, but, it could be a clogged high-speed jet.

 

 

Could also be a float level issue on one carb = running lean like its on and off running out of fuel.. Could wick it up a bunch in lower gears till she sputters a bunch a high R's and shoot the headers with a temp lazer and see if you find an odd ball running hotter than others = lean will heat em up.. Find a difference = stick a clear tube on the drain line = open drain and check fuel level/float height compared to others..

To clean Mainjet if needed, I would try pulling diaphram/slide and run a jet cleaning wire of right size thru main where metering rod slides.

Another thing to check for would be water collection in bowls IMHO..

Also,, wide plug gaps can cause intermittent high speed..

Dont forget to check tank vent and one way valve on tank vent while goofing with it = vacuum there can cause fuel flow issues. Check pump pressure and operation and filter status..

I had a Honda 350 that use to do that stuff all the time to me before I got my drivers license and all I could do (unless my dad went to work and wasnt watching me) was go round and round in the school parking lot when I was a kid.. After much fooling around and tinkering I finally figured out that I had carboned up the combustion chamber enough by not running the R's up that carbon was coming loose internally and causing misfires as the engine got hot.. Fix was taking that old 350 out and letting her stretch her legs occasionally - bike LOVED it, I loved it, Cops hated it!!

Puc

Edited October 12, 2017 by cowpuc

[BlueSky]

You may want to remove the spark plug caps and snip a half inch or so off the plug wire and reinstall. The caps screw off. The wire tends to corrode at that point and reduce the sprark intensity. It's easy to do.

[GaryZ]

Could also be a float level issue on one carb = running lean like its on and off running out of fuel.. Could wick it up a bunch in lower gears till she sputters a bunch a high R's and shoot the headers with a temp lazer and see if you find an odd ball running hotter than others = lean will heat em up.. Find a difference = stick a clear tube on the drain line = open drain and check fuel level/float height compared to others..

To clean Mainjet if needed, I would try pulling diaphram/slide and run a jet cleaning wire of right size thru main where metering rod slides.

Another thing to check for would be water collection in bowls IMHO..

Also,, wide plug gaps can cause intermittent high speed..

Dont forget to check tank vent and one way valve on tank vent while goofing with it = vacuum there can cause fuel flow issues. Check pump pressure and operation and filter status..

I had a Honda 350 that use to do that stuff all the time to me before I got my drivers license and all I could do (unless my dad went to work and wasnt watching me) was go round and round in the school parking lot when I was a kid.. After much fooling around and tinkering I finally figured out that I had carboned up the combustion chamber enough by not running the R's up that carbon was coming loose internally and causing misfires as the engine got hot.. Fix was taking that old 350 out and letting her stretch her legs occasionally - bike LOVED it, I loved it, Cops hated it!!

Puc

 

Thanks for the ideas Puc. I loved my Honda 350 too. It was my second one and it was a basket case. I pulled the jugs and found it was bored .50 over. I did a valve lap and replaced all eight valve springs with spec'd springs. It was a CB model with the taller gears and it would pull away from a CL450.

 

My reason for thinking it is one of the the main jets is because the throttle position seems to be the culprit. The engine will easily run up to red line in any gear as long as the throttle is not wide open (mid-range circuit). I can clearly feel the transition with the throttle. This leads me to believe that the problem occurs when the main jets are uncovered by the throttle blades. The mid-range circuit is the diaphragm needles/jets and slides, where is the main jet?

[cowpuc]

Thanks for the ideas Puc. I loved my Honda 350 too. It was my second one and it was a basket case. I pulled the jugs and found it was bored .50 over. I did a valve lap and replaced all eight valve springs with spec'd springs. It was a CB model with the taller gears and it would pull away from a CL450.

 

My reason for thinking it is one of the the main jets is because the throttle position seems to be the culprit. The engine will easily run up to red line in any gear as long as the throttle is not wide open (mid-range circuit). I can clearly feel the transition with the throttle. This leads me to believe that the problem occurs when the main jets are uncovered by the throttle blades. The mid-range circuit is the diaphragm needles/jets and slides, where is the main jet?

 

While I am far from a guru on this stuff and hopefully if I steer you way out into left/center field with my thoughts here a realdeal guru will jump in and school us both on this but, in the spirit of good ol campfire back yard mechanicism,, I will go out on a limb and give my opinion..

The throttle plates actually are more of vacuum control than anything else.. Most non CV carbed scoots that I know of (and there were LOTS of em) have no throttle plates (some do have something like a throttle plate that is only used for choking the engines air supply for cold start).. They simply use the slide and metering rod on the end of the slide to regulate fuel..

On the CV carbs with diaphrams like ours use - the throttle plates control the vacuum and the vacuum controls the slide activation instead of having a cable connected directly to the slide = make sense?? Probably not,, if not dont be afraid to say Puc,, your crazy.. If it does make sense = read on for more idea's from the mind of Puc..

The Main Jet sets at the end of the tube where the metering rod that is attached to the slide slides in and out of .. The Main Jet feeds fuel up into the area that the metering rod is metering. Most metering rods on both CV Carb slides and cable slides are tapered. They are tapered because they actually control the fuel for the fuel/air mix from right off the very bottom R's (idle) all the way to WOT (wide open throttle).. The main jet orvice that is replaceable and also adjustable in size in lots of increments is actually a big part of fuel air mix from the point the throttle comes up off idle all the way to WOT and basically shares this responsibility with the Metering Rod.. At WOT the metering rod is no longer in the emulsion tube where it slides in and out but is raised high enough that ONLY the main jet is in control of the mix at this point. Before that, starting right after the throttle opens off idle - its a mix between the taper of the metering rod and the main jet itself = still making sense??

If you pull a diaphram cover off your scoot and remove the diaphram with the slide attached to it, you will notice a long pin/needle sticking out of the bottom of the slide.. That needle is more commonly known in my world as a "Metering Rod".. If you now look into the carb body where the slide just slid out of and notice a hole at the very bottom of the slide area where the Metering Rod would slide into = thru that hole and laying right in the very bottom of it is where the Main Jet resides.. Make sense?

Thinking out loud here a little.. If I were tinkering with what you are talking about,, as well as doing as priorly suggested in this thread - I would also look very carefully at the Metering Rod and its relationship to the slide it is attached to.. I would make sure that the cap inside the slide is still in place and that the metering rod is not able to move around because the cap/spring that holds it in place has came loose.. If this were to happen, the Metering is still not able to fall out but could bounce around = maybe causing irratic running..

Sorry for the long windedness,, I know, I get and get carried away.. ALways in the spirit of trying to help though

Edited October 13, 2017 by cowpuc

[Bob K.]

I changed out fuel filter with a nice clear glass one from O'Reilly (with replaceable cartridge inserts). Wow, much improvement. I still suspect rust in my tank that might need addressed. I had great throttle response yesterday after good ride. It was a nice cool day and she always runs better. I would like to look into my diaphragms as suggested above, might be the final straw to getting this baby running near perfect. She only has 35k on her.

Paul--How did you (safely?) install a glass fuel filter in a metal bracket? I've got one that I've considered installing.

[SpencerPJ]

Paul--How did you (safely?) install a glass fuel filter in a metal bracket? I've got one that I've considered installing.

 

It was already complete. https://www.oreillyauto.com/detail/b/dorman-help--4422/performance-16477/engine-16841/filters-16562/fuel-filter-16704/fuel-filter-replacement-elements-screens-18492/b224f33beee4/dorman-help-glass-fuel-filter/55240/4528741/2005/gmc/yukon-xl-1500?q=glass+fuel+filter&pos=0

 

I thought mine had a few different end connections, but still, basically this. I still like it, and easy to see. Pain in the butt to install.

[skydoc_17]

Hey Spencer,

I am thinking that ol' Cowpuc might be on to something. Check out this link:

 

https://www.venturerider.org/forum/showthread.php?32121-Ebay-Carb-Diaphragm-Replacement!

 

Between the written description, and the pics, I think you will be able to take a look at your Diaphragms without any worries. We actually have contact with Cirrus Company where we get a modest discount on replacement Diaphragms. Keep up the good work, everything you are replacing is just making your scoot more reliable. If you have any questions, please feel free to ask.

Earl

[Bob K.]

Any suggestions? I did replace the fuel pump earlier this year with another used 83 off ebay. Thanks...

Did you ever find a solution for your issue? Was it fuel related?

[SpencerPJ]

Did you ever find a solution for your issue? Was it fuel related?

I replaced the fuel filter, and has been good ever since. Totally start there, nothing to lose.