Stalling out after bike is warm

Happy new year to all. I own a 1986 VFR700F2 that I've had for 20+ years. It has a Dynojet jet kit, Kerker slip-on pipes, K&N air filter and the air box cover is drilled out (per Dynojet's instructions). The bike had been sitting around for 10+ years until last winter when a friend of mine & I (with very little help from me) rebuilt/cleaned the carbs as well as replaced all of the filters, fluids, battery, and tires. The bike is now running like a champ with the exception of one recurring issue. After the bike is warmed up (usually about 5 minutes into a ride) it will starve-out and die. I'm assuming it's starving for fuel because if I pull the choke on before it dies, it usually keeps it from stalling out (although ithe revs climb up to 3000). In order for it to run again I then have to pull the clutch in, turn the bike off, pull the choke on full, start it up, immediately take the choke off and I'm usually good to go after that. Now that it has turned colder, it seems to by stalling out much more frequently, usually 4 or more times per ride. Am I not starting/choking it correctly? Did we miss something during the tear-down and rebuild? And more importantly, is there a VFR guru in Chicago that would be willing to help me out and/or take a look at it for me. I just got back into riding again this summer with a good group of guys here in town and don't want them to be waiting around for me while I constantly restart my bike. Any help would be greatly appreciated.

 

If you can't turn the choke off entirely after 1 to 1 1/2 minutes of warmup, possibly dirty pilot jets or clogs within the idle mixture screw passages. In cold weather (only) you could try using the hotter factory-recommended plugs. When's the last time your plugs were inspected and re-gapped ?? Fuel filter could be clogged or output from fuel tank could be reduced by crud or drek. If you tried (haha) would your bike easily do 125mph ??? Heat-related failures are most often electrical, maybe not in your case ?

 

Thanks for getting back to me. The bike will idle/run on it's own after 1 to 1 1/2 minutes of warm up, although I tend to choke it longer than that. We replaced the plugs and fuel filter last winter when we did the rest of the work. I should check the tank output and fuel filter again. Back in the day when I was much lighter I hit 135mph on a 2-lane Kansas highway... Thanks again for the response.

 

you should need NO CHOKE after 1 1/2 minutes (or less) of warm up, so if you use ANY choke longer than that, you most likely have a carb problem.

i'd advise inspecting all plugs immediately after it stalls out, looking for black, sooty deposits that usually indicate over-richness, maybe a leaky float needle.

 

It really sounds like a problem with the pilot jets to me. When you cleaned them, did you just use solvent and compressed air or did you use an ultrasonic cleaner? I've found that in extreem cases the pilot jets require mechanical cleaning to really open them up properly. This requires a thin strand of wire which you slide the jet up and down to scrub off the varnish inside them. You can see the crap come off on the wire. If they are not fully open, the bike will be lean. Does it backfire on the overrun? This would support the theory.

The other possibility is a vacuum leak. Have a close look at your manifolds to ensure that they are seated and secure and that all vacuum hoses are routed properly.

I hope you find the issue!

 

Thanks for the reply. I'm going to look at the plugs, fuel filter and fuel line tomorrow, and will now also look at the vacuum lines. I'm beginning to think that it may be the pilot jets. In our haste to get the bike put back together last winter (it was a very warm and very early spring in Chicago) we didn't run a wire through the jets like I now know we should have done. It looks like another carb cleaning is in the cards for this winter. Would partially clogged pilot jets explain the fact that it runs great 99% of the time and only dies occasionally? Thanks again!

 

Normally partially plugged jets run like crap all the time. Is it popping and snapping like it is lean? The fact that the choke makes a difference tells me that it is starving for fuel. Why only sometimes is a good question. Perhaps temperature or weather related?

Have you checked the tank vent? Perhaps it is restricted and the fuel isn't flowing to the carbs freely?

I know I would be pulling the carbs again to clean the jets and look for other issues that may be affecting the mixture. I wish I was still living in Crystal Lake, I would pop in to offer an extra hand.

 

Thanks for the reply. It runs great (no popping or snapping) 99% of the time then out of the blue it will start to die and only pulling on the choke saves it. I think it's starving for fuel also. It is definitely worse in colder weather. I will add the tank vent to the list of items to check, that's a good idea. I would definitely take you up on your offer if you were still in Crystal Lake. I'm tempted to pull the carbs this winter and have them professionally cleaned and adjusted, I read in another thread that Squirrelman is the go to guy for that (thanks squirrelman for the previous replies!). Thanks again.

 

I have had this type of problem on one of my bikes and the cure so far has been to bypass the fuel cutoff relay as prescribed by Mr. Squirrel. I found that after about six or seven miles of riding fine my bike would lose power as if it was running out of gas. Bypassing the relay and chucking it has cured the fuel delivery problems and no power losses since then.

You would want to make sure the rest of the fuel delivery chain is good though- gas cap vent is clear, fuel filter is good, lines are not kinked or binding and check to make sure your pump is pumping properly. Probably pulling your carbs again if the problem persists after doing the above and a thourough wire and compressed air in all orifices would be in order if the above measures fail.

 

Thanks for the reply, I will definitely look at that before I pull the carbs (again). Have you noticed any ill effects after eliminating the fuel cutoff relay?

 

Nope, starts easier and runs better.

 

Awesome, thanks! I know it's a stupid question, but what purpose does it serve then?

 

If your bike's been unridden for awhile, having the pump prime the carbs first makes starting alot easier. A finite quantum of fuel evaporates from float bowls every day, lowering the fuel levels too much. Bypassing removes a failure-prone component. Easier to refill carbs after service. Less battery drain when starting, less wear on the starter motor.

Subject of earlier international discussion and debate.

Check for any leakages or drippages before starting ! otstir:

 

Sounds like a carb issue to me as well. But pilot jets are usually not a random issue. I would be looking more at the floats either sticking or having fuel in them. My other first thought when I read your original post. Was what others have mentioned is your gas cap vent being clogged. Either way I would do another carb re-build but taking your time and really being meticulous. If you are not comfortable doing it yourself then taking them off and installing them yourself can save you a lot of money. I wish I were closer because I love rebuilding carbs. Goodluck and let us know how it comes out

 

It is supposed to cut off fuel flow if the engine is not running since it receives a pulse each time the crank goes around.
The problem is that these relays go bad with time and usually insufficient voltage and then it does not deliver as much fuel as it should. It makes for tougher starts if you have the float bowl drained because it only pulses with a complete revolution of the crank which means you can wear a battery down quick with a bad fuel cutoff relay.

 

Did you replace the carb insulators you could have a leak that only shows up after they heat up ans expand...

 

Thanks for the reply. I'm definitely going to start with the gas cap vent and the easier fixes mentioned above before rebuilding the carbs. I love watching people rebuild carbs, but these sausage fingers just don't have the dexterity needed...

 

I did replace the insulators and all rubber/plastic pieces I could get my hands on. They were in pretty bad shape.

 

I want to thank you all again for your responses. I tore the bike apart today and noticed that the fuel filter was installed backwards (not fixing my issue, but definitely not helping matters any!) I guess that's what you get when a friend helps you for free! I also noticed that the gas cap vent was clogged/stuck shut. I sprayed some carb cleaner into it and it seemed to have freed it up. Is there some sort of flapper inside the little black hole on the bottom of the cap? Because when I stuck the red straw from the carb cleaner can into the hole, it wouldn't go in at first but them something released and I was able to stick it in farther and when I sprayed the cleaner in then, it came out the square hole on the other side. I took it for a quick spin and it seems to be much better. I won't know if it's fixed for good until I can go for a longer ride (it is still winter in Chicago after all) and if the problem arises again I will try the next option of bypassing the fuel cut-off relay

 

What is the best way to bypass the fuel cutoff relay? Do I just disconnect it? Do I need to cut the wires before and after the relay and tape them together? What about the yellow wire? Any help would be greatly appreciated. Thanks, Kurt.