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Discussion Starter #1
My wifes '04 Honda VLX VT600 mysteriously starves for fuel and shuts down after idling or running fine at 1500rpm for 30mins from a cold start, or then runs only 5mins after which it stalls again. Oddly it restarts with a full choke and will run rough at half throttle pretty much endlessly until you let it idle down and it quits.

The video shows a 1500rpm run-to-stall at after a 30min run. You can barely hear it lean out as the carb slowly starves at the 15sec mark in the attched Youtube video.


Trying to track through the entire fuel delivery system I've tried:
  • Always run fresh Etanol free fuel
  • Disassembled and cleaned the carb twice w carb cleaner and compressed air
  • Cleaned and replaced the fuel petcock and in-tank screen
  • Emptied, flushed and soaked fuel tank over night w distilled vinegar, thoroughly dried and clean.
  • Replaced all fuel lines and in-line fuel filter
  • Inspected and cleaned the fuel line diaphragm assy
  • Inspected and cleaned the carb slide rubber diaphragm
  • Removed the fuel cap during test run to eliminate any tank vent vacuum possibility.
  • Motor runs smoothly otherwise and spark plugs show a clean lite tan tone.
  • Checked oil level (up to spec) in case there may be a low oil level sensor.
WTH am I missing????? Thanks for anything useful. Mike
 

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Is it for sure fuel starvation and not ignition failure from heating up?
When it dies like that on the video, drain the fuel bowls and see if there is an ounce or two in them. You could check them when first started, to get an idea of how much is in them when it runs good. Then see how much is in them when it fails.
If they are always about the same amount start looking to ignition.
A weak ignition can feel like running out of gas.
Do you have an old timing light? Put it on the spark wires and when it dies out see if the spark is dying .
 

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Discussion Starter #6
Thanks for the quick reply's!

  • (Vapor lock?) The fan kicks on/off fine and it doesn't seem abnormally hot but I'll sure ck temps tnite w an IR temp gauge.
  • (Hot coils? Battery full charged?) Seems odd that the bike would re-start with a bit of choke and continue to run by applying 1/2 choke and 1/3 or more throttle. Yes the batt is kept topped off with a batt tender.
  • (Float bowl filter screen.) Not on this one that I'm aware of and I've been all over it in addition to numerous new/clean screens/filters before the carb. I'd be thankful if somebody could sure guide me to any if they exist.
  • (Ck float bowls for fuel immediately after stall?) Wish I had a see-through bowl but I tried to get to the drain screw instantly after a stall within a split second but it's almost impossible to be that quick but I'll sure try again.
If you listen very carefully you can hear the motor lean out, revving slightly higher, just before the stall indicating fuel starvation. Seems unlikely to me that it might be coils or spark if it isn't over heating and even restarts with some choke to richen up the fuel supply and/or add vacuum pressure to the carburation system implying a vacuum leak or fuel delivery issue, maybe a tiny perforation in either the rubber fuel line diaphram thing or the slide diaphram??.....but I'm open to just about anything and feel stumped otherwise.

Is there a fuel pump on the 600 and what is the squarish fuel line diaphragm device in the fuel line mounted under the 3" triangular chrome cover on the left side in frt of the petcock? Could it just be old/tired and not pumping/supplying an adequate fuel volume at running speed?

Vacuum hose leak somewhere? On the other hand I suppose any vacuum hose leak would be a constant issue from the moment it starts rather than after 30mins of running......
 

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I'd try opening the gas cap when it happens, then see if it will re-start after the bowls fill, could be the tank vent hose is blocked, pinched or mis-routed. Will usually run until the pump can't override the vacuum in the tank again. cold weather might make it worse as the fuel vapor pressure can counter-act it on hot days
 

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The thing on the petcock that looks like a vacuum fuel pump is a vacuum fuel shut off.
If the engine shuts down it shuts off the fuel, but this can work both ways if you have a major vacuum leak, its gummed up or the diaphragm in the thing leaks.
There is a way to test it by pulling the fuel line off the petcock (engine not running) and then applying vacuum to the hose to the fuel shut off with your mouth.
Don't worry you likely won't get a mouthful of gas, but when you suck the fuel should flow. If it doesn't you may have found your problem.

I hope you got to read that it reads like it should be censored.
 

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The thing on the petcock that looks like a vacuum fuel pump is a vacuum fuel shut off.
If the engine shuts down it shuts off the fuel, but this can work both ways if you have a major vacuum leak, its gummed up or the diaphragm in the thing leaks.
There is a way to test it by pulling the fuel line off the petcock (engine not running) and then applying vacuum to the hose to the fuel shut off with your mouth.
Don't worry you likely won't get a mouthful of gas, but when you suck the fuel should flow. If it doesn't you may have found your problem.

I hope you got to read that it reads like it should be censored.
I bought a dollar store condiment bottle and collapse it down then connect it to the hose for vacuum if you don't like to use your mouth on it.
 

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Discussion Starter #12 (Edited)
CS had the right call, almost.....

SUMMARY RECAP: Bike runs fine for 30mins+/- then chokes down and stalls. Will restart, running roughly w some choke and 1/3 throttle.

The Vacuum Fuel Shut-off (VFSO) was the culprit.....sort of. I bypassed it last night and the bike ran at 1/3 throttle for an hour without a snag! HooRah.....almost.

I pulled the VFSO to tear it down AGAIN and it seemed to be in functional condition with no tears/perforations and easily retracted and held under a vacuum as it should. WTH!

Looking closer I noticed the short vacuum tube from the intake manifold to the VFSO was a little stiff being 15yrs old and in ok condition but was routed in a rather snug bend (not kinked) against the cylinder head before it made its way to the VFSO.

The way I figure it as the bike temps rose to 220*f+ during the 30min runtime, that cold stiff hose became hotter and eventually became flexible enough to fold over and kink, pinching off the vacuum and allowing the spring loaded VFSO to close. After stalling and sitting a few mins the vacuum could be reestablished until it slowly pinched off again. Adding choke on the restart increased the vacuum just enough to open the VFSO a tiny amount and let the bike struggle to run.

I said it wasn't going to be easy eh? o_Oo_Oo_O Thanks for all the input! Mike

On a side note: As promised I ran temps with my IR heat gun during the test run on critical components and was especially surprised by the temps on the rear coil (couldn't get to the frt one) at 150*f and the rectifier at 225*f. Wow! The rectifier has a huge heat sink on it for a reason. Looking for a load that'd cause such massive heat load I aimed it at the incandescent head light and the temp was over 200*f! Yikes, that old school amp hog bulb needs an LED swap out. The engine temps came in at an acceptable 220* +/-.
 

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  • (Ck float bowls for fuel immediately after stall?) Wish I had a see-through bowl but I tried to get to the drain screw instantly after a stall within a split second but it's almost impossible to be that quick but I'll sure try again.
To add to this and to what Swifty suggested:

You don't need a see-through bowl. Before a cold start, attach a piece of clear tubing to the drain nipple on the float bowl and open the drain screw. Make a small loop at the bottom and run the open end of the tube to at least the top of the carb level and tie it to something (another hose on bike, frame, etc.) with a zip tie to hold it. Now crank the bike. The fuel level in the clear tube will settle to the level that is in the float bowl within a few seconds of running. Make a mark on the tube where the fuel settles at and just watch it. You will know immediately of any fuel level changes that might make the engine stall out. A clamp is not necessary to hold the tube on the nipple as long as it was a tight fit going on.
 
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