Troubleshooting: Fuel Starvation Problem?

[beRto]

Hello,

I had been having a high-idle problem.  Adjusted valve clearances and re-set idle.  Today I took out my bike to see if the problem was solved, and the high-idle seems to be gone.

Unfortunately, at one point during my ride back home the throttle started to be unresponsive and a few seconds later the bike died.  I coasted to the shoulder, put the fuel petcock in "prime" and waited a few minutes.  Then I started the bike again and rode home.

Does this sound like the classic GS500 fuel starvation problem?  I've ordered a new petcock (the existing one is leaking a little bit); do you think that might solve the problem?  Is it possible something else is wrong?

thanks.

[frankieG]

clean out the two little holes in the filler cap, they get plugged and frig up the vacuum system.

[beRto]

Ok, I'll look at that.  But if that were true, wouldn't the problem have persisted until I opened the filler cap?

[frankieG]

i don't know if it is you only problem but is one that is commonly overlooked and a simple maintenance thing to do.

[beRto]

Are the holes obvious in the fuel cap (I'm guessing they're small)?  I haven't looked yet, but a hint on where to look would be good.

thanks.

[beRto]

Can anyone who has had the fuel starvation problem confirm that these are the symptoms?

Thanks!

[VSG]

That sounds like the symptoms for fuel starvation.  Especially if it was fine after you put it on Prime.

For the moment, I just put it on prime when I go out for a ride and fill up every 150 miles or so.  And I have no problems.

[Jeff P]

I've got some similar symptoms, mind if I piggyback?   

I only get the high idle occasionally, but I definitely have a "rough" warm up and once up to temp the power delivery just isn't as smooth as it should be.  And if I'm going 70+ for more than a few minutes it gets worse, to the point where I have the same dying engine deal as the OP.  Putting it in prime and waiting a few minutes brings it back to life for the time being.  Driving in prime all the time helps but doesn't solve the problem.

I changed the spark plugs last week and found something odd.  The right cylinder plug was a white ashen color, more than I've ever seen before.  The left side plug looked more like what I'm used to seeing.  Any ideas what that might mean?

jeff

[trumpetguy]

The "classic" GS500 fuel starvation problem is this:

When engine load is high (and thus vacuum is low), the petcock fails to get enough vacuum to open fully, so the float bowls gradually get too low and eventually the carbs can't suck fuel out of the bowls.  This often happens to me in 6th gear at 75+mph, going up hills and/or against the wind, with the throttle close to wide open.

Solutions:
1.  Downshift, keeping the engine in the powerband, and under less load so that it makes more vacuum.
2.  Slow down and close the throttle slightly when going up hills (not necessarily safe in interstate highways!).
3.  Put the petcock on PRIME before you encounter the problem situations (and remember to turn it back to ON when you get out of the hills, wind, or speed).

I generally use a combination of 1 and 3, depending on the situation.  The previous owner actually sold me this bike because he couldn't resolve this problem.  I have learned to live with it and have put 8,000 miles on it in 2 years.

Double check to make sure that the TANK petcock is wide open.  If it is only letting a little fuel out, the other petcock problem is multiplied.