im stumped on sporadic loss of power

[Flat6Valk]

Ok all.  I need advice.  My 98 standard developed a symptom acting like fuel starvation after riding 30-50 miles at freeway speeds.  More often than not I pull over and open the gas tank and restart and all is well for a few more miles.  The subsequent miles tho are shorter than the first before it acts like its running out of gas.  Mileage of bike is 42600.

So.  Here is what I have done.
1.  replaced petcock (by dealer) 
2.  checked vent line
3.  check vacuum lines
4.  replaced ICM (had a spare)
5.  replaced fuel cap

previous maintenance within  a year included replacing spark plugs, vacuum lines, sync carbs, air cleaner, etc.  All things that should be done was done.

The only thing I can think of at this point is the fuel line from tank to carbs is a quick disconnect type.  maybe I am getting air leakage there?

The only other thing I can say is it seems to be worse on hot days rather than cool.  I dont know if this is a factor.

All of this started about 12 days ago.  Prior to that all was good.

Greg
Flat6Valk

[salty1]

Remove the quick disconnect. Others have had problems with them, but once they were removed all was well.

[Flat6Valk]

thank you Salty..  I cant think of anything else.

[9Ball]

My guess would be the quick disconnect; however, if you want to cover all bases then you might also want to run a piece of wire through the fuel tank's vent tube to make sure there is no blockage or collapse of the tube inside the tank....

Sometimes even just slightly longer fuel lines will get kinks in them causing fuel starvation under load.  Depending on where the disconnect is in relation to the petcock there could also be an air bubble collecting there (just a guess).

[olddog1946]

When I was having similar problems with my std. and with a new petcock I found that I had a slight kink in the line that would get worse the warmer the weather was.  I had previously had a quick disconnect as well, which I'd replaced with a brass straight through. Took me an hour to find it as the line is up there tight under the tank.  Take the time to check yours.

[BnB Tom]

Put your extra key in the gas tank lock.   Do your normal routine of riding up to the point of loss of power.  Before pulling off the road, open your gas tank cap while still riding.  If power resumes, I would suspect your dealer charged you for petcock work not done . .  or not done properly! 

[John Schmidt]

Usually a starvation problem with a quick disconnect isn't from the QD itself. More often it's due to the fuel line not running downhill all the way. With the heat of summer plus the engine heat, you may well be experiencing a bit of a vapor lock in a low spot. Make a mental note of whether it does it more when low on fuel, as opposed to a full tank. If so, that pretty much narrows it down to the fuel line, possibly having a low spot. The QD itself has caused problems due to extra length fuel lines, which in turn causes a low spot to develop.

[Flat6Valk]

interesting John.  Makes sense.  Actually when starting with a full tank I can go about 50 miles before trouble begins.  I stop, open the fuel cap then close it and it seems fine for a few more miles, about 20-30 without taking an actual reading of the odometer.  One time tho, and only once I went about 80 miles without a problem, then filled up and immediately it ran poor.  Again I pulled over, opened the tank, closed the tank and problem temp cured.  That is when I changed the cap.  Yesterday was a cool day here, I ran 40 miles and thought I was feeling the effects of less power.  I let off the gas and it backfired like I was shooting a large caliber gun.  Then no problem for the balance of a 95 mile run. 

I am going to replace the fuel QD just to know I did it.  That is a cheap part.  The petcock not so much.

Greg

[salty1]

interesting John.  Makes sense.  Actually when starting with a full tank I can go about 50 miles before trouble begins.  I stop, open the fuel cap then close it and it seems fine for a few more miles, about 20-30 without taking an actual reading of the odometer.  One time tho, and only once I went about 80 miles without a problem, then filled up and immediately it ran poor.  Again I pulled over, opened the tank, closed the tank and problem temp cured.  That is when I changed the cap.  Yesterday was a cool day here, I ran 40 miles and thought I was feeling the effects of less power.  I let off the gas and it backfired like I was shooting a large caliber gun.  Then no problem for the balance of a 95 mile run. 

I am going to replace the fuel QD just to know I did it.  That is a cheap part.  The petcock not so much.

Greg

Sures sound like a plugged vent line. A vacuum is somehow getting created in the tank restricting flow. That's where I would focus my attention. Also as stated above make sure the fuel line is positioned in a "downhill" fashion for gravity to do its job. I don't think opening the gas cap would allow a petcock to flow more freely. FWIW   

[Flat6Valk]

thanks Salty.  going to check it all out 

[BnB Tom]

May not be petcock specific but definitely a vaccuum problem if it is solved by opening the gas cap while riding.
Several of the above comments lean toward pinched vac line.
Hope that's the culprit.  Would be easy/cheap fix 

[Toledo Mark]

Had similar issue after I installed a quick disconnect.  I couldn't get over about 75MPH no matter how far I twisted the throttle.  Removed it and all was fine.