Odd fuel starvation???

[QuaiChangKane]

Bit of a poser....


She runs fine, if still a touch rich. But at sustained speeds over the ton, she'll die of fuel starvation.


This has happened twice in as many weeks. First time was after about 20 minutes - 10 at legal speeds, 5 at awgeez speeds, and the last few at felonious speeds resulting in a complete loss of throttle response, loss of power, and subsequent four letter words on the left shoulder of the interstate. The second time happened yesterday after about 20 minutes of sustained high speed and a ~2 minute burst above the ton.


Both times, she wouldn't fire when cranked. I dipped a rag into the fuel tank, dropped the rag into the air box and she fired right up. She stumbled for a bit, then ran like a champ.

I rebuilt the petcock about a year ago, and it was in good shape even before I took it apart. I went on a 200 mile spirited ride in the twisties a couple of weeks ago with nary a problem - but never went above 80 on the way. Around town and at moderate freeway speeds she's fine...


I've also noticed that the float bowls will dry out in about 4 days instead of the usual 7-10 days. A shot of ether in the air box takes care of this, and gives the few seconds of running it takes to suck enough fuel into the bowls to keep her idling.

Unrelated problems???
Dirty petcock???
Partially clogged vent tube???


I completely cleaned and synched the carbs about 2 months ago, and she otherwise runs like a scalded cat....


As always, advice is greatly appreciated.


And on a side note - my ES donor bike arrives Friday!!!



-Q!

[dwarf8]

Ah Grasshopper...
When you can get air back into the gas tank, it will be time for your bike to take off like a rocket....

Sorry.
An original "Kung Fool"...

Sounds like fuel starvation caused by lack of air into the tank.
High fuel consumption causes it to die.

Fuel filter clogged?

[earlfor]

Tank vent hose pinched or blocked maybe. Have had that happen with sediment collecting on the petcock filter screen. High fuel flow pulls enough sediment to block it. Wait a few finutes after it dies and the sediment settles.
Will then run normally

Earl

[QuaiChangKane]

Yeah, but the second time I never cracked my tank open - I dipped my rag into someone elses tank (insert vague sexual reference here). The tank stayed sealed the second time, but priming it worked the same as the first time....

But I do think it's a vacuum lock - high speeds = high demand, clogged vacuum line causes the bike to stall with dry float bowls. A little primer and she starts up, runs enough to suck new fuel into the carbs and will keep running with the restricted vacuum line until I ask her for more fuel than she can give.....


Sometimes just talking about a problem will help it solve itself.



Still working on the whole walking on rice paper bit, though...






Thanks,


-Q!

[SqDancerLynn1]

Get a pingle fuel valve / Problem solved?

[focus frenzy]

what is the fuel level in the tank?
could the fuel line be a bit kinked?

[Sandy]

If you have a prime postion on the fuel petcock try running it in that position, you should have full fuel flow if everything upstream from the petcock is correct. If it only does it with the petcock in the regular on position or reserve then the problem is either downstream from the petcock or the petcock itself. One common problem often overlooked is a bad petcock vacuum hose. It can be either kinked, collapsing or leaking. Another quick fuel flow check is to put the bike on the side stand or preferably the center stand, place a container under the left carb, remove the float bowl drain screw, turn the petcock to prime and see if you have a good consistant fuel flow. Do this for a couple of minutes or more while sloshing around the fuel in the tank by wiggling the bike. This should more than mimic fuel flow at high rpm. If the flow reduces chances are the petcock screens are getting clogged or there is poor tank venting. If you remove the gas cap and flow resumes then it is a venting issue, if not then it would be clogged screens. Clogged screens usually only affect fuel flow when the tank is close to empty or on reserve as debris tends to collect only at the bottom of the screens. At full throttle your bike will need at least a pint of fuel every 2 minutes. My bet is that you have either a tank venting problem or a vacuum issue.

[dwarf8]

Grasshopper.... make sure you let us know if it's a kink/blockage in the vacuum hose or the venting of the tank.

When you lift out the hot engine from the bike and place it on the door lever, you will not have a dragon scars but nifty stripes up your forearms.

And about that pebble....
Best two out of three? :roll: