im narrowing it down to vapor lock, im almost sure of it?

Question

Could it be vapor lock?
it seem to run out of gas but is full i polished needle and seat and float is working. the filter goes empty and it will restart after a while if i shake the bike the filter fills back up, but it still takes a while to start. it only does it after a little while of hard running maybe 5 minutes. but if he rides slow on the street in front of the house it runs fine.im pretty sure it is not a carb problen as that is all working well,and has been cleaned a few times in the last week. i thought it was a dirty tank, it had lotsa rust, but we cleaned it out and lined it.any help would be great!!!! thanx!


Additional Details
i have tried that as well every thing in the fuel systen is as clean as if brand new, by the way it is a 1980 Kawasaki km 100


the filter fills with air,i first thought it was needle and seat or floats but i have checked that extensively and that is not the problem either.

    * 21 hours ago
    * - 3 days left to answer.

Additional Details
thanx for all the suggestions so far, here is more info..... it is 95 to 100 degrees F it does run.the tank has a new liner petcock flows freely.fuel line flows freely both before and after the filter. the filter media appears to be brass.the gas cap flows freely. the vents at the carb are also flowing freely.,i am stumped the carb is very clean as is the tank. it still happens with new filter.if it is vapor lock what can i do? i cant see that it can be anything else. will the gas mixture affect the engine heat,possibly causing lock?the engine is air cooled 2 stroke. i am currently running 4 oz of oil to 1 gal.... thanx again i really gotta get this bike going as my son is disapointed but wont say so,so all help and suggestions are greatly appreciated!

? · Accepted Answer

Next time it happens, instead of sloshing the gas around, uncap your gas tank and try riding it (without a full tank).
If it runs ok like this, then it IS vapor lock.

Also, a note about the fuel filter you mentioned. 
Many of them are uni-directional, i.e., they flow only in one direction, with a mark (usually an arrow) showing flow direction.

Kurt T · Answer

is the petcock a diaphragm type or a regular on /off / reserve type? some petcocks have a vacuum hose that attaches to the carb, ind you may not be getting enough fuel through it if it is not attached.if it is on prime,it will fill the carburetor enough to start, but not flow enough to keep the bowl full when riding.your filter my not flow well enough to keep the bowl full. is there a filter inside the tank,above the petcock? it may be restricting flow if it has  debris or liner material on it. try it without the in line filter,see if that helps.  I would bet that's your problem.

Anonymous · Answer

If it is vapor lock, insulating the fuel line may help. Wrap it with foil-backed bubble wrap. That has worked on some KLRs that were experiencing similar symptoms.

If it's a 2-stroke, you also have to be concerned about having good crank seals. Weak primary compression caused by poor sealing can cause some bizarre symptoms, including stopping when hot.

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im narrowing it down to vapor lock, im almost sure of it?

3 Answers