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Post by teckus on Jun 26, 2019 12:22:04 GMT -5
Yup. I'd vote for a slightly lean engine condition caused by low fuel flow. As the fuel level drops due to poor flow, the mix slowly gets leaner and leaner, finally being too lean to run. You stop. As you sit, the fuel slowly fills the float bowl again, and off you go. For a while. I would check the fuel flow with vacuum applied to the petcock diaphragm. Pull the fuel line from the carburetor, and direct it into a clean Coke bottle. Yes, it must be a CocaCola bottle. They are clear. Ok, any bottle you like, but it has to be clear. Apply vacuum to the petcock diaphragm. Fuel SHOULD flow, full-fuel-line-diameter, no dribbles, no weak plopplop, full flow, as long as there is fuel in the tank, and vacuum is applied. If not, check the filter, check the outlet from the tank. Check for blockage in the fuel line itself. Until you can get full flow as long as you desire, you will have problems. If you HAVE full flow, I would consider plopping in a replacement CDI. You can get them at low cost, they are easy to install, and you can carry a spare in your pocket to swap in quickly when the thing misbehaves. I doubt valves would act that way, as I doubt the heat would dissipate or increase that much unless you lived in NM or NV or AZ, TX, too. HOT places. If it were valves, you would slowly feel the loss of power as the heat increased, and changing the throttle position would have little effect. I think. tom I will check all of the fuel lines when i get home by sucking on them and seeing if they flow and will tell you the results. |
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Post by FrankenMech on Jun 26, 2019 12:45:30 GMT -5
We old guys have to test our 'flow' conditions all the time so we know about clear bottles, drips, and dribbles... With leaking valves the engine will run at full throttle due to dynamic compression but will die at slow speeds and be very hard to start, if it will start at all, -until it cools off. A stop at the Quick Trip for fuel or liquid refreshment will result in a scoot that is hard to start. The leaking valve will also heat up and make the problem worse and can destroy itself.
Don't suck on fuel lines, aspirating gasoline is very bad for the health and will send you to the ER.
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Post by teckus on Jun 26, 2019 15:07:42 GMT -5
We old guys have to test our 'flow' conditions all the time so we know about clear bottles, drips, and dribbles... With leaking valves the engine will run at full throttle due to dynamic compression but will die at slow speeds and be very hard to start, if it will start at all, -until it cools off. A stop at the Quick Trip for fuel or liquid refreshment will result in a scoot that is hard to start. The leaking valve will also heat up and make the problem worse and can destroy itself.
Don't suck on fuel lines, aspirating gasoline is very bad for the health and will send you to the ER.
Yeah i know it is pretty bad but i dont really do it much, i will look around the house first for something to help me |
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Post by GrumpyUnk on Jun 28, 2019 9:08:08 GMT -5
The only line that needs vacuum is the one from the intake to the petcock, diaphragm side. I do not remember if the GMW had a vacuum or manual petcock... If vacuum, apply suction, and fuel should flow due to gravity.
It wouldn't hurt anything to check valve clearance, but, when hot, you should feel the compression stroke as you kick it over. If it spins over freely, without any noticeable resistance due to the compression stroke, then the valve clearance would definitely be suspect.
If the valves were set properly at the factory, and you have very low mileage, in the hundreds or even low thousands, the clearance should not be incorrect due to wear(99% of the time it takes multi-thousand miles for wear to affect clearance to the point the engine won't run). And, again, you'd be able to feel the lack of compression, I think. OTOH, a valve could be sticking due to tight tolerances of the valve stem to guide. When hot the aluminum will heat and expand more, I think, than an Fe valve stem. Coefficient of expansion is higher in Al than Fe, but things...
tom
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