84 G1 AM4 J31 Fuel pressure

rerlund

This cart is a new project to a couple of car guys. Through research (mostly on this site!) we have determined it is a 1984 G1 AM4 (body vin J31 008671 - engine vin J31 105905). Some of the threads I have read show similar issues. The cart will run - but sporadically. Fuel pressure is minimal.
Question #1 - what should the fuel pressure be, how many pounds of pressure?
Question #2 - Why cant an electric fuel pump be used to eliminate this weird vacuum/pressure operated diaphragm fuel pump(refer to car guy thing earlier!!)??
Question #3 - I have seen several threads referring to "seals" having a major effect on the pump, but, these seals are not piston rings. I have not found a good description of exactly what these seals are.
Any assistance has already been and will be appreciated.

BGW

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GMB74

#1) I have never put a guage on the pump to measure pressure, but it isn't much and doesn't have to be. About 1 PSI maybe? Carbureted systems don't require high pressure, just good volume. You just have to keep the carb filled with gas. Disconnect the hose from the pump to the carb and put the end in a bottle. Crank or start the engine. If fuel comes out of the hose the pump is fine. This is right out of the Yamaha manual.
#2) An electric pump will have too much pressure and volume and will force too much fuel into the carb, blowing past the inlet needle and flooding the engine. You will have to step down the pressure and volume to make it work. It can be done, but why complicate a simple system that works just fine? If your system is not working properly, find the defect and repair it.
#3) The seals referred to are the crankshaft oil seals. 2-stroke engines do not have oil in the crankcase like a 4-stroke engine does. Oil is mixed with gas for lubrication. The fuel mix is introduced into the crankcase, compressed and fed into the combustion chamber. The crankcase must be tightly sealed for this to happen. After 25+ years, these seals tend to wear out and leak, causing loss of the crankcase vacuum and pressure pulse that runs the fuel pump. This leakage also allows fuel mix to leak out of the engine and/or air to be sucked into the engine causing a lean fuel/air mix. This will cause the engine to run poorly, and if not repaired will burn up the engine due to high combustion temperatures and loss of lubricating oil in the fuel mix.
As stated in #2 above, this is a very simple and effective system that has worked for many years and still works today. The fuel pumps are quite reliable and don't fail that often. Having said that, age and ethanol fuel are starting to take their toll on these old buggies.
I am an ex-car guy too, and unless you were around cars pre-1990 or so, you are probably used to fuel injection systems which are way more complex. Don't over-think the situation. Just find out what is wrong and fix it.

smallblock450sl

Now that is good advice

DOOmsman

GMB good post but just for clarity.

"""#3) The seals referred to are the crankshaft oil seals. 2"""

On both ends of the crankshaft where it exits the crankcase.

rerlund

TY. Input and information is greatly appreciated. Purchase of seals is being pursued as we speak! PS we are from the latter part of muscle car era - familiar with carburetion. I have little to no experience with 2-stroke or small engines. My buddy has a good amount of experience, so, between him and this site - I am learning a great deal!
Again - Thanks for info, and being very timely about it. I will post the outcome as soon as possible.

rerlund

The seals have been purchased and installed (engine removal made it way easy). $40 for seals and a few hours labor and the cart runs great. Someone before us had replaced fuel pump. We looked at old pump and don't think it had a problem! Information is key!! Many thanks - I have learned a lot! Put another notch in your belts - you guys have helped to recover another G1!!!! TY again.