Posted by JDEM on March 02, 2018 at 12:23:18 from (174.230.9.47):
I have a 4WD Suzuki there that is driving me nuts. Actually -I have two in my shop with problems - but I will stick to one that has me most perplexed.
1995 4WD Suzuki King Quad 250 cc. Four-stroke-cycle engine. Ran fine when I pulled it into my shop last Fall. I did a lot of mechanical drive-line work and NO engine work. I made one change to the fuel system by changing the fuel-valve under the tank.
Now - it will not start. At this point - I refuse to believe the fuel-valve is the problem. But like I said - I am beginning to lose my mind on this thing.
Here is how the basic fuel system operates. Fuel valve that I changed has two positions. "Run" and "Primer." It has a vacuum-gas-shut-off-valve. So when in "Run" position - no gas can flow without engine vacuum. When in "Primer" position, that valve is bypassed and gas runs out freely. I tested the valve and it works. From there - the fuel delivery line goes to what Suzuki calls a "vacuum fuel pump." My factory service manual gives NO info on it other then " if it fails, replace it."
I guess I do not understand how this pump is supposed to work. I have worked on similar looking pumps on two-stroke-cycle engines that worked off of crankcase impulses. This is however a 4-stroke-cycle. The port on the intake manifold it hooks to provides a steady 6-7 inches of vacuum and no pulsing I can perceive.
I took the fuel-pump apart and all looks fine. Diaphragms are soft with no holes. Two check valves look fine. Put it back together and tested it with a hand-held vacuum-gun. A steady-vacuum and it pumps no fuel. A on-and-off pulsing vacuum and it still pumps no fuel. BUT - I then tried blowing air into it, off and on with pulses. This way it pumps lots of fuel.
So I am almost at the end of my rope. Seems I never had to think this hard before about a pump like this. I am very temped to put on an electric pump but it is hard to find one that really runs at low pressure. I have tested a few rated at 2-4 PSI and they ran higher. Likely too much for this carb.
I stuck a gravity feed tank on top of the engine and it starts and runs fine. The built-in tank sits near at carb level and needs a pump. So - I am getting a mental fog here. Suzuki does call it a "vacuum" pump and not an "impulse" pump. It hooks to the intake manifold and I cannot figure how there should be any impulse there anyway. Just a steady vacuum.
Somebody here got an idea about what I am missing here?
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