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Jovee

Twin 16 Fuel Issue

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Jovee
I did work on an early style B/S horizontal twin 16 last summer and basically brought it back from the dead. Rebuilt carb, fuel pump, coil, fuel line, clean tank and other resurrective procedures. Now the engine is not getting fuel and all the basic reasons (blockage, filter, float etc..) have been explored. It does not have the antifire on it. I have a theory but dont have enough time on twins to know if it's the case. My briggs manual was of no use. This engine is only running compression at 50 in one bank and 55 in the other which I feel is borderline dead. Because the compression is so low, does that have an adverse effect on the vacuum being pulled thru the line to the fuel pump? I hope that it isn't the case and that Ive overlooked something. ??

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firefoxz1
The fuel pump doesn't work by engine vacumn but by pressure difference as the crank weights pass by a spot in the block, so the fuel pump should be unaffected by the low compression, in fact it may pump more because the engine would turn faster thus pump more while cranking. Maynard is correct in that it definitly effect the ability to pull and mix fuel in and through the carb.

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Jovee
Thanks for the replies. These twins were a new thing to me last summer and Im still obviously learning. Singles are much less complicated. I assumed since the fuel pump was primarily diaphragms and springs that the vacuum line running from it to the front of the block was the power source. All of the internal parts were replaced last summer but maybe something went wrong. It won't pull fuel thru the line at all but it will run fine with gas poured directly into the carb.

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Al
Hi, The fuel pump on this unit is built into the carb. It is a diaphram in the front of the carb. They are the most common source of trouble. Make sure the springs that are under the little ears on the diaphram are in there correctly. They are the valves in the fuel pump. If you have been running gasahol, they may be curved and distorted. They will not pump fuel then. The fuel pump runs from the pulses in the crankcase. Be sure the vacuum line in good and there no crankcase leaks, like the o-ring under the dipstick. When the pistons come together, they compress the air in the crankcase. When this happens any positive pressure is forced out through the breather valve. This should result in nearly zero pressure in the crankcase. When the pistons go up, they create a vacuum in the crankcase. This pulls the diaphram in the carb fuel pump and sucks a little gas into the other side of the diaphram. The inlet valve (ear) them flops down over the inlet hole sealing it off and not letting the fuel go back to the tank. Next the pistons come down toward each other and the vacuum is significantly less. The rubber in the diaphramm pushes the gas through the outlet valve (ear) and to the carb and the cycle repeats. 50 lbs should be enough to pump fuel. I would look at a fuel pump kit. Be sure the plastic block is not cracked. Good luck, Al Eden

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Jovee
Thanks Al - The plastic block and all the internal organs were replaced last summer. The nipple for the vacuum line was broken off the block which is why it was replaced and new hose ran to the block connection. The book called for 1.5psi pressure but I dont have a way to check that. Is it uncommon for those springs to become dislodged? It ran on normal gas for a month or so before it died in the middle of a field. I know the end is near but I dont want to attach the toe tag yet-

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Al
Hi, We have a test tank, a little 1 quart tank on a stand. We hook it to tractors so we have gravity flow gas to the carb. If it runs then, it is a fuel pump or fuel system problem. Gas should flow through the pump if the tank is high enough. Good luck, Al Eden

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Jovee
Al, its funny you say that. I was talking to a tractor friend about that very thing yesterday but wasnt sure if the gas would free flow thru the pump since it was a pulse operation. I wanted to post the question here but was afraid of sounding like an idiot (deet dee dee). I'll tear that pump off again when the weather warms up. Worst case would be mounting the tank on the hood. Thanks Al!!

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