I have a 78 fj40 stock engine and carb that I am having some issues with. When I bought it, it had an electric fuel pump that pumped fuel from the tank to the mechanical fuel pump on the side of the motor which pumped the fuel on up to the carb. Believe me, it is quite a heavy flow. However, I have a bypass line that goes back to the tank. Most of the time the cruiser runs and purrs like a kitten. But, occasionally while running on the road, it will suddenly die for a few seconds, and then it will fire back up and run fine again. When this happens, there is a strong smell of gas. Question - do I need both the electric and mechanical fuel pump on my vehicle. I know that the fuel flow into the carb is supposed to be checked by the float, but I am wondering if my pressure is so great that I am some how flooding the carb when this happens. Any suggestions. Sure would appreciate your input and help
Too much gas?????
- Thread starter gibgoaz8
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The only reason I can think of that your 40 came with both an electric and a mechanical fuel pump is that the PO was having problems with the mechanical pump. But, the stock Aisin carb requires 3-6psi of fuel flow.
Unless you know what psi your setup is sending to the carb, you could easily be flooding the carb.
You need to determine whether the mechanical pump is actually working if it's not, you can buy an oem replacement from @beno and remove the electric pump.
...or, buy a Big Block Chevy Blockoff plate, remove the mechanical pump, cover the hole with the plate (like THIS ONE) and use the electric pump - assuming it produces the requisite 3-6psi - if it produces too much pressure, you need a regulator to keep the pressure to 3-6psi.
Remember, if the mechanical pump has a bad diaphragm, it can leak gas into your oil system and potentially ruin bearings and such.
Your best solution is to run the OEM Mechanical Pump, but either electric or mechanical will work, but you shouldn't need both.
hth
Unless you know what psi your setup is sending to the carb, you could easily be flooding the carb.
You need to determine whether the mechanical pump is actually working if it's not, you can buy an oem replacement from @beno and remove the electric pump.
...or, buy a Big Block Chevy Blockoff plate, remove the mechanical pump, cover the hole with the plate (like THIS ONE) and use the electric pump - assuming it produces the requisite 3-6psi - if it produces too much pressure, you need a regulator to keep the pressure to 3-6psi.
Remember, if the mechanical pump has a bad diaphragm, it can leak gas into your oil system and potentially ruin bearings and such.
Your best solution is to run the OEM Mechanical Pump, but either electric or mechanical will work, but you shouldn't need both.
hth
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Secondary fuel pump COULD be a sign of partial blockage in the gas tank. If your tank looks original, you might want to prepare for cost of replacement.
Best
Mark A.
Best
Mark A.
X-2 Mark has a good point.
I seem to remember reading somewhere that the float needle can cover any pressure up to ~ 7 psi(1975-1978). If you have an elect pump supplying a mech pump, seems like you could easily be exceeding this press value(the mech pump has an internal bypass, but I don't know it's capabilities[flow, etc]). The mech pump was designed to take fuel at atmospheric pressure and increase it to ~3-5 psi--if you have an elect pump supplying it at say4 psi, the mech will increase the pressure accordingly--up to 5 higher than the suction supplied to it- so resultant discharge pressure could be in the 9 psi range.
As Danny said, one or the other--not both. - best to stick with the specs--that way, if you have other fuel issues, you can eliminate fuel pressure as a culprit.
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could pull the top off and check the needle for gunk and the fuel bowl also. While it's apart up can check the float to see if there's not a pin hole in it or if it's out of adjustment, which could cause over fueling, hesitation and cutting out. I rebuilt mine awhile ago and found gel in the bottom which caused my float to stick once in awhile. Gotta love the new gas we have now days. But having both fuel pumps I'd look into to see if the factory ones not working. Could install or hook up a pressure Guage to know where it's running also Napa has them for cheap
- Thread starter
- #8
Thanks for all of the replies and help. Just decided to disconnect the electric fuel pump and see what would happen. Bingo. Problem solved and cruiser runs better than it ever has. I seriously think I had too much fuel pressure going to carb and on occasion, it would flood out. Thanks again for the replies
Glad it's working!
I'm curious about the electric fuel pump though... is it possible that the electric fuel pump is connected to a toggle switch or something?
Sometimes, under certain conditions (uphill, low fuel level, etc.), the mechanical fuel pump may not be able to suck enough fuel to keep the engine from sputtering and losing power. Some people install a backup electric fuel pump that they can switch on to give the needed fuel boost.
Not saying that's the reason for your electric pump... just curious.
Happy New Year!!
