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  #1   IP: 96.245.193.169
Old 10-30-2022, 10:19 PM
Anchor1800 Anchor1800 is offline
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Mechanical Fuel Pump issue?

I've been lurking in this area all summer trying to get to the bottom of my engine shutdown issues. The long story short is that the engine will shut down after several minutes of running at half or higher power under a load, but seems to be able to run for extended periods while idling.

Early summer I rebuilt my carb and decided to yank off and look at the mechanical fuel pump at the same time. I found a broken spring in the fuel pump, replaced that during my rebuild with the kit from moyer. I thought this would help resolve my issues, I wrong.

So I decided to get the shutdown warning system from moyer and add a fuel pressure gauge while I was at it, it is all installed as of today, but the warning system hasn't been wired up yet.

Current behavior is that I can pump the fuel pump manually and get 6 psi at the carb. But once started and while running at an idle I am barely above 1 psi, and if I throttle up the pressure drops to barely registering above 0 on the gauge. While running I can manually pump the fuel pump and get it back up to 6 psi, only take 2 or maybe three pumps to get it there. While doing this I can feel the rod from the engine trying to run the pump.

Before I yank off the fuel pump again and take a look to see if I did something wrong, does anyone have any other areas to look into or any thoughts on my issue?

I did a bunch of other unrelated work on the engine back in the spring, I upgraded to electronic ignition, and replaced the plug wires, along with checking that other parts of the electrical ignition system were working.
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  #2   IP: 162.245.50.171
Old 10-31-2022, 09:49 AM
Dave Neptune Dave Neptune is offline
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At 1 psi the engine will mot get enough fuel to make much power at all. You need 2~3 at least. Time to check the pump and check valves. Not a bad job at all.

Also do be sure that the clamps and fittings all the way to the tank are tight so no air leaks. take a good look at the filters too.

You could also go the electric pump which is a good pump but not as good or safe as the mechanical pump IMHO.

Dave Neptune
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  #3   IP: 96.245.193.169
Old 10-31-2022, 10:29 AM
Anchor1800 Anchor1800 is offline
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Quote:
Originally Posted by Dave Neptune View Post
At 1 psi the engine will mot get enough fuel to make much power at all. You need 2~3 at least. Time to check the pump and check valves. Not a bad job at all.

Also do be sure that the clamps and fittings all the way to the tank are tight so no air leaks. take a good look at the filters too.

You could also go the electric pump which is a good pump but not as good or safe as the mechanical pump IMHO.

Dave Neptune
Thanks for the reply Dave, I would prefer to stick with the mechanical pump if possible, so I want to get to the bottom of this.

I had on my list to check connections back to the tank so I will do that next. If I have a bad connection would I still be able to manually operate the pump and hit 6psi?
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  #4   IP: 162.245.50.171
Old 10-31-2022, 11:14 AM
Dave Neptune Dave Neptune is offline
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Yes, you could still hit the high pressure but with little volume or flow for higher RPM's and power.

With the bail you have far more travel for pumping whereas the engine only gives a little pulse (travel) far more frequently.

Dave Neptune
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  #5   IP: 207.32.168.240
Old 10-31-2022, 03:55 PM
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capnward capnward is offline
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You may have a problem with the pump. Maybe the new spring was installed incorrectly. Or it could be an obstruction in the filters. Did you replace filters when rebuilding the carb? If not, junk might have gotten past the filters into the check valves in the pump when you operated the bail, since the bail will create more suction than the pump. I rebuild and clean my carb every year and replace filters then but haven't touched the mechanical pump in 20 years. I vaguely remember noticing back then that the check valves could be installed wrong. Changing to an electric pump is not necessarily an upgrade, IMO, although they are easier to replace. Once your mechanical pump works well, you can probably forget about it for years, if the fuel and filters stay clean. Use non-ethanol fuel, and especially treat the fuel with MMO, to keep the rubber diaphragm and valves in the pump in good shape.
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  #6   IP: 32.211.38.220
Old 11-01-2022, 07:41 PM
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Al Schober Al Schober is offline
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IMHO, the mechanical pump is a good thing. It's weakness is the strainer basket on the inlet which is useless and prone to leaks. I think Moyer sells a replacement strainer basket. Still useless, but less likely to leak.
I changed to electrical pump and used it for years. Issues with it are 1) that it needs the oil pressure safety switch, and 2) it's electrical. Every time it cycles to pump fuel, a little switch is going OFF/ON. I never trusted it.
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