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Discussion Starter · #1 ·
I'm considering putting an electric fuel pump on my 318 tractor, however I don't know what to do with the vacuum line from the engine. Do I need to plug it or just plug the in and out of the existing fuel pump? I'm in the process of replacing all the fuel lines and pickups from the gas tank. I can't figure out how to get at that line from the engine.
 

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Plug the line, or cap the nipple it’s attached to.

You have to pull the tin. You need to lift the motor to do it.
 

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Discussion Starter · #3 ·
Plug the line, or cap the nipple it’s attached to.

You have to pull the tin. You need to lift the motor to do it.
Thanks. Can I cap the in and out of the fuel pump? Just save me the work of moving the sheet metal.
 

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Thanks. Can I cap the in and out of the fuel pump? Just save me the work of moving the sheet metal.
You can until something breaks and you get a base vacuum leak.
 
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Discussion Starter · #5 ·
You can until something breaks and you get a base vacuum leak.
Thanks again, but now I'm confused. What is a base vacuum leak? My knowledge of gas engines is limited.
I'm trying to solve a "surging" issue. The engine runs sort of OK with the choke pulled halfway out. Everything I read says it's not getting enough gas. So far, I have resealed the manifold, installed a new carburetor, replaced all the gas lines and pickups in the tank and a new fuel pump and gaskets and fuel filter. I thought I would try an electric fuel pump to increase gas flow.
I'm at a loss of what to do!
 

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A base (crankcase) vacuum leak is bad.

You can cap the pump, but I wouldn’t do it.

There is a fuel flow testing procedure in the onan manuals.
 

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Discussion Starter · #7 ·
A base (crankcase) vacuum leak is bad.

You can cap the pump, but I wouldn’t do it.

There is a fuel flow testing procedure in the onan manuals.
Thanks for the quick reply. I looked at the test procedure in the Onan manual. Do you have any recommendations for that test equipment (cheap?)?
 

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Thanks for the quick reply. I looked at the test procedure in the Onan manual. Do you have any recommendations for that test equipment (cheap?)?
You don’t have a measuring cup?
 

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Thanks again, but now I'm confused. What is a base vacuum leak? My knowledge of gas engines is limited.
I'm trying to solve a "surging" issue. The engine runs sort of OK with the choke pulled halfway out. Everything I read says it's not getting enough gas. So far, I have resealed the manifold, installed a new carburetor, replaced all the gas lines and pickups in the tank and a new fuel pump and gaskets and fuel filter. I thought I would try an electric fuel pump to increase gas flow.
I'm at a loss of what to do!
Sounds like an air leak somewhere, it would be a good start to check the vacuum impulse line to your fuel pump.
 

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Thanks AJgrn78, that's a much nicer answer than the previous one from rydpirs.
Sure thing, another trick is to try carefully spraying some starting fluid or WD40 around areas of your engine when it's running and see if the RPMs surge, that would indicate an air leak. Especially around the carb and intake.
Don't get the wrong impression of Rydplyrs, he knows a lot about these engines and has helped many of us (including me) many times. The internet has a bad way of making people sound rude. 👍
 

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Discussion Starter · #12 ·
Sure thing, another trick is to try carefully spraying some starting fluid or WD40 around areas of your engine when it's running and see if the RPMs surge, that would indicate an air leak. Especially around the carb and intake.
Don't get the wrong impression of Rydplyrs, he knows a lot about these engines and has helped many of us (including me) many times. The internet has a bad way of making people sound rude. 👍
I have tried spraying around the carb and manifold with no change in rpms and since I have replaced these, as stated in my previous post, I'm thinking the vacuum line to the fuel pump is leaking. That's why I was looking into a electric pump and eliminate the vacuum pump. I don't want to pull the engine to replace that line.
As to the comment about a measuring cup. I wasn't aware that you could measure psi and in-hg with a measuring cup. The engine is getting gas but I don't think it's getting enough or it's fluctuating.
Thanks for your help.
 

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Your manual must be different, mine just says crank the engine for 20 seconds with the fuel line pointing in a jar.

You should get 6-8 oz of fuel.
 
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I have tried spraying around the carb and manifold with no change in rpms and since I have replaced these, as stated in my previous post, I'm thinking the vacuum line to the fuel pump is leaking. That's why I was looking into a electric pump and eliminate the vacuum pump. I don't want to pull the engine to replace that line.
As to the comment about a measuring cup. I wasn't aware that you could measure psi and in-hg with a measuring cup. The engine is getting gas but I don't think it's getting enough or it's fluctuating.
Thanks for your help.
I have a 316 Onan which is very similar but not identical to a 318, I am able to access the impulse line by removing the right hand side cowling without pulling the engine, but a 318 might be a bit different with the oil filter (no filter on a 316).
For what it's worth, I don't think it's a fuel supply issue, I have always observed surging to be a lean fuel mixture issue, and until you said you replaced the carb I was going to suggest checking the pilot jet for a blockage. If there are no air leaks, I would be looking for a way to richen the carb settings with a larger pilot jet. Does it run strong under load and just surge at idle or unloaded? Or does it surge all the time? My 316 surged at idle until I cleaned the pilot jet.
 

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Low speed surging is either an air leak or a blocked low speed jet. Do NOT enlarge the jet, but make sure it is clean. Air leaks can be from the split intake manifold as the seal dries out over the decades and needs to be renewed, or even from a worn throttle shaft. Lots of threads on WFM about rebuilding/resealing the manifold...

Chuck
 

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I put in an electric fuel pump when the vacuum fuel pump went bad on my 318. Plugged the ends of the stock fuel pump. It's been working for 8 years now.
 

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Discussion Starter · #18 ·
Hi Everyone,
Thanks to all of you for your help to solve this issue. I'm going to look into all of this some more, however I need to take a break from this for now to get some other stuff done around here. I will return with results, good ones I hope. I'm attaching the page I have from the Onan p218 manual on testing the vacuum and psi.
 

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