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Tractorholic
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Discussion Starter · #1 ·
I have a '79 SS16 Sears, it has the Onan twin on it. I'm putting a new electric fuel pump on it. I had rebuilt the carb about 3 years ago, including the stock fuel pump that's on it, and it never really ran since, I didn't have time to fiddle with it so I pushed it into the back of my shop and forgot about it.

Fast forward to this week, I decide to pull it out and get it going. Ordered a low pressure pump from Amazon and got going on installing it. Have it rigged up temporarily just as proof of concept, but she still won't run. The fuel is getting to the carb but not into the engine, fires fine if I squirt gas right into the intake. So methinks that maybe I need to alter something with the OE pump to let fuel pass through it? But I thought I'd ask on here first before I continue fiddling with it. I know there has been a few guys that have replaced the OE pumps on their Onan's with low pressure electric pumps. So how did you do it? Given enough time and money, I can fix anything, but I thought this might help fast track that process a bit lol
 

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I hope that you are completely by passing the pump. Check the fuel flow at the carb. If fuel is getting to the carb, the problem is in the carb. Good Luck, Rick
 

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Is the pump on the carb? I had to take mine off and make a plate to fit with a hose barb in it years ago!
 
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Red Tractor Nut & Diesel Addict
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You can block off the original vacuum fuel pump hose & pump directly through the carb's made on fuel pump, BUT the OE pump usually has lots of fines that build up inside it, which then can break loose & plug the float needle. Better to take the pump apart, clean out well, then give it a try. While in there, cut off the flappers in the gaskets that act as check valves.
 

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Tractorholic
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Discussion Starter · #5 ·
You can block off the original vacuum fuel pump hose & pump directly through the carb's made on fuel pump, BUT the OE pump usually has lots of fines that build up inside it, which then can break loose & plug the float needle. Better to take the pump apart, clean out well, then give it a try. While in there, cut off the flappers in the gaskets that act as check valves.
Thanks olcowhand. Like I said it was all apart and rebuilt but still didn't seem to function. I'll cut off those flappers and see what happens. Might get some down time in the am to play with it. It's silage time, you know all about that I'm sure.
2fcc16f9a6d55aed26cb43727b7b0f07.jpg


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Red Tractor Nut & Diesel Addict
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Thanks for the pic Mac. Nice Massey there! Yes, been doing silage every year of my life till last year. All my silage equipment has been sold. A small part of me misses silage time, but a larger part is glad that pressure is gone. I do love the smell of corn silage though, so once what I have left is gone, I'll have to go visit a dairy to get a whiff.

I would go ahead & make sure the needle seat & all passages are open while right there at the carb. Also, does it have the new style brass float, or does it still have the old composite float? The composite floats can easily distort & rub the carb bowl, which can lock it in place, either causing the needle to be closed, or stuck open.
 

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Jack of all trades, master of none.
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One simple thing to check. Did you put the needle in backwards ? If you do the float won't open the whole way on those onans
 

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Hi I converted my 16 HP Onan to an electric pump just removed the engine pulse hose and blocked it and put a cap on the fuel pump pulse nipple and it works fine no need to cut any flapper valves off but it might be a good idea to make sure there's no dirt blocking as posted also check that the float isn't hanging up on the bowl walls this can happen on those carbs and then the needle valve is stuck shut. Does it have a plastic or metal float in it?
 

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I recently brought home my first onan powered garden tractor. No prior experience with Onan. The people where i bought it said it needed a new carb and hadn't ran in 7 years. It had an electric fuel pump installed on the side blocking the access to the oil filter. The pump was dead as I would expect after 7 years, I have never had good luck with electric fuel pumps. I got the starter functioning checked the oil, it was up and clean. Pulled the plugs and spun it for about 30 seconds several times to distribute oil. Checked for spark, no spark, clean and adjust points, good spark. Hooked up a gravity feed line to the carb put the plugs back in and attempted to start. NO GOOD. Put a shot of gas down the carb. It purred just fine until the shot is burned and quits. Now I notice that the fuel inlet on the carb is the top and the dummy inlet is on the bottom, contrary to what I see in the online pictures. So I pull the side of the carb and discover OO this used to be a fuel pump, it had tiny brass read valves which someone had ripped out. looks like gass should pass hear without restriction so I put this part bak together and pull the top of the carburetor. The bowl is dry. I feed gas through the line, it comes up through a hole that is blocked by the gasket. Turned the gasket over reassembled. Put gas in the gravity feed pull the choke turn the key. it fires right up and idles just fine. Now the fuel pump problem. I go to town 30 miles away, buy 10 feet of 1/4 fuel line, to much is better than not enough. Fuel filter, USED Briggs impulse fuel pump and hose clamps. Come home mount the pump on the front side of the battery box run all new lines including impulse line to crank case. Looks like I did it on purpose and runs perfectly. Hope this helps someone, Don
 

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Tractorholic
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Discussion Starter · #11 ·
So I'm a dummy lol found the problem. I guess 3 years ago when I rebuilt it one of the gaskets went in backwards and was blocking the flow of fuel from the pump to the carb. The pump on it was brand new as well. Anyway, I gutted the old pump I had (saved the new one) and installed the electric pump. It needs some fine tuning but other than that she purrs like a kitten once again. Thanks for all the help guys.

4b515cf0c4a93e3e9a195b28d28b1511.jpg


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So I'm a dummy lol found the problem. I guess 3 years ago when I rebuilt it one of the gaskets went in backwards and was blocking the flow of fuel from the pump to the carb. The pump on it was brand new as well. Anyway, I gutted the old pump I had (saved the new one) and installed the electric pump. It needs some fine tuning but other than that she purrs like a kitten once again. Thanks for all the help guys.

4b515cf0c4a93e3e9a195b28d28b1511.jpg


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Yep Same problem I had, Different gasket. Small details count. Don in Washington State
 
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