My Tractor Forum banner

sears SS/twin with Onan Engine, fuel problem

4K views 22 replies 7 participants last post by  elsimon 
#1 ·
I have a older sears SS/twin I use to mow my yard. Every year I have the same old problem.Not getting enough fuel. I have replace the diaphragm in the fuel pump several times. It works for a while. I wanted to know if I could convert this over to a electric fuel pump? If you have been there and done that I would appreciate any help. Thank you for your time
 
#2 ·
I recommend you do not put an electric pump on.

Much of the time the problem of losing fuel in the lines is due to a few issues:

1) the fuel lines could have collapsed due to crummy ethanol fuel or could be dry and brittle- replace them all. you may want to do this every couple years unless you use fuel injection line, or at least put good ethanol resistant line.

2) the tank could have a blockage in the outlet

3) you absolutely NEED clamps on all the fuel hose joints or you will get air leaks and fuel will drain back

4) GET A BRASS FLOAT - it will save you headaches so often - the foam floats swell with moisture in crummy ethanol gas and will stick closed, or stick open and cause flooding.
https://www.ebay.com/itm/ONAN-BRASS...934046?hash=item5ae1000ede:g:lzwAAOSwAYtWHvei


5) use a sintered brass easy flow through style fuel filter
https://www.ebay.com/itm/10pcs-1-4-...748215&hash=item3b2453468f:g:FD4AAOSwkXFcBe~T


6)You can add a one way check valve that will keep fuel up near the carburetor so it should start quicker.
https://www.ebay.com/itm/2pcs-6MM-N...351436&hash=item4b2ba46b41:g:c9kAAOSwAHtZ9tOK


7) Clean the carb well- I am talking using hang tag wire to clean the idle circuit out, and make sure the carb cleaner will spray though all the passages freely.

8) Have Patience. When you get them to run correctly, it is so worth it!


I have rarely ever had to buy new parts for onan carbs. they get a bad rap mostly because i think people lose patience with them.
Most times, keeping them clean, and rubbing the diaphragm with transmission fluid or motor oil to soften it up will keep them running for a long time.

If you want to use an aftermarket pump, add a briggs style pulse fuel pump it will work better than the onan one.



You basically run you fuel line from the tank into this guy, hook your pulse (vac) line up to this, and the output of this pump goes to the inlet of the Onan fuel pump.
That works fine, but when I switch to a newer style pump, I try to (and I stress try to) find a onan pump off a 318 john deere, and use the fuel input plate from those instead of the pump plate on the onan.

this style john deere pump- you basically use just the inlet fuel plate, and take all the pump stuff off the Onan DD carb

this setup for me has worked the best

not sure if I forgot anything, but if I did, I will add more info.
 
#3 ·
Mods, this would be a good sticky- I have explained this literally hundreds of times
 
#5 ·
I just now replaced all fuel lines. Last summer i put new diaphram in fuel pump and it ran good all summer. Now when i try to start with choke on, it will run about 5 sec and die. What do you think i should do next - fuel pump, carburetor or something else?
 
#8 ·
have you put a brass float in the carb yet?
 
#7 ·
Hi
It was mentioned using fluid or oil on the diaphram, I use marvel mystery oil in all my onan tractor gas, seems to keep all the rubber parts lubed and soft as well as coating all the metal parts to keep down corrosion, I found the hard way you can't hide from ethanol, change fuel filters often, the paper element is bonded in with shellac and ethanol will disolve and eat up the bonding sealer and send into carb.hard to tell unless you cut the filter apart.
Have A Good Day
Jimmy
 
#9 ·
today i took fuel pump off cleaned and put some lub on the diaphrams. Tried again, it died after about 3 sec. Sprayed gas into carb, it will run until out of gas ,,,,,,,,,,,,, i guess my next step is the carb unless someone can think of something i didn't try. I am retired so i guess i have all day to putts around with the mower. We will just call it a work in process.
 
#11 ·
If you do install an electric fuel pump,make sure it is the lowest pressure version available--you only need like 1-3 lbs for a small engine,and Onans tend to flood easily,and they do have float issues and very fussy carbs--you don't want a crankcase full of gas,it wont live long once the oil gets diluted..

It might be your not getting enough fuel delivered from the tank to the diaphragm pump,a fuel fitting may have a screen in it that is now blocked up,or some rust flakes in the tank might block the fuel outlet..
 
#15 ·
pull the top off the carb and look to see what type of float you have. It doesn't take long to do, and if you have a foam/fiber float, change it out with a brass one and I gurantee it will work better. It may not solve all your problems, but so far I haven't seen you say if you have checked that yet. The foam floats swell up with the ethanol fuel, and will stick. If they stick down, your carb floods - if they stick up, you don't get any gas. If they dry out for a few weeks, often times they will shrink again and work for a short period of time.

I can't stress enough, check the float. If you don't do that, new pumps, new fuel lines, will not help.
 
#21 ·
basically you just bend it to adjust the height.
 
#23 ·
It may sound funny but I was having a similar issue earlier this year with The Ghost (18/6). I also replaced the points and that made a HUGE difference as well.
 
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top