I have replaced a rather expensive fuel pump, cleaned the carb, changed the fuel and filter, only to find that there isnt any or enough vacume pressure :wave: to make the fuel pump operate, what could be causing this problem?????? , the engine, a model B48M was reciently rebuilt and running fine last fall, it will only start and run now for a few seconds when you pour fuel into the carb throat.

did you pull off the fuel line going to the carburator and see if its pumping fuel ?

it doesn't have a fuel solenoid or a simple little turn valve to cut it off does it?

did you pull off the fuel line going to the carburator and see if its pumping fuel ?
The fuel pump mounts directly to the side of the carburator, Yes I can get fuel to the pump from the tank, but not thru the pump to the carburator, If I install an electric fuel pump on it, it would have to go thru the existing fuel pump as that is the only route to the carburator. I dont know if that is even possable, I have found a mechanic that has agreed to take a look at it,may-be he can figure it out, probably something simple !!, Thank all you Guys for your input.

No ,,There is fuel to the pump, but none past it into the Carburator.

may be a possible blockage. or well you could have hooked it up wrong.

sounds to me like it could be 3 different things , impulse hose , needle valve (float stuck) , or the diapgrahm , or what bugman said w ell that would make five lol hope you get her running let us know

I have tried all of the above so many times that I cant even remember what it looked like the first time, got a guy comming to take a look at it this afternoon I hope, I had a carb man assemble the new fuel pump and clean the carb, but who knows, he wasnt two familiar with the ONAN either. Probably something simple, will post if I ever get it running.

onan's a pretty good engine, right there with briggs. if you search google for onan you'll find they're website easily. carbs well they can be difficult if you don't know how to go about them. make sure you don't lose anything off the carb either do you'll be hating yourself

I too am having problems with the carburetor on my B48M Onan 18 hp. engine. It's in a Sears GT tractor and the gas tank is under the seat. I just spent $180 at the local generator business that supports Onan engines for a carburetor kit including the fuel pump. I got it started, it ran smooth for the 20 min. I had it running. Today I went to mow the grass and it wouldn't start. I had to hand choke it (place my hand over the carburetor opening) to get it running since the choke wouldn't do it. I mowed for about 20 min. during which time it shutoff once and I was able to choke it and get it running again. Now the only way it will run is if I pour gas in the caburetor opening. Carlton Bailey, I was wondering what your final outcome was? I have removed the tank and cleaned it, replaced the fuel lines previous to rebuilding the carb..

hey carlton bailey. Did you ever figure out what is wrong with your tractor? I am having the same problem.