# Welder motor won't keep running



## CIW (Oct 2, 2007)

I have a Lincoln Ranger 250. Powered by a 16 hp., Onan, "V" Twin motor.
I haven't run it for several years so I drained the fuel out and replaced it. Ran new fuel lines. Replaced the fuel filter. Changed the oil and filter. Put in a new air filter.
My problem is that it won't start and stay running unless I pressurize the fuel tank. And then dies as the pressure goes down.
Was looking and there is what the manual calls a vacuum pulsating fuel pump in line. Attached to the side of the carburetor. Took it apart. There are 2 butterfly baffles inside. Nothing seems out of sorts. It doesn't leak fuel.
Have any of you had any experiences with these kinds of problems? Do these commonly go bad? Just scratching my head.


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## simi-steading (Sep 27, 2012)

The carb is probably varnished up from the old bad fuel... You should take it apart and clean all the passages with a good carb cleaner.


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## Nimrod (Jun 8, 2010)

What Semi said is frequently the problem with motors that have sat for a while. The whole "runs when the gas tank is pressurized" thing doesn't necessarily support the gummed up carb theory. If the jets and passages in the carb were plugged up so much that the vacume generated by the piston going down can't suck in enough gas to keep the motor running, then I'm not sure pressurizing the tank would help. 

Try disconnecting the fuel line from the carb, turn the motor over and see if gas squirts out of the hose. If none or weak, replace the fuel pump. It only take a pinprick hole in the pump's diaphragm so it doesn't work.

One of my Briggs motors has a fuel pump that is driven by the pressure in the crankcase. It has a sealed crankcase so the pressure goes from pressure to vacuum as the piston goes up and down. I would check for a leak in the crankcase.


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## simi-steading (Sep 27, 2012)

I can't remember if the Onan has a rubber coated fabric pump diaphragm or not. If it is, it never hurts to replace that. I know Briggs are the rubber coated fabric... 

If a carb passage is partially blocked, it could be the problem... I've seen if you pressure the tank with an engine even without a fuel pump it will act like this with a partially blocked carb.. It/s kind of the same as running it with the choke.. It pushes it into different passages..


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## Bearfootfarm (Jul 13, 2006)

Put some Sea Foam in the gas when you get it back together and that will clean places you can't get to


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## CIW (Oct 2, 2007)

Well, I removed the vacuum line that comes from the crankcase and goes to the fuel pump. It was held on by spring clips. Replaced the hose and installed hose clamps on each end.
Started it right up.
I think that the hose was loosing vacuum at the connection ends. In fact it starts better than it did when I purchased it new.
Its funny how a couple of dollars in parts can have so much influence on the outcome of a problem.
I have a Miller welder that has to be cranked heavily to get it to start. I am going to check it to see if it has a similar situation.
Wherever they can save a buck when they build something.


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