billyO Posted January 7, 2013 Share Posted January 7, 2013 Hello all. Last fall, I was given an older gas powered generator/welder and was told, "The last time I used it, a few years ago, it worked fine." We did a basic cleaning of the fuel system (ie, purged old fuel, cleaned out the bulb, screen, tank, new fuel line) added some SeaFoam to new fuel and the engine started and ran for about 60-90 seconds. The following week, I changed the oil and have yet to be able to start the engine. Actually, if I use starting fluid, the engine will run for a couple of seconds only. I know more about diesel engines than infernal combustion, so I could use some help. I'm thinking a carb rebuild is next, do you think this'll solve the problem? If it's anything more involved than that, I need to take it somewhere. thanks PS - It's a Marquette welder with an Onan engine. We're guessing it's circa mid- 1950's Let me know what more info you need. Quote Link to comment Share on other sites More sharing options...
pkrankow Posted January 7, 2013 Share Posted January 7, 2013 Jet and float valve is plugged.Drop the carburetor bowl being very careful to not loose parts. Remove the float, flush the float valve and float valve seat, and jet(s) with plenty of carburetor cleaner. Reassemble.There may be varnish in the fuel tank coming free and proving a headache. The carb may also need a full rebuild. Running the engine is like an ultrasonic cleaner to the fuel tank and can break gunk free. Run the engine for at least 10 minutes, preferably 30+ minutes.If it stalls and acts the same way with the jet or float valve plugged up again, then you need to remove and clean the fuel tank since it has varnish build up in it. Use lacquer thinner and a known number of nuts, bb's, or similar to agitate. Plan to take a day or two to soak with agitation every few hours.If it stalls when fully hot and won't restart till almost cold then your coil is also bad.Phil Quote Link to comment Share on other sites More sharing options...
Herb Upham Posted January 7, 2013 Share Posted January 7, 2013 I agree with Phil and add ... do not loose or damage any of the caburator parts ... they are nolonger available. The symptom you describe is lack of fuel ... I really like the old Marquett generators, they are copper wound and have excellent arc stability. If yours is a generator/welder (as I think all were) inspect the bolts in the knife change over switch. The orignials were brass and I had one break and casue a short that resulted in having to have one field coil re-wound at a motor shop. Good luck! Quote Link to comment Share on other sites More sharing options...
pkrankow Posted January 7, 2013 Share Posted January 7, 2013 Onan is out of business, and no new parts are being made. There should be plenty of parts available since just about everybody used Onan for decades, and common carburetor parts are likely the same as on other brands, or even the same entire carburetor as other brands (without looking up everything, kinda hard to know for sure though. Finding an old timer at a small engine repair place is the best bet here)All the same...don't loose any parts. You don't need the headache, and Onan parts are getting harder to find.If the float is cork, you may want to try sourcing a replacement (brass or plastic). Cork floats are sealed with shellac which is impervious to gasoline but washed off by alcohol. 10% alcohol in modern fuel wash the shellac off...you will quickly have the opposite problem of flooding.Phil Quote Link to comment Share on other sites More sharing options...
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