4 Cylinder Gas Engine Updraft Carb Help

[MossRoad]

Well, since everyone was so helpful in this post about No Spark and we got it going, I have some more issues that I could use assistance with. It has an updraft carb. It is a Marvel Schebler. I took the air intake off so that I could see that the choke is operating correctly. It is. After I run it for a few minutes, the exhaust starts to belch smoke like the unit is running too rich. The fuel starts dripping out of the inlet of the carb, confirming, in my mind, at least, that there is more fuel than the engine can suck up. Where should I start looking for problems?

I've adjusted the idle adjusting needle screw to factory specs(one turn out) with no affect. Fuel keeps drippng out of the air inlet side of the carb. I'm guessing it has something to do with the needle and float system, but it's been a while since I've worked on carbs, especially an updraft. Any suggestions?

 

[theonlybull]

sounds like a needle and seat problem to me. mostlikely dirt.
take the carb off, take the bowl off, and clean it out good, then remove the needle and seat, and inspect them. they're probably fine, reassemble, and try it again...

our 56 jd 420c had about a 1/2" of rust in the bowl..... lol

 

[AntrimMan]

I take it this leak only happens with the engine running?
If so , then I agree with the needle and seat statement above and would also offer that the float may be a leaker itself and fill up and sink thereby holding the fuel inlet open and all this only if the engine has a fuel pump. When you have the bowl off take and shake the float and listen for fuel inside if it's the hollow style. What am I saying? it must be hollow in an updraft carb, I don't think plastic was invented yet! If there is a hole it can be drained and soldered with a three prong grounded iron, no flames,in an area away from all the other combustibles, if you can keep the repair light, and to keep it localized wrap the thing in a wet rag and solder the exposed portion. Sometimes the pivot will wear through and the float has no positive connection to the needle so look at that too. Set the float body level (parallel) with the gasket surface if you don't have a spec, that will be close enough. I have also seen gum buildup cause this overflow situation in an engine that wasn't properly stored so have a little carb cleaner available just in case. As the fuel evaporates the float drops and sticks to the gum in the bowl. If gum is the problem then you better remove the main fuel tube and needle and clean these passages out too.

Gasoline is dangerous in spillage situations, keep your eyes open, be alert and work cleanly and carefully. Have a suitable fire extinguisher handy and don't work alone if you can aviod it. My dad ended up in his underwear after using his clothes to try to smother a carb fire and save the family stationwagon in a remote parking lot, he was alone, desperate and very very lucky. A security guard saw what was going on, arrived with a fire extinguisher and save the day and the dad.
Diesel is better.

Best of luck,
Martin

 

[Maine_Polack]

I owned a B414 IH, with an updraft carb. Had the same trouble. Rebuilt the carb and then replaced the carb. Also did other things. Had the local tractor "experts" baffled. Sat there for months.

A wise old neighbor man finally diagnosed it. The previous owner could not find the correct fuel pump, and apparently replaced the gas model with a diesel one. Then wired the choke in position. The pressure in the fuel line was way too much, and forced gas through carb.

I could not find a replacement either. Ended up putting a fuel pressure reducer in the line and it worked fine.

 

[MossRoad]

Thanks, folks. I pulled the carb and dopped the bowl. The float sounds like it is empty, so I think it is OK. I'll check the needle and seat next week and let you all know what I find.

 

[Soundguy]

I'd look at misadjusted float, sticky float, 'heavy' float, or crud in the flaot needle/seat.

I've worked on lots of MS carbs.. all my fords use them. Common problem of gas flooding after running is a float issue.

here's a tip.. remove the float and shake it? got any liquid in it?.. also try this.. hold in in a glass of hot water.. if there is a micro pin hole or bad seam.. it will bubble as the air inside is heated and escapes.

For the ones that like 1/4 free play.. i like to use a 1/4 drill bit end to set my float.

Soundguy

 

[MossRoad]

Thanks for the tips. I hope to be working on it this weekend.

 

[MossRoad]

Picked up a rebuild kit(had to buy it all) to get the needle and seat. NAPA had them in stock.

Removed the old needle. Needles are supposed to be pointy, right? /forums/images/graemlins/tongue.gif Ours was concave; no tip. /forums/images/graemlins/shocked.gif I replaced the needle and seat, installed a new gasket, stuck it back on, fired it up and it started right up at idle. Ran real smooth, too. /forums/images/graemlins/grin.gif

Thanks for everyone's help and suggestions. I'm pretty sure I'll have a few more in the next few days as I get this beast running and up for sale.

Next project... exhaust stack and muffler, then replacing the sheet metal and grill.

 

[jimnagle]

nice to get simple, straight-forward answers to simple questions, somethings you can go out and put straight into use. thank you.

 

[Egon]

Moss; wouldn't it look better with four Webbers and tuned ram intakes?