Can a Carb sucking air causing soot deposits

ratface · May 22, 2016

Hi all. Tractor is a 1949 frontmount. Been running great except an exhaust leak at the manifold number 4 port. So I changed out the manifold with a new aftermarket. Tractor runs like crap now, soot all over plugs within 30 minutes run time while hogging, noticeable power loss. I clean the plugs it improves and then soot all over again. This tractor until this had zero deposits on plugs, always a nice grey color. I notice one carb nut is a little off kilter and not really tight and it wont tighten anymore. Pull carb and see I had left old gasket on which probably took up some thread space. Carb was on with two gskets. Thought this was causing the sooting. Reinstalled carb with one gasket thinking that would cure it and it did help a little bit but pulled plug and still getting black and sooty again. Does a gasket leak cause sooting? Maybe I'm still leaking, had to use the old gasket again but it wasn't too bad. The idle mix screws although I have messed with them some are about back where they were before my sooting issue but why is it still sooting?

Royse · May 22, 2016

If by sooting you mean carbon deposits, they can be caused by
a carb that is running too rich. Given the description of your
repairs on the manifold, that may be the case here.
Carb could have been adjusted rich to make up for an air leak.
Then you fixed the air leak and it is now running too rich.

Turn your main/power adjustment in a quarter turn and see if that helps.

It can also be caused by weak spark. How old are your points?
Granted, coincidence that it would occur at the same time.
But checking spark quality is free and easy.

Dell (WA) · May 23, 2016

rarface........it should be intuitively obvious, sooty plugs mean yer carbie is RICH. While the #4 exhaust often "erodes", that does NOT cause sooty plugs, just louder exhaust. Heres the way I recommend you adjust yer carbie. Adjust the down-pointing mainjet to 2-turns and LEAVITT!!! Adjust the side-pointing idlemix for FASTEST idle, NOT SMOOTHEST idle. Understand the difference??? The side-pointing idlemix is BASSACKWARDS; out fer lean; IN fer ENRICH. Usually ends up about 1/8-1/4 turn. Also recommend AutoLite 437's gapped 0.025. As fer yer front mount dizzy, points (0.015) are designed to be replaced on the kitchen table. Just un-snapple yer capple and remove the 2-bolts and walk. After installing the points (0.015) clamp the corner of $1-bill (cheap) between the points and PULL. Polishes the INVISIBLE CORROSION from between the points. Installation is a reversal of the removal ...except... finger start the 2-bolts and install the rotor. Now rotate the rotor until the OFF-SET tang fits the OFF-SET slot in camshaft. Now tighten the 2-bolts and re-snapple yer capple. Simple, eh? ........HTH, the amazed Dell

ASEguy · May 23, 2016

I would adjust the carb first, and if that doesn't clear up the issue then you might have gotten debris on the needle and seat and it's dripping fuel. I learned the hard way a long time ago to keep your carb upright to avoid problems when it has to be pulled.

Phil N · May 23, 2016

You may have stirred up some junk in the cab by setting it down sideways or upside down. Take the carb apart and clean every passage real good. Rebuild kit if you want. Try again and let us know how it goes.

Tim PloughNman Daley RIP · May 23, 2016

No to your question but I'd get the carb fixed first. "A little off kilter' -what does that mean? The carb manifold studs are differential type as are most all studs and that means they have a coarse thread on one end, which goes into a cast iron mating part, and the other end is a fine thread which in this case accepts the steel nut. If unable to perform carb rebuild yourself, a few members, myself included will do it for you. ROYSE is a very good carb rebuilder first choice...

Tim *PloughNman* Daley(MI)

ratface · May 24, 2016

Tim, "Off Kilter" one of the carb nuts was not sitting flat on the stud and it wasn;t really tight. It seems the threads are worn and not letting the nut tighten completely. Anyone know where to buy these locally, are they some standard configuration at a hardware store?

Royse · May 24, 2016

"Anyone know where to buy these locally"

If you have a hardware store or automotive store that sell Dorman
products they would probably have them or could get them.

Dorman part# 675-091 - Studs, Grade 8, 5/16 in.-18, 5/16 in.-24,
Threads, 1.250 in. Length. ( Would not need to be grade 8 )

I order them from Summit Racing because they're cheaper than
my local parts store on this particular item.

ratface · May 24, 2016

Thanks for the info Royce

Royse · May 24, 2016

You're welcome! By the way, if you find the ears of the carb
are stripped and you have to drill and tap to fit 3/8 in there,
the stud with 3/8 bottom and 5/16 top is 675-097.
Its not all that uncommon.

Can a Carb sucking air causing soot deposits

ratface

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Royse

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Dell (WA)

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ASEguy

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Phil N

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Tim PloughNman Daley RIP

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ratface

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Royse

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ratface

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Royse

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