Black smoke from gas tractor exhaust

chuckinnc

Member
I noticed black smoke coming a mf35 gas tractor I recently purchased, seems to run ok but rear exhaust has coated the limiter chains on the 3pt hitch arm for that side. I am not much on gas engines so I think it maybe running to rich? Anyone had this problem before?
 
It is normal for items behind the horizontal exhaust to be soot covered even if all is well with the engine.

That said, if you see black exhaust, push the choke in and verify that the air filter is clean and functioning properly.

Dean
 
Yes, that is pretty normal for those tractors.

A few things to check:

The air cleaner is a much neglected item. There is more to it than just cleaning the oil bowl. There is a mesh inside the upper canister that also needs cleaning. If it has not been cleaned, it will be so packed the mesh will need to come out, quite a job, but it can be done. If not fully clogged, it can be washed out with solvent or diesel.

Any other problems need to be addressed before attempting to adjust the carb. The ignition system needs to be right, valves properly adjusted, clean fuel, choke linkage adjusted, etc.

When parked not running, and the fuel valve on, does the carb drip gas? If so, the float valve, the float, or the float level may have issues. This needs to be repaired before trying to adjust the carb.

When adjusting the idle mixture, does it have an effect on the idle quality? If not, the idle air circuit is clogged, the carb will need to come apart and be cleaned. BTW, the idle mixture, the small screw at the top, adjusts backward of most carbs. With the engine up to operating temperature, idling around 400-500 RPM, back the screw out until the engine falters, then back in to best idle, then about 1/8 turn more in.

For the main jet, it adjusts in for lean, out for rich.

It is a little trickier to adjust. Again with the engine up to temperature, set the engine speed to full governed throttle. Turn the main adjust screw (the larger screw) in 1/4 turn.

Look in front of the carb, locate the governor link, pull it back to bring the engine to idle. Release the link, the engine should accelerate at full throttle back to governed speed. Listen to the engine as it comes up to speed. It should come up to speed without hesitating or faltering. Keep repeating the process, turning the main screw in 1/4 turn at a time, until the engine begins to hesitate while accelerating. Once you find that adjustment, start backing the screw out 1/8 turn at a time, repeating the acceleration test. Once the engine will take throttle without hesitating, that is where the main will be set. A single puff of black smoke while accelerating is normal.
 
We had a 35 with Continental gas engine. You should not see smoke normally but soot on the check chains is normal as they idle a bit rich even when tuned right then blow the soot out when you open the throttle.
 

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