MF135 Compression Test

I expect to jack up rear end and turn back wheels while in gear to get readings. Is this the best way to get readings? What's an 'Overhaul-now' reading?

Big Dean thought that new ones ran about 150 PSI (couldn't remember for sure) and suggested that 130 +- 5 was good and would mean the engine was in good shape from there on down... also needed to have no more than 10 PSI between cylinders.

Does this jibe with other's experience. I assume if compression is good then it could be valves or carburetor.

Also, in order to make sure that my carb is adjusted right, what's the procedure?

Thanks a bunch....

bd

Generally compression tests are done by cranking with the starter (all plugs pulled). Throttle full open. Choke full open. Clutch pedal pushed and transmission in neutral.

Black smoke is not oil, its fuel too rich. Comes from the high speed jet being a bit too far open but on my 4 cylinder gas MF-135 that's the condition that produces the most power... Just a bit of smoke. Smoke when accelerating is a hint the acceleration pump is a little ambitious. Both might be a hint that the float needle is leaking or that the float is sinking or is adjusted to have the gasoline level in the float bowl a little high. A leaking float needle and seat is common in older tractors. Its the first thing to replace with black smoke. Then its important that the air cleaner is itself clean, that the choke opens all the way and that all the insect and bird's nests are cleaned out of the precleaner and air intake plumbing.

Gerald J.

My aircleaners are like new and no obstructions in tubing. Carburetor was 'supposed' to be rebuilt before I bought it and it surely was worked on...but whether everything was rebuilt and adjusted???

How do I know if the float is set/operating properly?

How do I check to make sure that my choke is operating properly? Pulled all the way out, flap completely closed...Shoved all the way in...flap completely open?

The machine idles OK. How do I do a fuel adjustment..., can I screw in the adjustment screw until it labors and then back out until it doesn't? What speed of idle should such take process take place?

Is there a resource for this online? I have the manual, but don't recall seeing anything about adjusting the carb in it.

Thanks again...I value the help in troubleshooting and getting a little more educated.

bd

The carburetor tune up instructions should include the distance the float should be from the carburetor separation flange when the valve is closed.

There should be two mixture adjustments, one for idle (often an air adjustment) and one for high speed or loaded.

You adjust the idle mixture with the engine running as slow as possible. The governor will hide the results of your adjustment, but you can often use the throttle plate position as indicator of best mixture. You slow the engine down as slow as you can (might have to back off the idle speed adjustment on the throttle segment) and adjust the idle mixture for the least throttle opening. Or you pull on the governor rod to close the throttle and while holding the throttle closed you adjust for fastest idle speed with the idle mixture screw.

For the high speed/power jets, I adjust that for the fastest speed pulling a plow with the plow pulling hard enough that the speed is below what the governor would run. That usually results in the mixture being on the rich (a bit of black smoke) side but the engine runs coolest with the greatest power under that condition. Setting it leaner can improve efficiency though and may eliminate the black smoke on acceleration.

These two adjustments interact so you have to alternate them a few times until you find no improvement in either.

The choke should open completely when the choke button is pushed all the way in. You may have to take off the air intake hose to check its position.

There may be an adjustment for accelerator pump output and its set for a bit too much. Lowering the float (increasing the distance from gasket flange when the float valve is closed) will lean the mixture under all conditions, but I don't know about that effectively reducing the output from the accelerator pump. It may be that the orifices that the accelerator pump discharge from have been enlarged by excessively aggressive cleaning and need to be replaced.

An economical engine carburetor adjustment will leave the exhaust pipe interior coated with something gray, not black. But not much of a coat at all.

Some of this is in the owner's manual, some in the shop manuals, some in automotive shop manuals. I've read many, so I can't be sure exactly where each bit of information came from.

Gerald J.