Model M still won't run

For a longer time than I want to admit. I have been trying to get my Model M to go.When I at last got it to start, more or less,it would not keep running. After it has been setting for awhile it will start runs fast for a minute or less, then slow down and eventually stop.Then, it will not start again until setting a length of time.So, first thought it had to be all the rust and trash in the gas tank. Cleaned it out,used an epoxy sealer and the gas is clean.Maybe the mag I thought. Repaced it with a hot mag. Set it carefully at TDC.Changed spark plugs.Still no. So, got another governer. The carburetor I had rebuilt about first of all, however it still leaks out the bottom. Seems like it would be the float.Put in another float, no luck. Turned the carb upside down measured float distance at 1-25/64 I believe it was.Same results runs like everything for a minute, then slows down and stops. Sometimes I can keep it going a little longer by closing the choke about 3/4, but it still ends up stopping, then gas leaks out the bottom.Every thing is just about as it was in the beginning. Any good practical advice will be appreciated.











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You are either losing spark, or have a gas flow restriction.

Connect a test spark plug to one of the wires, and watch it as the tractor runs/stops. Does the spark change/fail/get weak as the engine falters?

If NOT, it's a fuel restriction.

(Since you didn't mention black smoke, we'll assume it's not severely flooding.)

Did you replace the fuel line? Have you tried to run it with the fuel cap off to see if that helps? When it stops can you shut off the fuel and remove the float bowl and see if there is fuel in it? If it is empty I would think it is a fuel problem. I always unhook my fuel line from the carb and blow compressed air back through the system till it bubbles in the tank to try and remove restrictions.

When you rebuilt carb, did you take the in line fuel filter out of the carb itself and clean that part out?
Jim

This has been suggested before--take the drain plug out of the bottom of the carb & put in a hose/plastic tubing connector. Put a section of clear plastic tubing on the hose barb & hold it up along side the carb- leaving the upper end open. Start the engine & watch what the fuel level does. If it remains at the same level, you probably don't have a fuel delivery problem. However, if the fuel level drops very far, you are having delivery problems. Could be a restriction anywhere in the fuel delivery system.

Bob,I had a F12 that I cleaned the carb,It wouldnt run,Had some one else clean it,still no good.Then another person worked on it,still no good,I got mad called YTmag,they told me the price for theres ,I fainted.Ordered one any how,Put it on and it ran perfect.I had a H the same way,it would run but rought,I got mad and sold it,The new owner took it home and ran the heck out of it and it straighten out and ran good.Carbs are tough sometimes,maybe its worth finding another carb and start over,They are 50+years old,and they do wear out

jimmy

There is a screen in the fitting at the carb inlet that is often guilty of plugging things up clean that as well as the other system parts. A stream of fuel should flow out the carb drain that is 3/16" diameter, and it should flow for at least a quart with no slowing down. If it does not, it is restricted. JimN

This so smells like a coil problem.

Another Bob,

I had the same issue with my 100 not too long ago. Are you running a distributor and coil? If so go out and buy another coil and swap it in for your existing one. You can test your coil till your blue in the face and even a bad coil will sometimes test OK when it's not. It is the center set of windings that will fracture and cause a short.

Go to AutoZone or a similar place and buy a new coil. They are under $20 and you can always return it after you try it if it doesn't solve the problem so you will have lost nothing.

Mine would fire for about a minute then die, let it cool down then it would fire again but then quit. I was getting gas, air, and juice to the distributor and plugs but just not enough. Once the coil got some juice running through it, it would heat and the fracture in the winding would expand and create a short or low voltage. This is an easy fix, report back to us with your results.

Patrick,

It's a magneto, and he replaced it with a known good magneto.

If the choke changes how the the tractor runs when it's dying, it's a fuel problem. My money is on either a fuel flow problem, due to a clogged sediment bowl or line, or a float/needle issue.

I know people get frustrated and just buy new carburetors, and voila, the problem is magically fixed, but they're wasting money. A lot of money.

Short of the carburetor being smashed to pieces, there is very little that cannot be fixed on a carburetor to restore it to like-new condition and operation.

The float and needle are the hardest things to get right, because you're working blind. There's very little clearance between the float and float bowl, so if you're slightly off, the float rubs the bowl and doesn't work right. Sometimes it takes several tries.

Very few people really know how to correctly rebuild a carb, I've found out. Just because you 'had it rebuilt' doesn't mean the rebuilder knew what he was doing, or didn't make a mistake, or didn't just take your money and play you for a fool...

Might still be a tooth out of time. I had a H with a Mag, and had to set it to where the mag was just ready to trip, and it was not fun to hold it there while trying to install it,,, but it would not run with it relaxed,, it had to be almost to the point of tripping before I tightened it down to get it to run,, before it would pop, and run for a second, but sounded real labored with little adjustment, bumped it a little like said and it fired right up. I still have the scar where the gear slipped and cut my hand open,,,,,,, LOL!

Patrick,
I have had this similar problem with my M last year. What i found out was the the float would actually get caught inside the carb and hang up. This would cause the gas to not stop, but pour out the carb sometime and another time it wouldn't let gas in. I used a dremel and smoothed out the inside of the carb and tweaked teh carb so it would not hit the sides of the carb. Hope this helps some. But it does sound like you have a fuel problem. - Matt

*Correction* I meant tweak the float so that it would not hit the sides of the carb. Let me know what you find out. Matt