Stumped on M Tuning

[topkeg]

My M runs great in 30 second interval and/or with no load. I have rebuilt the governor, brand new carb. It runs great but then sufferers and back fires. If there’s no load it recovers on its own. I’ve set and reset carb, messed with timing, all to no avail. One thing that could be a clue is it loves to be choked. Will not run with choke off. What next?

 

[rustred]

have you felt the coil when its acting up. if its from very warm to hot replace it.

 

[used red MN]

I would suggest a fuel flow check. Flow out of the carb bowl drain should fill a pint jar in 3 minutes and that is a bit on the shy side for an M. This does not count the first 5 to 8 seconds of flow after the plug is pulled while the carb bowl drains. If it goes to a dribble after 10 seconds or so you have to figure out where the blockage is. If you have an inline filter some of them don’t work the best on a gravity system. Often the top of the sediment bowl where it flows out of the tank get plugged with rust or crud. Use a good flashlight to look down around the outlet for crud in the bottom. You say you have a new carb, not sure if your fuel line may have a lot of crud in it but originally there is a fine screen in the fitting that screws in the carb for the fuel line to connect to. It may be plugging.

 

[560Dennis]

suggestion, remove the tuning (one eighth pipe Plug )from the intake manifold . Put a vacuum gage on it , tell us what happen on the gage ?
do you have domed pistons in your engine?

 

[rustred]

My M runs great in 30 second interval and/or with no load. I have rebuilt the governor, brand new carb. It runs great but then sufferers and back fires. If there’s no load it recovers on its own. I’ve set and reset carb, messed with timing, all to no avail. One thing that could be a clue is it loves to be choked. Will not run with choke off. What next?

you say you have a new carb , so it strikes me odd that you would not check the fuel flow. pretty much standard procedure when doing a carb job. plus a person should run some fuel out the gas line at carb end before hooking up the line to carb to prevent dirt entering your cleaned carb. fuel will run out at a full line flow depending on fuel in tank. i have never stood there and timed gas flow yet. i know what the flow should be from experience. and also cleaning the sediment bowl is also done when doing a carb job,... everything from tank down is checked. and with the points set to spec,.020 , then you set your timing to the factory spec. tdc static, can check the advance with a light when running. there is no reason to be playing with timing, when you know its set. the carb is always set after the timing , never before. plus make sure the main load screw at the bottom is 3 turns out for sure and up to 5 turns out for heavy pulling. set the mixture screw for max rpm, at a slow idle, then set your idle to 400 rpm. then when you advance the throttle quickly from this idle it should rev up to max idle with not spitting or sputtering. you said backfiring, and when you stop the engine it should start with 1/2 a revolution. a carburetor does not cause a backfire. it is improper firing order , burned valves that cause a backfire. a sputter and a backfire is two different things. i have had tractors run out of fuel and they dont backfire, they sputter. so when this "backfiring" and stopping is happening have your 1/2" and 5/8 wrench to remove the fuel line from the carb so you can get a visual on your fuel flow. if you have a full line of fuel flowing that is not your problem. and also feel the coil, if hot replace it, as it done. plus when did you have your valves set? it also can be a tight valve. spec. is .017 hot. and a valve setting is included in a major tune up. so a couple of easy checks here to find your problem, the post back what you find.

 

[used red MN]

rr, yes you know what the fuel flow needs to be for the tractor to run properly. The average Joe may not and it is hard to give a description of enough flow. That is why I give the timed test, it’s a “dumbed down” method but it is something anybody can do and get a qualified result. And if you notice I add in there if it goes to a dribble 10 seconds you definitely have a problem. Per the “last seen” how ever accurate that may be he missed your second post by 20 minutes.

 

[rustred]

rr, yes you know what the fuel flow needs to be for the tractor to run properly. The average Joe usually does not. That is why I give the timed test, it’s a “dumbed down” method but it is something anybody can do and get a qualified result. And if you notice I add in there if it goes to a dribble 10 seconds you definitely have a problem. Per the “last seen” how ever accurate that may be he missed your second post by 20 minutes.

well when you're draining the carb bowl it will go to a dribble in 5 seconds after the bowl fuel is drained, then you are only trickling the gas into the bowl from a 3/8 line through a 1/16 " hole in the seat. you have a dam already. i see no reason to stand there for 3 minutes watch gas dribbling out of a carb to fill a pint. it's not an accurate test any how as the sediment bowl inlet can have junk in it and be already restricted. it's important to check the flow right at the carb inlet not run it through a valve and time it. no different than doing a fuel pump check. i didn't think i needed someone to remind me how to do a flow check. do the check at the end of the fuel line and that should fill your pint in 10 seconds. and that is why the w9 tractors have a fuel pump to keep the bowl full cause they burn so much gas, and on a low tank of fuel the gas wouldn't run into the carb fast enough. and no the average joe dont know, but should be able see a good flow of gas out of a 3/8 fuel line. that is why i advise them to do a flow check watching the gas run into a can with a full flow of gas and if its not then the problem is very obvious. thats the way i do my fuel flow checks. you start at the tank, clean your sediment bowl watch and the flow, and proceed to the carb end.

 

[300guy]

When this starts happening, have a can of starting fluid with you and quickly spray some into the air cleaner cap to see if it comes back to life. If it does, you have a fuel problem. If not, you have an ignition problem. You can do this from the drivers seat.

 

[bc]

The new carb has me wondering if you have had any fuel tank issues in the past with rust, etc as I did a couple carb rebuilds to the point I wasn't sure I was getting all the passages cleared before buying one. Mine did the same think as it would only run on the fuel in the carb and then it would take a bit to refill the carb because of the rust blocking the line. Having acidized a tank about 3 different times only to have the rust come back it finally came time to have it coated inside. If you have a fuel problem then you can come out of the tank with a drip leg and tee off to the sediment bowl and the rust will fall down into the drip leg where you can remove the bottom cap to clean it. I've also cut a piece of window screen and roll it up and put it in your drip leg so it sticks up an inch or so into the tank so it will catch the stuff on the bottom and still let fuel in. If your sediment bowl screws right in to the bottom of the tank you can still roll a piece of screen to stick up into the tank.

A leaky intake manifold gasket will make it only want to run with it choked. I've never had a vacuum gauge but spraying a little starting fluid or carb cleaner around the manifold will cause an increase in rpm if there is a leak.

 

[560Dennis]

Wonder if got it running good ?

 

[used red MN]

Wonder if got it running good ?

He has not been back to look at any replies since your #4 yesterday. You can check the “last seen” in their profile.

 

[560Dennis]

He has not been back to look at any replies since your #4 yesterday. You can check the “last seen” in their profile.

Must got it going ,something simple ! That s good

 

[topkeg]

Sorry I didn't post results quickly. Yes it was just starved for fuel. I have a tendency to go down a rabbit hole and forget some basics. Rustred, you obviously know your stuff, but i'm sorry I don't have your knowledge level so excusuuuusssseee me for not seeing the obvious. I was getting flow at the point of carb entry... but only about half of what it needed. Used Red MN's idea was great. This old M needs a rebuild, but right now I don't have the time or money to go that route. Just need enough to pull dead trees into the pasture.

 

[used red MN]

Thanks for checking back, enjoy your tractor!

 

[560Dennis]

Sorry I didn't post results quickly. Yes it was just starved for fuel. I have a tendency to go down a rabbit hole and forget some basics. Rustred, you obviously know your stuff, but i'm sorry I don't have your knowledge level so excusuuuusssseee me for not seeing the obvious. I was getting flow at the point of carb entry... but only about half of what it needed. Used Red MN's idea was great. This old M needs a rebuild, but right now I don't have the time or money to go that route. Just need enough to pull dead trees into the pasture.

These old M last , before you rebuild share with us some measured data as to what is compression is for example. . Could save you an unnecessary cost and not gain any benefits for your effort. For your consideration best of luck with your M