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Farmall M starts popping after warm up


FarmallM96

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This will be a long post but bear with me. I have a 50/51 Farmall M with IH firecrater pistons that is popping like a miss, backfire out the muffler after the engine warms up to Run temp. It also wanted to die if i hit the brake to turn sharp but I might of been low on gas. Tractor was running fine last fall baled hay bushog etc no problems, so with down time I replaced the exhaust gasket, temp and oil guages. Then one day it starts popping and missing. Replaced points, plugs, wires. No avail. Tinkering little by little found a spring in distributor broke. Replaced with one from a new distributor I had with a 40 plate not a 22. Retimed it, to 22 degrees advanced wide open 5 degrees after TDC at very low idle @400 rpms (in order to achieve the 22 degrees) and same thing. Replaced coil points condenser plugs and wires again still same outcome. Checked valve clearance and adjusted to .017 hot, still the same. Took apart carb, cleaned, readjusted and still pops. Plugs are perfectly tan color. Everything seems fine without me breaking the head and engine apart. Question for you guys is what is your thoughts on cause, maybe a crack somewhere causing too much air intake, the spring, or worse news. Don't want to rip apart head amd engine unless absolutely necessary as the M is my workhorse for everything and cheaper than my 1466 to run. Sorry for the long post I'm tired and stumped been at it for months when not at work. My dad and others also stumped so turning to you guys.

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9 minutes ago, FarmallM96 said:

This will be a long post but bear with me. I have a 50/51 Farmall M with IH firecrater pistons that is popping like a miss, backfire out the muffler after the engine warms up to Run temp. It also wanted to die if i hit the brake to turn sharp but I might of been low on gas. Tractor was running fine last fall baled hay bushog etc no problems, so with down time I replaced the exhaust gasket, temp and oil guages. Then one day it starts popping and missing. Replaced points, plugs, wires. No avail. Tinkering little by little found a spring in distributor broke. Replaced with one from a new distributor I had with a 40 plate not a 22. Retimed it, to 22 degrees advanced wide open 5 degrees after TDC at very low idle @400 rpms (in order to achieve the 22 degrees) and same thing. Replaced coil points condenser plugs and wires again still same outcome. Checked valve clearance and adjusted to .017 hot, still the same. Took apart carb, cleaned, readjusted and still pops. Plugs are perfectly tan color. Everything seems fine without me breaking the head and engine apart. Question for you guys is what is your thoughts on cause, maybe a crack somewhere causing too much air intake, the spring, or worse news. Don't want to rip apart head amd engine unless absolutely necessary as the M is my workhorse for everything and cheaper than my 1466 to run. Sorry for the long post I'm tired and stumped been at it for months when not at work. My dad and others also stumped so turning to you guys.

Check your float adjustment, don't rule out bad ign parts, give a whiff of ether or C&C around intake and carburetor to rule out leaks, check Governor weight pivots and springs and cleanliness. 
@pete23@DWV@Mudfly

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My guess is new gasket didn't seal up for some reason and your sucking air on either intake or exhaust side. Last thing worked on before the problem arose is a lot of times the problem imo. 

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I believe you need the correct springs to go with the 22* shaft in order to achieve the 22* advance. The 40* springs are not the same so your total advance is probably off. 

You are using copper core plug wires, have good unrestricted fuel flow. What plugs are you using? Just a few other thoughts.

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Start with the correct spring in the distributor but I’d also be checking your manifold closely.  Since you stated it only does it when at operating temperature, you might have a hairline crack in your manifold.  Might be a long shot.

compression, ignition, and fuel/air.  Start eliminating things.  If valves are set right, and assuming you have compression, that leaves ignition or air/fuel.  You need to eliminate one or the other so you can focus on the root cause.

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Finding the correct springs for  a 22 degree distributor will be a real challenge.   Not clear on what shaft you have in there now but sounds like maybe a 30 if you say you get 22 at full throttle and 5 after at low idle.  I have filled the  hole in distributor shaft with liquid steel just enough to obtain 22 at full rpm and tdc at low idle but it takes some figuring and trial and error.  Also, done a lot of squeezing ends of springs to change tensions.  Don't over look the condition of the weights on their pins. 

The thing with the advance though is you want a gradual advance from low speed to high speed and not quick jump. In other words, when running like 1000 rpm it should be about half total advance. It should be steady also with spark not jumping around several degrees back and forth.  If you get that then you are good .

I'm thinking though, like others, you have a manifold leak. Get the spray can out and spray around all contact areas of manifold to head.  A lp torch is good, WD 40 used to work good, not as good now days I guess. Ether is rather dangerous. 

Set the main jet on carburetor, warm engine, full throttle, screw it in until engine starts to slow or die, back it out till rpm is back, then screw out another half turn. Should get you pretty close. 

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4 minutes ago, pete23 said:

Get the spray can out and spray around all contact areas of manifold to head.  A lp torch is good, WD 40 used to work good, not as good now days I guess.

What exactly is this process. Can you expand?

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9 hours ago, KWRB said:

What exactly is this process. Can you expand?

The process pete23 said is you take a can of PB Blaster or WD40 or a propane torch without igniting it and spray or wave it around the exhaust gasket manifold, the manifold itself and around the carb air intake coupling and if it's sucking air when the oil or gas gets to the hole it'll suck it in and run great. It shows you where your leak is or at least where the problem may be at.

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9 hours ago, KWRB said:

What exactly is this process. Can you expand?

Spray around manifold while running. If rpm changes you found your leak.

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9 hours ago, pete23 said:

Finding the correct springs for  a 22 degree distributor will be a real challenge.   Not clear on what shaft you have in there now but sounds like maybe a 30 if you say you get 22 at full throttle and 5 after at low idle.  I have filled the  hole in distributor shaft with liquid steel just enough to obtain 22 at full rpm and tdc at low idle but it takes some figuring and trial and error.  Also, done a lot of squeezing ends of springs to change tensions.  Don't over look the condition of the weights on their pins. 

The thing with the advance though is you want a gradual advance from low speed to high speed and not quick jump. In other words, when running like 1000 rpm it should be about half total advance. It should be steady also with spark not jumping around several degrees back and forth.  If you get that then you are good .

I'm thinking though, like others, you have a manifold leak. Get the spray can out and spray around all contact areas of manifold to head.  A lp torch is good, WD 40 used to work good, not as good now days I guess. Ether is rather dangerous. 

Set the main jet on carburetor, warm engine, full throttle, screw it in until engine starts to slow or die, back it out till rpm is back, then screw out another half turn. Should get you pretty close. 

Pete23 I have the orignial shaft for the distributor, You aren't even kidding on the parts and I don't have a caseIH dealer near me and finding one online is impossible so far. I will try to find a leak and if I was wrong in the process please feel free to correct. It's timed to your posts and does have a gradual advance and gradual degress when dropping from full throttle to low idle. I will look again to see if it is jumping around degrees and tighten the spring as well if it is.

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Since you had the manifold off and replaced the gasket, I would warm it up and then torque the intake/exhaust manifold.

Then run it awhile longer and re-torque it.

Popping is generally a lean condition.

I have seen some of those studs so far out of the head that they barely tighten the manifold.

If that is the case, the studs can be removed, chase the threads with a tap and then replace the studs.

Any good parts house should be able to get them or tractor supply house. 

If you remove it again, put a straight edge on the mating surface of the manifold. 

It may need planing.

 

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our 185 was doing the same thing

went threw the engine and found the distrubitor bushing worn and it had slop.

this will throw the setting of points off [doesent take much]

installed a new electronic kit and it runs great.

Mike

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If you by chance put Champion plugs in it, get them out and put another brand in. Not saying that is your problem, it’s just that Champions are crap plugs in my book. Have had nothing but bad luck with them for many years. 

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Possibly a bad coil or distributor cap?  Some night when it is blacker than black, start it up and watch for arcing around the coil or cap terminals. Might even be plug wires. If nothing shows up there, a compression test might show a cracked head. I have had all the above happen.

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It's not cap points condenser coil wires or plugs as far as ignition goes. Plugs are autolites, everything else is new and has been swapped around off of my C which is running fantastic to ensure I have good parts as nothing is made like it used to be. Still pops but C still ran like a charm. Distributor was great minus spring no play in bushing and the pin was good too heard to look at that too while I had it apart. I'm going to look and see if I have a leak in manifold area first and make sure I don't have sporatic jumping in timing and need to readjust/replace spring, then do a compression test will let y'all know this Sunday afternoon if I find something.

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1 hour ago, FarmallM96 said:

It's not cap points condenser coil wires or plugs as far as ignition goes. Plugs are autolites, everything else is new and has been swapped around off of my C which is running fantastic to ensure I have good parts as nothing is made like it used to be. Still pops but C still ran like a charm. Distributor was great minus spring no play in bushing and the pin was good too heard to look at that too while I had it apart. I'm going to look and see if I have a leak in manifold area first and make sure I don't have sporatic jumping in timing and need to readjust/replace spring, then do a compression test will let y'all know this Sunday afternoon if I find something.

Did you swap rotors out? I had a wobbly rotor that was doing weird stuff. I squished it on with some piece of plastic wrapper as a test and it all cleared up. 

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Ok guys so sprayed PB blaster around manifold did slightly better but not significant change I do believe though that is my problem. Dry compression test showed 85 on all 4 cyl which is a low in my opinion for those pistons but not that bad either as old as it is. As for timing I checked it forgot I put it back to TDC its TDC at low idle at 400-415 Rpms but at wide open it's 5 degrees past the 22 degree markband does jump around a degree or 2 back and forth at wide open but not at low idle half or 3 quarter. Will try to tighten the spring to see if that helps plus closely inspect the distributor again. Going to take the carb manifold etc off again put on another new gasket go through and inspect carb again. Don't know if that helps you guys thinking any but it's what I come up with.

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