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still struggling with a fumbling M


vtfireman85

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This M is something I have been going round with since last fall. I found the idle jet snapped off and mutilated in the carb, great, don't know how it ran before but it seemed to run well, until it didn't. last year I fought with timing it, when I found the carb issue I hoped I had solved the problem. 

This fall, I rebuilt the carb, full kit, jets, throttle shaft, bushings, the works, set the timing according to the manual, #1 TDC rotate mag until impulse clicks, tighten mag down. at @pete23 suggestion I set it to the 5 degree mark. To do this I had to retard?( anti-clockwise) the magneto drive gear 2 teeth, but now I am able to time it consistent with the instructions. When I did all this it would accelerate well, seemed to have power but still ran rough, popping at idle and audibly fumbling at WOT and no load, under load it seemed to smooth out. I decided it hadn't had the valves adjusted recently so I would do that, manual says .017 hot, I found them all out of adjustment, as much as .073, after adjusting the valves, now it wont accelerate smoothly. you get the stumbling you see in the video, regardless of what I do with the carb or where I adjust the mag. 

The carb is set, in the video with the air screw at 1.5 turns and the fuel screw at 3 turns, as per instructions with the kit. it doesn't seem to make much difference, half a turn in or out in either screw, it still pops and still stumbles on acceleration. Valves set to .017, compression is low but even between 71 and 75 on all 4, measured at WOT, plugs out,  while cranking with a 6V battery, Distillate head. 

any help would be greatly appreciated. 

 

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2 hours ago, vtfireman85 said:

This M is something I have been going round with since last fall. I found the idle jet snapped off and mutilated in the carb, great, don't know how it ran before but it seemed to run well, until it didn't. last year I fought with timing it, when I found the carb issue I hoped I had solved the problem. 

This fall, I rebuilt the carb, full kit, jets, throttle shaft, bushings, the works, set the timing according to the manual, #1 TDC rotate mag until impulse clicks, tighten mag down. at @pete23 suggestion I set it to the 5 degree mark. To do this I had to retard?( anti-clockwise) the magneto drive gear 2 teeth, but now I am able to time it consistent with the instructions. When I did all this it would accelerate well, seemed to have power but still ran rough, popping at idle and audibly fumbling at WOT and no load, under load it seemed to smooth out. I decided it hadn't had the valves adjusted recently so I would do that, manual says .017 hot, I found them all out of adjustment, as much as .073, after adjusting the valves, now it wont accelerate smoothly. you get the stumbling you see in the video, regardless of what I do with the carb or where I adjust the mag. 

The carb is set, in the video with the air screw at 1.5 turns and the fuel screw at 3 turns, as per instructions with the kit. it doesn't seem to make much difference, half a turn in or out in either screw, it still pops and still stumbles on acceleration. Valves set to .017, compression is low but even between 71 and 75 on all 4, measured at WOT, plugs out,  while cranking with a 6V battery, Distillate head. 

any help would be greatly appreciated. 

 

I’ve had to fatten mine up a bit to get rid of a stumble and advance the timing so they almost start hard. But they seem to load up with gas now and foul plugs. 

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I thought the main jet was closer to 5 turns out, but it’s been awhile since I did mine.  The 1.5 sounds right on the air screw.
 

Pretty sure you are running out of fuel on acceleration.  How is the fuel flow from the tank?  Do you have an inline filter?

 

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1 hour ago, Mudfly said:

I thought the main jet was closer to 5 turns out, but it’s been awhile since I did mine.  The 1.5 sounds right on the air screw.
 

Pretty sure you are running out of fuel on acceleration.  How is the fuel flow from the tank?  Do you have an inline filter?

 

Have an inline filter, tank is clean, I cleaned the bowl screen and the carb screen is new, float is adjusted, the carb kit instructions said 3 and i have seen that before, but I can try a couple more. The needle is loose in the threads, I had to use teflon tape to keep it from backing off or leaking. 

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9 minutes ago, nomorejohndeere said:

How do your spark plugs read?

lean?

 

Rich. But that was before I adjusted the valves.. so ..I haven’t pulled them after taking it for a ride. 

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8 minutes ago, vtfireman85 said:

I had to use teflon tape to keep it from backing off or leaking. 

This doesn’t sound right.  Was that at 3 turns off the seat?  The other immediate thought is to open the carb drain just to check flow thru the inlet valve.

When I was having trouble with an H carb this summer, the Venturi was stuck in the bottom half and I couldn’t get the metering nozzle out to clean it correctly.   I had similar symptoms, but yours is actually running better than the H was.  After a good soak, and got the Venturi out, I pulled the metering nozzle and the cross holes were dirty, not plugged but gummed up.  Between that and another cleaning pass at the idle circuit, it ran well afterwards.  
 

My M always seemed easier to clean, but the float is pickier on that one.  
 

Good luck.  

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My 400 has a jam nut on the main jet needle. Maybe the m is suppose to as well?

Oh and my manual say 5 turns out for full power but can be turned in some for light loads/ winter time use. 

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1 minute ago, iowaboy1965 said:

My 400 has a jam nut on the main jet needle. Maybe the m is suppose to as well?

Oh and my manual say 5 turns out for full power but can be turned in some for light loads/ winter time use. 

My My doesn’t, and the screw is snug. It has a brass bushing, I assumed it would compress a little and tighten on the screw, but it didn’t. 

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5 hours ago, vtfireman85 said:

This M is something I have been going round with since last fall. I found the idle jet snapped off and mutilated in the carb, great, don't know how it ran before but it seemed to run well, until it didn't. last year I fought with timing it, when I found the carb issue I hoped I had solved the problem. 

This fall, I rebuilt the carb, full kit, jets, throttle shaft, bushings, the works, set the timing according to the manual, #1 TDC rotate mag until impulse clicks, tighten mag down. at @pete23 suggestion I set it to the 5 degree mark. To do this I had to retard?( anti-clockwise) the magneto drive gear 2 teeth, but now I am able to time it consistent with the instructions. When I did all this it would accelerate well, seemed to have power but still ran rough, popping at idle and audibly fumbling at WOT and no load, under load it seemed to smooth out. I decided it hadn't had the valves adjusted recently so I would do that, manual says .017 hot, I found them all out of adjustment, as much as .073, after adjusting the valves, now it wont accelerate smoothly. you get the stumbling you see in the video, regardless of what I do with the carb or where I adjust the mag. 

The carb is set, in the video with the air screw at 1.5 turns and the fuel screw at 3 turns, as per instructions with the kit. it doesn't seem to make much difference, half a turn in or out in either screw, it still pops and still stumbles on acceleration. Valves set to .017, compression is low but even between 71 and 75 on all 4, measured at WOT, plugs out,  while cranking with a 6V battery, Distillate head. 

any help would be greatly appreciated. 

 

What is your manuals definition of hot? I have seen some define hot as room temp of 70° or more. So not 30 degrees but not actual operating temp either. 

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5 minutes ago, iowaboy1965 said:

What is your manuals definition of hot? I have seen some define hot as room temp of 70° or more. So not 30 degrees but not actual operating temp either. 

I don’t remember how it is worded, I adjusted them at operating temp, but I would have to look. 

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2 minutes ago, nomorejohndeere said:

flapper is a floppin

use an infrared heat gun while it's running to see if all cylinders are firing while your trying out adjustments 

 

I can try that, they are evenly sooty and dry however. 

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1 hour ago, vtfireman85 said:

The needle is loose in the threads, I had to use teflon tape to keep it from backing off or leaking

If that is the main fuel needle. There should be a packing behind the brass nut it screws into. Tightening nut tightens packing. Should have been a new packing in kit.

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Just now, snoshoe said:

If that is the main fuel needle. There should be a packing behind the brass nut it screws into. Tightening nut tightens packing. Should have been a new packing in kit.

I opened it on a cloth and i used all the pieces, whats it made of? Maybe I can make something.

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just did a listen and the M is not running on all 4, that throttle up is a dead giveaway. Get it firing on all 4's and you can take the rest of the day off. 😀

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1 hour ago, mrfred54 said:

Did you dig the old packing out? Like snoshoe said, it looks like a graphite bushing. Tightening the brass packing nut will keep the screw tight 

I don’t remember, I took it apart a year ago, all the pieces were there, but it’s possible I tossed or dropped the old packing 

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I don’t understand why you had to move the gears two teeth . What gears ? Confused. 

The mechanical advance in the magneto will if working correctly for flat top pistons out to 35 degrees advance the way I understand it. 
Set up starts are about zero or retard so not to give kick backs,to me crank by hand is very important.
 

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4 minutes ago, 560Dennis said:

I don’t understand why you had to move the gears two teeth . What gears ? Confused. 

The mechanical advance in the magneto will if working correctly for flat top pistons out to 35 degrees advance the way I understand it. 
Set up starts are about zero or retard so not to give kick backs,to me crank by hand is very important.
 

Because it had been dismantled and couldn’t be timed. 

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So, I took the carb back apart, i had boiled it in my ultrasonic cleaner, then in lieu of having aerosol carb and choke to rinse i used non chlorinated brake clean, and compressed air.
today I found The throttle shaft had a bit of movement despite having new bushings. I used a big brass punch to make sure the bushings were fully seated, might have swaged them a bit. I never did find the fuel screw packing, i rolled up some teflon tape and used that and an O ring, seemed to work. After reassembly I still have a pop at idle, but the stutter on acceleration has gone away. I am currently wondering if I got a bit of brass or some filings in the idle circuit when I extracted the broken jet. Also as seen the holes on the gasket didn’t quite line up, so I enlarged it. 

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Usually have to dig old packing out. Looks like the packing nut is screwed to far in to have much packing left if any.  Pete knew more about working on IH tractors than I ever will. Didn't want to argue with him about timing because maybe it worked for him. But the only reason TDC and the mark close was so someone wouldn't get mixed up with other mark on pulley that was used to line up grease fitting in flywheel with hole under housing. When late M went to the 12 inch clutch sealed pilot bearing was used. First mark to reach pointer turning engine normal rotation is TDC. Dave

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34 minutes ago, DWV said:

Usually have to dig old packing out. Looks like the packing nut is screwed to far in to have much packing left if any.  Pete knew more about working on IH tractors than I ever will. Didn't want to argue with him about timing because maybe it worked for him. But the only reason TDC and the mark close was so someone wouldn't get mixed up with other mark on pulley that was used to line up grease fitting in flywheel with hole under housing. When late M went to the 12 inch clutch sealed pilot bearing was used. First mark to reach pointer turning engine normal rotation is TDC. Dave

I am aware that my marbles are getting away but if I am wrong on this. I will have to retire from here.

Turning engine normal rotation. The first mark to reach pointer is full advance. The next to last mark is TDC and is where zerk lines up. Last mark is 5 degrees after TDC and is where impulse should trip and where 40 degree distributor should be static timed. Both giving 35 degree full advance.

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