F20 problems

[bvaughn85]

Have been working on getting an f20 running that has been sitting for 15 years. Started off with the basics. Clean fuel tank and sediment bowl, new fuel. Rebuilt carb( have done many for h and m but first for f20). Soaked and cleaned all passages. Float set around 1 7/8”. Spark looked weak so we got a rebuilt mag from brillman along with plugs and wires. Timed the mag according to book as well. Ended up finding a stuck valve on number three cylinder and freed it up. Set all valve clearances according to book. Compression is 70 across the board except for number three that is 50. Looking for any ideas of something we might be missing or need to try. Any help would be appreciated.

 

[Janicholson]

Spark at the correct cylinder at the correct time. 1342 firing order. Numbered from radiator back. Turn the crank slowly past TDC on #1 till the mag clicks. look at the rotor. Where it is pointing (if the rotor is timed correctly to the mag shaft gear) is #1 plug wire location. go from #1 to #3 then#4 then #2 in the rotor rotation direction. Jim

 

[bvaughn85]

Spark at the correct cylinder at the correct time. 1342 firing order. Numbered from radiator back. Turn the crank slowly past TDC on #1 till the mag clicks. look at the rotor. Where it is pointing (if the rotor is timed correctly to the mag shaft gear) is #1 plug wire location. go from #1 to #3 then#4 then #2 in the rotor rotation direction. Jim

Yes. Timing is correct. Mag sparks as soon as piston is heading down after compression stroke.

 

[used red MN]

Mag sparks as soon as piston is heading down after compression stroke.

You say “as soon as the piston is heading down after the compression stroke” I’m sorry if this is a little pointed but it has to be said so we know you are on the same page. You are aware that every time the piston is at TDC is NOT always the compression stroke. Every other alternating time it comes to the top it is on the exhaust stroke. So the actual compression stroke has to be felt by the pressure the piston pushes as it comes up when the valves are both closed for the compression stroke. Or it has to be found by watching valve movement. In which the intake valve would open and then close. then at that point it when the piston is coming up that is compression. Do you understand all of this? If you are convinced it is correct pour a couple of teaspoons of gas in 2 of the spark plug holes put them back in and see if it starts. Then if so that indicates you have a fuel problem.

 

[DeltaRed]

There are two priming ports on the valve cover. Open them and give each one a few squits of gas.As said,180 degrees out of time?Recheck,take off valve cover and watch valves. 50 to 70 isnt a lot of compression. That might be your problem,just not enough to run. If cranking doesnt work,hook a chain to it and pull it(high gear). Should start

 

[rustred]

Yes. Timing is correct. Mag sparks as soon as piston is heading down after compression stroke.

If it’s sparking soon as piston is heading down the spark is retarded. Feel the piston with a wire as someone slowly turns the engine with the crank. It must spark at TDC which means this is where the piston actually stops moving for maybe a couple degrees. Don’t even need to watch the spark. Listen to the impulse coupling click. Adjust to correct timing with the 2 1/4 inch bolts in the mag coupler. Correct Spark, gas, and compression , it has to run.

 

[John M]

If it’s sparking soon as piston is heading down the spark is retarded. Feel the piston with a wire as someone slowly turns the engine with the crank. It must spark at TDC which means this is where the piston actually stops moving for maybe a couple degrees. Don’t even need to watch the spark. Listen to the impulse coupling click. Adjust to correct timing with the 2 1/4 inch bolts in the mag coupler. Correct Spark, gas, and compression , it has to run.

If its in full retard, before grounding, it will be after TDC. (At least my 14 is that way.) If you adjust the mag one way or the other, its way off.

 

[Dave in NY]

If you are going by the book, you probably already know this. There is a hole in the front of the bellhousing on the left side of the tractor that you can look in to see a mark [line] on the flywheel that indicates TDC. Probably need a good flashlight to help see in there. And as stated has to be TDC on the compression stroke to check the timing of the mag. It's not terribly complicated, you will get it running. Try pouring about a dixie cup full of ATF in each sparkplug hole and let it soak a bit. Might help free up the rings and bring the compression up a bit.

 

[Fritz Maurer]

If its in full retard, before grounding, it will be after TDC. (At least my 14 is that way.) If you adjust the mag one way or the other, its way off.

Your 14 is out of time. The impulse coupling always trips AT TDC when properly timed. The spark lever has nothing to do with timing at cranking speed.

 

[John M]

Your 14 is out of time. The impulse coupling always trips AT TDC when properly timed. The spark lever has nothing to do with timing at cranking speed.

Well, if it is, there must be something wrong. Timing marks behind the front cover are right, the mag itself is timed correctly, and if I move to the next set of holes on the drive either way its too far off. In fact, I had it advanced one set of holes, and the mag retarded as it should be when cranking, and broke my wrist in 2 places. So tell me where its off. I fought this over 20 years ago and everyone here told me it was like that. Its only sligtly ATDC, and will fire right up like that.

 

[rustred]

If its in full retard, before grounding, it will be after TDC. (At least my 14 is that way.) If you adjust the mag one way or the other, its way off.

maybe post a pic of this mag and coupler. i dont see how it can be way off , the coupler has holes all around so you pick the holes that make the least change. i have not actually checked how much each hole changes timing , but i am quite sure its within a degree or two. sure if you pick the wrong holes its gonna change timing to way off. and is this the E 4 mag ?

 

[Fritz Maurer]

Well, if it is, there must be something wrong. Timing marks behind the front cover are right, the mag itself is timed correctly, and if I move to the next set of holes on the drive either way its too far off. In fact, I had it advanced one set of holes, and the mag retarded as it should be when cranking, and broke my wrist in 2 places. So tell me where its off. I fought this over 20 years ago and everyone here told me it was like that. Its only sligtly ATDC, and will fire right up like that.

Are we talking about an F14 ? With F4 mag? Don't know this front cover statement, the timing marks are on the flywheel of F12/F14.

That being said, the bolted coupling is capable of very fine adjustment; closer than it would appear just by looking at the bolts. IF you have all the factory parts on it and not some farmerized repair.


You also can't check the timing with your hand on the crank. It is impossible to stop the crankshaft right where the impulse coupling trips because the pistons are stationary and the crankshaft is at its point of least turning effort. Place a hydraulic jack under the crank handle just as the impulse coupling begins to wind up. This way when the coupling trips, the sudden reduction of turning effort won't propel the flywheel past the mark.

It is possible to make the coupling trip at 1-4 DC precisely.... not somewhere in the neighborhood.

If you broke your wrist it was because the trip was too early.... the spark lever has no control over spark at cranking speed. Never try to start it after messing with it timing BEFORE you ascertain WHERE it is tripping.

 

[Fritz Maurer]

Are we talking about an F14 ? With F4 mag? Don't know this front cover statement, the timing marks are on the flywheel of F12/F14.

That being said, the bolted coupling is capable of very fine adjustment; closer than it would appear just by looking at the bolts. IF you have all the factory parts on it and not some farmerized repair.


You also can't check the timing with your hand on the crank. It is impossible to stop the crankshaft right where the impulse coupling trips because the pistons are stationary and the crankshaft is at its point of least turning effort. Place a hydraulic jack under the crank handle just as the impulse coupling begins to wind up. This way when the coupling trips, the sudden reduction of turning effort won't propel the flywheel past the mark.

It is possible to make the coupling trip at 1-4 DC precisely.... not somewhere in the neighborhood.

If you broke your wrist it was because the trip was too early.... the spark lever has no control over spark at cranking speed. Never try to start it after messing with it timing BEFORE you ascertain WHERE it is tripping.

Furthermore, people often equate the spark advance on a F4 mag as working like one on a Model T..... it is not the same thing at all. A Model T has no impulse coupling and the spark lever will make it spark ANYWHERE during cranking, DC or otherwise, whether it has a battery or not. It can spark and injure a person even if they are not ready to crank it , just feeling around for the compression , and getting into position; the flywheel mag is that sensitive.

A properly timed F4 ( or any mag for that matter) CANNOT fire until the coupling trips.

 

[John M]

Are we talking about an F14 ? With F4 mag? Don't know this front cover statement, the timing marks are on the flywheel of F12/F14.

That being said, the bolted coupling is capable of very fine adjustment; closer than it would appear just by looking at the bolts. IF you have all the factory parts on it and not some farmerized repair.


You also can't check the timing with your hand on the crank. It is impossible to stop the crankshaft right where the impulse coupling trips because the pistons are stationary and the crankshaft is at its point of least turning effort. Place a hydraulic jack under the crank handle just as the impulse coupling begins to wind up. This way when the coupling trips, the sudden reduction of turning effort won't propel the flywheel past the mark.

It is possible to make the coupling trip at 1-4 DC precisely.... not somewhere in the neighborhood.

If you broke your wrist it was because the trip was too early.... the spark lever has no control over spark at cranking speed. Never try to start it after messing with it timing BEFORE you ascertain WHERE it is tripping.

Front cover, meaning the front cover of the engine. Where the timing gears are. When it was rebuilt, the marks were lined back up. ENGINE timing is correct. When I set the mag, I followed the instructions in the manual to the letter. Theres a video of what Im talking about. Ill look for it.

This is it, and exaxctly what my 14 does.

 

[John M]

maybe post a pic of this mag and coupler. i dont see how it can be way off , the coupler has holes all around so you pick the holes that make the least change. i have not actually checked how much each hole changes timing , but i am quite sure its within a degree or two. sure if you pick the wrong holes its gonna change timing to way off. and is this the E 4 mag ?

F4 mag rebuilt by a former member of this forum. Really he just cleaned it up and put new points and condesor in, thats all it really needed. The coupler is the one that was on it when I got it, but is the correct one for it. If I advance one hole, its hard to spin over, retard one hole it sounds labored, even at full advance. I put it back in the original hole, which is the one it came out of when I first took it off, it runs as it should.

 

[Fritz Maurer]

F4 mag rebuilt by a former member of this forum. Really he just cleaned it up and put new points and condesor in, thats all it really needed. The coupler is the one that was on it when I got it, but is the correct one for it. If I advance one hole, its hard to spin over, retard one hole it sounds labored, even at full advance. I put it back in the original hole, which is the one it came out of when I first took it off, it runs as it should.

If you have it running where you want it that's fine. I was merely pointing out that the timing can be a lot closer than ATC if you were having trouble , which apparently you are not. But it is absolutely possible that get the impulse coupling to trip dead nuts at 1-4DC . Why you can't attain that, I don't know. Possibly sheared or missing key on the magneto drive shaft in the support.

 

[kevinj54]

If you have it running where you want it that's fine. I was merely pointing out that the timing can be a lot closer than ATC if you were having trouble , which apparently you are not. But it is absolutely possible that get the impulse coupling to trip dead nuts at 1-4DC . Why you can't attain that, I don't know. Possibly sheared or missing key on the magneto drive shaft in the support.

It been many years since my dealer days but the OP is talking one hole increments which seem to be too much.

Since he states it runs fine putting it back to the holes where he tore it apart & now it is fine.

It seem that those hole are not even so you can make fine adjustments?

 

[Fritz Maurer]

It been many years since my dealer days but the OP is talking one hole increments which seem to be too much.

Since he states it runs fine putting it back to the holes where he tore it apart & now it is fine.

It seem that those hole are not even so you can make fine adjustments?

There is some mathematical equation in those bolt circles that I am not equipped to understand , but yes it is very precise.

The U shaped piece of metal that is erroneously called a shim is actually a location device that prevents one of the bolts from being forced into a hole that doesn't quite line up.