F20 help please

I recently bought a non-running but in good condition f20. After cleaning the sediment bowl and getting fuel to the carb and getting spark out of the mag I was able to pull start it. It ran poorly and I had just started to adjust the carb when it died and I have been unable to get it running since. I have rebuilt the carb, put in a new mag coil, points and condenser, plugs and plug wires and all I can get is backfireing and fire out of the exhaust. I have taken the mag off for what seems like a dozen times and re-timed following the book instructions. The valves seem to be moving correctly and there is compression on #1 when I bring it to TDC. The engine builds oil pressure. Does anyone have any idea of what I am doing wrong? Any tricks to this that I am not seeing? I must be missing somthing but cant figure out what. Is there any on-line service manual for this tractor? Any help would be greatly appreciated. Thanks, John.

Plug wires are off?Fireorder-1342.Stuck valve?

Are the impulses in mag working properly. Before starting did you check to see if all valves were opening & closing. Also that engine has oil pans over the rocker arms that need oiling.Engine does't pump oil to rockers.You put every thing new in mag. did you retime the gears in the mag?

Thoes will flood easily,turn the gas off then try to start it.

So frustrating, isn't it?

Just keep going back to the basics. Air-gas-spark. Sounds like you've got the spark covered. If all plugs spark, and you're SURE they're firing at the right moment - that leaves gas and air.

Make sure you're getting air - that's an easy one. But also make sure your choke is operating, don't assume it is.

Then your left with gas - which is where the problem almost always lies.

Have you tried starter fluid (carb cleaner works too)? That's a good way to isolate the carb as the problem - just don't go crazy with the stuff. Spray some in while cranking. You only need to hear then engine run for a second.

If it does that, you can then assume your ignition system is at least ok, and that you're not getting gas through the carb.

First start with basic carb adjustments.

It doesn't take much at all to block the carb - you have to be meticulous when cleaning and reassembling. But even then, hooking up a gas line can introduce a little chip of rust or something that will undo all your good efforts.

Point being - don't assume just because the carb has been rebuilt that it's working. There's a good chance some crap got into it.

Other than that, I'd also adjust the valve lash. Old valve seats wear, if the valve lash isn't adjusted to compensate for that wear, they can get to a point where one or more of them won't be able to close tightly. But your compression test would show that - if you did it on all cylinders - either way, it should be adjusted anyway since it's easy to do.

Of course, make sure you're using fresh, clean gas. Completely drain the old stuff - don't just add new to old.

you are not timed correctly, thats what causes backfireing. make sure your on compression on #1, and rotor is pointing to #1 cyl. on cap. it is even marked. also adjust valves. the reason it stopped in first place may be due to dirty fuel tank.

i have also seen the keyway shear off on mag drive due to being cranked when the mag was stuck.

Should the mag gears should be timed by having the dot on the rotor gear going between the two flat bevels on the other gear? Also, where would be a good starting place for load and idle screw settings? At #1 tdc are the dogs on the mag coupling supposed to be straight across? I will check compression on all four tonight after work. What would be a reasonable compression number for each cylinder on an engine that hasnt run for more than a minute in the last 15 years? Thanks, John.

At this stage you just want it to start, so you just want to be sure nothing is WAY off. Like no compression in one or more cylinders.

If all the cylinders are in the 80 range or more, and hold some pressure for a little while you should be fine.

As others have said, you can put a little oil in each cylinder to boost the compression while starting. That could help.

But I'd still try a blast of starter fluid first to see if it does anything. If it does, that'll tell you a lot.

i believe your correct on the gears. carb setting to start with, main jet 2 1/2 turns out. idle mixture 1 1/2 turn out. this screw is out for lean and in for rich.
have mag bolted to base.
get #1 on compression. line up timing mark to TDC. raise breaker housing to retard spark and remove it.lift timing hook to make impuse coupling in operatable.remove dist cap.rotate mag by coupling clockwise as from coupling end. rotate till the brush is coming into alignment with cap terminal #1.just as pionts are opening you are now in time. you can put a piece of paper between points to feel when they open. just as paper pulls out you are timed. without moving a thing put the 2 bolts in the coupling where they line up directly across from each other. replace cap and cover. to check yourself crank engine over on #1 compression and check points , just as they are opening the timing marks should be in line. release timing hook and start tractor.
as for compression i would say 80-90 psi.it will run good.

If its backfiring the mag is out of time. Take off the valve cover, its only 2 nuts, take out no 1 plug , when no 1 intake valve opens , watch piston come to top, impulse should trip just after TDC. You can also take off the inspection cover on side of block to see when rod is at TDC. But if it is popping out exhaust you are out of time or sticking valves.

Use the twisted belt method of trying to start it. It is safer and a lot easier to make adjustments to the carb, etc.

plug wires are on in correct order?

on the mag internal timing question, the answer is yes, you are correct. The dot on the large gear needs to be between the 2 teeth that have a bevel on them.

let us know the results of your tests.

As was said. Get another tractor with a belt pulley. put a hammermill belt on the 2 and start it up, WITH THE GAS OFF. When its just setting there humming, open up the gas. When it starts popping and back fireing, cut the gas back 1/2 ONLY. Make sure there is STILL a bit of gas going in it. It should still be popping ect. Now, if you KNOW that your wires are correct, And you might tell us how you have them in the mag, from the Fan back to the gas tank. Anyway, then just start walking them round the mag. If the mag is set right, Youll hit it soon enough and it will run like a chanmp. BUT IF, you go all the way around it, and it hasnt started yet, Take the mag to a mag shop and have them look at it. My Boys got a WD AC I bought him. It ran when I bought it, But, the coil was gone in it and somebody had put an external coil on it, It sat here now round 2 yrs and wont start. I bought a new coil, and we worked and worked. Nothing but what your hearing, I took it to a reputable mag man, and he took it apart and found that it was 2@ out of kilter. Were going to start it in 2 weeks.

The cam in the mag which opens the points may have twisted. My tractor had the same problem and the cam had twisted on the shaft. If you get a magnifying glass try to drive out the pin. About the size of a "4 nail. If it doesnt move may be sheared.

That is a good way to kill the coil in the mag. Where does the spark go when you are walking the wires around? It has to jump the safety gap or the insulation in the windings. Take all 4 plugs out and get it so you have spark at the end of the compression stroke on each cylinder.

Also check that the wires are installed in the correct direction (clock-wise vs countet-clock-wise). If they are in the wrong direction, 2 cylinders will be firing correctly at the top of the compression-power stroke and 2 cyclinders will be firing at the top of the exhaust-intake stroke. It may run (my W-30 did!) with a lot hot popping and wierd sounds.

It must be a bad way to kill the coil, as im 64, and ive done it ever since I was 18, and ive never replaced a coil on a mag. I assume you know what your talking about, and so, I suppose it isnt a good idea, I also know that Ive always did it like that with no harm to the coils ive had dealings with, that I knew anything about.

Got it going!!!!!!!!! After what seemed like a dozen times of timing the mag to the engine, pulling the tractor, trying to start with the belt pulley and everything else you could think of I found that I could get it to run with either numbers 1 and 4 OR numbers 2 and 3 wires hooked up. Would not run with all 4 even though each was getting a spark. It was then I realized that it must be carbon tracking inside the mag. I replaced what I thought was a decent looking rotor with a new one and cranked it by hand two times when it started and ran pretty well. I stood there shaking my head.... Thanks for the help and info on this. I really do appreciate it.