Xt 500 has weak spark(flywheel magneto with ignition points).poor when cold and now won't even start.fuel fine.isolated ignition(magneto,coil and points).changed coil.points fine,resistance satisfactory except from magneto source coil(just outside specs).also inside flywheel has some stubborn rust.can you help?

Yes it seems a fair assumption. All three should be the same.

https://www.google.com/search?q=Mantis+7222M+magneto+test

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With small engines, ignition is magneto. Four things can cause a lack of spark: (1) Faulty plug - try a new plug; (2) Bad, shorting, or disconnected spark plug wire - check for high voltage from ignition coil; (3) Bad ignition coil - check for low voltage at the coil input wires; (4) Magneto failure - the pickup coils next to the flywheel may be shorted, loose, or disconnected, OR the magnets on the flywheel may have lost their field or come out. I would troubleshoot this problem by checking and eliminating each of these possibilities in the above order. If all of the first three check out good; I'd have a mechanic check the magneto because this requires at least partial disassembly of the motor.

You bought a new ignition coil, how far from the flywheel was it mounted? Did you replace the spark plug?

I hope you get the old machine running soon.

Most small engines use a flywheel with a magnet embedded in it and an ignition coil with a core that sits a few thousandths away from the flywheel. Ignition coils are common failures probably because they come from our wonderful Chinese friends. They have demolished all US manufacturers. If you replace the coil, use some gauge to measure the gap between coil core and the flywheel magnet surface before removing the old coil. Otherwise you may spend a little time using trial & error to get the engine running again.
If your engine is a Briggs and Stratton, you can find very complete maintenance downloadable information on their website. This will pertain to the engine only, not the mower.
Dunno about Tecumseh, haven't had much need for service info on those.

hi there mwb15
have you made sure the ignition coil is producing enough voltage to fire under compression load ?

you may get a spark at the plug unloaded but under load it may be breaking down / weak making you think its got a fuel problem ?

does your system use a cdi coil system or point/condenser system ?
spark usually falls into weak spark, no spark catergory

if compression , fuel ( you replaced carb) and exhaust are ok , and you have air and vaccuum tight c/cases only things left are timming and spark

remember F A C T S

F = Fuel A = Air & ( air tight c/cases ) C = Compression T = Timming S = Spark

compression should be about 130- 140 approx if in good running order

take a look and let me know

cheers pauly46

Hi John and welcome to FixYa, I am Kelly.
The gap between the flywheel and the coil is 0.0125. The easy way to set it is to get a pack of book matches tear out the matches and use the cover between the magnet and the coil then loosen the coil mounting screws allowing the magnet to pull the coil onto the match book cover. (This has worked flawlessly for 40 + years on literally hundreds upon hundreds of engines regardless of brand.)

Weak spark is caused by either a parasitic load on the kill wire or a bad magneto

Your parts list is here:
http://www.briggsandstratton.com/document/index.aspx?doc=MS4864_B_LO.pdf

If the control wire item 270 of the below link is fine / not grounding or chaffed. This little wire is notorious for grounding at the flywheel brake engine stop terminal and under the flywheel before the magneto.

http://www.partstree.com/parts/?lc=briggs_and_stratton&mn=09D902-2022-E1&dn=48640005A
then the most likely failure is a weak Magneto (Item 333 above)

Also make sure to check the high tension lead where it comes out of the air-shroud.

Lastly... use a phillips screwdriver in the spark plug cap making a small gap to the engine for checking spark. A bad spark plug can act like a resistor and show weak spark. HOLD THE HANDLE only on the screwdriver.

The magneto is by the flywheel. Depending on the age, there maybe points under the flywheel. If so you remove the flywheel and there the points are. Sometimes bugs build cacoons between points, make them inoperable. Newer engines have electronic ignition though. Follow the small wire from the magneto coil ( where the spark plug wire goes) it will either go under the flywheel through a plastic bushing, or to an electronic module. The magneto coils do fail you can test with an ohm meter. Before that test for spark. You can remove the spark plug, and let it rest on the engine to get ground, and turn the engine over. You always need 1-spark, 2 fuel . If you have spark, see if it will hit on starting fluid, if it does, then you have a carb or fuel filter issue. Those shut off valves on the bottom of those tanks, can be a problem

FIRST check the gap of the flywheel magnet to the magneto coil. Use a business card as a spacer and adjust the gap. If unit has points rather than electronic triggering, check those and timing and gap.

unplug spark plug wire and hold it in your hand, pull cord like your trying to start, if you feel a jolt then you are getting fire if you dont feel anything then its probably not working. you can also try using sand paper on the magneto it may be to rusty to create a spark, then try step one again- good luck

Hello . If you have a weak spark it could be the ignition coil that needs adjustment or a bad ignition coil . To find the ignition coil simply follow the spark plug wire . To readjust the coil get a piece of paper , loose the bolts on the coil and put the paper between the coil and the flywheel (higher part of the flywheel or magneto) tight the bolts and remove the paper .
Check for spark . If still a weak spark just replace the ignition coil .
Hope this help.