mt 40 ran good 3 days ago now its back firing

[slwrdr]

Hey there friends i just got an MT40 by proxy i dont know much about it, it ran fine three days ago. Went to use it today and its backfiring through the carb, changed the plugs no help....its the first cylinder thats te problem i pulled the wire off and the back fire stoped, switched plugs around and the wires still no good....can someone tell me what it could be??

thanx in advance

 

[js5020]

Maybe a crack, moisture, corosion in the distributor cap?

 

[zman8537]

Maybe a crack, moisture, corosion in the distributor cap?

That would be the first thing that I would check as well. I had a similar issue after I tuned my model M up and it ran great for a day or two then started runing bad and backfiring. It turned out that a strap on the set of points that I installed was intermittantly shorting out. I put another set of points in it and that fixed the problem.