HELP! Snow blower backfiring

[merc_man]

I picked up a snowblower free on roadside and issue was it caught fire. Sonstart tearing into it and its real clean no nests or anything. So i go through carb clean it. Replace melted primer bulb and hose.
So get to the point where i can start it and cranking and it backfires a fireball out the carb. Engine still starts and when running runs with no issues.
So what i noticed was can prime more than once or fuel runs out carb. Thats why the fuel atcher is melted i assume.
What i have checked so far is replace spark plug, flywheel key is good, adjisyed the valves back into spec.
Another possible issue is when i checked spark i held plug against the metal and notived the spark arc was at the plug threads and not the electrode. I tried 2 brand new plugs and both like this. Could this be a coil isue?

Engine is a 2018 champion
Thanks

 

[Al Smith]

Could be coil related ,If it has a points type ignition with a faulty condenser it could be jumping the gap.By the same token some times a solid state unit will fire early if the trigger unit often build into the coil fails and it fires early .However it could be a badly burned intake valve that could also blow fire out the carb .Could also be an air leak in the intake tract .

 

[stretch5881]

I don't think it would be a coil issue if it starts and runs normal. It could just be a sticky intake valve.
If it were an intake leak it would run lean and wot would be higher than the max rpm spec. I can't find the max rpm spec on these engines, so I will assume it would be 3600.
Test it out clearing snow and it may clean itself up.

 

[stretch5881]

Al, I think we can eliminate the points and condenser, they stopped using them 45 years ago.

 

[Al Smith]

I had assumed that myself but in general conversation preignition could be the cause of it --or not .Fact I had a points type that was giving me fits I replaced with an after market solid state coil an "expert " told me it would not work .The same person also told me I could not retime the intake valve to increase the mid range torque .I'd already done it before the conversation ever arose .

 

[stretch5881]

Not trying to step on you, just that the OP stated 2018 Champion.

 

[Brad Button]

Pick up an in-line spark tester. Trying to ground a spark plug is not a good way to check for a spark; it is too easy not to get a good ground and get a false reading.

 

[merc_man]

Pick up an in-line spark tester. Trying to ground a spark plug is not a good way to check for a spark; it is too easy not to get a good ground and get a false reading.

I already checked with a light up style inline spark tester. Lit up real good.

 

[merc_man]

Ok so i tried starting it with out primer and just choke and no backfire.
Also pulled a plug boot off my known good champion chipper engine and it arcked the same.
So maybe it is a carb issue. Guess just start with choke few more times to see if starts fine then try primer and see what happens

 

[merc_man]

Might have found my problem. I had it running with the pannel off that covers carb area and went to put back inplace to bolt up and the engine starged acting up. Moved cover out the way and ran good. Wiggled some wires and and it stalls. the kill wire must have a bad spot in it. Will pull some more stuff off when i get time hopefully later and see what i can find.