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25hp Johnson back fire while cranking.

F

fredbriggs

Member
Been having on going problem with this engine. Was a no start had weak spart, and pushing a lot of fuel out #1 cyl, figured that out now have good spark too both plugs, rebuilt carb, new leaf valves, new fuel pump, good compression (135) both cylinders. Now still no start and and while cranking over back fires out exhaust only. Flywheel key ok, thinking something to do with timing? Brought #1 cyl up to top dead center with dial indicator in number 1 and marks on flywheel right on. Only problem I could see now is that the tiller handle linkage is slightly worn and when returned to idle position does not bring the marks on flywheel exactly to the throttle linkage roller but not off enough that it shouldnt start. Even if I manually put mark on roller still back fires? Plugs are getting wet with fuel but engine wont run? I did have the advance plate and stator off to check stator and all coils and trigger all checked good with ohm meter all within factory specs. Any suggestions would be appreciated
Thanks
 
So sorry was out of country and could not get to forum for some reason. Just got back into states and see your message.

I had the understanding that both coils actually fire at the same time? I did replace both coils and the power pact assembly, before doing these two things the motor at least tried to start on one cyl. Originally engine fired up but would not rev up acted like only running on one cyl even though it actually had spark when plugs were pulled. I felt was not a hot enough spark would not jump a 3/8" gap so tried coils then power pack once this was done had a hot spark ( over 3/8" jump) but then would not even attempt this is when it just cranked and cranked then all of a sudden and loud back fire thru the exhaust.
By the ***** eye it looks like both plugs fire exactly the same time if they are separate can you tell me which coil is #1 and which is #2, and where can I see a chart of color code for which wire from pack goes to which coil.
My next step was going to hook up a timing light to #1 and crank over both at idle and as wide open throttle to see when I had spark as to where on flywheel this occurs? Any other suggestions would be appreciated this seems like it really should be kind of a simple fix just have not hit the right combination.
Thanks
 
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