I have spark, compression and fuel...but just some minor backfiring....PLEASE HELP

I have been trying to get info for my early 70's Merc 9.8 110. I originally had one that I brought into a small engine repair shop last year after I had a complete loss of power and a hard time starting while I was out on the lake. He told me I had a coil issue among other things. I purchased another motor that is very similar that had great compression and spark...so I figured I'd get this one running. I brought it home and after some new gas and a few dozen pulls it was purring like an angry cat. LOL. I figured it needed a good cleaning so I cleaned the carb and tried again....NO SPARK. Cleaned the coils and found that it was the ignition box that was failing. Took the one off my original motor which had a bit of different wiring to the (what I assume) points.

Side note. My original motor had two brown wires go directly to the point, and my new one had two brown wires ground to the engine, then from the same bolt they would go to the point.

Long story short, I now have spark, and lots of it....however will the order of the brown wires connecting to the points matter? or can they be reversed? I have compression, and spark and fuel :S

From here I tried both ways, one i get nothing and the other I get some backfiring. Now, should I adjust the timing?

What else could be wrong?

Re: I have spark, compression and fuel...but just some minor backfiring....PLEASE HEL

Welcome to the forum!!

Has your engine got a switch box AND two seperate coils??! The wiring must be specific so that the correct cylinder will fire at the right time, however there is only two cyl's so one way will work, the other one won't ;-) So 50/50 guess if you can't remember what when where lol......

Anyway, serial no and pics would help to identify exactly what model you have as there were several different ignition systems fitted to these engines.

Let us know how you get on...

Re: I have spark, compression and fuel...but just some minor backfiring....PLEASE HEL

The serial number is 7036150

Its a Merc 110, 9.8hp with the Thunder Bolt Ignition system.



From what I can see...and I dont know small engines that much so please bare with me.

In the attached photo the two brown wires connect to the motor then go up to the rectifier? or whatever that part is, lol. On the parts motor the wiring didn't attach to the motor, it just went straight there. So...will having these in reverse cause an issue?

I'm getting a backfire from time to time, could it be a timing issue?

Re: I have spark, compression and fuel...but just some minor backfiring....PLEASE HEL

If there is any other info I can get you, I'll be more then happy to get more pics or anything you guys might need. Thank you!