1980 Johnson 175HP missfire/backfire problem

Hi people,

I have the above model engine which is miss-firing. Checked all compressions, and although I am not sure of the cylinder order, they range from 105 to 112 psi. The symptoms are that it seems as though a cylinder is firing early and backfires, and slows the rpm right down, at about 2000rpm it remains running, but at slow rpm it comes to a stop.
I have removed one lead at a time to see if I can pinpoint the area, but it doesn't make any difference, because the backfire persists. I would like to confirm the firing order is correct, as the wiring has been disturbed at some point, but have no manual.

I have just identified the engine and year via these forums, and will order a manual asap.
In the mean time, could somebody possibly tell me which color wire goes to which coil, and identify the cylinder numbers (logically I would have thought that the port side going down would be 1,3,5, & the star' side 2,4,6).

Many thanks
Regards
Les

Re: 1980 Johnson 175HP missfire/backfire problem

Cylinders are numbered from the highest to lowest (top cylinder on starboard side is #1, top cylinder on port side is #2, ..... bottom cylinder on port side is #6). The primary wires with the blue stripe goes to the top cylinders, primary wires with green stripe goes to the bottom cylinders, and the primary wires with no stripe goes to the middle cylinders.

The condition you describe sounds like a "lean sneeze". At idle and just above idle, if the mixture is lean you'll get backfiring into the carbs, and quite often the engine will quit as it backfires. Did it just start doing this? Or is this an engine you just got and therefore don't know it's history? (From your post it sounds like the later).

Once you get a manual you'll want to check the idle timing, check to make sure the carbs are synchronized properly and that the timing advance is coming in at the right time (a procedure referred to as link and sync). If some of the carb butterflies are open at idle it can cause this. If all of that is ok then you're probably looking at adjusting the idle mixtures (which really shouldn't be out of adjustment without something else happening), and then a carb rebuild/cleaning.

As far as manuals, if at all possible find a genuine OMC factory manual. I've always been lucky enough to locate them on ebay for a reasonable price. There's a company which sells reprints of the factory manuals (I can't recall the name, somebody on here will chime in), but it'll probably be less expensive if you can find a used manual somewhere.

Re: 1980 Johnson 175HP missfire/backfire problem

metriccrescentwrench said:

Cylinders are numbered from the highest to lowest (top cylinder on starboard side is #1, top cylinder on port side is #2, ..... bottom cylinder on port side is #6). The primary wires with the blue stripe goes to the top cylinders, primary wires with green stripe goes to the bottom cylinders, and the primary wires with no stripe goes to the middle cylinders.

Click to expand...

Excellent, thats just what I needed. Thank you so much.

metriccrescentwrench said:

The condition you describe sounds like a "lean sneeze". At idle and just above idle, if the mixture is lean you'll get backfiring into the carbs, and quite often the engine will quit as it backfires. Did it just start doing this? Or is this an engine you just got and therefore don't know it's history? (From your post it sounds like the later).

Click to expand...

That is correct I have aquired this engine from my nephew, and he is a bit vague about its history, I was told he has had someone else working on it, so I will start from scratch and try to work my way through it, and its problems.

metriccrescentwrench said:

Once you get a manual you'll want to check the idle timing, check to make sure the carbs are synchronized properly and that the timing advance is coming in at the right time (a procedure referred to as link and sync). If some of the carb butterflies are open at idle it can cause this. If all of that is ok then you're probably looking at adjusting the idle mixtures (which really shouldn't be out of adjustment without something else happening), and then a carb rebuild/cleaning.

Click to expand...

Something else to check, thanks

metriccrescentwrench said:

As far as manuals, if at all possible find a genuine OMC factory manual. I've always been lucky enough to locate them on ebay for a reasonable price. There's a company which sells reprints of the factory manuals (I can't recall the name, somebody on here will chime in), but it'll probably be less expensive if you can find a used manual somewhere.

Click to expand...

Ok, I will keep that in mind.
I can't thank you enough, I can crack on now, and hopefully get something achieved today.

All the best
Regards
Les

Re: 1980 Johnson 175HP missfire/backfire problem

i had exact same problem went thru and replaced just about everything come to find out it was one bad coil