20 hp Johnson "missing"

I have a 1973 Johnson 20hp that is not running great and I need help diagnosing the issue. What's happening is when I open the throttle up anywhere from 1/2 way to full, it will bog down, open up, bog, run, etc. very sporadically. Then it will run fine, even at full throttle for a few minutes, then start acting up again. Earlier in the summer it was running fine, but would "miss a beat" occasionally when wide open. It seems that whatever that miss was caused by has grown in both intensity and frequency.

I rebuilt the carb, and the issue did not change. So now I'm wondering what to look at next. Fuel pump? Fuel line? Or on the spark side, Coils? Plugs? Any suggestions would be welcome. My mechanical skills and knowledge are limited. Almost as limited as my funds.

Thanks

When my motor did that I had to stop, shut it down then tap the side of the bowl with a screwdriver. I think I had trashin the float valve, ended up replacing filters and unhooked the fuel line, started it and let it run until it died to make the float go completely down and hooked it all up and its been fine since. This I guess made the trash flush on through. Bit Definetly check the spark,fuel filters, primer bulb ( I had one where the valve inside stopped letting fuel through)

Thanks dr. I did a complete carb kit on it. And nothing changed.

I was wondering about the fuel line/primer bulb, but the problem comes and goes really quickly, and sporadically, which made me wonder if maybe a coil or some other electrical component was gradually breaking down and getting worse.

rule out the pump...

pull the line to the carb, spin it and see if fuel shoots in yer face. if it does the pump is prolly good.
:twisted:

Thought the sane thing. Same symptoms turned out to be trash in the float valve. Check your fuel line as there is one brand/type that the liner on the inside deterates with ethanol in turn clogging things up.

[url=https://www.tinboats.net/forum/viewtopic.php?p=333953#p333953 said:

Earlo » 07 Nov 2013, 15:07[/url]"]Thanks dr. I did a complete carb kit on it. And nothing changed.

I was wondering about the fuel line/primer bulb, but the problem comes and goes really quickly, and sporadically, which made me wonder if maybe a coil or some other electrical component was gradually breaking down and getting worse.

Click to expand...

i rebuilt the carb and fuel pump and i still have the slight miss. Ramrod (one of the members here) came over and checked compression and it was fine but he also put a spark chamber tester on each coil and found that one of the coils was hitting but not as hard. i have yet to change the coil(s) but plan to in the future to see if this helps. Ramrod also recommended a seafoam carb spray while running and cylinder soak to remove carbon build up.

Thanks all for the replies. I changed the spark plugs and the issue almost disappeared. Still the occasional "miss" or bog down, but was able to run w/o for long stretches without even a hiccup. I then ran the motor at varying speeds with no problem. Before, the missing was happening 80% of the time, Now, it's more like 2%. So I think that whatever the problem is, it's on the spark side of things.

[/quote] i rebuilt the carb and fuel pump and i still have the slight miss. Ramrod (one of the members here) came over and checked compression and it was fine but he also put a spark chamber tester on each coil and found that one of the coils was hitting but not as hard. i have yet to change the coil(s) but plan to in the future to see if this helps. Ramrod also recommended a seafoam carb spray while running and cylinder soak to remove carbon build up.[/quote]

I was wondering about the coils, or condenser. But I don't know much of anything about either. On this motor, there are two sets of coils (see attached, #'s 18 and 44). 44 is the exterior pair next to the spark plug and is called "ignition coil assembly". 18 is the pair that are on the under the flywheel, named "coil and lamination".

I guess the easiest next step would be to test the exterior coils. I don't want to pull the flywheel over a symptom that has now mostly gone away.