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1988 Johnson 48 miss at idle - Anyone experience this?

T

thill

Member
Am bringing a 48 SPL back to life.
No spark, fouled fuel system, but excellent compression - 135 psi in both cyls.

I noticed the power pack looked new, but wasn't grounded. Grounded it properly with a star washer and now I have spark. Jumps a 1/2" gap no problem. Good start! Cleaned the carbs and the rest of fuel system, replaced hoses, etc. Now she starts instantly and doesn't stall. Did a quick test run, and she ran strong. So far, so good!

The only issue now is a miss at idle, causing the engine to shudder and smokes a little. As the RPM's rise, she runs smoother. Just to narrow things...

* I swapped carbs with a good engine. No change.
* Checked and cleaned all electrical connections. No change.
* New spark plugs and wires. No change.
* Swapped the power pack and rectifier/regulator from good engine. No change.

Well, at least the parts are all good!

Next, I'll swap coils, but I doubt that is the issue with the strong spark I tested.

As you can see, I'm just swapping out parts, since I have them readily on hand, and it's fast. But I'm getting down to stator and trigger, and the parts motor has a completely different stator, trigger, power pack and rectifier.

Anyone have a similar issue with a miss at idle? What did it turn out to be?

Thanks.

.
 
Last edited:
Definitely not a lean sneeze. It's due to lack of ignition. Smoke and unburned fuel.

I was running it in a barrel, and after a while oil was floating. Definitely unburned fuel.

It's not running terribly, but definitely has a miss at idle...
 
yes, i've had that problem on an 87' 48. try removing the linkage rod between the carbs and see how it runs, and of course the roller can't be touching the throttle cam. any change?
when carbs were cleaned, were the core plugs removed?
 
thill said:
Definitely not a lean sneeze. It's due to lack of ignition. Smoke and unburned fuel.

I was running it in a barrel, and after a while oil was floating. Definitely unburned fuel.

It's not running terribly, but definitely has a miss at idle...
Click to expand...
That is normal when running in a barrel all carbed motors will leave that residue when running in a barrel. Have you done a link and sync on the carbs.
 
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