Idle Problem: 73 Johnson 65h

[tomoco]

I've got a 1973 Johnson 65 horse. New power head 10 years ago. Compression is good. Starts easily. Runs well WOT. Even El Shift works OK.
Idles OK at about 900 rpm.
Slower gets rough and stalls.
At 900 rpm I can remove top 2 plug wires, and it keeps running.
Remove lower plug wire (only) & it stalls immediately.
I think it is idling primarily on one cylinder, but I cleaned out the carbs last week and I believe the Idle passages are clear.

I could use some help!
Any Ideas??

 

[Joe Reeves]

Re: Idle Problem: 73 Johnson 65h

Compression should be 100+ psi and even on all cylinders. Is it?

Spark (with the spark plugs removed) should jump a 7/16" gap with a strong blue lightning like flame.... a real SNAP! Does it? NOTE... the 7/16" gap is important, checking spark by using the spark plugs is waste of time, don't do it!

If the above two areas are as they should be, then I would assume that you are overlooking something with the carburetors. Let us know what you find.

 

[tomoco]

Re: Idle Problem: 73 Johnson 65h

Several Months back the compression was 115,112 117.
As for the spark, I hear a real good SNAP when I remove the plug wire & put it back, but I have not actually measured it in some time.
Would a poor spark affect idle more than WOT running?
One more thing: I actually flopped the Top & Bottom carbs. It had little effect.
I'll check that spark tomoro!

 

[iwombat]

Re: Idle Problem: 73 Johnson 65h

Time to do a proper spark test methinks.

 

[R.Johnson]

Re: Idle Problem: 73 Johnson 65h

Do a sync,& lync, and if it has electric shift, it is not a 73

 

[tomoco]

Re: Idle Problem: 73 Johnson 65h

Johnson: You're absolutely right. It is a '72. My Typo.
Sync Is OK. I followed the Manual!!

Joe Reeves: Cyl1 & Cyl2 jump a 1/2" gap. Cyl 3, the one running OK, is erratic at 3/8".

Some years ago, I replaced the power pack, then coils 1 & 2. I remember that the coils made a huge difference. But, I dont think it has ever idled much below 900. Though it does seem to do a little better when thoroughly warm.

BTW I read your older posts on Idle Adjustments. Cyl1&2 dont give clear results. But I have found with this engine that if I set it with screws in as far as comfortable, that it will stall on accel. If I open all about a turn more, it will accel OK, though sometimes sluggishly. OK at WOT.

I might add it smokes quite a lot when started cold. Unused gas from 1&2?
Plugs are L77 JC4. Maybe I'll try a new set.
Can't hurt!

this makes no sense

 

[tomoco]

Re: Idle Problem: 73 Johnson 65h

All Right.
I must be "overlooking something with the carburetors".
I had another look.
The only thing I found suspect is those little odd-shaped Rubber gaskets around the outside end of the 3 Idle mixture screws. They all leak a little air out when I blow in the little hole in the side of the housing. Could this mean the idle circuit is sucking air rather than gas??