1967 Johnson 9.5 coughing, missing

[Chris in Indiana]

Hello,
I?m still having trouble getting my 1967 MQ-13 Johnson 9.5 to stop missing at low rpm. So far I have:

Cleaned the carb, blew everything out with compressed air and put in a full kit with a new float.
Installed new kill switch and wiring.
New plugs, gapped to .030
Set point gap to .020
Checked out all of the rubber isolators.
Prior owner just installed all new electrical before I bought it.
Cleaned out the lower vent and fuel pump.
Reset the carb with alignment point on cam.

I have noticed that if I apply the choke about 90% it runs great at low rpm but then it won't rev up. Also, adjusting the low speed mixture needle has no effect whatsoever. Very frustrating.

Any ideas? I?m totally stumped.

 

[Chris in Indiana]

Re: 1967 Johnson 9.5 coughing, missing

If I can figure out how, I'll try to add a video of it running.

 

[wilde1j]

Re: 1967 Johnson 9.5 coughing, missing

Carb may need cleaning.

 

[F_R]

Re: 1967 Johnson 9.5 coughing, missing

The fact that it runs when choked pretty much says that there is a problem with the idle circuit in the carburetor. Did you remove and inspect the passages behind the core plugs?
Either that or you have a major air leak such as crankshaft seals. If you don't know how to get at the lower crankshaft seal, you don't want to hear it.

 

[mbanko17]

Re: 1967 Johnson 9.5 coughing, missing

Chris, I just aquired a boat from my dad. 1956, 7.5 seahorse. It was sitting for 10 years. The same damn thing happens. I just talked to someone at the shop and they said first rebuild the carb, wich you already had done. So maybe not my problem. BUT, the next step would be the coil, Check to see if they are cracked. That is my next step. I had it on the lake and it ran fine wide open, after tweeking with the fast speed screw,but When you back her down, stall city. I am new to these old motors, but I will figure it out with the help of the internet.

 

[mbanko17]

Re: 1967 Johnson 9.5 coughing, missing

choked at low rpms only? Thats what i thought he was talking about. choke off at higher rpms runs fine? mine does.

 

[Chris in Indiana]

Re: 1967 Johnson 9.5 coughing, missing

Yea, choke off at high rpm runs fine. It's only when I tried to idle.

As to the core plugs, I cleaned behind them but there wasn't much there. On the small one I blew compressed air thru but the larger one hadd a plastic insert in the port. There weren't any holes or passagways in it. Perhaps I missed something? As I said, adjusting low idle needle does nothing.

 

[wilde1j]

Re: 1967 Johnson 9.5 coughing, missing

To clean a carb, you need to soak it in carb cleaner (overnight is good), the blow it dry with compressed air making sure all passages are clean. As F_R suggests, that usually means removing core plugs.

 

[Fuzzytbay]

Re: 1967 Johnson 9.5 coughing, missing

Assuming a correct carb rebuild, its either a coil, or an air leak.
I'd check the gasket, and or nut tightness on the carb, first, if you are 100
% sure the rebuild was done right. Then look to the coils. They could be missaligned, points slipped, or a condensers is gone, as well as a coil. Wouldn't be the first motor I have seen with one new coil, and one old coil that worked fine, just a wee bit longer than the first one did.

 

[Chris in Indiana]

Re: 1967 Johnson 9.5 coughing, missing

Can a coil be misaligned? How? There are two screws that hold each one down on my motor. I pulled each of them up slightly for inspection and didn't see any cracks.

I'll double check the coils tomorrow. Is an ohmmeter necessary or is the spark check generally sufficient.

Back to the carb, which is heavily under suspicion at this point. I did not soak it but cleaned thoroughly with a can of Gumout. Then I blasted everything I could find with compressed air. I have attached a picture I took while reassembling and you can see the open ports without plugs. The larger one has a plastic insert which I did not try to remove. Should I? The smaller one I hit with compressed air. Would it be worthwhile to pull the plugs and soak overnight? What do you recommend soaking it in?
Thanks very much for the assistance!

 

[Chris in Indiana]

Re: 1967 Johnson 9.5 coughing, missing

Oops, I meant I'm going to spark check the condensers tomorrow, not the coils. That might hurt.

 

[wilde1j]

Re: 1967 Johnson 9.5 coughing, missing

A decent auto parts place will have a carb solvent by the gallon. My dad a had a boat shop with a metal basin full of some dark brown liquid (never knew what the stuff was) and a metal basket that all carbs soaked in, and then were blown dry with compressed air. You need to be a little careful, as some plastic carb parts may be affected adversely.

 

[Chris in Indiana]

Re: 1967 Johnson 9.5 coughing, missing

If I pull the carb apart again I may as well use drill bits to be sure I don't have anything stuck in there. DOes anyone know what sizes should be used?

 

[mbanko17]

Re: 1967 Johnson 9.5 coughing, missing

Chris, I did a very quick fix for our problem. When the motor coughs at low rpm, you need to make the the mixture more rich. Take the low speed knob off and reposition it leaner, then retighten and turn it to a richer setting. Go from there bro thats what I did. Mine idles fine without rebuilding the carb.
Oh yeah, it was sitting for ten years! The carb was rebuilt back then,and the coil was replaced. Sitting that long didn't matter. just a few tweaks needed. 50-1 mix with Quicksilver and 87 octane. Before I got the motor, this is what ran in it. RUNS GREAT! TRY IT!