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Top Plug Fouling

J

jrs

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"After a week of fishing, I&#3

"After a week of fishing, I've suddenly started having a problem with the top plug fouling on my 1976 Johnson 35. It ran pretty decently for the first few days, then started missing badly. I changed the plugs, and within a few minutes it started missing again. I pulled the plugs, and the top one was black, oily and fouled. I changed plugs again with the same results. Last night I limped in running on one cylinder.

Suggestions, please?

Thanks"
 
"I would try a compression tes

"I would try a compression test first. If no surprises there, I would look for a carburetor issue causing excess fuel going to top cylinder (bad float, float valve, etc.)"
 
"I bought a compression tester

"I bought a compression tester today, and it was a good investment. The top cylinder shows about 130, the bottom cylinder about 125. Please forgive my density, but with a single carb, how would it send too much fuel to only one cylinder?

Thanks"
 
May be a weak spark on that cy

May be a weak spark on that cylinder alone--
if you switch the wires does the symptom move to the other cylinder?
 
Suggest You do a good decarbon

Suggest You do a good decarbonizing of Your engine with 'Engine Tuner' or 'Sea Foam' before starting adjustments or dismantling. Carbon build up un the exhaust system may cause problems like the one You describe.
 
"I hadn't considered switc

"I hadn't considered switching the wires as I figured the engine would not run that way. I'm building a spark gap tester, so that should answer the spark question anyway.

I've added Sea Foam to the last couple of tanks of gas, but I have not yet run any Engine Tune through it. I'll do that next time I'm able to get to the lake.

Thanks"
 
"Engine tuner is no gas additi

"Engine tuner is no gas additive. Run the engine hot and spray into the carb, close to the whole can. Stop the engine and let it sit for at least 1/2 hour, then start the engine and run it for 1/2-3/4 throtle until it runs smooth, then full throtle for a couple of minutes. May not be too popular to do it on a lake.......
I think Tom meant to do a crancking test with switched wires. Would be quite a problem to get the engine running. However You may switch the coils."
 
"Sorry about the confusion on

"Sorry about the confusion on the wires--
Morten is right--
I had gone through about a half dozen variations on that post and my first thought was carbon fouling. After a day of reading and responsding to about 45 graduate student papers via email, I was a bit fried at 11pm."
 
"OK, spark gap tester has done

"OK, spark gap tester has done its thing, and we have good spark on both cylinders. Next question is, if I can't get it to run more than a few minutes on both cylinders, will that be good enough to run the Engine Tuner through it? I'm assuming I can't do that at home in a barrel as it needs to be run at full throttle."
 
"The best and most efficient i

"The best and most efficient is to run it at sea, but You may be able to use a barrel but in that case no prop and no load. Note that the water will be rather messy! 'Play' with the carb throtle when injecting the Engine Tuner so the engine won't stop."
 
""Rather messy" aptly

""Rather messy" aptly describes the water in the barrel after running a can of Quicksilver Engine Tune this evening. Lots of oily carbon on the water. The engine still misses after the treatment. The top plug was heavily coated with carbon, so I changed it out and cranked the engine again. Still coming out coated with carbon. I'll assume this may go on for a while until the loose carbon is all blown out. Unfortunately I found parts in the bottom of the water barrel when I dumped it. The prop spacer and one oil seal came off the shaft during the operation without the prop. I need to go through the lower unit and replace the seals, shift dog and forward gear anyway, so no big deal."
 
"The worse the water, the bett

"The worse the water, the better! Means that You may have gotten quite some stuff out, and the rest may get out when You manage to put some load on. When the engine runs smooth again, You may probably be able to adjust the carb to a leaner setting and get rid of the fouling of the upper plug. Put the engine at low idling, turn the mix screw in 1/8 turn at the time until You get the highest rpm with same throtle setting. Then back out 1/2 turn and check the engine acc. If ok, leave it, if engine hessitates go out another 1/4 turn. Whach out for the timing/carb synch. Normally the carb should open just as the carb follower passes the mark on the ignition cam, but it is often better to let it open a bit (1-2mm) later than too early.
If there is still a problem with unballance between upper and lower plug the cause may be either the leaf plates or the lower cranck case/cranck shaft seal."
 
"Thanks to all for the assista

"Thanks to all for the assistance. I'll try to get it back on the lake next weekend and see if we accomplished anything.

In the meantime, I'm looking for lower unit parts (seal kit, clutch dog and forward gear). There seems to be a gap in everyone's online inventories when it comes to the 1976 Johnson 35. Did I buy an orphan troublemaker that nobody wants to support with parts?"
 
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