sneezing back through carb

[powerslide]

I have a 78 115 johnson. It ran decent the first two times i took it out, had a slightly cough every 5-10seconds at idle and seemed to idle a little low. None the less it ran great once we got moving.

Last time i took it out it was almost impossible to start and once i got it running it was back firing through the carb.

I bought this from a guy who said he replaced the blue piece under the flywheel because it went out. The arm that goes through the blue piece doesnt appear to be connected correctly it has some black urethane looking material on it and doesnt go all the way in. My understanding is this controls the timing. If its not in the correct location will it cause a miss/backfire?

Another question, the motor has been painted white and the grounds behind the coils dont appear to have been cleaned should i file the paint off and make sure they have a good connection?

 

[emdsapmgr]

Re: sneezing back through carb

The periodic cough is called a lean sneeze-an occasional miss at idle. That's a carb problem-not ignition-usually a fuel restriction. At idle the carb butterflys are closed and draw fuel from the idle circuits (passages) only. Once you crack (open-even slightly) those butterflys, the carbs will draw fuel from other jets. Once the carbs draw from other jets-usually the lean sneezing quits. You may need to disassemble the carbs for a complete cleaning-esp the small idle passages. Not sure just what the blue piece is that you refer to. Possible it is the timer base. That timer base has a link arm held in place by two ball and sockets-that connects to the spark advance lever. The arm needs to be correctly installed to provide the correct timing advance between idle and full throttle. If the timing is off significantly, it could cause the miss/backfire you refer to. You can have a look at the factory explosed parts diagram to clarify how those parts go together at this website: epc.brp.com. The coils have a ground wire which is mounted under the coil when it is bolted to the block. If your block was painted and the area under the ground wire was not sanded off, you might have bad coil grounds. After painting a block, I always to sand the ground area around that mounting bolt- by hand, so that the coil ground wire is making a good connection. Same for any other block ground connections, such as the main battery wire ground stud.

 

[powerslide]

Re: sneezing back through carb

If a coil is bad will it "backfire" or sneeze through the carb? On my racecar it will get backfire through the carb when the timing is off. but dont see bad coils in that enviroment to know.

Another question. The coil the spark plug is by is the plug it is intended for correct? I had them off and want to make sure i didnt switch them.

I took the carb off and cleaned them and reassembled and still had the backfire or pop and hiss through the carb. I Cleaned the grounds last night but havent ran it because it was too late. I will try after work, if still back firing will obtain new plugs before going any further. I bought new when i got the boat but that is cheap easy way to rule that out.

 

[emdsapmgr]

Re: sneezing back through carb

The only time I've seen a coil responsible for a backfire was when it was connected to the wrong lead of the powerpack, causing it to fire out of time. You might check the coil/power pack wiring with the factory electrical diagram at the top of the forum.

 

[powerslide]

Re: sneezing back through carb

ok so tonight i started it up after cleaning the grounds behind each coil. No difference.

I started the boat and pulled each wire. The left side(when facing forward) made very little difference on both cylinders. The right side it would die or almost die on both cylinders if you took them off.

So i think well it's both left cylinders so maybe its the power pack and switch them from left to right. no change.
So i switch coils from left side to right side. no change.

If the reed valve is messed up could it cause the backfire?
What things should i be looking for i have two problems the left side obviously isnt firing hard. Second is the back firing. I have been messing with this for a couple months and i'm at the breaking point.

I cleaned the carbs because the bulb wouldnt pump up and it was smoking pretty bad when running. Both those issues are gone.

 

[emdsapmgr]

Re: sneezing back through carb

You are correct, the problem is with the left side head. Any chance the the spark plug wires are crossed, or the two leads from the pack to the coils are crossed? Typcially on a dual power pack V4, there are two orange wires from the pack to the coils. The solid orange wire is to the bottom coil, the orange wire with the blue tracer goes to the top coil.

 

[powerslide]

Re: sneezing back through carb

I'm unsure if the spark plug wires are on the correct cylinder. I have the coil closest to each cylinder hooked to that cylinder. I will check the orange vs orange w/ blue tonight.

 

[powerslide]

Re: sneezing back through carb

Any old pro's in tulsa want to come look/listen? Starting to wonder if the kill switch might be limiting something on the left side...

 

[powerslide]

Re: sneezing back through carb

Mine is kind of like this. http://m.youtube.com/watch?v=k0WWU7jv-W0

After the backfire through the exhaust the carb hisses