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1978 Johnson 35 fouling plugs

H

Hubertcj

New member
Hey folks, we are getting close to having a decent engine I hope. Recently had a few days on the water and last 2 trips were rough. Here's what happens.

Start of the day motor is running nice and smooth no issues. Run for about 30 minutes at a combo of idling thru no wake zones and full throttle outside of them, and then the motor cuts to super low power. Basically won't run at above idle at full throttle and it runs sloppy. Pull the plugs and they are soaked and lightly fouled with oil. It's done this 3 times in the last few trips.

What I've tried: better plugs, dump out the gas and start with a fresh mixture at 50:1 ratio, mild idle screw adjustment, took the carb of sprayed out everything with carb cleaner and compressed air, lots of cussing. Also it may be important to note compression is around 90 PSI both cylinders but it has been running pretty good with that for a few weeks.

Any ideas? We are close to having a nice running engine. Thanks for your wisdom!
 
Is the thermostat in place and working properly ?-----Sounds like it is dropping to one cylinder.-----Test spark.-----Does spark jump a gap of 3/8" or more on both leads, yes or no ?----Looked for a leaking fuel pump diaphragm ?----Tell us more if you want to get results.
 
This seems to be a continuation of the problems already discussed in your previous thread started on April 17 http://www.marineengine.com/boat-fo...-running-but-not-for-long&p=677518#post677518


" Better plugs" you say
The recommended plugs are Champion QL77JC4 gapped at 0.030"

Personally I would also consider NGK BZ7HS-10 to be suitable, or even B7HS-10, but not NGK resistor plugs such as BR7HS-10.

You are not using resistor plugs are you ?

If a carb needs cleaning it generally needs the jets to be removed and cleaned but you said previously you'd cleaned it thoroughly.

Plugs are soaked ... presumably with fuel ? Perhaps the carb is flooding ?? Have you checked the float and float valve
Presumably you have an electric primer rather than a manual choke ? Have you checked that is is operating correctly


Have you checked the sparks ... you should be able to get a 7/16" spark from each lead
 
Thanks for the advice. I'll check these things when I get home today.

Electric choke is operating as it should. Fuel pump is new so I have not yet checked it for a leaking diaphragm, though no fuel is leaking around it.

I've been using NGK plugs not sure of the exact part number at the moment. Normal plugs not the resistor types.

Float and float needle recently replaced.

Will check spark and test coils with an ohmmeter this afternoon. I also have spare coils and power pack from a parts motor if these present a bad reading.

I'll update once this is done. Thanks y'all!
 
vics-----The electric primer came out in the 1980's on those motors.----Unless someone retrofitted a 78 model !--------Look for and test the thermostat on this motor !----Your compression numbers are low.----Test with another gauge perhaps.------Or inspect pistons and rings via the transfer port cover.-----Sparkplugs do NOT foul these days.----Something like cold combustion temperatures and an inefficient engine causes them to be unhappy.----Simple trouble shooting needs to be done here.
 
racerone said:
Is the thermostat in place and working properly ?-----Test spark.-----Does spark jump a gap of 3/8" or more on both leads, yes or no ?
Click to expand...
Confirm this first. As Racer said, plugs these days don't just foul unless there is an ignition issue. You might also check the spark when the engine is cold and when hot. It's possible you have a pack or coil failing once they get warm.

Also be sure the thermostat is there. Cold engines can definitely foul plugs.

KJ
 
Sorry my mistake confusing electric choke and electric primer

Brain is getting addled i think as a result of being "locked down" for 5 weeks. Furthest I have been is 26 times round the back lawn for exercise and the only other person I have seen to speak to is my neighbour when he collects my shopping list every week and leaves the shopping in the porch a couple of hours later.
At least I get to go out tomorrow .... to the hospital for a blood test ...... :(


Do make sure you have not put NGK resistor plugs in. The BR7HS plugs are often listed as equivalent to QL77JC4 ..... they are not!

If you do not get sparks which jump 7/16" ( or at least 3/8" ) You might want to go to the CDI Troubleshooting Guide. Testing coils with an ohmmeter does not tell you a great deal . At least good readings do not necessarily mean the coils are good,

Really unclear at the moment whether you have a fuel/carb problem or an ignition problem
 
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