1975 Johnson 9.9 running on 1 cylinder

[JTMAC]

I have a 1975 Johnson 9.9 HP (10R75C) given to me by my dad and having some trouble. I performed compression check on both cylinders (OK) Spark test on both cylinders with a tester (OK), Replaced the fuel pump, cleaned and rebuilt the carb, new coils and a set of points set at 0.020 gap on the set mark stamped on the crankshaft. Fuel line and tank appears to be OK. I tested it out last weekend and it ran on 1 cylinder for the first 30 minutes. I slowed the engine down and slowly brought it up to speed and could hear the 2nd cylinder kick in. It was running fine for 20 minutes and then back to one cylinder. I am confused at what may be the problem. HELP!

 

[racerone]

Check the reed valves.----Run with a timing light to see which cylinder might be loosing spark.

 

[JTMAC]

Check the reed valves.----Run with a timing light to see which cylinder might be loosing spark.

Thank you for responding. Are the reed valves also known as leaf valves which is part # 48 in the diagram from this link? https://www.crowleymarine.com/johnson-evinrude/parts/42975.cfm?mdl=VHGUV6

 

[flyingscott]

Did you replace the condensers?

 

[racerone]

Reed valves / leaf valves are the same thing.----I do not need to look at a parts diagram or manual to overhaul one of these simple motors.

 

[Crosbyman]

measure boot to engine frame & look for solid ohms value of "X" for those ignition coils.
old style coils run 4-8 kohms solid newer style ones may be 300ohms but either type should give a solid ohms value. try turning the throttle while testing

while measuring wiggle/flex the wires see if ohms are steady...while making certain probe contact is solid.

if you loose continuity suspect that coil circuit ..could be break or oxydation along the suspect wire (assuming coils are ok of course)

 

[JTMAC]

Did you replace the condensers?

Yes, replaced points and condensers.

 

[F_R]

Has anybody told you yet that those 1974-76 9.9 & 15hp motors are notorious for fouling spark plugs? We couldn't make some of them run one weekend when brand new. The factory couldn't keep them running either. Some will argue, but that was my experience with them back in "The Day". Sorry 'bout that.
Try new plugs. There is a newer plug # that some people claim better luck with.

 

[909]

Can confirm , my 76 fouls plugs like a mofo .
All these older models want is to be ran wide open.

 

[racerone]

I did a complete check over on 1975 model 9.9 about 8 years ago.----Idled like a charm.----Owner loves the motor , says he would never sell it.

 

[Crosbyman]

depending how much use of it you make every year ....
try some synthetic oil like xd-100 $$$$ but it contains carbon guard , no smoke no smell best oil ever for ETECs

you can buy Carbon Guard on it's own at the EV product dealers if you don`t want to buy $$$$ XD-100 oil to mix with your fuel .

https://domo-online.com/evinrude-johnson-carbon-guard-fuel-treatment-case-of-12/#:~:text=Carbon Guard is a gasoline additive formulated to,1 oz for every 8 gallons of gasoline.

 

[kbait]

If one cylinder comes and goes, it shouldn’t be the reeds. It could be one of the kill circuit wires randomly connecting to ground under the flywheel. Also could be a coil failing. And as stated, could be spark plugs. I use NGK B7HS spark plugs in those points motors @.030”
Good luck!

 

[JTMAC]

Check the reed valves.----Run with a timing light to see which cylinder might be loosing spark.

Here is what I found after pulling the head and taking a look at the reed valves. Not sure if they need to be replaced.

 

[JTMAC]

This is what I found after pulling the head and looking at the reed valves. Unsure whether I should replace.

 

[JTMAC]

If one cylinder comes and goes, it shouldn’t be the reeds. It could be one of the kill circuit wires randomly connecting to ground under the flywheel. Also could be a coil failing. And as stated, could be spark plugs. I use NGK B7HS spark plugs in those points motors @.030”
Good luck!

I use those too.