1974 9.9 Johnson running problems. I can get it started but then runs very ruff.

[WeezyJGW]

I have a 1974 9.9 Johnson which had extensive work done it a few years ago.it was running perfect until I took it to the Boundry Waters area. I took a full load of supplies to a camp, like ran it full blast for 3 miles. Then on the return trip with an empty boat I started having problems. Now I can get it started but it runs very ruff and or shuts down. Any ideas on problem would be greatly appreciated.

 

[Nordin]

First of all check compression and then for spark at both cylinders.
Compression should be 100 PSI or more at both cylinders.
Maximum 10-15% in different between them.
Spark should jump 3/8 of an inch or more in atmosphere.
If that checks out good pull the carb and clean it.

 

[jimmbo]

What did you mean when you said "Extensive Work done", and when was the last Time it was run, prior to the Incident you experienced?

 

[Crosbyman]

if sparks ok sounds like crud ending up in the carb... maybe just a bad grey hose plugged tank pick-up, venting etc...

sometimes badly stored engines end up with dried out fuel and running them years later loosens all that " varnish" and plugs the carb.

time to take it apart.

 

[racerone]

Was the impeller replaced as part of the work ?----Maybe something is stuck in a reed valve.------Maybe it over heated and then blew the head gasket.-----Maybe the fuel pump diaphragm ruptured.----Easy / economical to replace that diaphragm.---Possibly running on 1 cylinder.-----Does spark jump a gap of at least 5/16" on both leads?------Post the actual compression values.-----Should be easy to figure out what is wrong here.

 

[WeezyJGW]

First of all check compression and then for spark at both cylinders.
Compression should be 100 PSI or more at both cylinders.
Maximum 10-15% in different between them.
Spark should jump 3/8 of an inch or more in atmosphere.
If that checks out good pull the carb and clean it.

I just checked compression, it is 75 psi on each cylinder. Any suggestions

 

[WeezyJGW]

What did you mean when you said "Extensive Work done", and when was they last Time it was run, prior to the Incident you experienced?

It was running good before the incident. I am getting 75 psi on each cylinder.

 

[WeezyJGW]

It was running good before the incident. I am getting 75 psi on each cylinder. If it is not 100 psi what do you suggest I do next?

It was running good before the incident. I am getting 75 psi on each cylinder.

 

[cyclops222]

I vote a blown head gasket from the WOT for 3 miles.