70HP Johnson

[e5noddin]

I have a 1993 70 Johnson that refuses to run at trolling speed. It feels like its running out of gas. I had the motor rebuilt due to a loos of compression. They put in a new power pack (?), rebuilt the carbs with new jets,bored it out, new pistons, ect. The problem showed up after the rebuild. Been to two shops with no luck. Any ideas?

 

[jegervais]

Re: 70HP Johnson

Was the loss of compression in all cylinders or just one cylinder (which one)? Did they install ALL new pistons? How did the engine run immediately after the rebuild? Can you test fuel pressure? Are you certain sync & link are correct - many times when these engines won't idle the idle speed is simply set to low (spec is 800 +/- 50 in gear).<br /><br />You say it seems to be running out of gas - Is it lean sneezing? Sometimes the earlier carb covers would warp and cause an air leak (causes lean running), a quick way to check for this condition is to stick a round tooth-pick into the air bleed jet on the starboard side of each carb.<br /><br />-John

 

[e5noddin]

Re: 70HP Johnson

John, Thanks for the response. As to your questions, All cylinders were bored out with new pistons. The problem showed up immediately after the rebuild. I'm not sure on the fuel pressure and I don't have a guage. I believe that the engine idles at 800 to 850 but I'm not sure. If sneezing means backfiring that hasn't been a problem. Its funny but after the problem, I thought about buying a 70HP Suzuki but after reading some of the info on this site, I think I'll pass.

 

[tshoerichs]

Re: 70HP Johnson

e5noddin,<br />You may want to try a different octane of fuel. Go to the highest octane. If they put new pistons in they may have changed the compression ratio. Kinda like in a car when guys wanted more hp they put in higher compression ratio pistons. You know, the ones with the mound on the top of the piston etc. In cars, a high compression ratio engine does not like to idle well either

 

[Dhadley]

Re: 70HP Johnson

This may sound a bit off the wall but since you said it showed up right AFTER the rebuild I would ask them a couple of things. First what brand of pistons did they use? What oversize? Why did they install new jets? Did they change the jet sizes?<br /><br />Good luck!

 

[e5noddin]

Re: 70HP Johnson

Thanks guys, Before the motor blew, I used 93 octane Mobil almost exclusively. After the rebuild I went to 87 octane because I was told that our gas up here in Connecticut has a number of anti pollutants that tend to make an engine run hot. I'll try the fuel and ask about the pistons and comression ratio. Thanks