85hp Johnson vibrates, then takes off

[scully222]

I have a 1978 85hp Johnson that starts well, idles well, but when first taking it out, vibrates, bogs down a little, then takes off fine. Runs well after planeing out. If I stop and start again after running a little , it doesn't do it so bad and seems to improve the more I run it. I changed plugs thinking that might help, but still does it.

 

[steelespike]

Re: 85hp Johnson vibrates, then takes off

The motor uses 2 2 barrel carbs.The throttle plates must be syncronized
for optimum performance.Idle speed in gear is 650 rpm.Check the carb throttle / ignition syncronization.Just a couple of tips I picked up reading the manual.

 

[jtexas]

Re: 85hp Johnson vibrates, then takes off

If the throttle valves start to open before the timing is advanced enough, it'll fall flat when you put the hammer down, but you can nurse it up to full throttle. if that's what's happening, link & sync is the answer. short version is, throttle cam has to hit the roller right on the mark. if that doesn't help, check the compression and spark. if those check out, rebuild carburetors.