poor running 84' 70hp johnson

[Billy O]

Carbs been rebuilt and new plugs. Runs pretty smooth in neutral. Put it in gear and the darn thing starts shaking really bad. Vbrates all through the boat and will not get all the way on plane. Gonna check compression again cause it is running so rough.

 

[jonesg]

Re: poor running 84' 70hp johnson

Just a guess,...its not firing on one cyl, it will run ok in neutral but put it in gear and the load shows the imbalance,

so do a spark check with a gap tester from autozone, only $12 , set the gap to 3/8th inch.
You cannot use a sparkplug to test for spark due to the large gap required.
It must have a bright blue spark, yellow is no good, yellow will not spark under compression ( too many air molecules to jump).

When you find the dead hole, swap coils around to see if the problem follows the dead coil, check coil for cracks, if original its about due for the graveyard.
I'd change them all. Test plug wires the same way, swap em around, mark the dead one to keep track of where it is, replace them all if one is bad.

Check and clean coil grounds, should be nice and shiny where it mounts to block, use sandpaper and clean all grounds.

 

[Billy O]

Re: poor running 84' 70hp johnson

Checked the spark today and it is weak off the top ignition coil. Swapped plug wires around and no change on top coil. Have another and tried to swap coils. Both are early 80s but the wires going to the coils on this one go into the gel. The other one has wires from the connector that has plugs on them that fit over a post. Did a compression test anyway and it was 130,125 and 125 starting at the top with tat one being 130. Got 3 of 6 running but can't start other 2 until this one is done.