84-86 75HP Mercury.

[James R]

Trying to get this motor to run correctly.
Comps all 130, New pack. carbs rebuilt. new plugs. Sparks good.
I dont know much about how this motor runs but I note the following. It starts well on the fast idle and will idle once stable. Comes up on throttle happily in the tub off load. Everything appears ok but if I pull the #3 wire there is no change to the motor revs at Idle. I usually get sparks jump when I put the wires back on the plug, no jumping here. I recall that Mercury was messing about with only two cylinders active when idling. Is this one of those or do I have another problem. I have tried adjusting the idle jets and I get a good response from #1 carb and a lesser response from #2.
Any help would be most appreciated.

 

[racerone]

Your motor runs on all 4 cylinders ALL THE TIME.-------It was the later 4 carburetor ( 2+2 ) models that did not supply enuff fuel to bottom 2 cylinders at idle.-----Sounds like you need to look at bottom carburetor again.--Does spark jump a gap on all leads 3/8" or more ?-----And stop running this motor until you determine what is wrong.-----No fuel going in means no oil either.----How did this motor run for you last year ?

 

[James R]

Thanks for the response Racerone. This is a recently acquired project with little history. I think the carbs are ok. Spraying fuel mix into the intakes made no difference to the lower carb, but I will check the carb. Now I know that the cylinders run on all 4 all the time I will go after the sparks. Fooled me I think. I can see spark at each plug when grounded. That doesn't mean much of course. Will test the stator etc. The new pack that was fitted prior to my ownership could be a cheap one and not working.
The tests will show. I will post the results.
Thanks again.

 

[James R]

Ok. Checking the sparks revealed that 3 &4 not firing. Did the usual switching of wires including the trigger and everything seems to point to the pack. However this pack was fitted just prior to my acquiring this motor. Could still be the pack. To be sure I tested the stator. Disconnected the rectifier. Coil resistances look good and no shorts. Tested, using my DVA, between reds and got 250v plus. Tested between blues and got 40v.

From this all indications show the stator to be good and the pack bad. Do you concur?
I am using CDI trouble shooting as my guide.

Jim.