75 3 cyl running on 2 cylinders

[Sylva-Ranger]

Mercury mid '90 75 hp 3 cylinders S/N 0G039179
When run idle , remove the top spark-plug cap (cyl no 1) and make no difference at all.
No power on the water, bad holeshot.

-Compression is 125 PSI on all the 3
- Ignition is very strong on all 3
- Clean all carburetors , drain all fuel and try whit a portable fuel tank/hose whit new fuel make no difference.
-Remove the intake and Reed valves/gaskets on the cyl no 1 is ok
- Timing/ synchro is ok

Is like the top cylinder is runing dry. the spark-plug stay dry ..........

If i unscrew the mixture screw ( richer adjustment) all the way on the no 1 cylinder , run a little bit better so is like a fuel issues ont that cylinder. The spark-plug stay dry.

I temporary invert the no 1 and no 2 carbs and no differences : The problem stay on no 1 cylinder.

The TDC mark is ok when checked whith dial gage.

When checked whit starting fluid, not evidence of air leak around gaskets.

Any ideas ?
Thank you and sorry for the bad English, not mi first language.

 

[Dave1027]

I guess it's possible low fuel pump pressure could be impacting the top carb more than the others. Try pumping the primer bulb while idling/running. Does it make a difference?

 

[racerone]

Cylinder sleeve rotated ???------I would pull the exhaust cover to have a look.-----Just 20 bolts or so and a few .

 

[jimmbo]

Bad upper Crankshaft seal perhaps

 

[racerone]

Do not run this motor until you determine the issue.----If carburetor is blocked you are starving one cylinder of gasoline ----AND THE OIL !

 

[Sylva-Ranger]

I guess it's possible low fuel pump pressure could be impacting the top carb more than the others. Try pumping the primer bulb while idling/running. Does it make a difference?

fuel pressure is good and pumping the primer pump change Nothing

 

[Sylva-Ranger]

Cylinder sleeve rotated ???------I would pull the exhaust cover to have a look.-----Just 20 bolts or so and a few .

That what i'm going to check next, haved see that before on a johnson 3 cylinder 60 hp

 

[Sylva-Ranger]

Bad upper Crankshaft seal perhaps

i haved order a new one and try next week because when i removed the flywheel for check the seal, i't just maybe a little bit oil around it , but i'm not sure it will make a lot of difference like that a hi RPM but the new is ordered anyways .

 

[Sylva-Ranger]

Do not run this motor until you determine the issue.----If carburetor is blocked you are starving one cylinder of gasoline ----AND THE OIL !

Yes for sure the motor is not use until i find the trouble, but i dont think is the carburetor because that make no difference ( in idle when i change the top and bottom

 

[Sylva-Ranger]

Thant you for all the suggestions , i will comeback when i have new about this problem.

 

[Sylva-Ranger]

Just removed the exhaust covers : Sleeves are ok ( not rotated) , pistons rings and pistons skirts are like new .Ordered news gaskets and whil try whit the new upper crakshaft seal ............

 

[Sylva-Ranger]

Finaly after changed the uper crankshaft seal and the idle was about 75 % better

Also changed the top ignition coil after found a cracked magnet and the holeshot is now good and the idle too

Happy customer !

Thanks for your help !