1982 25hp top cylinder won't fire

[Ajacct]

Stumped with 1982 Johnson 25hp:

Both cylinders 105 psi, both getting spark (open plugs & timing light), vapor coming out both plug holes when out (but heavier out of top cylinder).

Will run with both plugs or only lower plug wired but not with only top plug wired. New ignition module and coils, no wires open or grounding out.

With timing light on top plug at idle, at 8 on ELEC CD at starter pointer, no timing change up to half throttle (stator plate rotates correctly),
???

 

[saltchuckmatt]

Need a spark jump test...about 3/8.

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You can also check your keyway under the flywheel and that your flywheel is installed correctly.

 

[Ajacct]

Spark jumps 3/8" ok for both plug cables.
Under flywheel is good.
Head ground is good.
Swapped coils, plug cables, top just won't ignite on compression (105 psi).
New ignition control module bad out of box?

 

[racerone]

Check fuel pump diaphragm.----Might be ruptured.

 

[saltchuckmatt]

If your spark jumps that good then why do you think those components can be bad?

If you hold your hand in front of the carb does it spray gas at you?

What plugs are you using?

 

[Ajacct]

Has new fuel pump (boat runs in water with fair power on only one cylinder, but lots of gas/oil residue out exhaust, naturally) . My original post said vapor comes out with plug out (cranking). Using spec QL77JC4 plugs. Possibly timing of spark is off from the new control module?

 

[Ajacct]

Has new fuel pump (boat runs in water with fair power on only one cylinder, but lots of gas/oil residue out exhaust, naturally) . My original post said vapor comes out with plug out (cranking). Using spec QL77JC4 plugs. Possibly timing of spark is off from the new control module?

(I've been working with various outboards, inboards and IOs since the 1970's. This one's a stumper. )

 

[racerone]

Good luck with it.

 

[tphoyt]

As mentioned check that fuel pump diaphragm
If it’s ruptured and adding more fuel to that cylinder it won’t go boom without more air.

 

[Ajacct]

As mentioned check that fuel pump diaphragm
If it’s ruptured and adding more fuel to that cylinder it won’t go boom without more air.

I read that, but ...one carb, two cylinders, one cylinder runs fine.

 

[tphoyt]

Fuel pump works off crank case pressure from top cylinder. If its adding fuel to that cylinder it could be to much. It cost nothing to inspect it.
Jmo

 

[racerone]

???----There are 2 separate crankcases on this motor.

 

[tphoyt]

Right but the pump is run by top cylinder if I’m not mistaken? If diaphragm was ruptured would it not add more fuel to the top cylinder?

 

[racerone]

It could add way too much fuel and the plug will not fire !!!

 

[saltchuckmatt]

Has new fuel pump (boat runs in water with fair power on only one cylinder, but lots of gas/oil residue out exhaust, naturally) . My original post said vapor comes out with plug out (cranking). Using spec QL77JC4 plugs. Possibly timing of spark is off from the new control module?

Timing is from the pickup coil.

 

[tphoyt]

Timing is from the pickup coil.

Sorry I missed the new fuel pump
Part. But at the same time new doesn’t mean much to me any more. Especially when it comes to things that are supposed to be fuel resistant.
On a side note I got a set a brake calipers for my buddys truck not long ago and one of them didn’t have a piston in it. And it even had a tag on that said inspected.

 

[saltchuckmatt]

Sorry I missed the new fuel pump
Part. But at the same time new doesn’t mean much to me any more. Especially when it comes to things that are supposed to be fuel resistant.
On a side note I got a set a brake calipers for my buddys truck not long ago and one of them didn’t have a piston in it. And it even had a tag on that said inspected.

I hear you.....junk everywhere.

 

[Ajacct]

Sorry I missed the new fuel pump
Part. But at the same time new doesn’t mean much to me any more. Especially when it comes to things that are supposed to be fuel resistant.
On a side note I got a set a brake calipers for my buddys truck not long ago and one of them didn’t have a piston in it. And it even had a tag on that said inspected.

 

[Ajacct]

Found several very tiny holes in pump diaphram. Poor quality rubber, I suspect.
Thank you tphoyt and saltchuckmatt!

 

[racerone]

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