Jonhson 25 cyl head?

laujok

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My question for you gurus is that is it possible that the cylinder head is warped dispite that I have 125psi on lower and about 120psi upper cyl? Plugs look clear and wet and idle is wery poor and smokey.
 

boobie

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Re: Jonhson 25 cyl head?

With that compression it sounds more like carb or ignition probs.
 

Beek14

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Re: Jonhson 25 cyl head?

What issue are you having exactly?
 

Chinewalker

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Re: Jonhson 25 cyl head?

A warped head would show up as blowing head gaskets... Sounds like your issue lies somewhere else.
 

laujok

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Re: Jonhson 25 cyl head?

My problem was/is (don't know yet :) ) that the motor ran like way too rich. I've checked the fuel pump for pin holes, carb float, jets, vacuum leaks, compression, coils, CDI, trigger switch, power coil, wiring harness, fuel mix for water, timing, water pump rubber grommet... Head gasket, exhaust gasket and left cover gasket are new. Plugs were wet and clear white so I thought that the only reason for all this is water going into the cylinders. I checked the head with feeler gauge, straightedge and light. Between the cylinders I could see the light under the straightedge so I sanded the head and now it's flat for sure. Test drive tomorrow..
 

laujok

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Re: Jonhson 25 cyl head?

My problem seems to be 1/2 solved. I installed a cyl head from a 88' 20hp Evinrude and both crank seals. I tested it in a barrel, started good and kept running but still with a shake+cough but runs a lot better and revs too but the longer it ran the more it would like to stall and when it stalled it had a lot of resistance when pulling the rope. Both plugs were wet when I checked, I also took out the by pass cover and there was black oil all over the lower part of the crankcase, upper was crystal clear. So, something is still not right..
Any ideas? Would be nice to have a running boat, vacation is coming...:)

Thanks
 

AlTn

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Re: Jonhson 25 cyl head?

fuel pump, carb, primer look to be the suspects...you can remove the fuel pump, block the pulse hole on the block, then gravity feed the carb with a tank and hose higher than the carb < 1 ft. higher= ~ 1/2 lb.of fuel pressure >..does it idle well now?...no?...then on to the other suspects
 

laujok

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Re: Jonhson 25 cyl head?

I did feed the motor directly to carb from the tank -> no help, it still coughs and smokes. I also disconnected primer when testing. Starts fine when cold but after about 1 minute idling likes to stall if I don't give more throttle. Plugs are still black and wet. Is it possible that the mating surface in the block is warped? If it is how can all this happen? I bought the motor as non functioning. Impeller looked fine when I checked..

Thanks
 

boobie

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Re: Jonhson 25 cyl head?

What size gap will your spark jump on an open air gap spark tester ??
 

laujok

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Re: Jonhson 25 cyl head?

It's J25RSSE year 2000 25hp. Spark jumps very good on a 7/16" gap (about 11mm).
 

Cofe

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Re: Jonhson 25 cyl head?

I noticed that you did not mention a proper cleaning of the carb. These symptoms describe a dirty slow speed circuit in the carb. Disassemble, clean, and rekit your carb. The slow speed screw should be set at 1-1/2 turns out for initall setting, then fine adjust from there.
 

laujok

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Re: Jonhson 25 cyl head?

Sorry, I forgot to mention that the carb is rebuild by a real mechanic (not me :) ) with a Sierra kit and all the slow speed circuit is cleaned too. Strange thing is that the motor likes to run normal idle only when the mixture screw is turned out only 0.75 turns but then it becomes too lean and stall in a few seconds.. If out like 1 and 1/4 or 1 and 1/2 it idles very rough and smokes a lot too. I tried with another carb from a 88' 20 hp Evinrude and the idle was a bit better but not much.. Also when i last tested it and tried to start after stalling there was a lot of resistance when I pulled the rope. Water in Cylinder?
 

Haffiman

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Re: Jonhson 25 cyl head?

A lot of interesting symptoms here.
Wet and white plugs?
Black sludge in by-pass cover?
Start by hooking up a timing light. First mark BOTH cylinders with TDC on the flywheel. (the upper is there already, add the lower at 180 degree)
Check with a spark tester that both cylinders have sufficient spark.
Run the engine with the timing light and check timing at BOTH upper and lower cylinder and that the timing marks for respective cylinder is only visible when hooked to that cylinder. If you may see both upper and lower marks on the flywheel when hooked to 1 or 2, change powerpack.
Check engine temperature preferably with an IR gun that both cylinders have same temp.
When you switched head, did you switch thermostats as well?
When you had the head down, did you check the water deflectors that they were in place and sealing?
 

laujok

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Re: Jonhson 25 cyl head?

So today I milled the block mating surface because had the head off. It was a little bit warped but not much. Reassembled and tested it in a barrel. Still the same. Tried with another carb too. Lower plug is dry and black on gap area but wet everywhere else. Top plug is wet everywhere especially on the gap. I didn't see any beads of water on any spark plug so I quess the possible water problem is solved. I also pulled plug wires one at a time, ran a bit worse when I pulled the upper wire but stalled instantly when I pulled the bottom one. So I think of an electrical problem but seems weird because have tried with different coils and power pack too. Didn't have much time today but trying again tomorrow with Haffiman's advices..
 

laujok

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Re: Jonhson 25 cyl head?

I gave up. Checked everything and no change. Now I have two motors that won't run..:) It seems that it had a random spark on both cylinders. I changed trigger coil and power coil from another motor but that didn't help. With my luck the parts that I swapped had gone bad in a few weeks. I don't know what to do with these things..

I still have my trusty 75' Johnson 6 Horse, ran fine last year but not big enough for my bigger boat. I need something between 20-30 hp to power my boat. What do you people think that is the most reliable motor from the 90's or 2000 up? Or should I continue to fight with these?:facepalm:
 

Haffiman

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Re: Jonhson 25 cyl head?

I gave up. Checked everything and no change. Now I have two motors that won't run..:) It seems that it had a random spark on both cylinders. I changed trigger coil and power coil from another motor but that didn't help. With my luck the parts that I swapped had gone bad in a few weeks. I don't know what to do with these things..

I still have my trusty 75' Johnson 6 Horse, ran fine last year but not big enough for my bigger boat. I need something between 20-30 hp to power my boat. What do you people think that is the most reliable motor from the 90's or 2000 up? Or should I continue to fight with these?:facepalm:


Random sparks??
Have you tried disconnecting the stop circuit?
Remove the black/yellow lead going into the powerpack.
 

laujok

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Re: Jonhson 25 cyl head?

I had the kill wire of from the 5-pin connector and it didn't make any difference in running. My fancy 30 euro timing light showed that both cylinders had random spark but more random on upper cylinder. I also checked the two wires coming from the CDI box to coils and they both had even and constant signal.
 

Haffiman

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Re: Jonhson 25 cyl head?

If consistent signal into the coils but random out, I would have 'pulled apart' or checked the plug leads.
Originally they are solid-core with a spring inside the boot in both ends.
Which plugs are you using?
Then carefully PUSH the pins and sleeves out of the rubber contacts (do NOT pull in the leads) between trigger, charge coil, power-pack, PP to-coils. Clean out the rubber contacts and be sure the pins and sleeves are clean.
 

AlTn

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Re: Jonhson 25 cyl head?

these coils ground through the coil body w/o a separate grounding wire?...have you cleaned the mounting surfaces and mounting screws?
 
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