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20 HP compression issues

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Cyangelo

New member
I checked compression (125 in both cylinders) and verified my timing marks correct. I believe I found my problem. A single yellow wire leading to a sensor threaded into block had not been routed properly, and it was cut in half by the timing pulley. I caused this problem when I replaced broken timing pulley and belt. I don’t know what that sensor does, but motor was not happy with its wire severed. I repaired wire and routed it correctly this time. Runs good in barrel. True test will be out on the lake when I get boat back in tomorrow. Can anyone tell me what that sensor does ? I need to get a service manual for this motor.
Cyangelo
 
jgmo said:
The yellow wire goes to the oil pressure switch. The engine was likely going into guardian (de-power) mode.

You can buy the GENUINE HONDA manual here:

Honda Marine | Shop Manuals Publications | Honda Power Products Support Publications

publications.powerequipment.honda.com publications.powerequipment.honda.com

Glad you found the problem.

Thanks for the update.
Click to expand...
Hello again, Cyangelo reporting back concerning my Honda 20HP 4 stroke. After repairing the broken yellow wire to the oil sender, I thought the problem of high speed miss was corrected, however it is still running lousy at mid to high speed. The problem I believe goes back to when the timing pulley broke and belt came off. I replaced pulley and belt, and that's when I caused the yellow wire to get severed. I am still unsure if this is an interference type engine where the valves may have contacted the pistons when the timing pulley broke. There were no metallic noises when it happened. The motor was running full speed on pontoon boat, when it just shut down like I had turned the key off. The compression checks good. I have since replaced the spark plugs, fuel filter, and water pump impellor. Engine does seem to run OK at first, starts right up and has good power for a while until it heats up it seems. I did just order the shop manual, and if there is a possibility that there is internal damage, I will need to disassemble to inspect. I am able to use boat, just can't go full speed, and hope I am not causing any further damage. any advice will be appreciated.
Thanks, Don Angelo ( Cyangelo )
 
Hi,

I can't say either if this engine is an "interference" engine or not.

But my experience with engines that have suffered valve and/or piston damage such as you suspect is that they typically don't start, idle and run well anytime afterwards. I don't think that should be written in stone but I think it's generally true. A bent valve stays bent and the symptom shouldn't go back and forth with temperature as you describe.

However, I do remember one 4 cylinder that had a loose valve seat and would miss terribly and then suddenly run perfect. So, I guess anything is possible. A slightly bent valve might move ok and then start hanging in the guide as things heat up. But that's just a guess.

The real difficulty will be diagnosis without disassembly.
I would want to know all I could before opening an otherwise seemingly sound engine unnecessarily.

Sadly, the first tool I would go to for trying to figure out what's happening would be a vacuum gauge. However, this engine has no vacuum test port or vacuum operated devices to aid with fitment of a gauge.
I suppose a port could be drilled and tapped into the intake pipe but I have never done that. Although I know I would consider doing so. This being a twin engine, the vacuum pulses would be "coarse" at best but I would look for a difference in what the gauge does during the transition from running "good" to when it starts running poorly.

But perhaps a borescope in through the spark plug holes might reveal valve to piston contact. Small flex cameras that plug into smart phones are readily available and cheap. I have a couple and I believe there's one that has a 9mm head that should do the job.

The fact that it starts and idles and runs good until warmed up makes me think it's not a valve but I've been wrong enough in my time to know not to assume anything.

Tell me...
...how much time...in measured minutes....does it "run ok" before starting to lose power?

Sorry you're having troubles.
 
Probably 10 to 15 minutes to get out to first fishing spot. Then turn off and fish a while, and then start up and try to run full throttle to next spot and will run bad. It seems like after initial run and shut down, the engine stays hot just sitting there with no water pumping through , then when start back up the hot engine runs poorly from mid to full throttle. I will look into a mini camera, and I ordered the manual. I really appreciate your advice and will figure it out. I’m 70 and retired, so taking it to dealer for repair would be too costly for me. I will let you know what I find.
Thanks again, Cyangelo
 
Well, this doesn't sound like a bent valve to me at all.

This could be a fuel quality or delivery problem. Although, I do recommend that you remove the valve cover and inspect/adjust the valves when your manual arrives.

Have you tried pumping the primer bulb when it loses power? And, it might be a good idea to check the bulb before taking off after that first stop. It should remain firm during a stop like that. If it goes soft, it could be that it's partially losing prime and the fuel pump is struggling to keep up.

Have you ever emptied the fuel chamber out? Item 2 in the link below...


The fuel chamber can trap water and cause problems. It's a good practice to empty it out once a season.

Just a couple of ideas.
 
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