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I bought a 50 HP Honda 4 stroke for the whaler, but it is running like crap. Starts, but I have to hit the choke to get it going, sounds great, then sputters and basically dies. so a little back ground...

I have a leak down tester, strange results. Shows 2% loss on Cyl 1 and 3, dry and cold motor Cyl 2 about 5%, Cyl 2 with a shot of fogging oil goes to 1.5 to 2%. I thought all was good when I bought it. However after I got home, compression test shows 70 to 80 Lbs on all 3, not good. BUT, if I crack the carb a little, the compression shows 130 lbs on all 3. Never seen that. I guessed the cam was worn badly and the intakes were not opening enough to suck in enough air to compress, but cam looks fine and crude measurement shows .350 at the spring lift. Not exactly sure what it should be, but not bad enough to cause that issue.



Bottom line is, engine runs like crap until a hit the choke to about 1/2, then sounds great, have not had it under load yet. Thought carbs, but someone put brand new ones in, clean enough to eat off of, jets clean, nothing. timing belt is also brand new. My guess is the guy I bought this from did a lot of work and it still ran like crap. I am out of ideas as to what the issue is. Never seen a good leak down, bad compression than get good if the butterflies are crack a little.

How about a burnt valve, bad head gasket?

It has been about 50 years since I played with that kind of stuff, but maybe Bruce has a better idea.

Steve Found this if it helps.

TESTING (WET)

Many automotive books describe a dry and a wet compression test. Usually these tests must be interpreted together to isolate the trouble in cylinders or valves. Unfortunately, the wet compression test is unreliable when performed on engines where the cylinders are horizontal (like the old VW). To perform the wet test, a tablespoon of oil is poured into the cylinder though the sparkplug hole before checking the compression. On horizontal cylinders, oil does not spread evenly over the piston crown, a necessity for this test.

With the above said, you squirt the tablespoon of oil (SAE 30W is fine) into a cylinder that is reading low. Crank the engine two revolutions or so to spread the oil then retest the cylinder. If the compression comes up markedly, 40 PSI or more, the trouble is poor ring to bore sealing. If compression doesn't increase much, about 5 PSI, then the problem is probably with the valves. It could also be pulled head studs or a warped cylinder head.

IF THE CHOKE HELPS IT RUN BETTER ITS A CARB ISSUE ETHANOL FUEL AND CARBS DONT HAVE A GOOD RELATIONSHIP
WHEN DOING A COMPRESSION TEST ALWAYS HOLD THE THROTTLE WIDE OPEN WITH ALL THE PLUGS OUT TO GET PROPER RESULTS

If you have to pull the choke on to run smooth the engine is running lean.
Either thru the carbs, gasket leak or hose off.
If all three cylinders are in agreement and come up to compression with the same amount of rotation, doubt you have an issue there.

My lawnmower tractor had the same problem this year. Came down to sticky linkage. I would spray all the linkage for the choke and carb with PB Blaster or WD40 or the like and work them a bit. Could be salt buildup or a bit of corrosion. Good luck.

You're definitely running a lean mixture. Yes, you have a new carburetor but do you know for sure that it's the right carburetor?!... Do you know whether the carburetor settings are correct?!...

I've always hated dealing with carburetors so I always had somebody else do them so I can't help you there...

You can carefully spray carb clean or other flammable solvent around the gasket area while running to check for the gasket leaks Bruce mentioned. If the leak sucks the solvent in teh mixture will richen up momentarily and the engine will idle up.

Sorry I did not reply, but found the issue. The lower compression was due to this engine has a pull start option, so with throttle at idle, the compression is low to allow pull starting, when at off idle, compression was 150 PSI. The issue with the engine was apparently a common one with Honda engines, the idle jets were cracked, in fact 2 of the 3, just an FYI for others. The mechanic said it happens often to these motors. Runs great now, but the mechanic was not cheap, or able to fix it quickly, to many others in front of me. Took about a month to get in the queue but If he had nothing to do, I doubt he would have been good enough to find the issue. Very good guy and very meticulous, worth the money to know it is not only fixed, but gone thru completely.

had the same issue with my 06' Yamaha 40 hp. constantly bogged down when I went full throttle out of the hole and was told it was ethanol issues... bought jets for a 25 hp yammie and look out, ran like a champ. something about it being a "high altitude" motor because of EPA regulations. not an issue ever since.