compression reading

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dakotahoku

Seaman Apprentice
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Dec 10, 2007
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I performed a compression test on my 95' 35hp johnson and got 110psi on both cylinder's. Does this sound ok? What would is the correct pressure reading?
 
HighTrim

HighTrim

Supreme Mariner
Joined
Jun 21, 2007
Messages
10,486
Re: compression reading

Reading is good. Most aim for at least 100 psi and within 10 percent of each other. Since all meters read a little differently, the difference between cylinders is most important. You're fine on both checks.
 
tashasdaddy

tashasdaddy

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51,019
Re: compression reading

if you have never done a decarb on this motor, this would be a good time.

Decarb, take a can of seafoam put 3/4 of it in the gas tank, with only 1 gallon of premixed gas. put the rest in a spray bottle. start the engine, and let it come up to temperature. then remove plugs, and them some real good shot of seafoam into the cylinders, replace plugs, let sit 15 minutes. restart, and spray the rest of the seafoam into the carbs, so the the motor almost stalls, wait and repeat until the seafoam is gone.then take for a wide open spin. then put in new plugs, ad premixed gas to the tank, and take it for a wide open throttle spin. it is going to smoke like a house on fire, during this process.

afterwards recheck compression.
 
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dakotahoku

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Re: compression reading

I did a decarb (seafaom), well sort of. I slowly sprayed half the bottle through the carb throat for 10 minutes then more until it died. Removed spark plugs sparyed a little in each cylinder and let sit for 15 min. Restarted and now it runs worst than ever. Before the decarb I had a bogging at higher rpm's but it idled fine. Now it misses and coughs and dies at idle. I plan to change spark plugs and rebuild my carb and hope for the best. Any ideas will be greatly appriciated.
 
jtexas

jtexas

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8,646
Re: compression reading

the decarb cleans the carbon build-up off pistons, cylinder walls, ports, etc....but can't clear a clogged hi-speed jet, which is a likely source of your bogging. spark test & carb rebuild probably would've been advised prior to the decarb if that symptom had been known. but don't panic - you haven't harmed your engine. carb rebuild with new kit(s) will do the trick.
 
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dakotahoku

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32
Re: compression reading

Should I do another decarb after I get it running right?
 
H

Harker

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Sep 21, 2003
Messages
452
Re: compression reading

No, I'd just run a 1/4 can in each tank of gas for a while. I like to run the last tank of gas for the year with about 1/2 can of seafoam in 6 gallons. Don't know if it helps anything but my motors start right up in the spring and run smooth.
 
HighTrim

HighTrim

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Jun 21, 2007
Messages
10,486
Re: compression reading

Also remember to change the plugs that were used during the decarb. Or better yet keep them for the next decarb that you do. The now foulded plugs from the decarb will give you trouble. Then clean out those carbs as JT said, paying special attention to those jets.

"http://www.meegsonline.com/tmd/TMDsVideoChronicle2.wmv"
 
D

dakotahoku

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Dec 10, 2007
Messages
32
Re: compression reading

Thanks for all of the great replies! I don't have a winter where i'm from so I need to get this engine fix because the fish a biting.
 
tashasdaddy

tashasdaddy

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51,019
Re: compression reading

you need the carb tool to get high speed jets out. i made mine
 

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dakotahoku

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32
Re: compression reading

Do i really need to remove the high speed jets in order to get them clean?
 
W

wavrider

Chief Petty Officer
Joined
Nov 26, 2007
Messages
543
Re: compression reading

dakotahoku said:
Do i really need to remove the high speed jets in order to get them clean?
Click to expand...

If you can at all remove them to clean the jets and passage ways then yes do so.
If you can not remove them due to lack of tool or jets corroded in place or no table to loosen the jet then a good cleaning. lots of compressed air and try to pass some welding wire through the jet to make sure it is clean.
Dirty jets will drive a technician crazy trying to diagnose the problems.
I have successfully cleaned carbs without removing the jets, I have also had to take carbs back off and RE-CLEAN them because I did not remove the jets, I did not have the removal tool at the time. I do now.
Good luck with the cleaning and this forum is a wealth of information and tips.
 
jtexas

jtexas

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8,646
Re: compression reading

if you don't take the jets out, they might get clean from the soaking and compressed air. if you don't have compressed air, aerosol carb cleaner is a pretty good if less effective substitute. take out the core plugs and clean behind 'em. it works sometimes.

the jet remover took me about 10 minutes with a barrel sander on a dremel tool. cut a screwdriver off flat with a cutoff wheel then sand it down. remove about 1/3 of the material from opposite sides (tiny bit more than 1/3), about 3/16 to 1/4" from the end. don't be overly concerned with precise measurements, but do take care to make the sides of the remaining tab flat and parallel. if it won't fit down in the slot after one pass, don't force it - just sand a little more.

I routinely run about an ounce of seafoam per gallon of gas.
 
D

dakotahoku

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Joined
Dec 10, 2007
Messages
32
Re: compression reading

Thanks guys for the useful info. I purchased a manual for my motor, but it looks like I won't receive it til next week. Should I try and remove the carb and soak it in carb cleaner while I wait for the manual to arrive. Just by looking at the carb it look pretty easy to remove. Is there anything that I need to look out for if I try to remove and clean without the manual or should I wait for the manual? Your thoughts?
 
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dakotahoku

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Dec 10, 2007
Messages
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Re: compression reading

Well I went ahead and started to disassemble my carb. Upon removing the bowl I noticed one of the core plugs was missing. My carb on the outside have holes on either side with metal screen covers which I think that one of the core plugs covers in the inside, but the hole on the other side the core plug is missing. Is this a problem or could causing one of my problems. It looks like the carb was serviced at least once before. The carb overall looks pretty clean so I am not sure that the carb is the problem. I am going to do some soaking with carb cleaner and wait for any of your thoughts.
 
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