Minimum compression

[79Glastron]

My neighbour knows I work on boat motors (Mercury) and he asked me to look at a 1969 Evinrude 9.5 that his father in law owns. He said it would run for a few seconds then stop. He had some shade tree look at it. They replaced the points and condenser (incorrectly gapped) and new plugs. They said the compression was low and wanted to pull the head, he said hold the phone and wanted to get a second opinion. I gaped the points put fresh gas in the tank and attempted to start it, no luck. I sprayed some gas mix down the carb. It fired and ran for a few seconds and stopped. I checked the compression and spun it over with my drill, I got 85 dry and 95 wet. My Mercury's have around 130-160 depending on the motor. I think this motor is worn and cannot run correctly with this low of compression. What do you experts think? I don't think a carb cleaning will correct this one, it will not run on its own at all.
Thanks!

 

[JB]

Re: Minimum compression

85/95 is okay for that outboard, Glastron, as long as they are close. The engine is clearly not getting fuel from the carb. That is your trouble. The fact that it starts and runs on introduced fuel clears mechanical and ignition troubles.

Could be anything from fuel tank, to fuel lines to fuel pump to carb itself. Start with easy/free possibilities; is air leaking into the fuel lines? Does the fuel pump squirt fuel into the carb bowl? Are the orifices in the carb clean and open?

Let us know what you find. For a little extra help, look here: http://forums.iboats.com/engine-frequently-asked-questions-faq/outboard-wont-start-158071.html

 

[79Glastron]

Re: Minimum compression

JB

I was getting 85 PSI on top and bottom dry test turning it over with a drill. Wet test I got 95 PSI both top and bottom. I would say those numbers are low, but again it still runs with a squirt bottle. The only other problem I could think if there is too much compression leaking past the rings there is not enough pressure difference in the crankcase to draw fuel/air through the reed valves and up into the transfer ports. If flooding the carb with fuel from the spray bottle it manages to get enough to run. Again, just a quick theory. I did pull the carb off and did see the float bowl full of fuel, so fuel is getting into the carb. I'll pull the whole carb again and give it a good soaking and blow out and retest.

 

[nwcove]

Re: Minimum compression

As JB stated, your average wet/dry compression of 90 psi is perfectly fine for that motor. ( it should start and run with the comp as low as 60 psi)

 

[boobie]

Re: Minimum compression

Did you take the plug out of the float bowl and check the high speed jet to make sure it's good and clean ??

 

[doityourselfer1]

Re: Minimum compression

Mine has 90 psi in both cylinders. I had the same problem with mine , and cleaned out the carbs twice and still was acting up.i ordered a carb rebuild kit and rebuilt the carbs.it seems like did the trick. Runing beautiful all day long pushing a 14 feet jonboat with 2 of us no problem. How ever this engines are sensitive to the air fuel mixture. There is the adjustment knob on the front of the engine.turn it clockwise all the way in,and 1.5 turn out.good luck with your project.

 

[HighTrim]

Re: Minimum compression

The 9.5s are low compression motors. As stated, those reading are more than enough for it. You cannot compare it to your high compression Mercs. Apples and oranges.

Try to clean/rebuild the carb first.

If that doesnt rectify it, an issue with the 9.5s is bad motor mounts. They are notorious for it. NOT a fun thing to fix either, ask anyone that has done it. They will run for a couple seconds, then due to the bad mounts, will shake, throwing off the points timing and killing spark/motor.

Not saying that is the current issue, but something to look at if in fact fuel delivery is not your issue at hand.

 

[79Glastron]

Re: Minimum compression

I got the carb off and found it full of junk, zero fuel delivery. I removed the plug on the side and pulled the plastic plug and cleaned out the idle holes. Its currently soaking yet. I ordered a kit for it. Will report back once kit arrives and carb is back on.

 

[79Glastron]

Re: Minimum compression

Got the carb all cleaned out and installed. Started on the first pull and ran great. It is very important to remove the welch plugs to be able to clean all the small passages that can easily clog in these small carbs.
Thanks!