Should motor run with these compression numbers

[matt194]

I have a 79 evinrude 115hp that I could not get to stay running in the water last time I took it out. I have since replaced the gasket on one bank of heads and lowered the idle to the correct setting. My question is should my engine run while in the water with compression number 95, 100, 102, 101? It runs good in the driveway. Also I bought the gauge from harbor freight tools and they don't sell the highest quality stuff, could that be the cause of lower numbers? The old gauge I had gave me higher readings of around 115 on all cylinders, that was about 6 months ago. Thanks for any help.

 

[HighTrim]

Re: Should motor run with these compression numbers

Those compression reading are fine, that is not your problem.

Give us a little more info on what it is doing.

 

[guy74]

Re: Should motor run with these compression numbers

Are you setting your idle speed in the water? It is supposed to be set at 650rpm, idling in forward gear with the boat unrestained. I've found, on the V4s I work on, that the idle needs to be set around 1100rpm on muffs.

 

[tashasdaddy]

Re: Should motor run with these compression numbers

as Guy said.

 

[matt194]

Re: Should motor run with these compression numbers

When I couldn't get the motor to run in the water the idle was set at 1800 rpm, so I set the idle speed in the driveway at about 1050 rpm. I have not tested the motor since I changed the idle speed. The problem that i had last time I was out was the motor wouldn't stay running for more than 20 seconds. I tried priming the bulb and raising the idle lever and none of them worked. Could my idle speed being set to high cause the engine to not run in the water?

 

[iwombat]

Re: Should motor run with these compression numbers

Not likely. There's something else going on there. Your compression numbers are just fine, so next step is to check spark.

 

[ezeke]

Re: Should motor run with these compression numbers

Having the idle speed with no load (like 1800) set too high will not cause the motor to stall. It will, however, ruin your gears.

Have you set everything up according to the factory service manual?

 

[guy74]

Re: Should motor run with these compression numbers

The last time I see a motor like your's idle at high rpm like that, it needed a link/sync. The bottom carb was being held open slightly by the linkage. In order to adjust the idle down to specs, the timing had to be backed off to the point that it wouldn't run in the water. Does that sound anything like what you have going on? Like ezeke said, "Have you set everything up according to the factory service manual?", that might be all that is wrong. Those motors idle with the throttle completly closed, all that adjusts the idle speed is ignition timing.

 

[matt194]

Re: Should motor run with these compression numbers

I have set everything to factory settings but have not tried it in the water yet. The spark is good on all four cylinders. It may run good in the water now. I just wanted to know if my compression numbers were keeping my motor from running, so I don't waste money going to the lake when there is a known problem. I am going out tomorrow and will let you know what happens. Thanks for the help.

 

[matt194]

Re: Should motor run with these compression numbers

Ok I took the boat out today and I had the same problem until I changed the frayed and blackened ground wire. Everything is running good except at idle and high speed. I had my idle at 1050rpm in the driveway but when I put it in gear in the water I only got 450-500 rpm. What should I put the rpms at in the driveway in order to get 650 rpms in the water? Also when put into high speed it either dies or bogs down, I think its carbs but I could use a second opinion. When I clean the carbs do I have to take out the round metal plugs to clean the jets?

 

[tashasdaddy]

Re: Should motor run with these compression numbers

http://forums.iboats.com/showthread.php?t=244013. idle fine adjustments in the water.

 

[iwombat]

Re: Should motor run with these compression numbers

Generally you set the idle to a ballpark range in the driveway and fine-adjust on the water.

 

[HighTrim]

Re: Should motor run with these compression numbers

Agree, I normally set my V6's to about 1100 RPM - 1150 RPM on muffs and that is usually close to the 750 RPM I want while under load in gear.