Compression Test on a J8RCSS

[Nanich]

Hello,

I am having troubles with my J8RCSS. It seems to start fine at first, but after it starts and then stops, it will not start again.

I just did a compression test on the motor. It came out at about 35PSI on both cylinders. I pulled several times to make sure it would not go up more. I know 35 PSI is way to low. I should be higher then 100 PSI. What is the cause of this?

Donnie

 

[JB]

Re: Compression Test on a J8RCSS

I would not worry about 35psi from a rope start engine as long as both cylinders are close. Differences in guages and technique can make as much as 50psi difference in readings.

Compression is not the cause of your warm starting problem. If compression was a cause it wouldn't start cold either.

Go to the Engine FAQs.

 

[Nanich]

Re: Compression Test on a J8RCSS

I had a look at the FAQ, but could not find anything on Warm Starts. Is there a common cause for engines that have troubles with a warm start.

My motor wants to start, it will putter a little when I pull the cord, and putter a more when I pull the cord. When it does starts it is like a putt.......... putt......... putt.... putt.. putt.. putt.puttputtputt and it finally starts. (if that makes sense.)

My manual says that the spark gap should be 0.40, but on here I have heard 0.30 and 0.35. Could that be the issue?

Donnie

 

[JB]

Re: Compression Test on a J8RCSS

.030" works better for sustained high speed operation, .040" works better for trolling. Either is acceptable.

Is the warm start trouble new or has it always been that way? Could there be something in your technique that doesn't work on a warm engine? Do you pump the primer bulb before trying the warm start? Choke or not?

 

[Nanich]

Re: Compression Test on a J8RCSS

It is a new problem. I have done quite a bit of work to it. I had heating issues. So I replaces the gear box oil, replaced the impeller and the thermostat. The heat is fine now. But the warm start has now become an issue.

On a warm start I know the primer bulb is fine, I do not do the choke. I am avoid of flooding the motor. As sometimes when I try the warm start I will pull the plugs and find that they are very wet.

Could warm start problems have anything to do with the SLOW ADJUSTMENT NEEDLE? Or the CARB?

 

[JB]

Re: Compression Test on a J8RCSS

Well, back to my original suggestion.

Start her up, get her warm, then shut her down and do the troubleshooting in the "Outboard won't start" article in FAQ.

Need to learn if it is fuel, ignition or timing related.

 

[Nanich]

Re: Compression Test on a J8RCSS

That FAQ for thee engines seems to be more for an Electric Start I did follow it, but I encountured something important that was not cover in the FAQ.

I got the motor warm and ran it for a bit. I shut it down, and tried to start it again. I choke was off, and I pulled and pulled. I took the spark plugs out. They were wet. The upper chamber was more wet then the other. (This was not directly covered in the FAQ)

I did not squirt the fuel in the chamber as the plugs already had fuel all over them. I think these suggest I look at the FLOAT NEEDLE. Does that make sense? I think that is a job for next weekend.

I also did do a compression test. It come out at 55psi at the top and 59psi at the bottome. Is that considered bad compression?

Donnie

 

[wbeaton]

Re: Compression Test on a J8RCSS

I think you need a new tester. It gave you +30 psi before and now its +50 psi. Compression probably isn't the issue. However, the theory is that a motor with marginal compression may start, but be hard to start when warm. I haven't actually seen that before. I've seen them either run or not due to compression. Are you sure the temperature is ok? Just because it pumps water doesn't mean its cooling effectively. A partially blocked passage will cause it too run hot.

I suspect the plugs are wet because you keep trying to pull it over. If it starts easy when cold it and runs fine then it shouldn't be the carb either.

 

[Nanich]

Re: Compression Test on a J8RCSS

Yes the temp is okay. I run my hand under the PEE hole and it is fine.

I just ran down to the boat to try one more thing.

I started it and started within a few pulls as usual. Seemed to run fine. Then I shut it down. I checked spark plugs right away without trying to start it. The upper spark plug was wet. Both the edges and both parts of the gap were wet. The lower spark plug was only wet on the edges.

Based on the FAQ, that suggests I look at the FLOAT NEEDLE. Is that true? What is the float needle and is it affected by temperature at all?

Thanks again. You folks are a great help!

Donnie