Combustion Problem?

[Panhandle Nick]

Ok so i just tested the compression. 60PSI on each of the two cylinders. I'm sure that's not good. Does anyone have a spec or direction on how to determine if the timing is right. I have a dot on the cam gear, an arrow on the casting of the case and the flywheel has an indentation. All these three line up. I assumed this was right. Maybe not.

 

[racerone]

Is there a compression relief feature on this motor ?-----This motor looks brand new does it not ?

 

[Panhandle Nick]

I don't know. Maybe bad rings are there compression relief feature LOL. The motor is 2009.

 

[Sea Rider]

If the motor is hard to start specially when cold say first morning start surely 60 PSI seems way low, if squirting oil into the each cylinder does the compression rises ? Paul surely has the cylinder compression chart for said motor...

Happy Boating​

 

[racerone]

It looks like there are compression relief mechanisms on this motor.-----So the 60 PSI means nothing !!

 

[Panhandle Nick]

It looks like there are compression relief mechanisms on this motor.-----So the 60 PSI means nothing !!

Hello Raceone,

I've been asked on this forum to check the compression. I thought this would tell me if rings are bad or valves not seating or maybe timing is off. Am I to understand in your opinion a compression test is not worth doing to diagnose my problem with this motor? I have spark, good spark, and I have fuel injecting into the throat of the carb, I also checked fuel pump and it's good. I have been told a particular passage in the carb having to do with low rpm idling could be clogged but I thing the motor would start and stall if that was the case. In any regard I will check that passage way. But still what is the deal with compression being irrelevant? Thanks for any input.

 

[MattFL]

He means that 60psi is after the compression release has let some of the air out, so it's not a useful reading. Most motors these days will have what's called a compression release, which lets some of the air out of the cylinder to make the pull rope easier to pull. The mechanism turns itself off as soon as the motor starts. To get a valid compression reading you would need to follow the steps in the shop manual to disable the compression release before taking the reading. Ditto if you were to use a leakdown test instead of a compression test. Did you try the starting fluid yet? Even a motor with low compression will start and run with that stuff.

 

[Panhandle Nick]

He means that 60psi is after the compression release has let some of the air out, so it's not a useful reading. Most motors these days will have what's called a compression release, which lets some of the air out of the cylinder to make the pull rope easier to pull. The mechanism turns itself off as soon as the motor starts. To get a valid compression reading you would need to follow the steps in the shop manual to disable the compression release before taking the reading. Ditto if you were to use a leakdown test instead of a compression test. Did you try the starting fluid yet? Even a motor with low compression will start and run with that stuff.

Ok so i was simply connecting the tester in the spark plug hole, then pushing the start button and the pressure slowly rose and topped off at 60 psi. In answer to the other question. I'm coming up with a way to get the fluid into the carb throat, because the air intake shape makes it hard. Thanks for all your input to all you guys who have responded

 

[racerone]

Very hard / impossible to disable compression release on these !!!----A leak down test would be easy to do if you know how the compression release works.----Just have to rotate the crankshaft so valves are both closed !!

 

[Panhandle Nick]

Very hard / impossible to disable compression release on these !!!----A leak down test would be easy to do if you know how the compression release works.----Just have to rotate the crankshaft so valves are both closed !!

Hi. What is a compression release? Is it some kind of one way valve like a pressure relief valve? Another question i can't seem to answer or find on line is how do i know the timing is set correctly. Can't find service manuals online for this motor.

 

[MattFL]

For the compression test, you need to have the throttle wide open, otherwise the cylinder won't fill with air and you'll get a lower reading.
For a leakdown test you also need to disable the compression release.
While you're checking things, check the valve clearances if you haven't already. Difficult starting is a common symptom for overly tight valves on a 4-stroke.
For a manual, check manualslib.com. I see some Tohatsu manuals on there and some of the Nissan and Tohatsu outboards are the same, maybe yours matches the Tohatsu 9.9 and you can use the Tohatsu manual. It should be obvious pretty quick.
A compression release is to make the motor easier to start. It holds one of the valves slightly open, usually the exhaust valve, to let a little bit of air out during the compression stroke. When the motor starts it turns off and the cylinder gets full compression. There are multiple different designs, here's an explanation of one, the general idea is the same for all:

 

[Sea Rider]

If starter fluid or pure gasoline can't make its way through the carb into the combustion chamber to check internal combustion, remove both plugs, inject a shot of starter fluid or pure gasoine inside, install plugs back in, start the motor and check what happens ? Belt timing doesn't go wrong from one season to the next if the motor was stopped and stored while previously was running healthy.

Happy Boating​

 

[pvanv]

Is there a compression relief feature on this motor ?-----This motor looks brand new does it not ?

Yes, it does.

 

[Panhandle Nick]

Yes, it does.

Hi Paul,

I've looked at the blown up diagrams of this motor and can't detect the Compression release but I'm assuming it has one as you've said. I understand that pushing the starter button and letting the motor spin is not an accurate compression test. So I'm still not sure if compression is my problem.
1. Can I be sure that a clogged passage way in the carb for low idle would not prevent starting? It would just die out after starting?
2. How do I conduct a leak down test? (I'm having a hard time getting a service manual) can't find on line. Perhaps a link?
3. I uploaded a picture of my motor showing the cam gear and flywheel position, is that showing that the timing is correct? Another reason I need a service manual.
4. I guess I could look in the spark plug hole and rotate the engine until the piston is at top dead center and then look at the valves and see if they are fully seated at that point. I'm assuming that would mean my timing is correct.

 

[pvanv]

Unfortunately the Factory service manual is now out of print.
The decompressor is a weight on the camshaft.
Clogged low speed circuit can be an issue.
You would need to buy a leak down tester. And you need compressed air.
Timing is seldom off. If the belt came loose or snapped, you would bend at least one valve. You can verify with a timing light.
Verify good spark and then clean the carb properly.

 

[Panhandle Nick]

Unfortunately the Factory service manual is now out of print.
The decompressor is a weight on the camshaft.
Clogged low speed circuit can be an issue.
You would need to buy a leak down tester. And you need compressed air.
Timing is seldom off. If the belt came loose or snapped, you would bend at least one valve. You can verify with a timing light.
Verify good spark and then clean the carb properly.

Ok so the latest is this, I took the carb apart and checked the ports and passage ways. Re assembled and using starter fluid it started and actually ran and when I gave it gas it accelerated. I think once the fluid was used up that's when it stalled. SO the good news is my compression and spark are good. A new carb is $260, or a rebuild kit is another option. What would you suggest?

 

[MattFL]

Re-clean your carb, you've missed something and it's still plugged up. Pay special attention to any small passages and tubes, tiny holes, etc.. Compressed air and carb cleaner spray (wear goggles). If you have access to a hot ultrasonic cleaner then that can dramatically help to soften and loosen up the junk that's plugging it up. Unless you have more money than time, in which case the new carb would be the easy way out.

 

[racerone]

Go back to post # 5------A novice sometimes needs to clean the carburetor 3 or 4 times before it is really clean.----Easy to miss some of the small passage ways.

 

[Sea Rider]

A new carb is $260, or a rebuild kit is another option. What would you suggest?

Never have seen a carb so gunked that was impossible to be cleaned to perfection.​

This carb was one step before being thrown into the deep blue. After an overnight soak in lacquer thinner and a meticulous manual clean up was fully recovered to work flawlessly. If still having gunked fuel passages inside the carb a carb kit won't do nothing...

Happy Boating​

 

[Panhandle Nick]

Ok, sounds like the route to go. Thanks for all the posts.