J15RSSM no idle

[Rudejonnie]

Hi all,

I recently acquired a 2000 Johnson 15hp (J15RSSM). It starts up and runs at higher rpm’s but will die at idle. Started with the typical full carb rebuild with an OMC kit (even swapped in a known working carb from a different motor), checking compression (100psi on each cylinder), checking spark, link and sync, fuel pump is good, ensuring bulb pumps till firm, good fuel/tank from working motor, etc with prior suggestions on different posts here and other forums with no change in the no idle issue.

I did notice the installed fuel pump is part number 438556. The correct fuel pump should be 438562 (already on order).

My question is would the incorrect fuel pump cause the no idle issue? Perhaps the 15hp not providing a strong enough pulse to supply the correct amount of fuel flow for idling?

Thanks in advance for any insight.

 

[tphoyt]

Primer leaking?

 

[Rudejonnie]

Primer leaking?

Primer bulb? No. No leaks anywhere.

This is a pull start model so no electric primer.

 

[saltchuckmatt]

Everyone probably knows the next question, spark jump 3/8 of an inch with a nice blue crack?

 

[tphoyt]

Manual primer valve in the correct position and no leaking o rings?
Just wonder if it’s getting more fuel than needed at idle. Being you have tried 2 different carbs it doesn’t seem to be an idle circuit issue unless they were both dirty.

 

[Rudejonnie]

Everyone probably knows the next question, spark jump 3/8 of an inch with a nice blue crack?

Have to get an adjustable tester to be sure. That’s on the list. Tested with in-line testers and it was a bright spark on both cylinders.

Manual primer valve in the correct position and no leaking o rings?
Just wonder if it’s getting more fuel than needed at idle. Being you have tried 2 different carbs it doesn’t seem to be an idle circuit issue unless they were both dirty.

Yes, I used a tank from a working motor. No leaking anywhere. I should have the new, correct, fuel pump later in the week to see if that makes any difference.

Thanks for the replies!

 

[tphoyt]

I’m talking about the primer valve on the
motor Does it have a red lever?
I could be way off base but it just a thought.

 

[tphoyt]

Ah right you said it was pull start.
So you have a pull primer then correct?
If so is it closing all the way and not bleeding extra fuel?

 

[Rudejonnie]

Ah right you said it was pull start.
So you have a pull primer then correct?
If so is it closing all the way and not bleeding extra fuel?

Oh do you mean the choke? It does close all the way but I can’t say for sure if it’s bleeding extra fuel or not. I’ll take a look next time I work on it. What’s the next step if it is, or isn’t, bleeding extra fuel?

The motor is a bit hard to start. The only way I’ve gotten it to start is by pumping the bulb till firm, choke pulled, wants to start on third pull of the rope, push choke back in, starts up after a couple more pulls. Spraying premixed fuel into the carb before starting or during running does not make a difference that I could tell. Once running, it will only stay running in high rpm’s. Dies when throttle is returned to idle position.

 

[tphoyt]

Can roller in correct position and all in one pice?
Might help to do a link and sync or at least walk through the process and confirm its all good.

 

[saltchuckmatt]

Tim,

Pretty sure no manual primer on that model. I have one and it's a choke.

I'm guessing weak spark, still something in carb/float or plastic carb parts.

 

[Rudejonnie]

Can roller in correct position and all in one pice?
Might help to do a link and sync or at least walk through the process and confirm its all good.

Yep. Good to go. Plate starts to move just as the cam hits the mark

 

[Rudejonnie]

Tim,

Pretty sure no manual primer on that model. I have one and it's a choke.

I'm guessing weak spark, still something in carb/float or plastic carb parts.

Correct, choke.

I’ll be getting the adjustable spark tester to be sure it’ll jump a decent gap.

I rebuilt the carb and also used a carb from a good running motor and still the same issue.

 

[saltchuckmatt]

Bring it up to the speed that it will just run and do a cylinder drop test.

 

[tphoyt]

 

[Rudejonnie]

Bring it up to the speed that it will just run and do a cylinder drop test.

Good idea. I’ll try that when I get some free time to work on it again . Thanks

 

[Rudejonnie]

An update for anyone curious…

I pulled the flywheel to check if the key had sheared. Confirmed it was good. While in there, I noticed some ooze seeping from the charge coil (see pic). Wondering if this could be the culprit. Have one on order as well as a sensor. Figured I’d change them both while I’m at it.

 

[saltchuckmatt]

Changing parts for the heck of it isn't always advised.

Make sure you mount them correctly.

 

[Rudejonnie]

Changing parts for the heck of it isn't always advised.

Make sure you mount them correctly.

Absolutely. However, just checked them with a multimeter and both are way under spec. I’ll update once I get the new ones installed.

Thanks again