Yamaha 15 hp 4 stroke primer start

[Hoppi84]

So would a failing primer start cause the rpms to drop on cold start??? If I'm backing the boat off the trailer I have to give it a little more throttle or the rpms slowly drop... Once it's warm it don't seem to be an issue...

 

[99yam40]

when you fire up the motor, you should let it warm up before putting into gear.

It is not called primer start

 

[Hoppi84]

Prime starter assembly my bad sir...Itll do it in neutral too... It's like before it would start up at 1200 rpms or so and drop down to 1050ish.. now it starts at like 900-1000 and drops below 850.. but if I give it more throttle it'll pick up and run 1050+-..

 

[99yam40]

well, if you motor will not idle properly after the motor has warmed up and the timing is set back to normal idle timing , you probably need to clean the carbs.
something is causing the pilot /idle jet or passages to not furnish the proper amount of fuel to air.

 

[Hoppi84]

Once it warms up it idles fine at 1050ish... It's just the initial cold start where it'll start at 950ish and slowly drops...

 

[99yam40]

use a timing light to verify the timing is in spec . and changing as it should when it should.

I know nothing about your 15 4 stroke motor.
I have run into 2 CDIs on 2 stokes that had problems with timing at idle and people jacked the carb linkages all out of spec trying to make the motor run properly

 

[Hoppi84]

Appreciate the responses sir... And will get a timing light and check timing...thanks again

 

[99yam40]

My1999 C40TLRX 2 stroke has 2 temperature switches on the head, one tells the CDI when the motor is warmed up and the other tells when the motor is overheated.
I have no idea what tells you CDI or ECU when the motor is warmed up so it can change the timing at idle or even if there is something like that on your motor,
but if it does have it and that device is not working properly, it might be changing the timing before the motor is warmed up properly to run while still cold.
Just some random thoughts from me.

 

[QBhoy]

You’ll get a back pressure on the exhaust, the deeper into the water you go. Set up the idle speed when she’s warmed up and in gear at idle. You’ll be good there after. Just as long as there aren’t other issues like a carb clean required. Setting things up when the carb is in doubt…just means you’re compensating

 

[Hoppi84]

I set it in a barrel but with it leaking it's definitely higher water level then when the boats in the water.. still plan on checking the timing but will try and set it out on the water next time. Thanks again

 

[Hoppi84]

You’ll get a back pressure on the exhaust, the deeper into the water you go. Set up the idle speed when she’s warmed up and in gear at idle. You’ll be good there after. Just as long as there aren’t other issues like a carb clean required. Setting things up when the carb is in doubt…just means you’re compensating

Just so I'm clear when you say set the idle are you talking about the throttle stop screw or the pilot jet??? I'm gonna go back over the owner and service manual but not sure it said what rpms should be in gear at idle??? Pretty sure it's at about 950 give or take now...