Yahama F40 idles rough and dies with throttle

[JGator]

2000 F40. Ran fine a month ago, not now. New fuel and cleaned with sea foam spray. When we lifted the Prime Starter assembly up in its socket just a bit and all ran well, both idle and open throttle. The parts stem does not change positions regardless of the ignition switch position. Is this normal? How does this part function normally?

BTW it was warm, as I've read it should be in another thread http://forums.iboats.com/showthread.php?t=547480&highlight=PRIME+STARTER+ASSY.

TIA

Jim

 

[99yam40]

Re: Yahama F40 idles rough and dies with throttle

Prime start is for starting and the initial warm up. as motor runs power from charging system heats it up and closes off the extra fuel.

Sounds like you need to have the carbs cleaned properly and then readjusted using proper equipment,.
spraying stuff at carbs does not clean the passages and jets and yours are plugged if it will not run

 

[JGator]

Re: Yahama F40 idles rough and dies with throttle

Prime start is for starting and the initial warm up. as motor runs power from charging system heats it up and closes off the extra fuel.

Sounds like you need to have the carbs cleaned properly and then readjusted using proper equipment,.
spraying stuff at carbs does not clean the passages and jets and yours are plugged if it will not run

OK, so can you tell me why lifting the prime start piece 1/8 inch up seems to improve the rough idle and stumble issue when opening up the throttle?

 

[JGator]

Re: Yahama F40 idles rough and dies with throttle

Prime start is for starting and the initial warm up. as motor runs power from charging system heats it up and closes off the extra fuel.

Sounds like you need to have the carbs cleaned properly and then readjusted using proper equipment,.
spraying stuff at carbs does not clean the passages and jets and yours are plugged if it will not run

Also should the stem piece move from its cold start position at some point?

 

[JGator]

Re: Yahama F40 idles rough and dies with throttle

Prime start is for starting and the initial warm up. as motor runs power from charging system heats it up and closes off the extra fuel.

Sounds like you need to have the carbs cleaned properly and then readjusted using proper equipment,.
spraying stuff at carbs does not clean the passages and jets and yours are plugged if it will not run

99, I see you were at one time as curious about this piece of technology, prime start system, as I now am http://forums.iboats.com/showthread.php?t=357552

I have no problem with your suggestion of carb cleaning...just wondering how simply raising the device 1/8 inch made the engine run much better...

Jim

 

[99yam40]

Re: Yahama F40 idles rough and dies with throttle

Probably lifted the needle out of the seat and let the extra fuel into the motor.
Did you try running in the open position to see if that made a difference?

If you read that thread then you should have a good idea of how it works and what Rodbolt had to say at the end about the F40 needing to idle for a while before running up the RPMs. I am not sure how close the 2 and 4 stroke systems are to each other, but rodbolt did mention the 2 stroke had the diaphragm but he did not say that about the 4

Also Rodbolt has said that the F40 is a hard one to clean and set properly, the passages and jets are small and plug easily.

 

[JGator]

Re: Yahama F40 idles rough and dies with throttle

Probably lifted the needle out of the seat and let the extra fuel into the motor.
Did you try running in the open position to see if that made a difference?

Thanks for the information, it's truly appreciated, but not sure what you mean by running in open position. Throttle? Or the prime start piece?

Jim

 

[99yam40]

Re: Yahama F40 idles rough and dies with throttle

prime start emergency switch

 

[JGator]

Re: Yahama F40 idles rough and dies with throttle

prime start emergency switch

I'm trying to locate this emergency switch, would you happen know where I should be looking?

Jim

 

[99yam40]

Re: Yahama F40 idles rough and dies with throttle

Not sure about a F40, but on my C40 it is on the front of the prime start mechanism. It has a normal,open, and closed setting
your owners or service manual should give you that info if it has one

 

[JGator]

Re: Yahama F40 idles rough and dies with throttle

prime start emergency switch

So I found this thread showing a photo of the switch you mentioned. http://forums.iboats.com/showthread.php?t=449669 I'm not seeing anything remotely similar on mine.

Jim

 

[JGator]

Re: Yahama F40 idles rough and dies with throttle

I've allowed the prime start piece get cold, 50?~ and measured the stem then ran engine on idle for 5 minutes then measured the stem it was 1/8 inch longer. So it appears to be working as designed.

 

[handle]

Re: Yahama F40 idles rough and dies with throttle

I have the F40 06 yamaha with poor low speed and idle running conditions. Don't know enough about the prime start device but will tell you that the pilot jets on my motor are so small that they clog easily. On my particular carbs the F30 has larger pilot jets than the F40. Maybe it's time to increase the size. Nobody seems to want to address this matter.

 

[JGator]

Re: Yahama F40 idles rough and dies with throttle

I have the F40 06 yamaha with poor low speed and idle running conditions. Don't know enough about the prime start device but will tell you that the pilot jets on my motor are so small that they clog easily. On my particular carbs the F30 has larger pilot jets than the F40. Maybe it's time to increase the size. Nobody seems to want to address this matter.

I'm wondering if it wise to run the carbs dry if the boat won't be back in the water every few weeks.

Jim

 

[JGator]

Re: Yahama F40 idles rough and dies with throttle

Got the boat back from my newest best marine mechanic friend! System had much debris in fuel likes and carbs, one bowl needed replacing do to corrosion. Took the boat out today and it started in less than 2 seconds, ran great in all RPM ranges.

Carbs were rebuilt, fuel hoses replaced, pump cleaned and internal filter/strainer replaced.