Yamaha 40 2 stroke Prime Start not working

[2004yam40]

I have a 2004 40 hp 2 stroke with cold start issues. I did find a number of suggestions here on the forum and after reading the related posts I felt my problem had to reside in the Prime Start System. I disassembled the centre carb, which was very clean internally, checked the diaphram in the enrichment unit and all passages. I do know it is a lean start condition because before reading about the red lever, the motor would start quickly by covering the inlet to one of the carbs. I did not check the wax pellet for expansion as that shuts off the enrichment, but I am now wondering if the pellet is not retracting to the cold setting. The strange thing is it felt more like a solenoid than a wax pellet as it seemed to have spring tension on the needle when applying gentle pressure. When it does finally start it is difficult to keep it running however I am reluctant to just order a new pellet as they are fairly expensive. Any thoughts or suggestions?

Thanks, John

[99yam40]

pull and Clean the carbs. pilot Passages and jets may have some plugging that you cannot see. also clean the prime start passages

[2004yam40]

I did check and clean the pilot passages and disassembled the centre carb which houses and supplies the start system, however there was no improvement. It seems more like the needle is not retracting to an open position when cold. I have not tried using the emergency lever, does turning the red lever bypass the needle circuit completely? The manual is very brief in reference to it's function.

Thanks, John

[99yam40]

yes it bypasses everything and pumps fuel into the intake behind the carbs.

I would pull all 3 carbs, completely disassemble and clean with carb cleaner, then blow out all passages with compressed air. sometimes it takes a few tries to get all passages clean.
hopefully your does not have the no tamper pilot screws that you have to dill and remove to access.
Reinstall carbs and do the link and sync procedure in the manual.
My c40 starts usually on the second 2nd 2-3 second turn of the key. make sure your idle lever is not lifted while starting
Seems I read a thread from up north that the guy said he turned the needle assembly and it moved the needle to allow more fuel while cold , but I have no idea if the is a good idea or not

[2004yam40]

As it is very difficult to do any major work now that the boat is in the water for the summer and I am hesitant to remove the carbs a second time in deep water, I did try the red lever this past weekend. The motor fired up immediately and ran well during warm up. I stiil feel that all of this points to the Prime Start needle not retracting to the cold position. Given the favorable results starting this way it seems that the start pump diaphram, passages and the carbs themselves are OK. It appears the red lever bypasses only the wax pellet shut off needle circuit. Any further thoughts on this or am I just over simplifying my diagnostics?

Thanks, John

[martine4161]

It is very good post to discuss about Yamaha 40 2 stroke Prime Start. I think you have to pull and Clean the carbs from engine. You can also clean the prime start passages.U Have A Stuck Plunger In Your Primestart. Try all this if you having same problem then you have to change your engine oil. You can try with castrol oil.

[99yam40]

In my opinion, if the carbs were working properly the motor would not run properly with the red lever in the open position. There would be too much fuel dumping into the cylinders from the carbs and the Open red lever. At least mine will not it floods out. The diaphragm in the Prime Start system pumps liquid fuel directly into manifold bypassing the orfice in the system
I believe the manual calls for turning to open to start motor and then to off for running just to get back to port if the are carb problems.

but fix the motor before going out again if you run cylinders lean it will eat pistons

[hacrwj]

I had the same problem, however, in my case I just bought the boat and discovered the 'red' lever after the engine wouldn't start yesterday morning. I flipped it from 'closed' to 'open' and the boat started then I flipped it back to 'closed'. After researching on this forum, I am now just realizing the lever should have been in the 'normal' position not closed which means the lever was in the 'closed' position when I bought the boat. The engine runs fine (except for cold starts). I have been out twice with no issues fishing. Engine starts immediately (once warm) and runs great.

I also noticed a female connector that is not attached to anything (see picture). Is it possible the previous owner removed the fuel enrichment system and was just running the boat with the system 'off'. Also, am ruining the engine by running this way? I know I need to get an service manual but want to go out fishing again this week but not if I am damaging the engine.

[99yam40]

How does it act when in the normal position?

As said before running a motor with lean conditions will eat pistons,
I am not sating that yours is running lean,
Just that if a motor is not running properly . fix it. other wise you can hurt it
The only wiring to the prime start is the blue and black wire. not sure what that connector is for. I will have to look at my 40 to see if it has that, but it is still dark outside right now.
Are you missing the silencer from the front of the carbs or did you just remove it for the pic?

It is best to start a new thread with your info and questions

[rodbolt]

there are 3 positions on that red lever, open which manually enriches the engine for cold starts,closed which shuts ANY enrichment off and normal which allows the prime start to function normally.
that open socket simply indicates its not rigged with a digital tach, its for the tach visual indicates.
should have been capped with a water proof plug.
also like its been pointed out, never raise the warm up lever on a prime start engine.

[2004yam40]

It is very good post to discuss about Yamaha 40 2 stroke Prime Start. I think you have to pull and Clean the carbs from engine. You can also clean the prime start passages.U Have A Stuck Plunger In Your Primestart. Try all this if you having same problem then you have to change your engine oil. You can try with castrol oil.

Finally back to the forum after a too short summer boating season, all the while putting up with my cold start problems. Having suspected a stuck Prime Start Plunger early on I am curious about Martine4161's comments regarding oil as I am using Yamaha 2 stroke oil in the oil injection system, I don't understand how oil can affect the start system. Please elaborate.

Thanks, John

[99yam40]

He is just a spamer putting stuff out there that means nothing and sees if someone will click on his link at the bottom. when you see stuff like that report it by clicking on the icon at the top right corner of his post and tell what is going on and hit send