40hp yamaha - starts and then stalls

[mmd5]

I have a 1992 40hp yamaha that was running just fine until a week or so ago. It now stalls shortly after start-up (video link below). I have cleaned the carbs three times now paying special attention to the pilot jets. They were completely clean, I hope because I'm anal about fuel and stabilizer. I cleaned the fuel filter (there was small particulate in the bowl, but none on the 'exit' side). I have rebuilt the fuel pump and tried a couple of different fuel tanks. I believe the carbs are synchronized properly and I haven't touched the timing (or checked it).

As a side note, the fuel enrichment system has never worked properly. It has never made a difference if it is connected or not. I have always just opened the cover and manually triggered the override lever on it. This has worked just fine for four years (however I would love to get that running properly - I've spent many hours reading here and just rebuilt it and replaced the electro thermal valve with the same result)


Thank you

http://www.youtube.com/watch?v=4VaR7ea7fpQ

 

[99yam40]

Re: 40hp yamaha - starts and then stalls

So, what is the motor doing that you think is a problem?
How do you normally start your motor? Do you advance the throttle any while starting?
how old is the fuel?
have you done all this carb cleaning (3 times)in the last week?
how did you clean the carbs?
did you check the diaphragm and check valves in the prime start pump and clean the passages in it also?
Did you test the electro thermal valve or just replace to see it it changed things?
How did you sync the carbs?
I was thinking that Making sure the timing is correct is part the link and sync of the carbs along with adjusting the pilot adjustment screws
I always think it is better to test things and then fix what is not doing what the manual says it should be doing.

I always check compression and spark on all cylinders and then make sure the timing is doing what the manual states it should be doing. If all of that is good the look at the fuel. A fuel pressure/vacuum gauge will show any delivery problems and a clear piece of tubing in line to carbs will show any air being sucked into the system. Then cleaning the carbs needs carb cleaner and compressed air to blow out all passages along with all jets. Maybe a sonic cleaner would help if that does not work.

 

[mmd5]

Re: 40hp yamaha - starts and then stalls

So, what is the motor doing that you think is a problem?
Not sure yet - I'd guess coil / wires or carb sync / settings.

How do you normally start your motor?
Just engage the choke and turn the key - always has worked this way (right or wrong)

Do you advance the throttle any while starting?
Nope - don't touch it

how old is the fuel?
10 days - fuel line was flushed as well. I have a new fuel and primer bulb I'm going to try later today. I try to use non ethanol fuel if at all possible

have you done all this carb cleaning (3 times)in the last week?
Yes - thinking I must have missed small small passage or something

how did you clean the carbs?
Dis-assemble, removed jets and bowls, needle valve, inspect and spray with carb cleaner both jets and carb body. Blow out with air gun. I never noted any blockages or gummy stuff anywhere. I didn't soak them overnight yet though.

did you check the diaphragm and check valves in the prime start pump and clean the passages in it also?
Yes

Did you test the electro thermal valve or just replace to see it it changed things?
No, I didn't test it. I had a NOS parts lot a bought off ebay that included the valve and just threw it on hoping for a good result. I will test both of them later today and see what the readings are.

How did you sync the carbs?
I made sure all three carb shutters closed and open in unison and the thottle lever operated freely - I didn't touch the timing lever that works off and gets its advance from the throttle lever

I was thinking that Making sure the timing is correct is part the link and sync of the carbs along with adjusting the pilot adjustment screws
The air pilot screws were set at 1 1/4 turns (+/- 1/4 turn) per my manual.

I always think it is better to test things and then fix what is not doing what the manual says it should be doing.
I agree, I was just frustrated and threw the new enrichment valve on thinking that might have been the ticket.

I always check compression and spark on all cylinders and then make sure the timing is doing what the manual states it should be doing.
Will do and post results

If all of that is good the look at the fuel. A fuel pressure/vacuum gauge will show any delivery problems and a clear piece of tubing in line to carbs will show any air being sucked into the system. Then cleaning the carbs needs carb cleaner and compressed air to blow out all passages along with all jets. Maybe a sonic cleaner would help if that does not work.

I'm going to check the coils and wires, plugs, and check compression and will post the results

A sincere thank you for the help thus far

http://www.youtube.com/watch?v=4VaR7ea7fpQ

 

[99yam40]

Re: 40hp yamaha - starts and then stalls

There is no choke on a Prime Start motor.
If your problem is it runs ok at higher RPM but will not idle I would still think it is plugged pilot jets/passages

here is a thread I started on link and sync if that may help
http://forums.iboats.com/showthread.php?t=366637

Here is one on prime start also, read all of it, the 1st posts do not say much.

http://forums.iboats.com/showthread.php?t=357552

You can do a search and read more on prime start.

The red lever should be in the normal position for it to work properly, full counter clockwise

 

[mmd5]

Re: 40hp yamaha - starts and then stalls

Last night I checked compression (125psi across all three cylinders) and verified the voltage for the coils. I then pulled the timing advance lever arm from the CDI and moved it manually while at high idle - see below video

http://www.youtube.com/watch?v=IlUrjpCp_0I&feature=channel

I adjusted and advanced the timing a little and reset the idle RPM. All seems to be running like clock work now. I'm not sure why this change was necessary though, maybe something got bumped / turned during trialering (just put 350 miles on).

I'll see how it works on the water later today. Thank you for you help 99! - much appreciated.

Hopfully I'll be able to do some trolling for some salmon tonight now that it idles correctly.

 

[99yam40]

Re: 40hp yamaha - starts and then stalls

Did you check to see what the timing was and where you adjusted it to?
It is important to have it set properly essentially at WOT so that it will not hurt the motor if advanced to far.I ended up haveing to change the CDI on mine to get the idle timing corrected.