Carbs...Post-Rebuild

[wodtheiii]

After google sent me to this site for 9 out of 10 boat repair questions I realized that I should just skip the middle-man and sign up. So here goes...

I thoroughly cleaned and rebuilt the carbs on my '08 Yamaha 50hp 2stroke electric start. They were full of broken down fuel. After putting everything back together, I still could not get her started. The plugs are a year old so I'll be replacing them later today, but I'm wondering if anyone has some other suggestions/tricks for me to try. Will I need to let the starter crank longer than usual or are short repetitive cranks the way to go? This is new territory for me so any clues about what I can expect from this point on will be a big help.

Thanks, Will.

 

[99yam40]

Re: Carbs...Post-Rebuild

1st off what model # is it you are talking about and what was the problem to start out with. Have no idea if you have prime start or chokes.
Did you read the 1st post about the best way to get a response?
Are you still using the old fuel or did you dump it and clean the tank and lines?
Are you getting fuel to carbs?
Do you have spark?
Do you have good compression on all cylinders?

 

[wodtheiii]

Re: Carbs...Post-Rebuild

1st off what model # is it you are talking about and what was the problem to start out with. Have no idea if you have prime start or chokes.
Did you read the 1st post about the best way to get a response?
Are you still using the old fuel or did you dump it and clean the tank and lines?
Are you getting fuel to carbs?
Do you have spark?
Do you have good compression on all cylinders?

Yamaha 50TLR

After sitting for a month, engine would not fire. Upon inspection, bad fuel had fouled the carbs

Prime start

Just read 1st post

Fresh fuel

Pretty sure the carbs are getting fuel, how can I tell for sure?

Has spark but I'm not sure if it's enough. That's why I'm replacing the plugs today

No idea how to check compression

 

[99yam40]

Re: Carbs...Post-Rebuild

What do you mean by bad fuel had fouled the carbs?
What did you find in the carbs?
Did you dump, flush, and clean tank, pump,primer bulb, and fuel lines of old fuel?
Open the bowl drains one at a time and pump primer bulb and see if the fuel is getting into each one.

Did you try to put the Prime Start Switch in the open position while trying to start the motor?
Compression is checked with a compression gauge.

I you have fuel,compression, and spark at the right time it will fire up.

Sounds like you need a manual for the motor you can find them online or at a Yamaha dealer

 

[wodtheiii]

Re: Carbs...Post-Rebuild

Gas had evaporated in the bowls, leaving behind the thick, golden gelatinous stuff that smells like varnish. It had clogged the high speed jet and as well as the float valve.

Primer bulb and all fuel lines were good.

Fuel pours from each bowl drain.

I'll try it with the primer switch in the open position.

Don't have a compression gauge.

 

[wodtheiii]

Re: Carbs...Post-Rebuild

Alright, I set the switch in the open position and she started right up. After letting it run for a bit, I turned it off and set the switch back to the regular position. Again, she started right up but only ran for about 30 seconds before shutting off. I then switched it back to the open position, started up again and ran until I shut her off a few minutes later. Now I'm really lost.

 

[99yam40]

Re: Carbs...Post-Rebuild

Did you pull and clean the low speed jets when you pulled carbs and Take apart the Prime Start and clean it up also?
you need to pull and clean everything real good if the carbs were full of the stuff you said they were. the Prime Start system has the emergency open position to be able to run motor when low speed jets get plugged up so you can get back to the dock

 

[wodtheiii]

Re: Carbs...Post-Rebuild

Thanks for all of your help. I did clean the low speed jets but not the Prime Start. I found that that with the switch in the normal position, I could keep the engine running as long as the rpm's were elevated. As soon as they dropped, it cut off. This makes me think that I didn't get the low speed jets completely clear. I wouldn't be surprised to find the Prime Start clogged however since the middle carb was the most effected by far. I'll check that tomorrow.
Again, thanks for everything.

 

[wodtheiii]

Re: Carbs...Post-Rebuild

Prime switch was completely clear. No debris at all. Took carbs apart again to check on low speed jets. They're good as well. I then put everything back together and started her up. Now, if this were a car engine, I would say that one of the cylinders was miss-firing. This prompted me to check the spark plugs (which are brand new) where I found the bottom and middle ones darkened and the top one clean. All three smelled of fuel but the top one was noticably cleaner. All three had spark when I last checked a couple days ago. Any suggestions?

 

[99yam40]

Re: Carbs...Post-Rebuild

Check the spark again just to make sure all are getting good spark.
Have you pulled the plug wires one at a time while running to see how it affects the running?
If #1 is sparking but not hitting then I would suggest pulling the top carb and clean again.Did you blow all passages out with compressed air?

You did not say how you had to start it. Did you have to move the switch to open again or did it start up with no problems in normal?

Have you done a link and sync on the carbs like the manual says after putting back together?

 

[wodtheiii]

Re: Carbs...Post-Rebuild

Per your suggestion, I pulled the plug wires one by one and to no surprise the top spark plug was not firing. I won't be able to check for spark until later (I'm by myself for now) so I removed the top carb and have had it soaking in carb cleaner for a couple hours now. She seemed clean but we'll see what comes out after this process.

I have to set the switch to open to start it the first time but it starts in the normal position from that point on.

I don't see anything in my manual about how to perform a link and sync. I'll keep searching but I haven't found much on the 'net either.

 

[99yam40]

Re: Carbs...Post-Rebuild

do you pull the carb completely apart when you clean them,needles, jets, etc and blow out with compressed air all of the passages?

Does your manual say anything about adjusting the linkages on the carbs, needle, and rpm?

What is your starting procedure? These motors do not want you to lift the fast idle lever when starting just turn the key for a few seconds , stop for a few and do it again.

Pull the line off the prime start system where it attaches to the intake behind the top carb and see if you can get any fuel out of it when you turn over the motor cold with it in the normal position. I would think that you should, but I do not, only when it is in the open position does fuel get pumped out by the prime start pump. I even blew air by mouth into the line I took off back to the carb and in the normal position to see if passage was plugged, it was not and air is coming out of the vent on top of the center carb without much effort on my part, still have not figured that one out yet.
My motor starts on the 2nd or 3rd 3 second turn of the key when cold whether or not I have the line even hooked up. But it has been in the 70s and 80s here so it is not very cold.
I was just wondering if your's does the same thing.

 

[wodtheiii]

Re: Carbs...Post-Rebuild

I checked the plugs again and all three have spark.

Yes, the carbs have been totally dissassembled, cleaned and blown out.

My manual doesn't mention adjusting any of those items. If the carb linkage is off, could that cause one cylinder to misfire? Could the timing be off on only one plug? What's the general procedure for performing a link and sync?

It normally starts up on the 2nd or 3rd try even in winter. I never use the idle lever to start it.

 

[99yam40]

Re: Carbs...Post-Rebuild

The CDI controls the timing, I guess it could mess with just one but I do not think that to be likely.It is easy to check with a timing light.

Synchronizing the carbs makes sure they all are moving exactly the same so all cylinders are getting the same fuel.This is very critical at idle in my opinion maybe not as much at higher RPM but still important.
Basically you adjust the linkage to make sure all butterflies are closed completely at the same time, tighten the linkage and then adjust the idle and idle mixture to fine tune. There should be a procedure in the manual that needs to be followed step by step.
When ever you reinstall carbs they are close but just a small amount of movement from where they were at can affect this setting.
Make sure your battery is fully charged it will make a difference on how fast it turns over and that may affect your cold starting.

 

[wodtheiii]

Re: Carbs...Post-Rebuild

As time goes by, the engine seems to improve slightly. She turns over on the first try with the prime switch at normal. For the first 10-15 seconds, she sounds perfect: no missing or sputtering. Eventually, however, the RPMs reduce dramatically to the point that she shuts off completely. In order to keep her going, I have to increase the RPMs...this is the point at which the missing occurs.
I checked the linkage and found that the butterflies are all syncronized but now I'm curious about how to adjust the "idle and idle mixture." That's not covered in my manual so I need to find some step by step instructions.

 

[99yam40]

Re: Carbs...Post-Rebuild

Is it starting first turn of the key when the motor is cold, 1st start of the day?

If it is it is doing better than mine, mine takes at least 2 two or three second turns of the key to fire up 1st time of the day. 1st turn after that

My C40TLRX motor starts at 4 degrees BTDC and after the motor warms up the CDI drops the timing back to 7 degrees ATDC at idle according to my manual, but mine drops back to 12-14 degrees ATDC. That is how it controls the fast idle during warn up.
Check your timing with a timing light and make sure it is doing what it is suppose to.
Did you adjust you mixture needles to 1 3/8 +-1/4 turns out for the starting point of adjustments? I think that is correct for a 50 but do not know for sure on yours.

 

[wodtheiii]

Re: Carbs...Post-Rebuild

Mixture needles? I have no idea...not in the manual. Are you talking about the pilot screw?

 

[99yam40]

Re: Carbs...Post-Rebuild

yea, I guess that is what the book calls it, Pilot mixture screw

 

[wodtheiii]

Re: Carbs...Post-Rebuild

I have to drill out the brass plugs to get to them right?

 

[wodtheiii]

Re: Carbs...Post-Rebuild

Also: in your opinion, how could a simple carb clean result in the pilot screw being out of wack?