Syncing carbs?

[kbert1171]

My carbs need rebuilt on my 1986 Yamaha 50ELJ. Will they need synchronized after they are re-installed?

 

[airshot]

If you have multiple carbs....yes...they require sync to run right. Hope you have a " factory" service manual to follow to the letter !! No place to cut corners here!! Also use a factory rebuild kit with new parts, just quick clean and put back together rarely works !!

 

[99yam40]

I have found that a good heated sonic cleaner bath is the most helpfull if a quick regular cleaning does not do what is needed.
if the gaskets/orings need to be replaced then a kit is a good choice.
just because the bolts and hole that mount the carbs to the intake are not tight fitting, there can be some need for sinking the carbs to have all throttle plates set to the exact same when fully closed, not just at idle position

 

[kbert1171]

If you have multiple carbs....yes...they require sync to run right. Hope you have a " factory" service manual to follow to the letter !! No place to cut corners here!! Also use a factory rebuild kit with new parts, just quick clean and put back together rarely works !!

I only ever purchase factory parts, and I have the carb rebuild kit for this instance. I do not have the "factory" manual, only the Seloc. But I will find one before I start. My only problem will be the carb sync tool. I'll check with my local auto parts stores to see if they have one to loan out.
Thanks for the advice. I appreciate that.

 

[kbert1171]

I ended up purchasing a sync gauge set. I'm sure I'll need it again sometime, and a few buddies have motorbikes, so it'll come in handy.

 

[brodmann]

If you're talking about a vacuum gauge to sync carburetors, you'll have no need for that tool. The "sync" that we describe here is basically making sure your carburetors open at exactly the same time and the same amount. I don't think you'll find any place to hook up the vacuum lines on your carburetors, unless yours are different than most. Hope you haven't opened the package yet.

 

[99yam40]

as was posted already a Yamaha service manual will have the link and sync procedure, and it does not talk about a sync tool.
just make sure all carb throttle plates are linked together with the plates completely closed not touching the idle speed screws.
and timing is also part of the procedure

 

[kbert1171]

I downloaded the manual. 1 5/8 turns out on the needle valve.
So why don't the carbs need synced with the gauges like other outboards, including yamaha?

 

[airshot]

Cant speak for Yamaha, only had to do a linc and sync on my jonny 70 with three carbs. Everything in the manual was mechanical dimensions and feeler gages to get them set correctly. After all settings were done, minor idle fuel mix adjustments were made in water under power at idle with a 1/2 turn total allowance. Worked perfect on my omc 70 hp.

 

[99yam40]

I would imagine once you set all throttle plates together with them completely closed they are synced.
the same amount of air will be flowing into each cylinder where even you place the throttle.
And if the carbs are properly clean the jets should allow the same amount of fuel to be sucked in with that air.
all you can do is do a slight adjustment of the idle mix.

 

[brodmann]

I don't know that I've ever seen an outboard motor that has a nipple for connecting a vacuum gauge. Maybe it's because there's nothing on an outboard motor that operates on vacuum.

 

[kbert1171]

I don't know that I've ever seen an outboard motor that has a nipple for connecting a vacuum gauge. Maybe it's because there's nothing on an outboard motor that operates on vacuum.

Doesn't the fuel get drawn into the cylinder by vacuum? And that tiny bit of vacuum is what is measured by the gauges.
And I've seen several outboards that have small ports in the intake to hook up a gauge to tune the carbs. I simply assumed mine did as well.

 

[99yam40]

Doesn't the fuel get drawn into the cylinder by vacuum? And that tiny bit of vacuum is what is measured by the gauges.
And I've seen several outboards that have small ports in the intake to hook up a gauge to tune the carbs. I simply assumed mine did as well.

you should have looked before buying the tool

 

[airshot]

I would imagine once you set all throttle plates together with them completely closed they are synced.
the same amount of air will be flowing into each cylinder where even you place the throttle.
And if the carbs are properly clean the jets should allow the same amount of fuel to be sucked in with that air.
all you can do is do a slight adjustment of the idle mix.

On my jonny, the instructions called for setting the plates to a certain dimension opened, I used drill bits of the proper dia called for, then a feeler gage was used to set the gap on the lever that controls the plate. This is the only one I have done, so not sure about others.

 

[brodmann]

Yeah, I know the vacuum gauge your talking about. Used to use one all the time on motorcycles and cars. I've just never seen anyone use one on an outboard motor, and I've never had an outboard motor that had the fittings for the vacuum gauges. Maybe yours does.

 

[kbert1171]

you should have looked before buying the tool

 

[kbert1171]

You're right. But it's no big deal, as I can send the tool back.