1999 200 hp Yamaha Carb Question

[Windknotnc]

I recently put a 1999 200 Yamaha SWII Model #S200TXRX on my boat and had the carbs cleaned at a local shop to solve a rough idle problem. During this I was told that the middle carb on the engine was not the correct carb. When you look straight at the carbs the throats of the top and bottom carbs appear to be the size of a 1/2 dollar. The middle carb throat is the size of a quarter. Is this correct? I have read that the prime start system enriches the middle carb so I was wondering if that had anything to do with it. Regardless, the engine is still not idling well and sometimes cuts off and sneezes a little then cuts off. It is also rather difficult to start requiring several 5+ second key turns with the key pushed in before it will hit. Any way, if there is any advice or answers to the carb questions it would be greatly appreciated.

[99yam40]

it is always best to give the motor model # so everyone knows exactly which motor you are talking about

[Windknotnc]

Model Number

1999 200 Yamaha SWII Model #S200TXRX

[boats.net]

Not sure what model you have, a model SX200 is an OX66 model which is fuel injection model and wouldn't have carbs on it, would have throttle body.
The carb model 200 motors has three dual throat carbs and all throats should be same diameter.

[Windknotnc]

It is a S200TXRX...I made a typo...definitely carbureted... Not sure if this replaced carb would cause these problems. The top and bottom carbs are 64ESO and the middle is a 6G405.

[Windknotnc]

Pics added

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Here are pics of the carbs. The top and bottom carbs have 64EOS stamped on them and the middle has 6G405 stamped on it. Does this help?

[Tucker]

[ATTACH]739[/ATTACH]

[ATTACH]740[/ATTACH]

[ATTACH]741[/ATTACH]

[ATTACH]742[/ATTACH]

Here are pics of the carbs. The top and bottom carbs have 64EOS stamped on them and the middle has 6G405 stamped on it. Does this help?

I had '98, same model. All my carbs were identical.

[boats.net]

The carbs for a S200TXRX should be 64E carbs, you can look at parts listing and the first part of part is the model designator. The 6G4 carbs were used on mid 80's motor's.

[Windknotnc]

The engine seems to run fine with the 6G4 carb...can you tell me if there are risks using it or should I replace with the 64E version?

[99yam40]

hard to say for sure, but my thoughts are that all the cylinders are not breathing the same with the different carbs.
And that is like hooking different motors together and trying to figure out how to sync them together so that they run exactly the same at all RPM, just about impossible in my opinion.

[Tucker]

There are used carbs all over ebay. Rebuild the carb to be sure all the jets are clean. Shouldn't cost too much.

[TownsendsFJR1300]

Carbs

Having a smaller bore carburetor will limit the CFM to those 2 middle cylinders. You can sync them to idle evenly but in the higher RPM's, the center carb won't be able to keep up with the others. It may not run lean but will definitly limit performance... IMHO, I'd find the correct carb and replace it..

As for the stalling, the idle jets inside the float bowls are most likely clogged and need cleaning. The orifices are very small and doesn't take much to clog. If your not using a fuel stabilizer/fuel system cleaner it'll gum up even faster.

BTW, with a choke throttle blade on each carb, ALL 3 carbs are choking the engine on start up..The solenoid or manual choke will close all six plates at the same time/rate...

Chevron "Tectron" is a good cleaner as is Seafoam. A product I found that works extremly well is K100: K100 Fuel Treatment : Fuel Additive, Fuel Saver . Besides being a fuel system cleaner it helps rid of any moisture built up in the system. All above products, once the carbs are cleaned, should prevent further clogging.

As well as these products work, the carbs (jets specifically) need to be cleaned first..

BTW, On my old Evinrude 140, (V4), before using a fuel stabilizer, I had to clean the carbs (2, two barrells) as they too clogged up. Two weeks later same thing, get to do "a do over".

After that, the marina I dealt with recommended 2+4 (an Evinrude fuel additive product). Once I began using that, I NEVER had clogging again after that.