1984 Yamaha XT600 Carburetor Overhaul

January 09, 2015 admin user 0 comments

 An 84 XT600 showed up recently with a top end misfire. This wasn't too much of an issue around town but was a real problem at freeway speeds.

 
The XT600, and Yamaha TT600's of the same vintage, had a dual carburetor induction with the primary manual (i.e. driven by throttle opening) and secondary in effect a CV (i.e. vacuum operated) sourcing from the primary fuel bowl.

 
As the misfire was only evident at high revs the secondary carburetor was a likely candidate. With that in mind, the intent was still to disassemble, clean, replace the serviceable items and check and re-set tolerances.

 
Here is the removed carburetor on the workbench with an overhaul kit (Japanese sourced - this is our default for Japanese carburetors) and the tools for the job.

 
Here is the fuel bowl removed. As you can see the rubber gasket has work hardened, flattened, and begun to perish.

 
At this point, had we not had a rebuild kit, one would have to have been sourced. This gasket could not be re-used.

Onto disassembly. Lets face it, this is the most enjoyable part...

Here we are removing the mixture screw. Is always worth counting the turns in, noting the result, and then backing out. Is a great reference if you haven't personally set the mixture screw previously. In this case it was set at 2.5 turns out, the factory spec.

Here is the main jet and emulsion tube assembly being removed by a ring spanner. Don't be lazy and tempted to use an open end spanner, jets are brass not steel... 

This is the retaining screw for the fuel valve seat. Once removed the brass valve barrel will require some persuasion to be removed. In this case we had a replacement in the overhaul kit so pliers were deployed. If you were not replacing the valve seat some paper or an old sock would suffice as scuff protection. 

This is the pilot jet being removed. Notice the largest blade driver that will fit being used. Again the fittings are brass, not steel, so care and the right sized tool are important or it will all end in tears.

Removing the retaining bolt from the throttle valve actuating lever. This is the first step...

 

..followed by removing two small slide retaining screws. 

This allows removal of the needle and slide. Take care not to lose the small spring.  

 
And now to clean (ultrasonically) the carb body and parts, and inspect the needle and slide for scratches, wear or foreign particles...

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