Hard to synchonise Honda BF50A - 98

[ErSa]

I bought an Syncro Motion Pro synchronizer, so far so good. But after done every possible check of the motor,
comp, spark, valves, cleaning and new gaskets in carburetors
the top carburetor stops with double vaccum compared to the other two carburetors. An other difference is that whem I "close" the
mixure screw on the top carb the rpm drops less than the other two carbs. The motor is idling OK but I guess it could be better.
The only difference in the top carburetor, compared to the others, it is slightly corroded.
Could that be the cause of the high vaccum?
PS I have changed the tubes in the synchronizer but get the same result. Any ideas?

 

[MattFL]

Did you clean the insides of the carburetors, in particular where the butterfly valves close against the carburetor? If not, then check that first. Once that's clean, use the adjustments on the linkage between carburetors to get them all balanced. If you haven't been adjusting those, then that's likely the issue. You'll likely need to alternate between adjusting the screws on the linkage and the idle screw as you get them synchronized.

As-is the top one is letting less air through, meaning the top cylinder is contributing less at idle, so this is why the idle drops by less when you turn off the fuel to that one.

 

[ErSa]

PROBLEM SOLVED!
It was to hight friction between "inner" and "outer" trottle valve arm. I had no control where
#1 carburetor trottle valv was positioned. Some oil and exercise solved the problem with dead carburetor!
Thank you for your advices. It gave me new ways of thinking. Erik

 

[MattFL]

Excellent great job!