Suzuki 2 Strokes

I'm repairing/restoring a 75 GT380, and the repair manuals I have list multiple model numbers/specs for the Mikuni VM series. Where or how do I find the VM model number on the carbs on my triple?

I did some research and it appears that the size of the opening on the manifold side of the carburetor determines the model number. The caliper reads 24 mm therefore I have Mikuni VM24SC carburetors on my GT 380. I set the floats to 25.7 mm per the specifications of my repair manual. However I am getting a rough unsustainable idle with the center cylinder intermittently firing. Any ideas on how to fix this? I found another repair manual the recommends 24.25 mm for the float setting. Would it be beneficial to try this height?

Difficult to say. Rough idle can be a number of things. I would make sure all of the pilot circuits in the carbs are absolutely clean, and try to synch them. It could be a simple adjustment problem, or it could be electrical. Lots of possibilities.



Lane

Thanks! It appears to be a combination of both. It's running rich and fouling the spark plugs.

When you have the carbs off to clean them, replace all 3 pilot jets with new genuine Mikuni parts and also the main jets. They are not expensive and you will have avoided trying to work out what a PO did to jam things through the jets to clean them in the past.

Then check that there is no fuel in that center cylinder float. It's not uncommon and that makes the float sink and allows the mixture to be way too rich.

A trick I like to use is to blow carb cleaner through one drilling in one carb and repeat on the other two. That way I can see if one is flowing much more or much less than the others. repeat as necessary on the other drillings.

When you are 120% sure that the carbs are perfect, clean and check the points and fit new plugs. Another trick you can try is to remove the plugs and insert a spark tester into one plug lead and ground it and turn on the ignition and kick it over. Open up the gap on the tester to see where it stops sparking. Repeat on the other two and if one circuit is weak, it should be easy to see.

You could also remove the SRIS valves from the front of the motor and see if that center cylinder is full of oil. If it is, that may be a sign of a leaky oil feed valve.