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Hi, I have a 1981 Suzuki GS750E in India and its a rare one here. I have restored the motorcycle but the carburetor has been giving the problem since the time i bought from the previous owner. the Carbs had stiff Diaphragm that would turn on well when the bike is cold but as the engine gets hotter, it would open up a bit more and the idling would come to around 2000 rpm in the neutral position. also the bike would get overflow and won't start after resting a few days. and then lately only two cylinders seem to be working. I don't know if these are interrelated but pls guide through this.i tried looking for the new Diaphragm but they're expensive and hence I'm thinking of changing the whole carb to a Mikuni RS38-D19-K.

I want Your advice over
1) does changing the whole carb assembly makes sense?

2) are these interrelated problems

3)the best possible solution.

Much Thanks in advance,
Freddy
 

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I am assuming by diaphragm you are referring to the part that raises the needles and slides. If these are old and brittle you will have no other alternative other than replacing them. The overflow issue is seperate I would assume and it has nothing to do with the aforementioned parts.

This problem may be as simple as fitting new float needles...the tip often wears and allows fuel to seep past causing the float chamber to overflow. Remove one and check the tip...a wear ring around it means it probably wont seal and if one is like that then all the rest are likely to be too.

Alternatively one or more floats may be leaking leading to a sunken float whereby the fuel will continue to flow. Another fault may be frozen float pivots. The flaot levels must also be set correctly. All of these will need the carbs removing and inspection of said parts.

I am not too sure of the float measurement...I had a 79 GS 750 years ago and had to set the float heights. You take the measurement by inverting the carb allowing the float to gently sit on the needle without depressing the tip.The measurement is taken from the carb top face to the float base but I cannot remember what it is. I do know it has to be accurate.

If the boots...the parts that attach to the carbs to the engine and air box are old and hardend then they will need to be replaced also. You cannot fix these and air leaks here will cause the fuel ratio to be lean and also cause the engine speed to rise as you are experirencing.

I wonder if you are confusing these with the diaphragms as I wouldnt think heat would have anything to do with exasperating the problem were it the diaphragms.

Finally swapping the carbs over to another set .You will have to be sure these will work properly with your engine and you may be opening a whole new can of worms should you go with that option. I would be inclined to try new parts as surely they will be a cheaper option?

Good luck
 
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