VM29SS Carb Tuning

[Guest]

About a year ago, I swapped a set of RS34 carbs for a set of VM29SS carbs. I was told they are pretty rare and are a good performing set of carbs (basically 4 TM33 carbs with a 29mm bore racked together.) My bike is 79 GS750l with pods and a 4-1 exhaust. I have no idea how to tune these carbs. Has anyone messed with these or messed with the TM33 at all? The bike is trying to start while cranking the starter, but it just won’t fire up 100% and take off. I put on a Pingel fuel valve and I know I have great fuel flow.

I appreciate any any help at all.

[Big T]

Did you clean the 29s and replace the O rings and gaskets?

[Gearz]

Well the person I bought them from (someone from this community) said they gave them a good cleaning and that the jetting should be very close to what I need. So I am taking their word for it. My next step was to go over the timing again and then I’ll crack into the carbs and check them out. But do these carbs have adjustable mixture screws on them?

[Big T]

Adjustable idle mixture screws, yes, just like most motorcycle carbs

The fact that the bike won't start indicates fuel isn't going thru the carbs

I'm working from the assumption that the bike ran fine before you swapped carbs

[Gearz]

Yes, it ran with the RS carbs on it. It hauled at higher rpms, but ran awful down low. I’ll pull them off and check them out to rule that problem out.

[Big T]

How are you going to check the Tiny passages in the carb body?

[Gearz]

I remove all the jets and needles and use carb cleaner and air.

[Steve]

I don't know that much about the VM series carbs, but the 750 came with VM26 carbs. Jumping up to 29s (sleeved-down 33s?) seems to me that you have too much carb for the engine. Even with "proper jets", you may not have enough air speed through the venturis to get the right mixture.

I could be wrong, actually, I hope I am.

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