Switch from Mikuni CV carbs to VM carbs? (81Suzuki GS450, Mikuni CV BS34)

Finkelstein5

Finkelstein5

New Member
I rebuilt the CV BS34 carbs last summer but I have been reading a lot and it appears that it is just better to switch to the VM carbs because the CV carbs get gunked up too easily and a bunch of other problems. Since I have the CV BS34 I read that the best option would probably be a VM30 or VM32. I get to work on my bike soon for spring break so I would like to order them now with some K&N air filters and put them on when I get back. Also what would i have to do with rewiring the throttle cable for the VMs?

Thanks in advance for the help!
 
I own an SV650s that gave grief from gummed carbs, I swapped them out for another set I had bought. My point is if they are working fine ,simply take care of them,add fuel injection cleaner in your gas periodically and DRAIN your float bowls when in storage. Don't trust CHEAP fuel stabilizer. Had I have done this in the first place ,,,,,read back !!! this bike has 62000 kilometers and 15 years old, save your money
 
Those carbs are pretty good. The same design was used on all sorts of bikes including the GT750 Suzuki that I drag race from time to time.

Seafoam is a good cleaner, but as Wee Todd said, modern fuel is junk if left in for more than a couple of weeks at a time and will tend to clog jets in any carb.
 
Ya right now I am in school away from my bike but for storage I left Seafoam in the tank. I have a break coming up where I can start to take it apart and build it and I was just curious about the carbs because when I rebuilt them, I damaged the airbox so now air is sipping through the intake slots and its not tight around the carb intake. I also think I need to make sure the diaphragm is flush and the float valve needle is working. When i last ran it, it ran much better after I cleaned and rebuilt the carbs but when I would rev it, the rpms wouldnt drop and it would all of a sudden be idling at like 4000 rpm. How could i fix that and why might that be? Also, I am getting rid of the airbox and putting on k&n filters and new exhaust eventually so I know ill have to rejet them. I thought of switching to the VM carbs also because I have heard that the CVs dont run so well with them and need the airbox.
 
I have an 1981 GS 450 and decided to toss the cv carbs and bought the VM carbs from dime city cycles. If you run the vm32 you will need to buy e intake couplers for the Yamaha xs650. You oval out the mounting hole a tiny bit to fit a narrower bolt pattern and it fit great. The jetting for the cb550, which is what Dime Ciy has here carbs projected for is to rich and so far the best improvement I've made is changing the needle jets to 159 p0. It's great at the bottom end and full power but I'm still figuring out the mid range. (5-7k rpm) it has a little stumble like its to rich but rideable. I bought the universal throttle cable which requires some trimming and soldering cable ends onto the cables but take your time it works. Measure twice solder once.
 
Okay Thanks a bunch! I have been looking around everywhere for someone who has done the carb swap. If I have any more questions I will let you know.
 
are you sure its running rich

p0 is very small for that size engine and could be causing the stumble at that throttle opening

nave you got a p-6 p8 or even q0 you could throw in and give it a try?

also what size slide do you have
 
I started with a combo of 159 P5 and a #6DH7. Switch it to a 159 P0 and a #6FL14 and put the "E" clip in the second slot from the top. I also have a #3 slide. The bike has K&N filters and a 2 to 1 exhaust with a megaphone type of tailpipe with baffle installed. It runs a bit rich but the stumble is nearly gone. If I hold it wide open from 3k RPM to redline in a tall gear it bogs slightly around 6k and if I hold it at 5k and roll it slowly to widopen it may stumble 50% of the time. I think if I went to a 159 O-5 or -6 it may be perfect. I know it's rich from looking at the plugs and pulling the baffle out for inspection. The plug looks sutty on the edges but good around the electrode. The baffling is very sutty. I plan on giving it new plugs and a long ride to get a better picture of how it's running.
 

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Ok so I stand corrected, after a longer ride the stumble is still there. And if you enter the stumble zone slowly it takes longer to recover and pass thru it. If you just crank it wide open its less noticeable. Here are the plugs after the ride.
 

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So now my current set up is #3 slide, 159 P0 needle jet, #6DH7 jet needle with clip in the bottom slot (richest). The bike seems the happiest so far. Just can't run a steady 5-7k RPM with throttle between 1/2 to 3/4 without sputtering. I also checked compressions found to be even at 120 per side, 150 if I do it wide open throttle. Not sure which way is best.... Spark looks good as well. Anyone have any thoughts I'll read them. I wish I had a dyno and every needle and jet needle in the book.
 
compression check is done with the throttle wide open always

seems a bit lean from the plugs i would try a larger jet needle if you have something around a p-4 give it a try see what happens

drop the needle down a bit at the same time
 
I had a P5 in with the #6DH7 but it was worse. I even moved the needle to each slot and the top slot worked the best. I now have the #6DH7 in with the P0 and the clip in the bottom slot. Still stumbles in the mid range. It's a tough one to figure out.
 
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