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My bike has the Mikuni BST36 CV carbs. I redid them last year by taking them apart & using a sonic cleaner with Pine Sol and hot water. I found one of the plastic slide guides had cracked, so I replaced all 4 from a site that had 2 variations listed, but only had 1 type in stock. Used new carb kits and replaced the o-rings on the carb boots. The bike ran great for a few weeks and then it acted like it was only running on a couple of cylinders at lower RPM but runs good at full throttle. The idle is also erratic, it dies out when cold and idles faster than normal after a ride.

I'm looking at what options are available. The fact is my carbs are almost 30 years old, so I would not mind putting something new on, but it doesn't look like anyone makes CV carbs anymore. I've reed also that these carbs have problems with needles and emulsion tubes. Mikuni has the RS series that are available in the correct spacing. I've read a few threads here, and it appears the CV carbs are a better fir for street use. I see the FCR Keihins are highly regarded, but they are also highly priced, well beyond my budget.

I'm looking for advice on my options here. I would not mind shipping them off for a professional rebuild, as I'm sure that would be less costly than new carbs. I'm also not looking for mega-power, I commute to work on it on good days to save gas.
 

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My bike has the Mikuni BST36 CV carbs. I redid them last year by taking them apart & using a sonic cleaner with Pine Sol and hot water. I found one of the plastic slide guides had cracked, so I replaced all 4 from a site that had 2 variations listed, but only had 1 type in stock. Used new carb kits and replaced the o-rings on the carb boots. The bike ran great for a few weeks and then it acted like it was only running on a couple of cylinders at lower RPM but runs good at full throttle. The idle is also erratic, it dies out when cold and idles faster than normal after a ride.

I'm looking at what options are available. The fact is my carbs are almost 30 years old, so I would not mind putting something new on, but it doesn't look like anyone makes CV carbs anymore. I've reed also that these carbs have problems with needles and emulsion tubes. Mikuni has the RS series that are available in the correct spacing. I've read a few threads here, and it appears the CV carbs are a better fir for street use. I see the FCR Keihins are highly regarded, but they are also highly priced, well beyond my budget.

I'm looking for advice on my options here. I would not mind shipping them off for a professional rebuild, as I'm sure that would be less costly than new carbs. I'm also not looking for mega-power, I commute to work on it on good days to save gas.
sounds like a vacuum leak. theres o-rings on the mixture screws, under the throttle slide guides, and under the vacuum nipples on the carb caps. replace them all if you haven't already. worn emulsion tubes and/or needles will do the opposite and make the bike run rich. also check your float heights and check to see if the float needles/valves are working properly. the brass choke tubes that run outside the carb bodies have a tendency to leak with age and could even fall off, check to see if its a possibility

another possibility could be the throttle butterfly plates not returning to fully closed
 

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Discussion Starter #3
Thanks for the tips. I'll give them a try. I know the o-rings under the slide guides were new, and the ones under the caps were new from rebuild kits. Not sure about the mixture screws.
 

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i like these bikes, but hate carbs. carbs suck.

anyhows, it sounds like the idle and/or slow speed circuits might be clogged. one easy thing you can do, is insert a thin piece of metal wire into the air jets, then experiment with the idle mixture screws. if not, you will have to remove and re-check everything again. fun.

could also be your fuel tank is dirty, so you may want to run a fuel filter. especially if it ran fine in the past.
 

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Discussion Starter #5
Thanks for the advice. It turns out the float levels were off. I had some time this weekend & reset them, bench-synched them, and also fixed an exhaust leak. A short test ride & it's back to running good again. I'll take it for a longer ride soon.

I run Wix inline filters before & after the pump. I try to remember to change them annually. This bike was a rolling basket case when I got it in 2012- it had sat for years. The tank among other parts had to be replaced. I treated it with some epoxy sealer and that has held up well.

Also not a fan of carbs. I'd like to retrofit an EFI system to it (partially laid one out on a GSX parts bike I have) but don't have the time or money right now.
 
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