Carb Rebuild Questions

[Aladinbama]

Well, it sat too long. I replaced the battery and got it started, ran around a bit, but a "while it's cold" sputter remains. The #2 pipe also doesn't seem to be warming like the others. The other day I rode to get it inspected to renew registration and the clutch began slipping. I was going to change the oil today and bleed the clutch, but when I removed the oil fill plug I smelled gas which could also explain the clutch slipping. I figured I'd wait on the oil until after the carbs were done.

LSS, is there anything specific to this bike that makes rebuilding the carbs any deferent than any other bike? Any upgrades that can be done while I'm in there (that don't require other modifications)? Are there any specific kits that are better than others for this bike? I also plan on sticking to stock jet sizes unless recommendations say otherwise. And yes, I have rebuilt carbs before and have the gauges to balance them when I'm done.
Thanks!

[Nails]

I don't think there's any special Go Magic besides just rebuilding them right. (But I'm definitely NOT Mr. Leo.)

Mine also sat for too long and had an odd miss. One problem (of several) was a stuck oil ring. I don't know the history of your bike or whether that's at all in the cards ... this is a total shot in the dark ... but you might want to run a compression check. (Yes, it's a PITA on this bike.)

I apparently solved mine by putting that piston on the bottom and filling the cylinder with Seafoam. It leaked into the crankcase, which was fine. (Your "gas in the oil" comment made me think of it.)

[Micoproviso]

Well, it sat too long. I replaced the battery and got it started, ran around a bit, but a "while it's cold" sputter remains. The #2 pipe also doesn't seem to be warming like the others. The other day I rode to get it inspected to renew registration and the clutch began slipping. I was going to change the oil today and bleed the clutch, but when I removed the oil fill plug I smelled gas which could also explain the clutch slipping. I figured I'd wait on the oil until after the carbs were done.

LSS, is there anything specific to this bike that makes rebuilding the carbs any deferent than any other bike? Any upgrades that can be done while I'm in there (that don't require other modifications)? Are there any specific kits that are better than others for this bike? I also plan on sticking to stock jet sizes unless recommendations say otherwise. And yes, I have rebuilt carbs before and have the gauges to balance them when I'm done.
Thanks!

I rebuilt mine last year after they had sat for 15 or so years with gas in them, and it runs like a brand new bike. Also, I’ve done this many times before on different bikes and ATVs that sat for long periods. The key to doing this properly, is getting the gunk out of all the tiny passages in the carb body, jets, etc. The only way I’ve found to do that, is to use a heated sonic cleaner and a good cleaning solution. I like Master Stages 2020. Strip them down, but leave them attached to each other. Put everything in the sonic cleaner until they look new, and blow out all the passages with compressed air while still wet with the cleaner. It could take several hours in the cleaner depending on how bad they are. Replace the float valve pins and any other rubber parts that are questionable.

[GrandpaDenny]

Who was it the other day who stated that when his idle changes with the weather he rejets his carbs? Wow, that's an awful lot of work especially considering the black idle speed adjustment knob on the left side of the carbs is such an easy and convenient way to adjust idle speed, ain't it?

[Nails]

Well, I said that if the bike won't idle right with that black knob (wants to either idle too fast or stall), that's often a sign that the carbs aren't "balanced": not idle-vacuum synced (air-flow balanced); slow jets set differently (fuel-flow balanced); float bowl levels not identically right; dirt clogs somewhere; &etc. One carb wants the knob here and another wants it there.

I also think that turning the slow jets out the same number of turns doesn't always mean they're passing the same volumes. Some folks who want to get fussy with this install ports in all exhaust manifolds to test the individual cylinders with an EGA.

I've lost many precious hours of my life fussing with constant velocity carbs including MGs, racing a 70s-era Husky 2-stroke (that needed to be rejetted with just a few hundred feet elevation change), and all but one of the rest of the bikes I've ever owned (that one is a thumper with two carbs -- don't ask). In some parts of the world CV carbs are called "constant depression" designs, for reasons that seem all too self-evident to me. They can be very finicky, and it's generally best to avoid messing with them if you can.

If you can't ... well, climb aboard the learning curve.

For the 250cc thumper I'm building to tour on BDRs, I'm replacing the CV with a slide carburetor. This design is based on different compromises, especially regarding throttle snap (CV carbs notoriously have a lag). Small displacement engines reportedly do well with this mod ... once you get used to not pinning the throttle and flooding it when you need to grab a handful. At 300cc per carb, I have to wonder how the XII would do with such a radical mod. But I won't be the one to find out -- life is too short as it is.