[PhilJ]

What size the CV Carb is on the AVL? Just planning ahead in case I need a flat side. I was thinking about the same size as I'm not after more HP, but more torque would be nice. It seems the same size would give similar gas mileage.

[PaulF]

Phil, without literature here in front of me, I believe its a Keihin VB29, or 29 MM. I could be wrong on that but the size makes sence.

I hate that carb BTW. Can't tune the damn thing for nothin'. A nice Mikuni is on my list too.

[1 Thump]

I thought it was  Mikuni 28 knock off.

[Ice]

Iron Barrel; Micarb VM 28 round slide , built under license from Mikuni.

AVL; 29mm CV

[ace.cafe]

It's a Mikuni BS29, or some India-made variant of that.
29mm CV.

[HMR]

It's a Mikuni BS29, or some India-made variant of that.
29mm CV.

Its made by Ucal Fuel Systems in a JV with Mikuni
http://www.ucalfuel.com/html/products/gasolinesystem2.asp

HMR
Mumbai

[1Blackwolf1]

Phil, without literature here in front of me, I believe its a Keihin VB29, or 29 MM. I could be wrong on that but the size makes sence.

I hate that carb BTW. Can't tune the damn thing for nothin'. A nice Mikuni is on my list too.

  I thought the BS29 was very easy to tune/rejet..actually almost easy next to my 28Mikarb.

[PaulF]

Will, it's partially my fault. If I had that much determination, I would have a proper dyno tune done. But no one around "these parts" does that.

So, its carb off, carb on, jets up, jets down, needle up, needle down. One setting too rich, one too lean. Right now, its running on the rich side, which is where I like to err instead of on the side of too lean. It leaves plugs black, but they're not fouling me to the side of the road and it has nice higher-speed manners, so there it stays.

I just remember my old conventional round slides being more forgiving and tolerant.

[PhilJ]

Thanks guys. The carb is stamped with Mikuni. So if it is a 29 MM, what Mikuni Flatside would be it's equal? I Googled Mikuni and found 28 mm and 32 MM, and then CMW has a knock-off Mikuni at 30 MM. Got any Ideas on which would get the closest to stock?

[Vince]

     It is a 29mm carb. Jets are readily available for tuning except for the jet needle and slide. Vacuum diaphragm carbs operate differently than throttle slide carbs. When you twist the throttle the cable operates a butterfly valve between the carb and the engine. This regulates engine vacuum, which is then utilized to lift the slide. This gives much smoother throttle response, particularly down low, and better gas mileage. With more precise throttle regulation a bigger carb can be used than if it were a conventional throttle slide. This allows for more usable power over a wider RPM range. A conventional throttle slide carb can offer more power potential, but at the expense of some throttle response and a narrower ROM band of best efficiency. Check Ace.Cafe's posts about port sizes to choose a carb suited to your needs. My favorite for all around usage is the Amal 30mm.
     Paul, other issues can contribute to plug fouling. Check the plug cap for resistance. A dirty air filter can be a culprit. Sometimes it is just the rider's riding habits or style. Giving a thorough warm up on the choke will skew your readings. Sometimes you need to go down on the main, but richen the needle. If there are no adjustment notches for the needle clip you can stack washer(s) under the needle clip to raise (richen) the needle.

[PhilJ]

Thanks Vince, but.... I thought you indicated the due to CV method of operation that a larger carb could be used. But then conversely to use a slide carb you would go down in size. Obviously, there is a short in my old brain. Not quite getting it.

[1Blackwolf1]

Will, it's partially my fault. If I had that much determination, I would have a proper dyno tune done. But no one around "these parts" does that.

So, its carb off, carb on, jets up, jets down, needle up, needle down. One setting too rich, one too lean. Right now, its running on the rich side, which is where I like to err instead of on the side of too lean. It leaves plugs black, but they're not fouling me to the side of the road and it has nice higher-speed manners, so there it stays.

I just remember my old conventional round slides being more forgiving and tolerant.

   Guess I must have gotten lucky when I rejetted wifeys Electra..only took me three trials to get it pretty much nailed down.  Much more frustrating on my Iron.  Used info from Ace and got it ball park close.  Took a little head scratching to get it inside the diamond.

  Now I'm beginning experiments with a Keihin 30MM flatslide PWK.  This one is going to be a real challenge to figure out.  Vince is right some of these higher cap carbs are a real joy..smaller operating parameters for proper operation.  Oh well if I could tune Strombergs of the past this shouldn't be a big deal (maybe).

[Vince]

     Phil, I should have been more clear. Comparing apples top apples:
     With both carbs being the same size, the throttle slide type will offer more power potential than the vacuum slide type, BUT it will not be as efficient at lower RPM. To get better response where most people use their engine most manufacturers will opt for a smaller throttle slide carb. So a 26 or 28 mm throttle slide might be used instead of a 29mm vacuum slide. This limits top end power potential in return for better response. Using the 29mm vacuum slide carb offers the low RPM response of the smaller throttle slide and a higher power potential. The down side is complexity, and the absolute power potential is pretty close to, but  not quite as good as a 29mm throttle slide carb.
     So manufacturers will often opt for a larger vacuum slide carb for more general all around use, but all out performance would require a throttle slide.

[PhilJ]

Ok, thanks Vince, I'm clear on that now. I seldom go over 4K RPM ~68 mph and that is very rare. Mostly 3-3.5 K rpm 50-58 mph or slower. So I could easly go with a 28 mm flatside it seems, If I were to change at all.

[PaulF]

Yes Mikuni. Why the hell did I type Keihin? Must be channeling the spirits of Kawasakis past.