vm29 A2, A7, A12

does anyone know what the A2, A7,A12 means on the vm29's
i am wondering if the pilot bypass is going to be different sizes between the models

I do not know what if any differences there may or may not be on size of fuel passages. I have seen some info that could indicate the A2 was set up for single OHC Honda. The A7 for Kawasaki's and the A12 for Suzuki;'s.  Am I saying this is what the IDs mean. NO, just that some jetting guides indicate such. I am sure there are others here who know much more about the vm29ss than I do and will chime in on this post, if for no other reason that to correct my response.

I will say it is my understanding that pilot-bypass openings are only on carbs that have a pilot screw and not an air screw and I thought all the vm29ss carbs were air screw only. But what do I know?

Benz1991 wrote:

does anyone know what the A2, A7,A12 means on the vm29's
i am wondering if the pilot bypass is going to be different sizes between the models

Those are just the designations given to identify the application they are set up for off the shelf from Mikuni with differing jetting ,needles and slide cutaway for each machine.
Apart from that they are all identical as far as body, internal drilling and air screw and all could be used on any of the other machines with the appropriate component changes.
Also there is no pilot bypass on the VM29's , only a pilot outlet which is the same size on all versions and whose flow capabilities are controlled by the pilot jet size.

Good to know, thanks
I am struggling with a honda 750 dohc running very rich no matter what pilot size 15 to 25
The float level was higher than the gasket surface so I lowered to 2mm below gasket at the front of the bowl and when I move the clear tube to mid bowl the level is about 4mm below due to the angle the rack is sitting at.
should I lower the level again by 2mm to try to lean out more?
Colour tune is blue at idle but 1/8 throttle it sputters a bit. Anything over that will take off good.

Below is the VM29 application chart to check which machine your carbs were original spec'd for.

The fuel level needs to be set to the correct 23mm fuel height at the main jet so take the measurement at the mid point and forget about the high and low readings fore and aft due to the racks angle .
The pilot jet should be 17.5 ( If your VM's are the correct spec for the Honda).

The rich running and splutter may have two seperate causes.

The persistant rich condition may be due to leaking choke plunger seals which will also cause low end rough running due to fluffing so ensure that they are sealing .

The splutter may also be caused by a seperate issue which is fuel dropout just off idle and may be due to the main air jets needing adjustment as these fine tune the fueling on the transition from the pilot jet to the jet needle ( the same as my air corrector jets for the stock VM's) .
These are positioned at the six o'clock positon in the mouth of the carb and are part number BS30/97.
The stock size that comes in the VM29 is 0.9 but on average 0.6 is the size that cures the hesitation so i'd start with those if the choke seals don't cure the Splutter.

 
 

Thanks for the great info!
I found timing to be out. I had a brain fart and had 30 deg at idle not total. Had run through all the jet sizes again...from 15 to 25 pilots and from 110 to 125 mains. With 15 and 125 i was able to get rid of slight sputter with adding more air screw. Plugs werent black but can still see the clean white porcelain after 20 min ride. All around 3/4 turn out, but doesnt want to idle. Everything else seems to be pulling hard, harder than the stock cv's that's for sure
trying to get better idle I put 17.5 and 125. Idle all day long fairly smooth around 1200 but when riding and stabbing wot falls on its face. Slowly rolling into it will take it but not pulling very hard around half throttle now...
I found sync gauges change from one to another when adjusting idle speed screw. 
I might try 117main and see what happens there
plungers are new and the seats seem to look smooth. 

You have to remember these are non stock race carbs, they are going to want to idle a bit higher than a stock carb so don't think you can get them to idle at 900 RPM. I would not spend too much time worrying about the idle RPM as long as it idles then pulls cleanly.

You also need to realize the stock idle air screws have a cross hole in them, so they can't be opened up as much as a regular air screw. From what I can remember 1/4 to 1/2 turn is all they can be adjusted before they close off the hole. You need to check the air screws to see if they have a cross hole or not.

If ever I am having a pilot issue I spray carb clean thru all those tiny orifices to make sure they work (air or fuel)

Your post is a little confusing, one sentence says it won't idle and one says it will at 1200.

If its bogging at WOT the signal to pull enough fuel for air is weak.

Sorry if I lost everyone, my mind works faster than my thumbs! The Pic roughly explains the testing of jets
The air screws have the cross hole. I read that filling them in with silver solder will make them act like normal air screws so i did that. I do have a set of new ones but didn't try them after timing correction
with 15 and 125 the plugs stayed spotless and and soot free but poor idle great mid and top
​with 17.5 and 125 the idle is good but mid to top suffers. Picture of plugs after 10 min ride and 5 min idle