VAC 91 Carb BS.......

[Tom Foley]

h34r:After seeing several of these carbs fall off due to non loctited bolts etc ..I'm assembling the motors this morning and when the carb is tightened the barrel binds up in the bore ..WTF Just venting here but wondering who at CMB decided this heavy MONOLITH of a carb was a good idea !! Because the mounting bolts go alll the way through the GIANT carb housing , when tightened they distort the body enough to make this happen GGGRRRRRRRR . Anyone else having this BS ? h34r: h34r:

 

[Piston1]

I did, and it is an aggravation. Careful, barrel leakage can make tunning your twin difficult.

 

[Stuart Barr]

Tom,

I have told CMB about this. Sorry. I have had the same problem with the 45VAC carbs. Best way to fix is to pull the back plate off the engine and loose mount the carb to it. I use diamond lapping compound and oil between barrel and carb body and hand spin the barrel while you start to tighten the carb to the housing. Doing this once or twice will fix the problem.

 

[Joe Warren]

Well I can tell you how I fix the EXR picco carb & it has the Same Problem. Problem #1 is the carb hsg is final honed Static. Not Stressed... Empty out the carb hsg. Torque the hsg to the intake plate .012 inch lbs. (I use a old intake hsg. But you can use the new one) Find you a boom tube that will almost fit the bore & wrap a piece of 320 -400 wet paper around it about 3 times. Take it to a sink with dish washing soap & a little water running & gentle roll the tube W paper thru the bore. Your tight spot will be on the stressed side (engine side) You will only have to strike it 3-4 times. Remove your tube. rinse the hsg & check the barrel fit with a little soap while it is still torqued to the hsg. When you get it to fit correctly & it will Not Take Much..... Clean all parts... Time to reassembly & lube & install onto the engine loctite & torque the bolts back to .012 inch lbs. Your carb not will not have to go thru a beak in period. READY to ROCK!! IF THE MFGER WOULD STRESS HONE THE CARB HSG THE PROBLEM WOULD NOT BE THERE. It has become another thing to do. While prepping the engine before run in...... Hope this help you resolve the problem. & USE A TORQUE WRENCH

 

[Joe Warren]

TOM IF YOU CONVERTED THE CARBS TO ROTARY DESIGN MAKE SURE YOU HAVE SIDE CLEARENCE ON THE BARREL VALVE TOO. Mine work perfectly if you follow the above Destructions. :blink: :lol:

 

[Tom Foley]

Thanks for the support guys , I actually did a similar deal and final loctited and assembled the carb body on the intake housing off the engine and used 400 paper around my pinkie and wd 40 to lap the bore and then finished with 1000 . Then lapped the od of the barrel and noticed that it had linear high spots on it that would "bump ..bump ...bump as you turned the barrel . So I kept at it for a while and she is good to go now . It is just so frustrating that guys that are so knowledable in all phases of design , manufacturing, physics and metallurgy can take a totally proven design ( old style flange mount ), and screw it up like this !!! The Mac carbs were the Mac Daddy !!

Anyway ..thanks for the heads up and the solutions ...on to the next carb .

 

[thomaselkins]

no problem yet out of the box

 

[Tom Foley]

no problem yet out of the box

Ha !!! Pleeze !!

Boat ran good today after work with all the carb mods , further running in this weekend .

 

[Tom Foley]

I am happy to report that the mods to the carbs for rotary only function worked well at the Fall Nats and the engines and carbs worked very well . I also saw other methods of conversion to rotary that looked good as well . These 91 VAC's are nice strong engines .