Big bore carb

[Don Ferrette]

" For now, all I'm gonna say is:............"

That's 'cause the OS needle can't flow enough. We've had this conversation before, haven't we Andy ......... <_<

 

[Slideblues]

You two crack me up :lol: Bet you've known each other for a while eh ?..............

 

[AndyBrown]

Naw... we'er just Newbies..... :lol:

 

[DaveMarles]

I think I can manage to get a decent fuel flow through an OS radio needle and so I think there is more to it than that. Any other radio needle that I've tried fixed to the carb disintegrates on the .90 and I can't use a remote needle, throttling is not good enough and an OS radio needle properly modded can flow enough fuel on the 12mm carb to be so rich at full throttle the motor will stop. I figure that if the needle can flow enough fuel on the 12mm to do that then it should do it on the 14mm. I figure that a bigger carb is the way to go on the .90 but the jetting system needs improving. Guess I'll just have to try a powerjet.

 

[AndyBrown]

........and an OS radio needle properly modded can flow enough fuel on the 12mm carb to be so rich at full throttle the motor will stop. I figure that if the needle can flow enough fuel on the 12mm to do that then it should do it on the 14mm.

I knew that conclusion would be coming sooner or later. B)

 

[Anders_Martinelle]

What pipe do you run Dave??

Anders

 

[Bart Drieghe]

Nine out of ten , the pmc one lol

Bart

 

[DaveMarles]

Anders, I'm testing with my own tuned pipe, CS5A. Whats your experience with different pipes affecting the fueling at high rpm?.

Andy, If you and Terry think its as simple as the fuel flow then I'll finish making my flow meter and test some different fuel supply setups.

 

[Anders_Martinelle]

The things i have seen is that you need to open up the pipe the same way as you do with the carb..

With a std pipe with 12mm or less outlet it`s harder to get to work with the big carb then if you increse it to 14 or16mm (even bigger).

I have the feeling that it`s more sensitive for back pressure then with a small carb... <_<

The only thing is to test, test and more testing

Anders

 

[Don Ferrette]

........and an OS radio needle properly modded can flow enough fuel on the 12mm carb to be so rich at full throttle the motor will stop.    I figure that if the needle can flow enough fuel on the 12mm to do that then it should do it on the 14mm. 

I knew that conclusion would be coming sooner or later. B)

I want to bring this topic back to the forefront as there has not been a posted solution. Myself, I would get rid of the needle that's residing in the side of the carb for starters. Set up a seperate 3rd channel needle off the carb. I have a 9B on my CMB 90 but the needle is not in the carb, it's seperate. I also dumped the stock OS fuel inlet nipple, retapped carb body & put in a big bore nipple. I have tried the CMD/Kalistratov needles & I can say I have seen a difference on the bigger motors on top end throttling vs. the OS remote needle, I believe it's a volume issue. There are striking differences between the OS & CMD/K needles in that the bore size of the CMD/K needle on inlet, outlet & bore of body is significantly larger as is the needle itself with far more taper to it as well. Even though you might get the same reading on a flow meter as far as rate of flow, there is a difference. I wouldn't have believed it if I hadn't seen it personally.