Hitchcocks Forum

Hi all
anyone got any views on what would be the optimum size carb for performance, I have a 2006 500 classic with the standard carb re jetted and with a conical air filter to suit my 535 conversion, its also fitted with a watsonian sports silencer our hosts close ratio gear set and boyer ignition it goes well but was wondering if there's any benefit from a larger carb.
many thanks for any thoughts and a happy xmas to all.

Are you running the micarb with that set up? It should be an Amal mk 1 concentric 30mm jetted to suit from our hosts.

There is a calculator on this webpage. I suspect finding out the Volumetric Efficiency for your bike could be a problem.

Then of course there is the problem of how much "meat" there is on the inlet port to blend it in with a larger bore carburettor.

Oops The webpage link:-

http://www.gtsparkplugs.com/CarbCFMCalc.html

Our American friends with running tuned 535 Bullets get good results with 32mm flat slide Mikunis. Our hosts don't sell these, though they do have the VM32 round slide kits. What state of tune is your 535 engine in? Regards, A.

The ‘ideal’ size of carb for best performance depends on the state of tune of the engine. Nothing is gained by ‘over-carbing’ the engine, you’d lose performance instead of increasing it if the carb is too big.

For a 535 a normal carb size would be approx 32mm (1¼ inch); if the engine is tuned (e.g. higher comp piston, larger valves, performance cams) then a 34mm (1 3/8 inch) carb would probably be as big as you’d want to go.

If you’re not going to ride the bike ‘flat out’ most of the time (and I guess you won’t be!) then the larger carb isn’t really necessary.

Hi folks

thanks for the replies, at the moment the bike has the 28mm micarb on it with a 30 pilot jet richer slide p4 needle jet 150 main and conical filter, its got the 535 barrel and high comp piston but at the moment runs the standard head and cams and actually goes well it pulls a 19 tooth sprocket easy but I was just wondering if there would be any more benefit from a larger carb, I didn't know if it is under carbed if you know what I mean.

happy xmas to all

Hi badger man... my experience with the 28 mm Mikcarb on a 500 cc Bullet is, that it is too small (under carbed). I have the tuned head from our host, a 7,6:1 piston and the exhaust is pretty free flowing. I have had some "over heating" problem from the too small 28 mm carb. Not enough fuel mixture to the combustion chamber causing a hot running engine. At a certain stage I was running a 30 mm Amal MK2. It was good, but had a tiny crack in the carb housing making it impossible to tune correctly... So now the bike is fitted with a Mikuni 32 mm flat slide (TM 32-1). The carb has a Malossi foam filter. It works great for my set up... You can read more about running a Bullet with the 32 mm flat slide carb at this site: https://groups.yahoo.com/neo/groups/Ace ... llets/info ... good luck with your hunt for the optimal carb... Jacob