Jack, my bikes are for the street and yes they're rejetted. The main jet size is currently 150, the needles have been lifted and it seems to be running well but this is at running in rpm and not sure how this will pan out at higher rpm.aerojack7654 wrote:Thanks for the info! Are using either bike on the street or are these vintage race bikes? Also, I assume that you had to rejet the original carbs, do you happen to have the jet and needle specs for what you're running? In general I've been happy with the Amals, but I've got a little low to mid-range softness and some backfiring off throttle that I've been trying to clean up, but the Amal's adjustability is problematic. I've been thinking of putting on the old Keihins to see what I can do with them, I've got a jet kit for them that I've never used.
Thanks again for the info,
Jack
Carbs for 350cc upgradePretty sure that this is where Bernard gets his valves from......
http://www.gsvalves.co.uk/race-engine-components.html Page 23 of the catalogue. Inlets 33mm and Exhausts 28mm They were originally specced by Dennis Murfin who had a pretty successful 350 CB77 race bike I have some of those and they are pretty nice. G
'60 C77 '60 C72 '62 C72 Dream '63 CL72
'61 CB72 '64 CB77 '65 CB160 '66 Matchless 350 '67 CL77 '67 S90 '77 CB400F
Big valves / big carbsHello
Masonmart, just being nosey here but who told you that the fastest CB77 ( as 350's ) ran 38mm inlet valves ? The largest ones I have heard of were 35's, even the 350K racers with the larger bore and shorter stroke usually don't go much above this. As you already have the 38's fitted and running they obviously must work OK with the std. cam but from experience even the 33mm ones can have valve to valve clearance problems with some race cams ( with extra duration ) and must be "sunk" back in the head just to clear each other. Needless to say this causes other problems with flow and even in extreme cases things like tappet / rocker clearance. Not sure if this is relevant for the road but be careful with the R.P.M. if you have the std. springs fitted. Hope this all makes sense, not much help on the carbs but I would see how it goes with the std. ones first, do you have the long inlets and standard filters on them ? Have fun. Gordon SAFOJ Re: Big valves / big carbsGordon, where did I say that the fastest CB77's had used these valves? I have them from advice given by experts and the 350cc pistons and I want to know if the standard 305 cc model carbs I have are OK. I think that they can't be, that is the point of the post. I believe they have to be 28mm and jetted accordingly.
Last edited by masonmart on Fri Jul 17, 2015 4:22 pm, edited 1 time in total.
My second post says "The inlet valves are now 38mm and the ports have been gas flowed to blend in the increased diameter otherwise the ports haven't been opened up. The advice I was once given regarding carb size was that they should be around 75-80% of the inlet valve diameter which would make the existing carbs a size too small for 350cc and the bigger valves. I believe that there are quite a few bigger bore CB77's around and possibly a few that have the bigger valves too, I just wondered if anybody had gone to the next step of increasing the carb size to match? I've heard that the Mikuni VM28's work well as do the carbs that were fitted to the K0 CB750's also Amal 625's?" Were you referring to this "The valves are based on valves that were used on good CB77 racers"
Last edited by masonmart on Fri Jul 17, 2015 4:29 pm, edited 1 time in total.
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