Hitchcocks Forum

This may be one for Paul (Bullet Whisperer).

Whats the maximum size inlet valve that can be fitted to a 350 bullet?..

Cheers

Tom

Hi Tom, this might come as a surprise, but I use the standard size valves [our host's slim stem type] for the 350 race engines and these are more than adequate for the standard bore / stroke dimensions. These are the same valves as can be used in the 250 Crusaders as well. We once saw over 37 BHP at the rear wheel of the 350 using such valves, although that was a very 'good' day on a dyno we can no longer use, as it was destroyed in a fire, but we still see low to mid thirties on the one we currently use, which seems to take about 3 BHP off anything we test on it when compared to the old one. Regards, Paul.

Hi Paul Wow thats some power for a 350 single.. What carb type and size were you using.. PS I'll be a Lydden Saturday to watch lol

Hi Tom, that is with an Amal TT carb, of approximately 34mm . We saw up to around 32 BHP with a 389 Monobloc, 1 3/16" carb, but wanted a little bigger and the regs meant a MK II Concentric would have been out of the question. The 350 Clipper will be racing at Lydden this weekend, along with a Ducati 250. My Brother, Ian, will be riding and displaying the number 4 on his bikes, as usual. My Father, Dave, will also be there, but I will not be going to this one, this time. Regards, Paul.

Hi Paul

Well mine will be road going so no race rules but i want to keep it tractable for street use.. i was considering using a Mikuni or Keihin etc etc..
Nothing against Amals either but was wondering about an accelerator pumped carb.. such as a Mikuni TM 33 flat slide with accelerator pump..

Obviously I want to keep the intake velocity up .. What diameter Mk2 concentric would be a n optimum size?

Tom

Hi Paul

I've settled on approx 10:1 comp ratio (head skim) with a 30mm Keihin carb with accelerator pump..Suitably ported head together with MrH's performance valves Samrat rockers performance cams and uprated oil pumps. Exhaust will be a pipe of some description with nowt up it!

Hi Tom, that all sounds good. If you get an actual 10:1 C.R., that is about what we have on my Father's Redditch 350 café racer and where they really start to wake up - that machine is quick, with strong accelaration a 90 mph top speed and runs well on ordinary unleaded petrol. It also uses Redditch 'R' cams, 1 3/16" 389 Monobloc and Meteor Minor Sports piston, with shortened barrel and ported head. The gearbox has our hosts close ratio conversion fitted. Regards, Paul.

Hi Paul

How much was the barrell shortened by?

Off of the spigot I presume! I am using MrH's higher comp piston

Tom

Hi Tom, I shortened the barrel by 2mm from the underside [base gasket end]. I also had to enlarge the inlet valve cutaway in the piston crown a little to allow that valve and the piston to clear going over T.D.C. on the overlap. Regards, Paul.

Paul

That sounds like a mean 350..

Did you skim much off of the head?


Tom