carburetor

Hi,help! is there anyone that can give me some information on how to source a suitable carburetor for my own design 60 degree,four stroke twin..It has a bore of 34.1mm,stroke 38mm,displacement 0f 35cc per cylinder. the inlet ports are 12mm,I havent machined the manifold yet, as I need educating on what the bore size should be. In an ideal world, the carb would be of the diaphragm type as it was designed for aero use.I did have a manifold 12mm dia through to a pattern walbro ,fired straight away assisted by drill,but had no throttle response,then as I choked it ,it got slightly better,but was obviously weak.Then I learnt about the positive/negative pressure factor on the diaphragm,for two strokes,and am left wondering if I am wasting time going down that route.

Mick,

diaphragm type carburettors don't work too well on four strokes. I would be tempted to use an equivalent sized carburettor as that used on a glow engine, for your size engine I reckon a Carburettor from a two stroke equivalent to .61 Cu in should work ok. "Just Engines", if you are based in the UK might be able to supply.

They worked very well on my BMW R65 and Kawasaki. May be they don't scale to small sizes very well.

JA

A lot of (small) Briggs and Stratton engines used diaphragm carburettors. Whether or not B&S engines "work well" is a matter of debate of course...