Big 7 carb jetting for A7 engine…

[Ruairidh Dunford]

Has anyone successfully jetted a Big7 carb to run on an A7engine?

Currently it is on 55 and 88.

               

[Ian Williams]

What state of tune is the engine Rory. I have used several similar instruments both on my Nippy and other specials that have been through my workshop. I will have notes on Venturia and Jet sizes which I can look up for you, but I don't think they will be of much help without engine specs being similar. I have a big tin of jets that I mix and match until I obtain the results I am after.

[Ruairidh Dunford]

Many thnaks.

It has 3/4 radius cam followers - everything else is pretty much standard, with a H/C head.

[Ian Williams]

Looks like you have improved manifolding as well which will help breathing. My immediate thoughts are that you have it a little too rich. My Nippy runs very well on 80 Main and 50 Comp, it is an unmodified Speedy type engine, factory head, cam, manifolds etc. I will probably have a larger choke tube than you though? I have in my notes from other cars two similar carbs C855A and C1228 both engines were well tuned with modified cams etc on those 85/55 and 95/65

[Ruairidh Dunford]

Thank you Ian, I have also been passed some very useful notes from a standard build, I will report back my findings.