just traded a engine and received a .46fx with 4d .46sf carb on it, will this run? other than that the engine and carb have very low time. also the fx rear crank case cover was also changed with a sf cover.

Rod:

It should run, but if memory serves the SF carb was a smaller bore than the FX carb as well as being an air bleed type.

Just checked my FX, it's 8mm carb bore, sold my last two SF engines 8 months ago, can't check them.

Bill.

My 4D carb (from a 40VF) is twin needle and has a bore of 7.5mm so this means the area is .88 the size of the larger carb. It'll actually be a bit less than this because of the spray bar but I doubt in practise you'd see any difference unless you run the engine around the 16,000+ mark. At normal revs the smaller carb should actually be better.

DU:

Then it would seem Rod is mistaken abouot the 4D being from an SF engine. The SF engines I had (matched pair for a twin) were fitted with air bleed carbs right out of the OS box.

Bill.

I don't believe Rod is mistaken about the 4d being from an SF engine. I have an OS ".40SF ABC" and it has the 4D carb on it. BTW I purchased it new back in the 80's so I know this is correct. I also had a .40fp which did have a smaller bore "Air Bleed" carb. as far as I know the fp series had air bleed carbs and the SF series had twin needle carbs.

Oops.

Mack, you're right. My air bleed pair were FP engines, not SF.

Senior moment, failing memory. Sorry.

Bill.