was wondering if anyone would know what jet size i should run on my 650 barry grant demon carb. on my 85 gslse streetported engine. any help would be great thanks.

 

Wow, not a very popular setup, i have no idea... Good luck

 

What engine?
Porting? Exhaust? Mods?

Generally, a 650cfm is way too big for a stock ported 12a or 13b. You'll have no velocity down low to pull the fuel and atomize it, so your low end will suck (or rather, it won't and that's the problem, lol)

But if it's all you've got to work with, you might be able to find a way to adjust it so that it's kinda streetable. Larger accel pump shot to make up for the gaping hole created when you open the gigantic primaries...

I can't offer much more than that because all my experience is with stock carbs and Sterlings (which flow 465cfm like the Holley 465s but have better velocity in the primaries).

Remember, flow isn't everything. Too much flow kills you just as bad as not enough. Even worse, too much flow (and thus, not enough velocity) kills you off the line, where as not enough flow kills your top end.

Jon

 

The problem with a question like "what jets should I run" is that there is no definite answer.

The answer will depend on a huge number of variables. For one, engine, porting and exhaust. Then, given identical stuff there, you have altitude, age of engine / compression, driving style (this is a huge one often overlooked), mods to things like flywheel, clutch, fuel system, etc....

So there's no proper answer because even if I had the same carb on the same engine with the same exhaust and mods, I'm not at the same altitude, I don't drive the same, and my engine hasn't necessarily been treated the same way throughout its lifetime (which may be more or less kilometres than yours)

So ... my best advice would be to read as much as you can about carbs and carb tuning even for carbs that aren't yours, and learn what you can about tuning it yourself. Grab a fuel jet and air bleed kit for your carb and go nuts.

Or toss the 650cfm beast and get a Sterling, lol

Jon