Offroad-Express

A friend of mine recently gave me a standard spare carb he had, in unknown condition. I swapped it out for my one because I know mine is crap (poor idle, stumbling on acceleration, etc). I'm having trouble tuning it or even knowing where to start.

It will only start with the choke fully on
It won't idle for more than a few seconds without a bit of throttle
When it does run it runs awesomely - good throttle response, no stumbling, nice and smooth, etc

I noticed that the mixture screw was wound most of the way out, so I wound it in to roughly the same position on my other carb. But it didn't change much. I have no experience with carbs, other than the basics.

Does anyone have any ideas? Or a good process to start to tune this?

If you can get your hands on a haynes manual they have a good blow-by-blow.

"Two and a half turns out" isn't a miracle but a good place to start on everything from weedeaters to cars.

Needing the choke fully on suggests that it's running lean, so give it more fuel or less air. (one at a time)

How do I do either of those - more air/less fuel?

And the 2.5 turns out. Are you saying wind it the whole way in and then out 2.5 turns?

Appreciate the help mate.

Sausager wrote:How do I do either of those - more air/less fuel?

And the 2.5 turns out. Are you saying wind it the whole way in and then out 2.5 turns?

Appreciate the help mate.

You got it man, seat them "nipped up" and then back them out. If it's running good at the top end then just leave that screw where it is.

Both air/fuel settings could/should have a screw, one may be marked "air pilot" or "idle circuit" - that is for air. one will be near a fuel line - that's fuel.
Winding screws out increases the flow, but too much fuel will flood and cut out just the same. Set aside an arvo (and a box!) and take it slow.

Worst case is that there's a seal inside the carb that's actually shot, in which case all the tinkering in the world wont help. Also check all the hoses to and from for fuel, air, or vacuum leaks.