Carburetor: Main jet vs Needle jet

[Rick]

I just found out that the main jet is responsible for fueling the engine at high rpms. On the other hand, the needle jet is responsible for low rpms.
Of course, you guys probably already know this...

I've always been tuning by using the main jet for large adjustments and then using the needle clip to do minor adjustments. Now I find out they have to be tuned separately.

Anyone have any other helpful hints or suggestions when jetting/needling a carb? Especially a Del'Orto carb for a DD2. :)

[MPIGP - Phillip Gordon]

I just found out that the main jet is responsible for fueling the engine at high rpms. On the other hand, the needle jet is responsible for low rpms.
Of course, you guys probably already know this...

I've always been tuning by using the main jet for large adjustments and then using the needle clip to do minor adjustments. Now I find out they have to be tuned separately.

Anyone have any other helpful hints or suggestions when jetting/needling a carb? Especially a Del'Orto carb for a DD2. :)

I'll give you my 2 cents.

In the DD2 under Rotax rules, you cannot change the inner or outer pilots. Only the needle and main jet. I try to run the largest main jet the weather will allow and 'choke' it down with the needle adjustment. I only run sprint tracks with the DD2.

On sprint courses, in the shifter where pilot jet changes are allowed, I run a smaller pilot, a little fatter needle and I keep the main jet just big enough to supply fuel on the long straights.

On the road courses, I run the fattest pilot that will allow the motor to start without flooding, a leaner needle and a big main jet.

[Rick]

What are these "screws" people keep referring too? Some things I've read say that there are screws you can turn to also help tune a carburetor. Is that legal for DD2?

[MPIGP - Phillip Gordon]

What are these "screws" people keep referring too? Some things I've read say that there are screws you can turn to also help tune a carburetor. Is that legal for DD2?

They are talking about the 'air' screw on the side of the carb. Yes it is legal to adjust it and it can help with low and mid-range throttle response.