3/28/10 10:03 p.m.

Trying to improve the tune on the DCOE on the mgb gt.

Can anyone explain the relationship between the main and auxiliary venturies on a DCOE? Current set up is 36 for the main and 45 for the auxiliary ventury.

02Pilot Reader
3/28/10 10:34 p.m.

The auxiliary venturi is a much smaller air passage (yours is a 4.5, not 45) that helps to create good fuel distribution when the airflow is too low to allow the main venturi to do the job. If the main is too large, a smaller auxiliary can help smooth things out at lower engine speeds.

3/29/10 6:13 a.m.

O2 Pilot:

Kind of what I thought. What I am trying to do here is eliminate a bit of transition stumble that this car has always had. I am converting the car from a track focused car to more of a driver,hence the stumble is more annoying. Most noticealbe at low rpm.

Going back to the 3.5 auxiliaries might not be too bad an idea?


gjz30075 New Reader
3/29/10 6:50 a.m.

I would leave in the 36 and 4.5 aux for now. Start with the basics. Where is the throttle plate in relation to the first transition hole? You can see this relationship when siting down the hole (currently covered by a brass plug) closest to the throttle plate.

The throttle plate has to be downside of the first hole, or just starting to uncover it. Then adjust your idle mixture screws from there.

The off idle stumble is a pain to correct and there's a fellow in CA who is attempting to make the DCOE act as good as FI.

Tons of reading there and good learning. I cured mine with a step up on the idle circuit jet.

02Pilot Reader
3/29/10 7:50 a.m.

Yeah, the stumble is one of the things that gives DCOEs a bad reputation as street carbs, but it is completely curable with proper tuning; the problem is that DCOEs have so many tuning variables that it can be hard to pin down exactly what's off. Once you find it, as often as not you then have to adjust something else.

If you don't have it already, get the Pat Braden Weber book. It's a good reference to have when you're trying to figure out how all the parts work together on these things.

gjz30075 Reader
3/29/10 9:34 a.m.

+1 on the Pat Braden book. And look for any one authored by Des Hammill.

Our Preferred Partners