View Full Version : TR6 TR6 Cold Air Induction - Mixture

09-06-2008, 06:36 PM
Ran the old girl a bit without hood or filter, couldn't resist. Ran great without any adjustment to dizzy, carb etc. Installed air box, hose and filter from GP and noticed hesitation at speed when adding throttle, also slight backfire when backing off throttle. Symptoms disappear with hose disconnected or choke pulled slightly. Obviously at speed the inducted air is causing a too lean situation.

My question is: Can this be alleviated by simple mixture adjustment or will it likely be necessary to try different needle profiles?

Always more fun to overthink before trying anything. :crazyeyes:

09-06-2008, 07:28 PM
You should be able to richen the mixture a bit to compensate. Is your engine stock or modified? I know that other needles for the ZS carb exist, but they're much harder to find than SU's.


09-06-2008, 07:55 PM
Eric, the backfire upon deceleration is commonly caused by a throttle bypass valve not opening when called upon.
Also, this may not apply to the air box that you have, but if the air intake on the box favors the front carb in volumn of available air, then the rear carb may be denied adequate air.
While not noticeable at low air demands such as idle, when you adjusted your mixture, at speeds it's another matter.
Some air boxes need to be modified with additional inlets specifically for the rear carb.
But as I said I'm not familiar with exactly what your set-up has.