Mix screws for 1966 BJ8 carbs...

[VelodromeRacer]

Hey all,

I need to verify the location of the mix screws for the SU carbs on my 1966 BJ8. Also, just to check, does someone know if you screw them out, or up away from the carb, does that lean the mix or enrichen it?

Can someone check their mix screw and tell me approx. how many full turns out it is so that I can check mine?

I used the Gunson colortune I bought and it is a cool item to have, but I really didn't think I was getting the changes in combustion that I should have. When I try to start this car cold, it really backfires through the carbs at least until it warms up.

Thanks

 

[GregW]

Backfiring out the carbs says lean mixture to me.

 

[VelodromeRacer]

Thats what I thought, but Gunsons colortune says that it is kinda rich.....although as you raise the throttle, the combustion gets more yellow as Gunson states because more fuel is being dumped into the chamber.....

 

[VelodromeRacer]

I want to make sure that I am adjustign the right screw on the carbs.

I understand the 1966 BJ8 has 2 HD series Su carbs?
If I am peering down to the top of the carbs while standing over the left fender, what screw in plan view is the mixture adjusting screw that I should be adjusting?

 

[VelodromeRacer]

After some looking, it looks like I was trying to adjust the slow idle screws. I used a great Webber book that had some fantastic diagrams of the SU carbs and found what I needed. The colortune works pretty well.

 

[healeynut]

When you get prefiring out of the carbs, that is almost always caused by lack of correct 20 WT dashpot oil in the dashpot piston tops. You get the pre-firing when you step on the gas ans it's cold, right?

 

[Dave Richards]

When you get prefiring out of the carbs, that is almost always caused by lack of correct 20 WT dashpot oil in the dashpot piston tops. You get the pre-firing when you step on the gas ans it's cold, right?

I'd never heard that before. I've just tuned my carbs and am pretty happy with the performance, mixture and idle, but when it's cold, it's a little crabby, including an occasional backfire when stepping on the gas...

 

[MarkA]

Backfiring out of the carbs can be caused by a lean mixture. Cold engines require a richer mixture and some extra advance on the distributor. An engine that runs fine when warm but coughs when cold may indicate that the mixture may be marginally lean or the timing is marginally retarded. If your dashpot oil is too thin or the level is low, then you will get a leaner condition on acceleration. Once again, this may not cause a problem when warm.

You should check all three areas: mixture, timing, and dashpot oil. With the dashpot oil level, as long as the dampers are in oil before being screwed in, you are fine. You can feel this when pushing them in after pulling them out. Too much oil in the dampers only gets causes a mess. I keep enough oil in my dashpots so that the dampers hit oil at ¼” before the threads contact the dashpot body.

Also remember that your mixture may lean out after time if your air cleaners were oiled too heavily. After the extra oil drains out or gets sucked in, the mixture will be leaner and need to be adjusted again.

When starting my BJ8 on cold Southern Cal mornings (40 – 50 degrees), I find that I need the richness of the choke for starting and a moment longer. I still keep the idle up for a minute or two. After that, the car runs fine. My mixture settings are such that I still get 20 – 22 mpg on a combination of city and highway driving.

Mark