BJ7 HS6 Carb Baseline Setting

[PeterB]

I had new throttle bushing put in my carbs and I just finished rebuilding them. I am ready to put them back in the car to tune. Can anyone recommend the baseline settings to start with? I know the Jet is supposed to be down 2 full turns or 12 flats from flush of the bridge. What about throttle adj screw and fast idle adj screw? I heard throttle adj screw is 1 1/2 turns. Is that from what, screw just touching stop or after it is flush with bottom where it is screwed into.Thanks in advance.

 

[vette]

Your 12 flats should be a good start for the jet. Nobody gets to excited about the throttle adj screw because as soon as you start the engine you'll know if it was a good starting point. I think 1 1/2 turns on the throttle adj screw might give you a pretty fast idle. The turn count would start at the point that the screw just touches the stop. I have been using HD8 carbs for awhile so my counts might be off.

 

[steveg]

FWIW - Des Hammill, p44: jet drop of .040" for 1-1/2" carbs. Jet measured down from the bridge with tail of a caliper. This is a starting point.

Tom Bryant has a good article on tuning the HS6:
https://thosbryant.wordpress.com/2015/10/04/su-carburetor-tuning/

 

[PeterB]

Ok, so installed the newly rebuilt carbs in the car. 2 full turns on the jets and the throttle screw and fast idle just touching the cams but not engaging. Car fired right up fast but went up to about 2200 rpms and there it wants to stay. The car has never started so good or fast. Raised the jet 1 flat each and it didn’t seem to change much. The choke is not engaged either. Any ideas where to start to lower the rpms? Thank you

 

[NutmegCT]

Peter - maybe I'm missing something, but have you checked that the throttle connections are free, and not binding on something?

I remember on my TR3 the gas pedal connection that ran under the dash was frequently getting stuck on the firewall - result: high idle!

Tom M.

 

[PeterB]

That was the 1st thing I did as I thought something was holding the pedal down.

 

[vette]

If you have that fast of an idle with the adjuster screws not turned at all past first contact then something is hung up or the jets are still dirty, or bent, or just plain stuck. First thing I would do is to loosen the interlock clamps on the throttle shafts to make the carbs independant then make sure the throttle plates are all the way closed when at idle position. then make sure the shafts aren't sticking. Then make sure the throttle plates aren't sticking. Close the jets all the way up to full lean then make sure they can be pulled down with no sticking and that when released they return to full lean. then turn the jets down a few flats at a time and pull them down and release at each position to make sure they aren't sticking. I'm going to guess that your throttle shafts and blades aren't right. Also check the piston that it is not sticking and also that the needle is centered and not bent.

 

[John Turney]

I had that at one time. A small piece of debris was holding a throttle plate open.

 

[British_Recovery]

Check for a vacuum leak. Some fitting might also be missing. The drain tubes on the bottom of the intake manifold sometimes go missing.
Bob

 

[vette]

Check for a vacuum leak. Some fitting might also be missing. The drain tubes on the bottom of the intake manifold sometimes go missing.
Bob

Absolutely, good point.

 

[PeterB]

It ended up being the interlock clamps on the throttle shaft. Once I adjusted them things dropped to normal. Thanks all.