HD8 Carb Set Up and Adjustment

[fwtexasbj8]

Hey guys, I need help again getting the old girl back running well after not being driven much for the past few years.

I recently rebuilt my BJ8 carbs and since, I seem to have very little power and the engine seems sluggish. I have gross jets in the floats and when I get the airflow the same and the jets adjusted, the tops of the jets are between .125 (front) and .165 (back) below the jet bridge. I have removed the float covers (again) and adjusted the float levers to 7/16" per my service manual but when I look down into the jets, it looks like the fuel level is 1/8-1/4 inches below the top of the jets. The car was idling good up until recently when I am starting to see some decay as it gets hot. I am convinced the timing is good and I checked the valve rocker clearances when I had the cover off last weekend and they were all good.

Does anyone know approximately where the top of the jets should be relative to the bridge and how far below them the fuel level should be? I have read the fuel level should be "just" below the jet top but am unclear how far. Do the gross jets have any effect on float lever setting?

When I rebuilt the carbs, I verified the needle diameter but it has a tapered neck without a clear indication of where it should be installed flush with the bottom of the piston. I did my best to set it right where the needle starts to taper and then was careful to set the other one with the same amount below the piston. Does anyone have a better way to set tapered needles?

Finally, any other tips to correct the lack of power? I really think it is carburation since the car had good power before the carb rebuild but have about tapped out my guesses.

Doug

 

[Bob_Spidell]

There are two variations of needles: one with a "shoulder" where the tapered length meets a straight length and one with a groove (most common in rebuild kits). With the shoulder type, the needle should be fitted into the piston such that the shoulder is even with the bottom of the piston, with the grooved type the BOTTOM of the groove should be flush with the bottom of the piston (counter-intuitive to me, but correct).

I use Grose jets, and adjusted the arm so that the jets were closed with the proper clearance (7/16"), just like you would with a needle valve. This adjustment is critical.

Working from memory--I couldn't find a reference in my SU tuning guide--the main jet should be between 1/16" and 1/8" below the venturi bridge (sounds like your back jet sits too low). The fuel should be about 1/8" below the top of the jet.

Did you center the jets? If the needle(s) is(are) dragging it could cause your symptoms, but my guess is the rear carb needs the float level adjusted.

BTW, why did you rebuild the carbs if the engine had "good power" before?

 

[fwtexasbj8]

Bob,
I did center the needles and they still seem fine today when I checked them. I originally rebuilt the carbs because as I was trying to adjust them, I noticed the jet bearing screw had become loose and the rear jet was very loose in the bore.

Doug