If I pull off a vacuum cap on my carb at idle, my vacuum speed jumps 2-300 RPM. Is this normal, or is it a sign i'm running rich at idle?

Thanks

 

normal...it's called a vacuum leak

 

damn, ok, back to the drawing board...



hey, side note; if you got heavy throttle, then push in the clutch while rolling, and the idle drops way low, and tries to stall, sometimes does... what does that mean? I don't think it's too low float level, 'cuz if I keep my foot on the pedal i'm fine...?

 

side note....i don't understand your question? you're flooring the car, then letting off and taking it out of gear right away and you wonder why it stumbles?

 

are you talking about accelerating hard and the car dies out, but if you are light on the throttle it works fine?? sounds like either carb jetting, a vacuum leak, or timing......i am in the same boat too.

 

I mean accelerating hard, not extremely so, maybe 1/2 throttle or more, then taking it out of gear, and letting it idle....
I did have holes in the butterflies, now sealed and running off the idle circuits (barely). It doesn't seem to do it now, but I can only manage a 500RPM idle, before I have to crack the throttle blades too far over the transition slots.


i'm pretty sure there are no vacuum leaks, and timing is bang on. I know it's all carb issues. I've got a thread in the carb board, but there isn't much traffic, and the thread has grown enough to deter people from posting there. I'm just hoping to gain some general carb tuning info, so that I know which way to go on my carb....

 

If your running a Q-jet carb...you need to alter the primary metering rod spring tension.The installation of a modified cam usually lowers the vacuum,and the spring needs that vacuum to keep the primary metering rods in the jets.If the vacuum is low the spring will overcome it and raise the needles out of the main jets.Your increasing the opening of the throttle blades to compensate for the additional fuel.The spring is just about the same size of a ball-point pen spring.You will need to remove a few coils off of it..its a delicate process.

 

yea, I bought the calibration set of piston springs from edelbrock. I *think* I have the right one in there. I've got ~10" of vacuum now at idle, used to have 13", so I think right now i've got my tune not ideal.... I'll have to double check what vacuum level it starts opening... any suggestions?

 

check the vacuum in drive for a more precise reading..You can use a small needle type tool or pocket screwdriver and insert it into the air vent in the center of the primary air horn.If I remember it will need to go at an angle to touch the top of the primary rod/hanger assembly,to see if its up or down during idle(in drive)it wont be a straight shot.If its not down in either park or drive you need a weaker spring.If you used all the springs and still cant get it down you will need to cut some coils off the spring.BE Careful if you cut too much you just ruined your off idle enrichment and will need to get another spring and start over.Your on the right track..if you had a holley you be purchasing a power valve rated at just under your vacuum reading(in drive).

 

yea, standard trans, hence the confusion... Should I just take my vacuum while taking off slowly from a stop say, which would probably give about what it would be in drive with an auto... Then subtract a few inches?

 

[quote=Sonix]yea, standard trans, hence the confusion... Should I just take my vacuum while taking off slowly from a stop say, which would probably give about what it would be in drive with an auto... Then subtract a few inches?

Yup...do just that.I had a Lunati solid cam that had little to no vacuum,power brakes didnt even exist after I installed that cam.I had to install a 2.5 power valve(holley) just to keep it from dumping fuel at idle.I think I had like 5 inches of vacuum in drive..Like the Mexicans say "thats low".