Fluctuating idle

[cwhubb]

I'm having a problem with the idle on my car, I get it where I want it then when I rev it it idles way too fast. The linkage doesn't visibly move when I pull it back towards the return spring but the idle does slow down after a few seconds but it's too slow the car barely runs, again I set the idle where I want it the cat idles great but rev it and the cycle starts over. I had the carb off to re-do the jetting before I took it off I didn't have the idle problem so I know the return springs work plus they worked with the old carb I had on it. the car runs really strong under acceleration with out any stumble misses or back fire.Its a Holley 950hp carb, the initial power shot pump is set at around 15 using a feeler gauge any theories?

 

[67 coronet]

first,check to see if accel is binding.take off your linkage and see if it still has the same prob.
check for vacuum leaks.(cover the carb with your hand and see if it chokes out while running)
also,good idea to check condition of timming chain.put a timming light on it and watch while you rev it up.if it comes back and stabalises it is good.if it floats around you could have a worn chain.
easy places to start.

 

[cwhubb]

thanks I'm thinking it may be sucking air from some where

 

[Hemi Rebel]

What engine is this on? Whats your combo?

 

[ZombiePopper]

950 is a lot of carb,
I'm also curious what set-up this is on (?) does the car smell "gassy"?
My first instinct is to say vacumm leak as well...

 

[cwhubb]

the 950 is actually 830cfm my combo is 440, 10:5:1 cr the cam is a mp 509 410 gears, stock heads, stock intake. the carbs not leaking gas so no fuel smell, and the car really pulls hard and is fast, it just does the faster idle thing even when running on the street.
@ 67 coronet the timing chain is good, I recently timed it and it holds steady

- - - Updated - - -

just a thought here, will a leaking head gasket or sticking valves cause a vacuum leak?

 

[WAYNES WORLD]

If its not the carb chect the springs in the dist. I had a car doing the same thing and after going over the carb a millon times I was messing with the timming and noticed it would just jump 4-5 degrees at idle all by it's self. That would bump the idle. Turns out the springs and weights were sticking and then when they loosened up it would change the setting. I pulled the assembly apart and cleaned/lubed everything up and never had another problem.
Wayne

 

[cwhubb]

I think I figured out the problem, the base plate on the carb is a little skewed, when I manualy pull the linkage assembly back it idles nice, I'm going to have to get a new base

 

[cwhubb]

conclusion of the problem...it was the old carb base plate namely weak springs. the new one works great, problem solved