Off-Road Forums & Discussion Groups - View Single Post - Holley Carb ?'s
Thread: Holley Carb ?'s
View Single Post
post #8 of (permalink) Old 05-09-2009, 02:33 PM
TeamRush's Avatar
Join Date: Mar 2009
Location: So.West Indiana
Posts: 826
Thanks: 0
Thanked 0 Times in 0 Posts
Originally Posted by mdn86cj7 View Post
TR thanks for the in depth info. Once I can get it to start I'll do exactly that.

Currently it won't run at a normal idle. If I set the curb idle very high it will stumble and 'run' with black exhaust (still haven't gotten exhaust done past the header). I've tried adjusting the idle mixture screws with no discernable effect.

It seems to be dumping too much fuel into the intake at idle, even with the idle mixture screws set 1/4 turn open.

I rebuilt the carb (new gaskets, power valve, accelerator pump) while the engine was in pieces. Broke off one of the mounting fingers on the base plate when mounting and then found a 7448 carb on ebay and used the base plate from that carb with the upper from my original.

More description to follow.
You really CAN NOT play 'Mix & Match' with the throttle bodies...
There are different vacuum routings, and some carbs were 'Emissions' models, and their throttle bodies are completely different than the rest of the Holley line.

Two things you might consider,
If you CAN NOT get the engine to IDLE,
And the idle mixture screws are set at 1.5 turns out,
Then you have fuel FLOODING the engine.

Chances are your float level is WAY OFF!
This is what it SHOULD look like if you remove the 'Lock Screw' in the top,

Many times, you will find the needle and seat inlet valve screwed WAY DOWN below the ADJUSTER NUT...

BE VERY CAREFUL getting the Needle & Seat Inlet Valve back out!
It's made of brass, so it's fairly sturdy,
But the BOWL IS NOT! IT's made of a high quality Zinc, and the threads will distort and be damaged VERY EASILY!
SO BE CAREFUL while you are recovering the Inlet Valve!

Turning the 'Nut' RIGHT LOWERS the fuel level.
Turning the 'Nut' LEFT RAISES the fuel level.

If your curb idle setting is open far enough that it's uncovering the TRANSFER SLOTS, then you are NEVER going to have 'IDLE' since you are getting into the Main Jets once you uncover the transfer slots...

Make sure the BACK BLADES are closed,


Then adjust your front Curb Idle so the blades in the throttle body are covered...


A third option for WAY TOO MUCH FUEL if the float level is properly set,
And the transfer slots aren't uncovered is POWER VALVE PROBLEMS...

One of the BIGGEST problems I run into is blown power valves (no backfire valve in the throttle body) and the WRONG GASKETS under the power valve.


Something that DOES happen, but is fairly rare...

Siphon from the accelerator pump circuit...
If some of the check valves stick open, and there isn't a 'Anti-Siphon' valve in the Venturi body,
You can get fuel siphoning from the Accelerator Pump Nozzles ('Shooters') and running right directly down the Venturi bore.
TeamRush is offline  
For the best viewing experience please update your browser to Google Chrome