Visit The Dirt Forum for More Information

Author Topic:   Stumblin' Holley 750 Double Pump
WesternAuto17
Member
posted February 23, 2004 03:02 PM
Here's the parts - 750 mechanical secondary Holley double pumper on a 11:1 406.

Here's the problem - Under race conditions, this carb shut down at 3000 rpm about 50% of the time. It was like someone closed the choke on it. It would keep running, but thats about it. It pulled fine up to 3000, but nothing more. The carb did this little trick on 2 different motors and with three different fuel pumps. Also, the original motor burned a piston under this carb. After the carb did the same thing on the second motor, I swapped carbs and had no trouble.

Any ideas on whats wrong with it?

Thanks,

Ego Racing
Member
posted February 23, 2004 03:48 PM
Chech the float level, See if the accelerator pumps are blown, Check the power valve to see if it is blown, Make sure the air bleaders are not plugged up.


chomme
Member
posted February 23, 2004 05:28 PM
Blown power valves will only make a carb run overly rich and not starve it for fuel (which is the condition you're describing).
Either your bowls are running dry or the carb is just plain not jetted right. Also, a plugged air bleed(s) can cause major stumbling but usually will affect how it idles too (unless, of course, it's just plugged main air bleeds).
Verify your fuel pressure first, then set the idle circuit, and verify the carb's floats aren't just failing.
After doing that, we can proceed further down the list of possibilities.

Hope that helps, and let us know.

KP

Raz_900
Member
posted February 24, 2004 09:34 AM
Have you pulled the bowls off and cleaned them out? Even with the best airfilter, dirt will eventually work it's way into the bowls. I had a similar issue with a 750 vac. sec. that turned out to be dirt in the bowls. Wouldn't run over 5000-5500 on a 355. Make sure the secondaries are opening too. Might have a busted up linkage.


WesternAuto17
Member
posted February 24, 2004 09:45 AM
Are there any good books on maintaining and rebuilding the racing-type Holley carbs?

I've had really good luck with them up until this one, but I need to start figuring out more about their inner workings.

Thanks,

Ego Racing
Member
posted February 24, 2004 11:44 AM
I think HP Books has one. I have it but a friend has it right now.
KP... In the book it tells you if a power valve is blown and the float not high enough it will empty the bowl faster, and sooner than just the low float.


KPLugnut
Member
posted February 24, 2004 12:47 PM
Yes, it will empty the bowl, and while it's doing that, the engine will be WAY rich, since raw fuel will be dumping right into the intake. That's what I meant about a rich condition.
You are right, that once the bowl gets emptied THEN the thing goes very lean very quickly (since the jets start sucking air instead of fuel).
BOTH situations are not at all good for an engine.

KP

WesternAuto17
Member
posted February 24, 2004 01:24 PM
Yeah, to say it was not good for the engine is a bit of an understatement.


krace72
Member
posted February 26, 2004 07:58 PM
I dont know if this will help but this past summer we had the same problem with the same carb and it ended up having a pin hole in the float.Replaced the float ran like a new carb.The heavy float was causing the engine to dive at 3000 to 4000 rpm just like the choke was being pulled.over rich at idle!


Back to the Archives