Need Holley DP troubleshooting help.
Thread Starter
Drifting
Joined: Nov 2002
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From: Loveland, CO
Need Holley DP troubleshooting help.
I have a Holley 4781 DP on my rebuilt '73 BB. Due to altitude here in Denver, I have dropped jet sizes from 80 stock to 76 on primary side and 80 to 78 on secondary side. Power valves are 6.5's. Idle vacuum about 8.5. Idle and running appears very rich. Will hook up LM-1 when I get some of the bugs out of it. Float level appears to be OK with gas just leaking out of the sight holes.
What has me confused is that each time I shut off the engine, gas pours out of the primary booster nozzles and looks like it is draining the float chamber (ie, quite a bit of gas). The car is then hard to start from gas flooding the manifold. What is going on?
Any suggestions?
Ralph
What has me confused is that each time I shut off the engine, gas pours out of the primary booster nozzles and looks like it is draining the float chamber (ie, quite a bit of gas). The car is then hard to start from gas flooding the manifold. What is going on?
Any suggestions?
Ralph
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yes, it sounds like needle valve is not sealing.
I highly recomend putting on a carb Isolation plate, when I did the carb. tempature dropped nearly 100 degrees. on mine.
I highly recomend putting on a carb Isolation plate, when I did the carb. tempature dropped nearly 100 degrees. on mine.
Last edited by 69Vett; Sep 22, 2008 at 09:47 PM. Reason: poor typing !
Thread Starter
Drifting
Joined: Nov 2002
Posts: 1,688
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From: Loveland, CO
Thanks for the comments.
Why would the float level show OK with the motor running and gas just dribbling out the sight hole? What has me confused is why it only does it when you shut off the motor. I can't figure out what is different.
I have a 1/2" "plastic" insulating spacer under the carb.
Ralph.
Why would the float level show OK with the motor running and gas just dribbling out the sight hole? What has me confused is why it only does it when you shut off the motor. I can't figure out what is different.
I have a 1/2" "plastic" insulating spacer under the carb.
Ralph.
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From: At my Bar drinking and wrenching in Lafayette Colorado
Ralph -
Are you just testing me to see if I'm reading the Forum?
I have some brand new needle/seat assemblies right here - I'll bring them over and swap them out with you.
Lars
Are you just testing me to see if I'm reading the Forum?
I have some brand new needle/seat assemblies right here - I'll bring them over and swap them out with you.
Lars
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if the float level is set to high it will not apply enough pressure to make the seat valve close completely, when in doubt lower the float level for increased needle/seat pressure.
Man, I wish I could get Lars to come over by just posting !
sounds like your in good hands now ! 69VETT
you only just notice it with the motor shut off..
Man, I wish I could get Lars to come over by just posting !
sounds like your in good hands now ! 69VETT
you only just notice it with the motor shut off..
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I was thinking fuel percolation as he has the typical symptoms. If you already have a good carb insulator, that should not be an issue anymore.
-Mark.
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I would do that first, but then the question is why does it only cause problems when the engine is shut off? If it was trash, it should flood all the time, right? He did say rich all the time so maybe it is a small piece of trash?
I was thinking fuel percolation as he has the typical symptoms. If you already have a good carb insulator, that should not be an issue anymore.
-Mark.
I was thinking fuel percolation as he has the typical symptoms. If you already have a good carb insulator, that should not be an issue anymore.
-Mark.
When it's running you can see it too, usually not as bad because gas is being used in other parts of the carb. It will be hard to start but it will run, just not as good as it should. Hopefully the OP will take 5min on this as it would not hurt anything and he will most likely fix his problem
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we forgot to mention the needle seat adjustment is dependant upon fuel pressure,
if you are running some monster electric pump with high pressure above 7psi,
this gas pressure can push past the needle seat valve, also, and require further float adjustment. 69VETT
if you are running some monster electric pump with high pressure above 7psi,
this gas pressure can push past the needle seat valve, also, and require further float adjustment. 69VETT
Thread Starter
Drifting
Joined: Nov 2002
Posts: 1,688
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From: Loveland, CO
Fuel pump is stock unit. While looking into carb while running no evidence of extra fuel coming from squirter or other nozzels. I would call the problem a burp after shut off.
Pulled out both inlet valves today, no evidence of debris. Haven't run engine since checking inlets. I installed the inlets from a Holley trick kit and they are not the viton (rubber) seats. They have a ball shaped sealing mechism, looks like a BB on the end of the float controlling part of the valve. Maybe they are the wrong inlet valves.
I may have to call on Lars.
Ralph.
Pulled out both inlet valves today, no evidence of debris. Haven't run engine since checking inlets. I installed the inlets from a Holley trick kit and they are not the viton (rubber) seats. They have a ball shaped sealing mechism, looks like a BB on the end of the float controlling part of the valve. Maybe they are the wrong inlet valves.
I may have to call on Lars.
Ralph.
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From: Who says "Nothing is impossible" ? I've been doing nothing for years.
I have never seen the debris either, much too small to detect by eye. I blow them out and then the carb works the way it is supposed to.
Let us know how it runs now with the new needle and seat
Let us know how it runs now with the new needle and seat
