Quick Fuel 650HR Help

Jim Dewar

Supporter
I have for 16 years run my 4150 double pumper carb backwards on a Edelbrock RPM Airgap Performer intake manifold. It’s simply easier to run the throttle cable instead of fabricating a bell crank. I have never been satisfied with the idle quality and wonder if this might be the problem.
Opinions greatly appreciated!
 

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Randy V

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Orientation on the carburetor can be in either direction without a problem.
Having recently fought with dragons over poor idle quality on a similar situation, I found that the PCV line had been plumbed to the vacuum port on the intake. This caused the cylinder on that intake channel to run so lean as to misfire. I re-plumbed the vacuum lines and the car now idles fine. I also routed the vacuum advance on the distributor to the manifold vacuum port on the carb and it’s like a brand new car. I can’t tell how all your lines are oriented from your picture - so just offering this advice somewhat blind..
 

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Orientation on the carburetor can be in either direction without a problem.
I do not agree on this one, and most manufacturers will advice against running a carb backwards and most carb related books do say also.

Primary bowl always up front, cause when accelerating the fuel sloshes to the back, and so on into the primary metring system with the most importance, it keeps the emulsion tubes filled. (main jet - emulsion tube - air correction jet)

Running a carb backwards, on accelerating will slosh the fuel from the primary system to the back of the float chamber... out of the carbs fuel system, lowering the fuel level of the emulsion tubes, creating a lean mixture. (flat spot, hesitation, bogging, misfire, etc).
These issues won't show up on the dyno as the car stands still.

For fast accelerating cars Holley offers jet extensions for the secondary float chamber to keep the jets fueled. But thats for the secondary float chamber only.

I made myself a long enough throttle cable ( & a spare one ) to run the carb the right way around.
 
I do not agree on this one, and most manufacturers will advice against running a carb backwards and most carb related books do say also.

Primary bowl always up front, cause when accelerating the fuel sloshes to the back, and so on into the primary metring system with the most importance, it keeps the emulsion tubes filled. (main jet - emulsion tube - air correction jet)

Running a carb backwards, on accelerating will slosh the fuel from the primary system to the back of the float chamber... out of the carbs fuel system, lowering the fuel level of the emulsion tubes, creating a lean mixture. (flat spot, hesitation, bogging, misfire, etc).
These issues won't show up on the dyno as the car stands still.

For fast accelerating cars Holley offers jet extensions for the secondary float chamber to keep the jets fueled. But thats for the secondary float chamber only.

I made myself a long enough throttle cable ( & a spare one ) to run the carb the right way around.
very true....
Paul
 

Jim Dewar

Supporter
Thanks guys for you response. I spoke with Edelbrock today and they confirmed what Paul said, I may have problems with hard acceleration as Paul stated but not in many cases. This problem has not occurred for me probably because of my driving style.
 

Randy V

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I tend to agree with the comments above (re:fuel slosh), but have seen many run “backwards” with no apparent ill effect - even on track cars and many boats. I would retract that recommendation for cars that are used in high-G acceleration runs like very fast Drag cars. However - food for thought - The secondary metering blocks of the Holley carbs would also suffer the same fate when oriented properly…
 

Terry Oxandale

Skinny Man
So if direction matters, Why wouldn't the same detrimental effects of acceleration be apparent on the secondary metering block (jets are facing opposite direction from the slosh than the primaries face?
 
I tend to agree with the comments above (re:fuel slosh), but have seen many run “backwards” with no apparent ill effect - even on track cars ....
Mostly cause their mechanic's don't even know what they are doing...
Most don't even know how a racecar should perform on track. for most on trackdays Its way easier to just buy a bigger engine to go faster then to just fine tune the engine you'll have.
I have told many on trackdays your carb is wrong way around and they thought I was a fool. Loads of teams have volunteer mechanics who like to wrench but have no clue what they are doing, like adjusting ignition or rejetting while carbs are just out of sinc.
I have spoken to many of those later on, telling me I was right on the spot. Issues they all had just vanished or cars performed way better then before.

I even met a guy at Spa a few months back, who swapped main jets of his Holley several times with no results.. so I asked a few questions and it seemed they never set float height of the Holley carb. I told them friendly well easy to check (side plug out) & check. Eventually the car ran better then before.
Its the average knowledge of teams I see on classic race events. Its running fine by their perspective.
 
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