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Discussion Starter · #1 ·
Randy explains the ins and outs of Holley carbs. A good video watch for a rainy day. He covers multiple aspects of metering blocks and power valves and air bleeds. Stuff I never even considered. good information.
start with this video and see the rest As you get pulled into watching this good ole boy.

 

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Great video Mario! And very timely as I'm pulling my Quick Fuel carb off the '39 today to find out why it's so rich. I did notice he never mentioned the minimum idle screw that goes up from the base plate to set minimum idle opening? When addressing how much of the transfer slot is exposed I'd have thought he'd mention that also as a possible adjustment if backing off the external idle screw didn't get the plates closed enough.
 

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my pop bought me a couple of holley books back when i was a kid . best books i ever read . the holley is really tunable if you take the time . back when we raced we had one of the few that would set and idle without loading up .
 

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Mario, I just put my Quick Fuel carb back on the '39 after making several changes. First off the 650 double pumper had 72 primary, and 74 secondary jets. Much too large for my engine build with it's lower compression ratio. and also with my 10" of vacuum the 6.5 power valve was also too large. I changed primary jets to 64 and secondary to 70, which should help with mileage and smell. I changed the power valve to a #4.5, as the next smaller I had was a #2.5, and I kinda wanted a #4 really.
I also checked the throttle plates position, and both were fine, and fully closed. So I got my numbered drill bits and drilled all 4 plates with a #70 bit. Reassembled the carb, and set the idle a bit high until it warmed up. Then turned it down to 800 in neutral, and began readjusting the air screws on all 4 corners. Once I got maximum vacuum for the settings, I dropped the idle rpm back to 800 again, and went to give the tailpipe the sniff test. It's way cleaner smelling than it's ever been since I first got it together!
I'm really not sure why I've waited so long to check the jetting and power valve size? But since it seemed to recently begin to use the gas up a bit faster I had to check it. Glad you posted the link as I doubt I would have thought to drill the air bleed holes in the butterflies had you not. I think that certainly helped to make it less rich at idle for sure!
Thanks Mario!

PS-I was pleasantly surprised to see my Quick Fuel carb has jet extensions in the back metering block! A nice feature I never see on stock Holley carbs! Keeps the jets in the gas under hard acceleration.
 

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Discussion Starter · #5 ·
Mario, I just put my Quick Fuel carb back on the '39 after making several changes. First off the 650 double pumper had 72 primary, and 74 secondary jets. Much too large for my engine build with it's lower compression ratio. and also with my 10" of vacuum the 6.5 power valve was also too large. I changed primary jets to 64 and secondary to 70, which should help with mileage and smell. I changed the power valve to a #4.5, as the next smaller I had was a #2.5, and I kinda wanted a #4 really.
I also checked the throttle plates position, and both were fine, and fully closed. So I got my numbered drill bits and drilled all 4 plates with a #70 bit. Reassembled the carb, and set the idle a bit high until it warmed up. Then turned it down to 800 in neutral, and began readjusting the air screws on all 4 corners. Once I got maximum vacuum for the settings, I dropped the idle rpm back to 800 again, and went to give the tailpipe the sniff test. It's way cleaner smelling than it's ever been since I first got it together!
I'm really not sure why I've waited so long to check the jetting and power valve size? But since it seemed to recently begin to use the gas up a bit faster I had to check it. Glad you posted the link as I doubt I would have thought to drill the air bleed holes in the butterflies had you not. I think that certainly helped to make it less rich at idle for sure!
Thanks Mario!

PS-I was pleasantly surprised to see my Quick Fuel carb has jet extensions in the back metering block! A nice feature I never see on stock Holley carbs! Keeps the jets in the gas under hard acceleration.
Awesome Vall. Just FYI. I think the power valve may have been opening at idle making it rich so you did the right thing using the 4.5. I’m just a little concerned on the 64 primary. Keep an eye on the plugs and water temp especially when cruising. You may have to come up half way in between. Don’t forget you dropped the power valve to 4.5 so it might lean out the partial throttle.
glad to hear you benefited from Randy’s video.
 
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Mario, you don't think a #72 primary was a bit "fat" for a lower compression 350 like mine?
I will check the plugs after I have some freeway miles on it, to make sure they're not too lean looking. I figured it was blubbering and too rich, but you're probably right about the power valve being the main culprit.
I drove the Austin to our Thu. night get together, and when I moved the '39 back into the driveway it was really loading up badly. Worse than it ever has, which prompted me to finally do something with it.
 

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Discussion Starter · #7 ·
Mario, you don't think a #72 primary was a bit "fat" for a lower compression 350 like mine?
I will check the plugs after I have some freeway miles on it, to make sure they're not too lean looking. I figured it was blubbering and too rich, but you're probably right about the power valve being the main culprit.
I drove the Austin to our Thu. night get together, and when I moved the '39 back into the driveway it was really loading up badly. Worse than it ever has, which prompted me to finally do something with it.
Well I’ve seen 68’s in mild builds and 72 may be a bit fat. I have (72) in the MG right now As my primary But I think I have more duration Than you do And with the tunnel ram it needs more help. just do a check. If it doesn’t hesitate or show a flat spot on take off then leave it but confirm the plugs are tan Color.
 
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I ran 78's on my tunnel ram on my BBC in the Falcon. Of course that was after it ran hot all the time and you recommended I should check the jet size, and I discovered they were 64's! I was shocked when I put the 78's in it you recommended, and it never ran hot ever again! Never seen jets make such a difference in engine temps! I even removed my two auxiliary small coolers, as it didn't need any help after the jet change!

My cam is a .525/.530" lift, with 280/288 duration, and 109 LSA.
 

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Discussion Starter · #9 ·
I ran 78's on my tunnel ram on my BBC in the Falcon. Of course that was after it ran hot all the time and you recommended I should check the jet size, and I discovered they were 64's! I was shocked when I put the 78's in it you recommended, and it never ran hot ever again! Never seen jets make such a difference in engine temps! I even removed my two auxiliary small coolers, as it didn't need any help after the jet change!

My cam is a .525/.530" lift, with 280/288 duration, and 109 LSA.
You have more lift than I do. My duration is slightly more. Tunnel ram needs more fuel.
 

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You have more lift than I do. My duration is slightly more. Tunnel ram needs more fuel.
I looked at various Howards camshaft specs, and those with lower lift all had much more duration, and were designed for higher rpm ranges. I liked the higher lift, with less duration, and the 109 LSA, which makes it operate in the 1800-6200 rpm range, and work without a high stall converter.
I did put a large spacer on my Edelbrock RPM Performer, just to get a little more high rpm performance. Still not a tunnel ram, but my 700R4 wont work with a tunnel ram.
 
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