Holley rebuild questions

[HSSS427]

I'm in the midst of rebuilding my Holley 4150-9379 - 750 cfm, no choke, mechanical secondaries, double pumper w. dual 30cc accel pumps, 68 jets on primary, 81 on secondaries. Primary accelerator shooter was a 28, secondary was a 31.

Engine is a '65 block 427 side oiler w Shelby aluminum heads, Isky cam 250 duration, .525 lift, '66 aluminum medium riser police interceptor intake. Running 9.5:1 compression.

So far I have:
1. Disassembled and cleaned everything
2. Replaced main body w. ProForm main body
3. Replaced throttle plate with ProForm plate - the original plate had an older style secondary linkage that used a shaft cast on the old main body so had to get a set up with the newer secondary linkage - plus the new one is purple and looks cool
4. Went down a size in jets: 67 primaries, 80 on secondaries
5. Installed a 50cc accelerator pump on the secondaries. Kept the pink cams on the primaries, and have the brown ones on the secondaries
6. Right now have the accelerator shooters that the Proform came with, but they don't have any numbers stamped on them so don't know the sizes - was going to change primaries to 35 and secondaries to 37s
7. Installed the blue removable gaskets
8. Installed new nitrophyl floats
9. Installing a 1/2' phenolic spacer so the 50cc accelerator pump will clear - it's tight now between the scoop and air cleaner - a 1" spacer was too high.

So, here go the questions:
1. If the 2 trains are approaching when will they pass? OOPS, bad flashback to word problems.......

1. Anything glaring with the above set-up as a starting point? Haven't run the car yet so don't even know what response I'll get.
2. Should I trim the gaskets to the size of the holes they match up to? ie the transfer slot holes are bigger than the holes in the gasket - should I ream out the gasket? Same for other areas?
3. I have the 6.5 power valves in. Am I going to need to get lower ones?
4. I'm assuming I put gaskets between every "layer" of the stack, with no sealer or anything on them. I've got a turkey pan, so I go gasket between intake and pan, gasket between pan and spacer, gasket between spacer and throttle plate.
5. Any problems using the original metering blocks, fuel bowls, inlet needles (replaced w. new but same as original) with the new main body and throttle plate?
6. Any other stuff I've overlooked or would be a good tip to take care of before I put it all back together and start up?

I'm now in for about $300 - probably should have just gotten a new Barry Grant, but it's been fun to learn. Like disecting frogs for the first time

Thanks for bearing with the long winded message......
Scott

[Zoom This]

The move to a 50cc pump, a brown cam and the squirters at 35 and 37 seems extreme. How did the carb perform on the motor before? If you were to put the car with the proposed accelerator pump mods on a chassis dyno and an A/F sniffer up your exhaust you would more than likely see not only black smoke out the exhaust until the accelerator pump and cam has run its course, but the A/F ratio would dip way down into the 9 or 10:1 ratio, affecting your HP for several thousand rpms. I know this because I went through a string of carb mods while on a chassis dyno with my 850 Holley on my 418 stroker. I wound up settling with pink cams on both pri and sec side and 25 squirter on the front and 28's on the back with #73 jets on both pri and sec. I know our two motors aren't very close to the same but just keep this in mind while sorting out your new carb. Your power valve seems to be in the ballpark, but will depend on what vacuum you are drawing at idle.

[HSSS427]

One of the first things I'm going to try to do is get back on the dyno and adjust jets and accel shooters. In the last dyno run the tech suggested I up the accel shot as I was getting a dip when he punched it. He also said I needed to lean the jets and probably had too much advance. I've changed all these, but may have gone overboard per your note. Wish there was a calculation or something you could run, but as far as I've heard the only way to do it is run it and play with it. Kind of like the eye doctor when he starts saying "Is this one better, or this one?" I'll keep your comments in mind and head that direction if it's not running well.
Thanks!

[webebob]

?

[Frank Messina]

I agree with what Zoom has advised. I would stick with the pink cams and make sure you have them adjusted so that you get fuel out of the discharge nozzles at the slightest throttle movement. Start off in hole 1 and if you need a litle more pump shot go to hole # 2. In a light car like a Cobra it's doubtful you would ever need a 50CC accelerator pump. Adjust your idle mixture ( secondary idle mixture screws will be 1/4 to 1/2 out from lightly seated) and take an idle vacuum reading as soon as you can to determine correct power valve opening point. You can use either 1/2 idle vacuum or 1/2 plus .5 as your formula. Your choice, both work. Make certain your floats are adjusted so that fuel just runs out of the sight plug hole at idle and is not shaking or splashing out if you have a big cam. A low float level will delay startup of the main jets and give you that "dip". Go back to the #25/28 shooters Zoom suggested. Once you get those items squared away you'll only be working on fine tuning the jetting. Number 73's all the way around is a good starting point although I'm guessng # 70's on the primaries is going to be real close.
HTH.
Frank

[HSSS427]

Got the laptop here on the bench, so will take ya'lls advice as follows:
1 - Remove the 50cc pump and go back to 30cc with no gap between the pump arm and acctuator screw head. Pink cams on both primary and secondary
2 - This then keeps me from needing a spacer. However I have a 1/2" phenolic 4 hole spacer on the way from Summit. Should I still use it regardless?
3 - Change the primary jets to #70 - up from #68
4 - Change secondary jets to #73 - down from #80
5 - Initial adjustment on the idle screws as Frank indicated
6 - The ProForm body has the removable air bleeds so any further info on what I might try there is appreciated

Will post results as I get them. Hopefully the next one is that the car will run!
Thanks!
Scott

[Zoom This]

The phenolic spacer is always a good idea to help rid your carb of percolation in hot weather. I have a 3/8" phenolic spacer on my manifold and it does help. See to it that the carb and intake manifold are clear of the edges of the spacer.

Finally, I found during my carb true up details that when you are turning your idle mixture screws for the best idle and rpm, take care to follow up with how that all transitions from the idle circuit to the transfer circuit and on to the main jet circuit. I adjusted my idle mixture screws using an electronic exhaust sniffer for maximum idle mixture. However, what happened on the street was a slight cough when leaving from a stop as the carb trransitioned from idle circuit to transfer circuit. All I did to fix this was to turn each of the 4 idle mixture screws out about 1/8 to 1/4 turn. Good results as well as much better off idle throttle response when cracking the throttle open..... at the expense of a richer idle mixture.

[HSSS427]

Zoom,
So how many turns out from lightly seated in total are your primary and secondary idle screws? Were you 1 1/2 turns out and then did an additional 1/4 turn out for total of 1 3/4 turns?
Thanks!
Scott

[Frank Messina]

Scott,
A four hole spacer is going to be counter productive on your motor as it effectively reduces the size of the carb. It's a band aid on a motor with a too large carb. A 750 on your 427 is not too big. Run an open spacer or none. Start with your secondaries at 1/2 turn from lightly seated and the primaries at 1 1/4. From there, just adjust the primaries to dial the mixture in. You'll most likely be starting off a little rich. Go slow with this. Turn the screw 1/8 turn and wait for the motor to settle down then go again. Keep in mind that stopping at highest vacuum reading is going to leave you fat. Keep going until vacuum drops and or RPMs drop then back up to regain Vacuum/RPM's. Remember, go slow.
Frank

[Frank Messina]

Scott,
Regarding your idle air bleeds, just make a note of the size and write it down somewhere. They're stamped with a number and hard to read. You don't need to mess with them unless the motor just wont idle without more air. In other words, if you have to turn the idle screw so far that the throttle blades break into the transfer slots, then you go to a larger size idle air bleed or drill a hole in the throttle plates, but you're not there yet and I suspect you won't be either. This is just FYI and not something you need to concern yourself with at this stage. HTH
Frank

[Zoom This]

Scott....I settled at 3/4 turn for both pri and sec. Your carb and motor may require much different. When I got my carb back from a Jet Performance stage 3 massage last year it was way rich everywhere. Idle mixture screws were like 1 1/2 turns and I had intermittent puffs of smoke out the sidepipe at idle. Hmmmm....way too rich for my particular application. Good luck, and let us know how it all turns out.

[HSSS427]

Well, here's what happened:
1. The car started - didn't want to idle and I ended up with the idle adjustment screw all the way in just to keep in running. Noted that the old throttle plate did have the holes drilled in the throttle plate so thinking I'll have to do that on this one as well.

2. I adjusted the secondary idle screw in a bit, and ended up with them being about 1 1/4 out. Had the primaries all screwed up with the passenger side being 1/2 turn out, and driver side 1 turn out. Basically ran out of time to spend adjusting as I had to meet WWW and her flying monkees at the pizza place.

3. Regardless of the above, I was determined to drive up to the pizza joint - which is just in front of the neighborhood about 1/2 mile away. Car did not want to respond at low speeds at all and had lots of hesitation so I was jumping all over the place just trying to cruise out in first.

4. Got back and noticed some fuel had leaked into the turkey pan in front - I think from a loose fuel inlet connection, but will check the bottom of the front bowl.

5. I'm optimistic that I've just got some adjusting to do and maybe the throttle plate holes. Any suggestions on doing this without having to remove the shaft and disassemble the plates? I understand that is a pain.

6. Going to take the carb back off the car. Will report back on how much of the transfer slot is uncovered as it sits and see if I can pinpoint the leak. Will re-read your messages again for clues and dig into the Mike Urich Holley Carb handbook.

I sense that all the answers are within your brains!!! Keep the advice coming.....
Thanks!
Scott

[HSSS427]

I checked the air bleeds and found the following: Idle bleeds are #75 on primary and secondary. Main circuit are #36 all around. Also the power valve on the primary side is 6.5, and there is no PV on the secondary plate - it has a plug in it so trying to determine if I should install a PV on that side as well. Also need to check the vacum level and float levels as I didn't have a chance to do that either.
Thanks!

[webebob]

?

[Frank Messina]

Bob,
We are talking about the same thing. As you probably know, on most garden variety Holley carbs the idle air bleeds are not removeable. This feature showed up more recently on the high end carbs. Prior to that, you had to drill the throttle plate with a small 1/8" hole to get more air. Drilling the idle air bleeds and the high speed bleeds was always a tuning step best left to the pros.

Scott,
If you're going back to the 73's on the secondary, put the 6.5 power valve back in there. Then verify the opening point with your vacuum gauge as outlined previously ( 1/2 idle vac). I've set up Holleys both ways and tricked out beyond description and never found there was any advantage to removing the power valve. You can do it either way, it just doesn't seem to matter. The newer carbs all have a check valve in them to prevent power valve blowout in the event of a serious backfire and is easily retrofitted to older carbs.
Frank

[webebob]

?

[HSSS427]

So, want to verify if my simple mind grasps this correctly:

- First, I have the ProForm main body on the carb, having replaced the original Holley 4150-9379 - which had the fixed air bleeds that you'd have to drill out. On the Proform it does have screw in removable brass bleeds that kind of look like small main jets.
- Second, changing the idle bleeds won't fix my idle problem ie not enough air getting by the throttle plate to keep me from having to screw the idle stop screw all the way in, and thus causing problems by exposing too much of the transfer slot. As I understand it from some reading, the idle bleeds basically let a given volume of air into the circuit which controls how much air is mixed with the fuel in the idle system, and I guess how rich the idle mix is.

The Mike Urich book seems to say a couple of times to just stay away from the air bleeds. As such, I guess I'm now in for drilling the throttle plates with 3/32 holes - as the old ones had.

On the secondary power valve topic. As I start thinking about it, I don't think the metering block for my secondaries has the PV channel restriction holes drilled in it. As such I would have to get a new metering block. Can anyone tell me if that would be worth it? I'd probably then be getting really close to the cost of that new BG carb
Thanks!
Scott

[Frank Messina]

You don't need to buy a metering block. Just stick with what you've got. If you go and buy a new BG carb you'll have to tune that too. Don't drill anything yet.
Turn the secondary metering screws in until they are 1/2 turn from lightly seated and then leave them. Work on the primaries as suggested earlier. Good luck.
Frank

[HSSS427]

I've put it all back together and on the motor. I've cranked it over and have gotten 2 flaming back fires through the carb. Any ideas?

[Zoom This]

Sounds like timing is way off.