[OrigOwner77]

Car in question is my 80 T/A:
1968 "YA" 400, possibly 30 over. 1969 #62 heads. Motor internals are supposedly stock or very stock-ish (cam, etc). Edelbrock Performer, Holley 750 cfm 3310 carb (vacuum secondaries). Rebuilt HEI (Proform HEI tune up kit used). TH400 automatic, approx. 3.42 rear gear. The motor is getting tired, but still runs like a top (aside from a bad valve guide/seal).

The car runs very well, in my opinion. I have a couple small quirks with carb tuning though. For example, the car pulls strong off the line in gear, but then revving in park/neutral produces a slight stumble. Also, when in high gear doing about 40 mph, if I coast and then accelerate again (slowing down, and then resuming speed), the car almost feels like the trans slips. I am fairly certain this is a carb tuning issue and not transmission-related as the issue has occurred slightly later/earlier through a couple years of carb tuning/tweaking. It doesn't sputter, per se, but gives a slight rock/shudder for lack of a better term.

The carb is all stock, as shipped by Holley. I've added a quick-change secondary kit to it and I believe I have the medium spring installed. I've not touched jets, squirters/shooters, etc. I'm running the orange pump cam in position 2 at present, as this has helped the throttle response.

Can anyone make any suggestions on tuning for my combination? I know that there are a lot of "unknown" variables with the car/motor, but any suggestions (Jets, shooters/squirters, accel. pump cam, etc) would be appreciated to try to get the most out of this setup.

[Tom Vaught]

Before you mess with your carb, make sure the timing is right. I have seen shudders from the vacuum or mechanical advance sticking and the carb was blamed.

Tom Vaught

[OrigOwner77]

Thanks for the advice Tom.

I run 16-18 degrees of initial timing on the car. I have an adjustable vacuum advance unit that I installed "out of the box" that came with the HEI Upgrade kit. Everything inside the distributor was cleaned thoroughly, and new weights were installed. I can't remember which springs I used off the top of my head. Vac. advance is hooked to the PORTED vacuum port on my carb.

My buddy used his dial-back timing light and found I only had, I believe, 24-26 degrees of total timing at approximately 2500-2800 rpms. The timing didn't seem to advance much after that point either.

Isn't it recommended to have about 32-35 degrees of timing around 3200 rpms?

Low-rpm timing seems close, but higher-rpm timing needs to be tweaked. I'm betting that my adjustable advance can needs to be adjusted. Does this sound right, at least to start?

EDIT: Also, I've heard these heads are fairly high compression. I run 92-94 octane pump gas in the car, occasionally with a lead substitute. Is it safe to run more timing on the car with the supposed "high" compression of the motor?

[72blackbird]

I run a 406 with ported no.48's, same carb and manifold as yours, Crane 284H cam, Hooker comps and 2 1/2" exhaust. I rebuilt my engine about ten years ago and it still runs strong, even with the crappy 91 octane we are stuck with here in SoCal.

I radiused any sharp edges in the combustion chamber on my heads, especially the ridge that shrouds the valves, and held the chamber volume to 85cc- lowered the CR to around 9.5:1 and made it possible for me to run pump gas. I run the GM distributor with a Mallory Unilite, Crane adjustible vacuum advance and weights, with 16 degrees initial and 32-34 degrees all in by 3000 rpm.

All the components on an engine work together and will determine how well your engine runs from idle to 5500 rpms. My setup runs well and pulls hard from 2000-5500 (when the e-performer starts to choke the engine). It also idles with a mild lope, but has enough vacuum to run 4 wheel disc brakes.

The stock carb out of the box will not run your 400 well- I started by replacing the rear metering plate with a secondary metering block kit, which lets you run jets. I also replaced the floats with better solid nitrophyl floats, and installed clear float plugs to set fuel level easier. Do these upgrades and then go with a jet eight numbers higher on the secondary side, reset your idle mixture screws to get the highest vacuum possible, and then see if that gets rid of the stumble. You may also need to put the lightest secondary spring back in.

You didn't give cam specs, but if you're running a stock cam you're running to much compression with the heads you have. I also need to know what kind of exhaust you have.

Geno

[OrigOwner77]

Car has cheapy Hedman headers with 2 1/2" pipe going to dual Flowmaster 40's.

This engine is coming out in the near future for its needed rebuild. I don't want to get tooooo crazy with the carb, just because I'll probably be running a stock low-comp 400 with this carb in the meantime while this motor gets rebuilt.

I've also used my friend's vacuum gauge to adjust the idle mixture screws. I've got clear sight plugs and keep the float level just above the bottom of the hole. This works great on our '77 and this '80 seemed to like it as well.

Jetting the secondaries 8 numbers up? Will the car like it that much better? If anything, I figured the majority of the tuning/work would be done on the primaries. :?

I'll look into your suggestions this coming spring though. Thanks!

["QUICK-SILVER"]

Originally Posted by OrigOwner77

Thanks for the advice Tom.

I run 16-18 degrees of initial timing on the car. I have an adjustable vacuum advance unit that I installed "out of the box" that came with the HEI Upgrade kit. Everything inside the distributor was cleaned thoroughly, and new weights were installed. I can't remember which springs I used off the top of my head. Vac. advance is hooked to the PORTED vacuum port on my carb.

My buddy used his dial-back timing light and found I only had, I believe, 24-26 degrees of total timing at approximately 2500-2800 rpms. The timing didn't seem to advance much after that point either.

Isn't it recommended to have about 32-35 degrees of timing around 3200 rpms?

Low-rpm timing seems close, but higher-rpm timing needs to be tweaked. I'm betting that my adjustable advance can needs to be adjusted. Does this sound right, at least to start?

EDIT: Also, I've heard these heads are fairly high compression. I run 92-94 octane pump gas in the car, occasionally with a lead substitute. Is it safe to run more timing on the car with the supposed "high" compression of the motor?

You need to get the centrifical advance coming up like it's suppose to. Forget the vacuum advance for now, its timing goes on top of the 32-35 mechanical/centrifical.
If all you're getting is 8° to 10° of centrifical advance over base, somethings wrong with the centrifical advance. Double check weights an springs.

The 3310's usually run pretty good on the older stock cam, stock high compression engines. Hotter cams are when the carb usually needs more than screw turning or bolt on modifications. Sounds like you've got that under control.

Something else FWIW, base timing on the older high compression engines was in the 10° range. You may want to look into that also. Later model low compression did set quite a bit higher.
You just need to play/tune/tinker with it some more.
Don't be worried with how it revs in park or neutral, in gears where it counts.

[OrigOwner77]

I didn't know baseline timing was only 10 degrees on the early motors. Maybe I'll play with the weights/springs when I get the car out, accounting for this new info. I don't get any pinging (at least audible) with the setup as it is right now, but I'll assume that's because of the limited advance I'm getting.

The car pulls to 5000 rpms pretty even, but I just feel like it could perform a little better (pull a little harder).

I know my Dad's 77 likes more advanced baseline timing (30-something degrees initial according to the slipped balancer, lol), but the '77 W72 motor was, what, 8.2 to 1 compression or something? My setup is probably 9 or 10 to 1?

I appreciate all the info. I may dig out my other springs if I can find them. If I can't, what is a good HEI spring/weight kit to use?

[OrigOwner77]

Also, I *think* when I changed the HEI springs, I also used the new weights from the kit as well. In reading some old posts on here, that may not have been such a great idea.

Pending I pull the cap in spring and see replacement weights, what should my course of action be? Mess around and try to recurve the dist. with what I've got, get another new recurve kit, or scour eBay/junkyards to find original weights?

EDIT: Maybe an admin/mod can change my topic title to "Holley 3310 Tuning / HEI Tuning" or similar? Please?

[ericwy]

Originally Posted by OrigOwner77

Car in question is my 80 T/A:
1968 "YA" 400, possibly 30 over. 1969 #62 heads. Motor internals are supposedly stock or very stock-ish (cam, etc). <snip>

For example, the car pulls strong off the line in gear, but then revving in park/neutral produces a slight stumble. Also, when in high gear doing about 40 mph, if I coast and then accelerate again (slowing down, and then resuming speed), the car almost feels like the trans slips. <snip>

The carb is all stock, as shipped by Holley. I've added a quick-change secondary kit to it and I believe I have the medium spring installed. I've not touched jets, squirters/shooters, etc. I'm running the orange pump cam in position 2 at present, as this has helped the throttle response.

You didnt mention what your idle setting is, but if this "stockish" engine has a lower idle
(600 - 850) shifting the primary orange (#41R466) pump cam from #2 position to #1 to
eliminates the delay in pump action. Position #2 rotates the cam so that all the pump shot is available for more open idle throttle settings. This will delay the shot for lower idles.

[OrigOwner77]

Originally Posted by ericwy

You didnt mention what your idle setting is, but if this "stockish" engine has a lower idle
(600 - 850) shifting the primary orange (#41R466) pump cam from #2 position to #1 to
eliminates the delay in pump action. Position #2 rotates the cam so that all the pump shot is available for more open idle throttle settings. This will delay the shot for lower idles.

About 900-950 in Park, 700ish in gear. Give or take. As the car has a manual choke and is driven pretty much daily in spring/summer/fall, I like to keep the idle a tad higher.

I've got the orange cam in #2 as this produced the smoothest/best throttle response thus far. I may try every cam in #1 this spring, but that gets tedious. LOL. Heck, if I adjust the accelerator pump arm nut a 1/2 turn in either direction, keeping the pump cam the same, the throttle response either gets better or a LOT worse.

[ericwy]

Originally Posted by OrigOwner77

About 900-950 in Park, 700ish in gear. Give or take. As the car has a manual choke and is driven pretty much daily in spring/summer/fall, I like to keep the idle a tad higher.

I've got the orange cam in #2 as this produced the smoothest/best throttle response thus far. I may try every cam in #1 this spring, but that gets tedious. LOL. Heck, if I adjust the accelerator pump arm nut a 1/2 turn in either direction, keeping the pump cam the same, the throttle response either gets better or a LOT worse.

With the throttle blades open more it make sense that it works better in the #2 position.
The blue (#41R427) pump cam will give you a quicker shot with more total lift. My 4175
Vac Sec was a bear to get dialed in due trying to balance the A/F ratio, jetting, pump cam, and secondary opening rate. It ended up needing the pink cam (41R427) in #1 position to
keep a constant shot spray as long as the throttle was opening (slower initial ramp). The
orange cam is about done at 60% throttle. Final solution included fattening up the idle A/F ratio so it did not start lean and the lightest (white?) secondary spring.

I am running a 4165 DP now, which was easier to dial in IMO due to fewer variables.

["QUICK-SILVER"]

I'ld post here at PY that you need some weights.
I may even have some donors.


Tightening the nut on the pump spring will make the shot stronger. It does mess up shot timing+length and is not the best way to do it. Given the results you're having, it may be time for a bigger squirter.

Just remember, timing, fuel mixture and pump squirt, all work together. Messing with one could mask something else.

You need to mark or print Eric's pump cam info in case you need it later.

[OrigOwner77]

I used to have that chart a while back...glad you reposted it ericwy. Thanks!

Quick-Silver, are all the OEM distributor weights the same? Or is there a specific set I'd need? My Dad may have his stock weights & center plate from his '77 somewhere...so I'll check for them before posting on here.

I'll probably play with the pump shot and secondary spring before changing the squirter.

You say that altering the nut/spring tension messes up the shot timing/length.....as you have to re-adjust this with each pump cam installed, how is one to find the "correct" position? Holley's tuning DVD recommends having AT LEAST (xxx)" of clearance between the pump arm and bolt head with no play at idle and no pre-load. Plus, a 1/4 to 1/2 turn on the nut makes a world of difference, at least on my car. How do I find the "best" position to use with each pump cam? Or should I try each cam, and slightly mess with the nut as well?

EDIT: And, on the pump cam chart, is that for position 1 or 2? My understanding is that position 2 delays the pump shot, but also changes the volume of the shot as well (according to an older Holley tuning book I have).

[ericwy]

Originally Posted by OrigOwner77

EDIT: And, on the pump cam chart, is that for position 1 or 2? My understanding is that position 2 delays the pump shot, but also changes the volume of the shot as well (according to an older Holley tuning book I have).

I believe its for position #1. The total volume would only be reduced if the peak lift cant
be reached before hitting WOT. Most of the primary 30cc cams reach full lift by 60% throttle.
The only two that dont would be pink/black. The brown/yellow are for 50cc pumps.
I guess you could measure the total lift at each position and see if there's a difference.

[OrigOwner77]

Given all the info in this thread, here is my plan of action:

I'll start by setting my baseline timing to somewhere around 12 degrees. I'll then get the dist. curve set to provide about 30-some degrees of timing in before 3,000 rpms. I won't worry about vacuum advance for now...just leave my adjustable unit alone.

Once the timing is squared away, I'll play with the carb. I'm thinking of dropping my idle to about 600-650 in gear (depending on if it is smooth enough for my liking) and trying the cams in position 1. Just for fun. If i get it close and can live with the lower idle, I'll use that.

Sound reasonable? Any initial starting points, such as which pump cam, which distributor springs, etc that can be suggested (rather than trial and error)?

["QUICK-SILVER"]

Weights and center plates are different. The ones out of the 77 will have plenty of advance. I'ld use stock type or strong springs to start with, given your compression, dont want to promote any ping.

When adusting the pump lever spring, just make sure it doesn't bottom the pump diaphram out. Spring pivot arm on highest point of cam and pump lever bottomed out with finger, I adjust spring so that you have .010 to .015 between diaphram pump lever and spring loaded bolt head.

Pump spring compresses to give a long continuos squirt. Nozzle size determines how fast it lets out. Tightening up your spring forces more fuel through the nozzles, because of higher pressure. Thus shortening the shot. Adjusted like that, it may not last long enough to get you off idle and moving.

Someone started a thread recently about different distributor weights, advance rates and numbers. Question was brought up about flipping chevy weights over to use in a Pontiac. Need to look for it, don't know how far they got with info or what they came up with.