I recently bought a new remote coil, mechanical tach, HEI distributor for my 1974, 454.

I did this because the old one, which was the same model, was warn out and the tach would not work. Replacing the tach gear did not help.

The car was running great before I put in the new dizzy, and now it is horrible. Starts instantly, but idles like it has a cam, it doesn't, and backfires out the right side.

I have tuned, retuned, and checked all the obvious stuff, now I'm trying to verify that the dizzy and coil I bought are a proper match.

Can anyone tell me if these two items can work together?

This is the coil I am using:

https://www.summitracing.com/parts/sum-850496#overview

This is the dizzy I bought and installed:

https://www.ebay.com/itm/202259384358

 

That coil seems to have the correct resistance as required by distributor retailer. Back fire. Is your distributor installed one tooth off perhaps.? Can you get a timing reading while engine is running rough. All sparks plug wires in correct location per firing order, also could be all shifted ahead or behind on cap. I’d start there. Then check ohms resistance for coil with a meter. Lots of faulty coils these days. Finally, never knew they made such an inexpensive tach drive replacement distributor. Keep us posted.

 

The HEI Dist. you refer to is a points conversion Dist. Take out that Dist. and replace with the old one and see if the problem goes away. Leave the new coil in place. If problem persists then remove new coil and replace with old coil. If problem still persists then you have an install problem.

 

Well, much to my frustration I solved this problem today.

The dizzy and coil are correct.

My main issue, and this is very annoying to a septuagenarian who thinks he has seen everything, was the number 2 cylinder. Anyone with a 454 knows which one I mean. The hardest plug to reach tucked in under the compressor.

When I did the dizzy I also did plug wires and plugs. Good ole AC. Anyway, I had done a compression check a couple weeks ago, and all was well. Did them all, except number 2. Today I figured, what the heck, I've done everything else it's the only thing left. So after skinning a few knuckles and a good talking too, the plug came out.

Plug was bone dry, like brand new, like it just came out of the box!!!!! No gas, no oil, nothing. UGH, I took off the brand new, made for the 454, heavy duty high dollar plug wire for number two. Low and behold, the wire that contacts the metal clip that slips over the plug was NOT CONNECTED. The cable was flat, the wire inside was not extended and folded into the clip like it was supposed to be. A five minute fix, Three weeks of hell tracking it down.

Fired right up, smoothed out and tuned up nicely. For some reason though, it does not like the vacuum advance. If I connect the vacuum advance, the car will eventually backfire. No advance, no backfire and the car runs and accelerates fantastic. I simply plugged the vacuum advance and fitting on the carb. Car runs fabulous.

Now I'm curious about the vacuum advance. I timed it disconnected. When reconnected, the car backfires and doesn't like it. Without it, run like a raped ape.

Could this new development have something to do with the new dizzy? Never ending.

 

Did you connect the new dist. vacuum advance to the ported tube high up on the carb?
THAT port has NO vacuum at idle and vacuum increases as engine rpm increases.

OR did you connect it on the base of the carb where it has continuous vacuum?

 

Do you know what the VA canister advance range is, and is there a possibility that the internal diaphragm is defective/leaky?

 

I really appreciate all the help on this.

It is fixed now. I went to Summit and picked up an adjustable vac can.

I always connect to the Ported Vacuum on the carb for one very simple reason. There isn't any lag when you stomp on the gas. On manifold vac, the idle is already advanced on the vac can. At least 7-8 degrees. On the ported vac, there is no vacuum at idle. When you stomp on the gas, or at least take off aggressively, ported vac will add advance as the engine needs it smoothly. If you use manifold, it is already advanced at idle, so when you step on the gas there is a sudden lag because vac drops to zero, then has to catch up.

The ported vac on the 454 Q jet is the one on the front closest to the accelerator linkage. If looking at it from the front of the car, the lower right. Manifold vac is on the left side, where the choke is. There is a long tube coming out from the choke linkage on the carb that has manifold vac. I believe this is often used on the small blocks for the auto trans. Otherwise it's not needed.

Anyway I tried this with the initial timing on the balancer at 8, 10, and 12. (I use an adjustable degree wheel type timing light so this is accurate)

On the vac can, you insert the little allen wrench and turn it all the way to the left to shut off the vacuum completely.

Then simply try taking the car off idle with can open 180 degree turn of the allen wrench to the right. Mine starting to pop and spit at 1 1/2 turns.

I then backed it off 1/8 turn to the left until I had it dialed in perfect.

My car is very very happy with 12 degrees at idle, and the open 1 1/4 from full off.

This means the vac can is actually adding less advance than it would if you just installed a non adjustable one.

You can see and hear my car at this link.

 

The new distributor more than likely has a different advance curve than your original one.
And your original curve was an emissions related curve anyway.
The use of ported vac advance, was also only for emissions.
Ported advance will make the car run hotter at idle. 12* is simply not enough.
A lot of engines like 20*+ at idle, with static + vac combined.

A typical GM performance curve has worked well for 50 years, and is listed in the old GM Powerbooks.
It goes something like this:

• 12* or so static timing at idle, OEM is usually 4-8-10 less.
• 36* exactly with mechanical (centrifugal) advance all-in. OEM is usually 3-4* less.
• 36* comes all-in somewhere above 2600 but below 3600. OEM is usually 4500-5500, far too slow.
• Vac can limited to 10* OEM cans are usually much more, up to 18-20* That doesn't work anymore on today's gas.
• Vac can on manifold vacuum. All GM used ported advance after 1964, due to emissions. For a hotter running exhaust at idle, designed to let the "new" AIR pumps work better. A "poor-mans" catalytic convertor, cleaning the exhaust.

Most of the settings can be tweaked a little to fit each engine, but not usually the 36* one very much.
Yes that will give you 22* at idle under no load. It will also give you from 36-46* at cruise under light load.

There are even ways of testing the amount required at each rpm, by vacuum level.
The trick to not having the bog you mentioned is to have the vac can pull-off at the correct level, and that means around ~2" Hg less than your idle or cruise vacuum. And that is the part that usually requires an adjustable vac can, and tuning the pull-off with a vacuum gauge. A bog means you pulled off too much timing, too fast.

I have tuned a 100 cars like this, and it can add 15-30 HP & TQ at different parts of the curve.

A low 8.2 CR engine like yours typically likes more advance than the older ones.

As long as it runs good, that is really what matters most!
That means you are getting closer to what it likes best.
If you are within 2-4* of the ideal setting for your engine, at every throttle & rpm, you are close enough, and could not feel the difference.
But you are likely 10* low at idle and could feel the difference. For a faster/crisper throttle blip from idle. Probably not while driving. But it would idle cooler.
The rest I can't say.

 

I don't disagree with anything you said. In fact, all good information and advice. My beast just seems to have a different personality.

I've been tuning on this and it is running fabulous. Better than ever.

I was able to up the idle to 16 with no problem. I believe you are right about that. The factory recommendation of 8 is kind of ridiculous. The 12-16 is kind of standard for the 454.

When I put the vac can to manifold, it immediately runs a little rougher. When I step on the gas it instantly bogs down, backfires and runs horrible.

I put it back on ported, and it runs like it should. Fast, smooth acceleration to speed. I'm getting about 32 total vacuum at 3000 rpm

Not sure what I'm doing that's different. On the 383's I've built, I've been able to run manifold vacuum, but not on any stockers. My car does not have the A.I.R pump. Other than that, and the remote coil HEI, it is bone stock.

 

First intelligent thing I heard all day. I too use ported vacuum advance. I see that distributor includes bushing to recurve/limited the mechanical advance. IMO that's much better way to achieve the timing needs for both idle and high RPM operation.

 

I agree only that backfiring means you are over-advanced at that point.
But I can not help you more without some more #s. I know nothing about your vac can for instance.
You could be at 16* initial + another 16* from vac can. Who knows? But it is backfiring.

I will suggest this tuning scenario, in order:

• Set total timing to 36* mechanical only, all-in, what-ever rpm it is.
• Adjust that all-in rpm to around 2800 with spring changes.
• See where the initial idle timing is. Subtract initial from total to see what your centrifugal advance is. Anywhere around 12* with a stock cam is probably good. That would mean you need 24* centrifugal.
• If you feel a need to up the initial, you must change bushings in the distrib to lessen the centrifugal. You can not go over 36* total.
• Then add the vac advance. test it to be sure it is only 8-10* hook it up to manifold vac. Plug-and-unplug at idle so you can verify the degrees. 12* initial + 10* vac should give you 22* at idle with both
• Test your gauge vac # at idle and also normal cruise. Then test your vac can and find out at what vac level in " Hg it begins to pull that 10* advance back off. You will need a hand mity-vac pump for this. That is your vac can "set-point"
• Adjust the vac can "set-point" until it is 2" of vac less than cruise or idle, or slightly more. Not too much more, but it can not be less.

Your backfiring means you are missing one of the tuning steps somewhere.

A high performance street cam with overlap, should like 14-18* initial. But a stock cam, with much less overlap, should only like 8-12* initial. With the 10* vac can on top of that. You kind of confirmed that by it liking 16* initial with no vac. It may like 22 even better.

Listen for light pinging, jerking, trailer-hitching, or backfiring. Any of those means you need a timing curve adjustment.

If you need more detail, check back, or ask Lars for his how to set your timing curve papers.