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69GPModJ · 05-11-2004, 06:29 PM

This isn't really a "racing question" but I think it applies.

I've got just under a thousand miles on my new 468 and I've had the car WOT a few times but never over about 4,500 RPM. This afternoon I took it out to one of our local highways and let'er rip.

Above 4,500 RPM the car starts to miss, pop, and lose power. Don't want this happening when I *do* take it to the track.

Until just a few miles ago the carb was way too rich but I've changed the jets. I've got a new set of plugs to install in case the old ones are fouled. While I'm at it I'll make sure none of the plug wires aren't touching anything--though they don't arc at low RPMs.

What else should I look for?

I'm running the following:

- HEI with new cap, module, plug wires
- Autolite 3924s with 0.045 gap
- Holley 950 with 76s in front & 78s in back
- 1/2" fuel line from tank to carb
- Holley fuel press. reg set at 6 lbs
- Holley electric fuel pump (sorry don't remember which one--not my install--just know it's LOUD)

69GPModJ · 05-11-2004, 06:29 PM

This isn't really a "racing question" but I think it applies.

I've got just under a thousand miles on my new 468 and I've had the car WOT a few times but never over about 4,500 RPM. This afternoon I took it out to one of our local highways and let'er rip.

Above 4,500 RPM the car starts to miss, pop, and lose power. Don't want this happening when I *do* take it to the track.

Until just a few miles ago the carb was way too rich but I've changed the jets. I've got a new set of plugs to install in case the old ones are fouled. While I'm at it I'll make sure none of the plug wires aren't touching anything--though they don't arc at low RPMs.

What else should I look for?

I'm running the following:

- HEI with new cap, module, plug wires
- Autolite 3924s with 0.045 gap
- Holley 950 with 76s in front & 78s in back
- 1/2" fuel line from tank to carb
- Holley fuel press. reg set at 6 lbs
- Holley electric fuel pump (sorry don't remember which one--not my install--just know it's LOUD)

goatseeker · 05-11-2004, 06:38 PM

Kerry,
Check out my thread below on this very same subject. I have been trying to trace this same problem on my car and think I may have it solved. Hopefully my experiences will save you some time and aggravation.
I don't know how to post a direct link - but look just a few topics down from yours in this forum.
Tim

High rpm misfire - help?

69GPModJ · 05-11-2004, 06:47 PM

You're right. Lots of good suggestions there. I'll give some a try and see if they make a difference.

Half-Inch Stud · 05-11-2004, 06:49 PM

...try a Q-Jet and see if the problem goes away.

HIS

69GPModJ · 05-11-2004, 07:12 PM

Hmmm... Don't have one laying around--only another Holley.

issach428 · 05-11-2004, 07:31 PM

fuel delivery??? Are you running power valves? If you have good vacuum and too low of power valves you will lean out realy badly at wot once the vacuum rises. I recently did this, put in the proper power valve and it fixed the problem. Float level set correctly? Clean fuel filter?

69GPModJ · 05-11-2004, 07:49 PM

It's possible it's fuel delivery. Not too long ago I got some crap stuck between the needle and seat, which made the carb puke fuel into the manifold--so much so it wouldn't run.

I'll check the fuel filters.

Regarding the power valves, yes, the carb has them--30 cc versions (I'm assuming power valves are the same thing as accelerator pumps). The carb is a Holley 950 HP. I'm a carb know-nothing but mine has mechanical secondaries. Do the power valves still operate on vacuum. I'd assumed not.

Paul Spotts · 05-11-2004, 08:00 PM

Make sure you have 12 volts to the HEI distrib. If you use the coil wire (from the car's harness) from a points coil (on a pre 74 car - you have a 69 GP?) then you do not enough spark

Early Pontiacs with points run a resistance wire to the coil that knocks the votage down from 12 volts to approx 9 volts

It does sound more fuel related though

mrdan7 · 05-11-2004, 08:55 PM

Great suggestion Paul, without that $6.00 replacement wire, the car acts just like fuel cut-out at higher RPM's.

MRDAN7

69GPModJ · 05-11-2004, 09:18 PM

The fellow who had the car before me did the HEI conversion, had the car for 20 years, has been a mechanic for more than 20 years, and the wire you've pictured looks just like the connection to the HEI unit.

Moreover, the original 428, which had the same HEI unit ont it, revved like a trooper as far as you'd push it.

goatseeker · 05-12-2004, 04:42 AM

Anyone have any idea what was the reason for the resistance wire? Why did they not want 12V going to the coil in the older model ignitions?

6567GTO · 05-12-2004, 05:01 AM

Guys, My 65 was misfiring last year too and I may still have the original resistance wire in my 65. I'll have to look but how far back does this wire travel? To the ignition switch?

Phil

mrdan7 · 05-12-2004, 05:52 AM

6567GTO-Phil, The Resistance Replacement wire, starts at the HEI, & goes all the way into the fuse-block at the firewall.
Remove the fuse block at the firewall under the hood, and make certain you have the correct wire before removing. I would suggest getting the wire from PY, as theirs has the correct connector that plugs right into the Fuse-Block. The one I posted is from Summit, notice it does-NOT** have the correct metal pinch type connector for the fuse Block end, also it is not long enough and you do not want to splice THIS WIRE AT ALL. I can post a pic of an old one if you need it. MRDAN7

mrdan7 · 05-12-2004, 06:24 AM

MO-CRAPP-OUT... Here is an actual pic of the resistance wire I removed from my 70. Notice the Metal-connector present, this plugs into the firewall Fuse-Block, under the hood-side. You new wire should have this connector on one end, as well as the HEI Plastic coupler that fits into your Newer-HEI-Distributor.For my application the new wire needed to be 3 feet long, PY sells these I believe. BIG-TIME-DIFFERENCE. I have seen 30 year mechanics miss this trick! Then replace entire fuel systems, and upgrade to Ignition systems that were beyond what they could actually use!!

GTO · 05-12-2004, 06:30 AM

The resistor wire was used to drop the voltage while running so you would not burn your points. On start up, I believe you bypassed this resistor wire and put full 12V on your system. This would help give you more spark for starting. ... Eric.

69GPModJ · 05-12-2004, 07:54 AM

Well, I'll have a look at that too. Don't want to miss something because I *think* someone else has taken care of it.

6567GTO · 05-12-2004, 08:46 AM

Thanks MrDan7! I'll check mine out. I did replace my original under hood wiring harness a few years ago with one that I purchased from PY.

Kerry, didn't mean to hijack your thread.

Phil

69GPModJ · 05-12-2004, 08:57 AM

No problem Phil.

Between this thread and the earlier one, there's got to be a solution.

TinInjun · 05-12-2004, 03:35 PM

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by MRDAN7:

MO-CRAPP-OUT... Here is an actual pic of the resistance wire I removed from my 70. <HR></BLOCKQUOTE>

News flash. That isn't your resistance wire. The resistance wire on a '70 is under the dash. It it black with pink print. It runs from the ignition switch the the bulkhead connector in the passenger compartment.

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