Crapp'n Out at higher RPMs

[GPModJ]

I've got just under a thousand miles on the new engine 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.

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)

[triple66]

Have you got a rev limiter in the ignition? They have been known to have component failures and cause that sort of trouble.

[GPModJ]

No, no rev limiter. Maybe in the future but not yet.

[Pontiacshack]

Well, it sounds a lot like the problem I had. The first time I went to Mission, the car started to crap out right at 5100 rpm. I first thought it might be the Canadian air :wink: , but soon found out the coil had gone bad. I installed a new one and problem solved. I was running an MSD coil and box, so I'm not sure if the HEI coil would fail in the same way, but it sounds just like the problem I had. Good luck.

[GPModJ]

Thanks for the tip. That'll be one of the things I follow up. The coil is original to the HEI unit (at least as far as I know), so maybe that's a place to look.

[THOR]

I hope it's an easy fix, good luck pinpointing the problem, it's driving season and you're probably jonesing to eat some fried rice and to chase that down with a 5 liter something !
Are you planning on a Tiger Run trip or bringing the GP to any events like Langley cruise, or Mission Drags, or a NW Legends event around Seattle?
I'd enjoy seeing that beautiful GP !

[GPModJ]

I'm going to try making as many events as I can this year, starting with Tiger Run. However, if I make it to Tiger Run, it will likely be for one day only.

I'm also thinking of making it over for the Mission Drags (though I don't know if I'll run the car there).

Anyway, I look forward to meeting some Legends!

[Unknown_Authority]

Normally that sounds like a fuel starvation problem, but with 1/2 inch line and an aftermarket pump maybe not. Maybe the timing is too advanced? What are you running for total advance? Is this the EFI motor? Can you hook that up to a laptop and see what's going on? Good luck.

[GPModJ]

No, it's not an EFI engine. I've got a Holley 950 HP.

Most people have been pointing me toward fuel starvation problems. Like you, I don't think that's it but I'm going to go through that stuff anyway if some of the simple stuff doesn't do it.

Would insufficient jets cause such a problem? I'm asking because I just switched from 78s (come with the carb but proved much too rich) in the front to 76s. Maybe I should try some 77s.

[triple66]

The stock HEI modules were notorious for high RPM missing. Yours is lower than the usual problem, but it is worth checking. Also the end play in the distributor shaft can cause strange things if it gets excessive. As Stef mentioned, those coils are not always trustworthy either.

Hey, are you in for the club drags at Mission on June5/6?

[GPModJ]

The module is an MSD unit--at least that's who manufactured it. Also, the coil is apparently an MSD unit too. I've replaced the cap with a new MSD unit, as the old cap was almost burnt through at the top where the button connects to the coil. The only thing I haven't touched yet are the springs and rotor.

Distributor end play is something I haven't checked but that I'll put on my list.

Regarding the Club Drags, I'm planning to be there but I don't think I'll be running the car. Aside from the current issue, I still have some stuff to do before I run it.

My Dad and sister live in Mission so I might make a weekend of it if I can set aside enough time.

[THOR]

A shot in the dark but among the things I did when I put the 468 in my car was to take the sock off of the pickup inside the tank per SD's recommendation. I

[GPModJ]

Okay, another good tip to follow up. Thanks. :)

Since SD recommended it anyway, I'll probably just go ahead and do it. 8)

[theJUDGE]

I babied my rebuilt Ram Air III motor for 500 miles, then pinned it going onto the freeway.
To my disappointment it did what you are describing at high RPM.
I put a fresh set of plugs in it & problem solved. Rearview mirror rubber..8)
The lugging around pussy driving fouled up the plugs for me, but the mentioned "too rich" conditions you experienced & fixed may have fouled up your plugs.
I hope it's your easy fix too. :idea:

[GPModJ]

I'm hop'n the same thing. The plugs and plug wires are the two things that get checked first--this Saturday.

[THOR]

Any word on this GPMod ??

[GPModJ]

Actually, your question is timely. I just got back from taking the car for a burn and it revs all I need without complaint.

The problem? Fouled plugs.

Heh, heh. I feel a little stupid. I didn't think it would be the plugs, though I knew it was running rich for awhile. It ran for only a couple hundred miles with new plugs before I swapped 76 jets for the 78s the carb came with. Yet, it seems the new plugs got fouled in that short span.

So, yet newer plugs and it's running fine. Plugs look better too with the new jets. :P

At least it wasn't something hard to track down.

[THOR]

The wisdom of The Judge, Mark D, is spot on here. Glad to hear that it was such an easy fix. Now for the next questions...How does that baby feel from 4,000 to about 5,200 or so RPMs ? Are you bringing the tasty GP to Tiger Run?

[GPModJ]

The car pulls great from 4,000 to 5,200 but I think there's more there. I'm going to swap bigger jets (77s) up front to see if that makes a difference and also check to make sure the throtle is opening all the way.

When I broke the gas pedal, the pedal rod broke and I welded it back together. Unforunately, I welded it crooked and had to adjust the linkage as a result. Consequently, there may be a bit more throttle than I'm getting right now.

Regarding Tiger Run, right now it's not looking as though I'll make it. :cry:

However, I'm going to be at the All Pontiac Show in Surrey on the 6th and am trying to make it over to Mission for the 5th for the Club Drags (though I probably won't run my car).

[THOR]

That's right ...mr. leadfoot, you broke the gas pedal, you are a major league leadfoot, just like me :lol: Too bad you won't make TR, another time later in the season perhaps

[GPModJ]

ROTFL!!! I replaced the welded pedal and rod with another one my friend dug up. I put them side by side and, not only did I weld the rod on crooked, I bent the pedal itself. When you look at the pedal I removed, it now has a curve in it! Man I didn't realize I'd been tromping on it like that.

I think it had something to do with the fact the throttle wasn't opening fully. It seems that since I welded the old pedal rod, I wasn't getting full throttle. I crushed the pedal trying to squeeze that last bit of juice out of it. Now I am--and what a difference. :twisted:

I'm sorry I'll be missing Tiger Run too. I know I'll be making one or two events this year though so I'll still get a chance to meet some Legends. :)

[THOR]

Hehehe, yes, 1,000 PSI or so on the pedal will break it :twisted:
I cannot say that I have EVER heard of anybody breaking a gas pedal.
You must have a rather large green right leg sort of like the incredible hulk

I'm not sure where I read it but I believe that Milt Schornack, famed racer and supertuner behind the Royal Pontiac performance program, broke a Hurst shifter handle on his 4 speed in half during a race, I'd bet that the shifter breaking is more common but you would still have to really slam the thing to bust it !