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Discussion Starter · #1 ·
So i got my 69 back from the shop on the 18th after having them do the rear main and putting the flowtech headers on. It cost way more than i budgeted due to unforeseen issues so currently i only have open headers with just 2.5" collectors. Before the headers, with factory exhaust and stock style mufflers, the car would spin about 1/4 the way through first from a dead stop at idle by just stomping on the pedal and pull pretty nicely all the way to second gear, then pull well on into 3rd. Now it will burn all the way through first, shift into second, pull like the dickens halfway through second and fall flat on its face up until 3rd, then pull again and flat on its face... I'd say it feels like it lost half the power on the top end... The only thing that changed is the exhaust. Currently since i have an hei, the hood tach doesnt work so my guess is it's dropping off around 4000 to 4500. I've farted around with the timing, the carb and even tried non ethanol fuel and all i can manage to do is make it miss and idle rough or run worse. I did put a new air cleaner on that hit the hood so i put a 1/2 plastic spacer in and took out the 1" aluminum spacer i had originally, but i swapped all that back to the old stuff and nothing changed so im sure the new air cleaner and spacer have nothing to do with this. Its almost like its loading up on the top end but it isn't blowing black smoke nor does it smell likes its loaded up, plus its only a 600 carb so there's that...

Timing is set at 6deg at idle with the advance disconnected. The vac adv is hooked to manifold vac normally, switching it between port and manifold changes nothing but the idle. my 1970's sears timing light does not have the advance knob so i don't know where its timed with the vac adv hooked up but iirc its in the same place it was before the headers... all adjusting the timing does is make it worse...

XS code 69 350, stock cam (i think), 1971 #94 heads, edelbrock rpm intake, 600 summit carb, pertronics flamethrower hei. stock TH400, 3:23 safety-trac rear.

I'm thinking maybe I need more carb now? My fiance suggests maybe since it has sooo much more bottom end, the top just feels pathetic now...

Thoughts?
 
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Sounds like a fuel issue, but opposite of what you're thinking -- not enough. Engines need more fuel at higher RPM, and won't be happy if they don't get it.

Check the simple stuff first. Could be a dirty fuel filter. I had one that gave the engine vapor-lock after a few miles. Cost me a $600 tow bill because I didn't think of a $2 filter. Carb could also need cleaning, dirty jets maybe. If that's not the problem...

My old man's '69 Judge had a similar issue after an engine rebuild (car had sat for years and he didn't think about rebuilding the carb also), but in all gears. Almost the moment the secondaries opened, the engine would bog and fall on its face. Culprit turned out to be a pinhole in the fuel bowl float that had flooded it with fuel, keeping it at the bottom of the bowl. This prevented accumulation of sufficient fuel for hard acceleration.

Basically, it had enough fuel until you really opened it up, then it fell flat on its face in the same manner you describe. This was on a Q-Jet, not sure if yours is also. I won't promise yours is doing the same thing, but it's a likely scenario, and certainly sounds like it. Unlike loading up, it won't blow black smoke and it won't stumble under certain conditions.

If that's what's going on, possibly the float is just starting to flood, which is why it pulls okay until higher rpm. Another possibility is the accelerator pump. In either case, it sounds like something in your fuel system needs attention. If it's carb issues, I would rebuild if it's been okay until now. One other thing -- the lift pump (mechanical arm pump that feeds the carb) could be going bad also.

Fuel issues really are simple, the engine can't burn what the carb can't give it, and the carb either gives the engine what it gets, or what it can give.

If any of this is the case, though its timing might seem interesting, don't scream at the shop, it's nothing they did, just something that happens over time. Unless they opened the carb to poke a hole in the float, and I really don't see them doing that for an exhaust job.
 

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@Boomstick if you have a stockish 350 with a 600 cfm carb, and it's spinning a posi with 3:23's, through 1st and into 2nd, then you should be the happiest guy on Earth. My modified 400 with an 800 cfm carb, pro billet dizzy with complete timing curve, headers, and 336's won't do that.
 

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@Boomstick if you have a stockish 350 with a 600 cfm carb, and it's spinning a posi with 3:23's, through 1st and into 2nd, then you should be the happiest guy on Earth. My modified 400 with an 800 cfm carb, pro billet dizzy with complete timing curve, headers, and 336's won't do that.
No offense, but it sounds like you've got some tuning issues or perhaps a restrictive exhaust. My old man's '69 400 (also slightly modified) would burn all four gears without moving 10 feet. Of course, it had 4.33s, but it was also a posi. I just think if you have a modified 400 it shouldn't have a problem breaking loose. Carb seems a bit large TBH -- Lots of people go too big on the carb assuming bigger is better, but it is possible too big a carb can hamper performance. Just my $0.02.
 

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Thanks for the thought and advice, but if you do a quick search, you'll see that there's not many areas of my build which havent been dissected to death here, over the last year. 3 dizzys, 2 cams, 2 carbs, 3 sets of mufflers, 2 sets of rockers, 3 coils...

The difference between 336's and 355's is significant... but 433's would be like strapping a rocket pack on tit mouse. IMO, your underestimating the advantage of such low gearing, especially with a 4 speed and shorter car.

As for the carb, I agree that with the chevy and ford crowd "over carbing" is a big issue, but it's usually the opposite with Pontiac. Most people here under carb. Anything less than a 750 on a Pontiac 400, is generally considered a move toward pure economy. That being said, I run an AFR gauge and do my own jetting, so as it sits, Im well on the lean side.

My car will burn the tires a good amount, from a stop at idle, break loose in 2nd, and chirp 3rd at 80mph, with 336's. Yet I agree with you that it seems well under powered compared to my last two Pontiac 400's. However, I think 355's or 373's with a 2800 stall would be a game changer.

I also drive my car far, "a lot", so gearing down isnt high on my list, but I am converting to a manual soon.
 

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I agree with the idea that the most likely cause is it's running out of fuel. If all your filters, including the sock on the fuel pickup inside the tank, are open and not causing a restriction, then the next suspects are the fuel pump itself not being able to keep up with demand, and/or the whole fuel line between the tank and pump needing to be of larger diameter.

Bear
 

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Discussion Starter · #7 ·
@Boomstick if you have a stockish 350 with a 600 cfm carb, and it's spinning a posi with 3:23's, through 1st and into 2nd, then you should be the happiest guy on Earth. My modified 400 with an 800 cfm carb, pro billet dizzy with complete timing curve, headers, and 336's won't do that.
@Boomstick if you have a stockish 350 with a 600 cfm carb, and it's spinning a posi with 3:23's, through 1st and into 2nd, then you should be the happiest guy on Earth. My modified 400 with an 800 cfm carb, pro billet dizzy with complete timing curve, headers, and 336's won't do that.

Sorry, I didn't mean for it to sound like it spins all the way through first, just until it shifts which is quite early, say maybe for 2 or 3 seconds at most at about 15-25mph and it doesn't spin into second but it pulls way more after it shifts. Plus it's one legging and I'm running 275 35 18 nankangs on the rear which are significantly smaller in diameter than 235/15's and are about as sticky as plastic. That's with it just in drive, I haven't tried to shift it manually yet, the shifter still needs adjustment and won't shift to second manually ratcheting it.

Anyway, say I'm sitting at a light, it changes and I mash the pedal, it'll spin for about 2 second, shift and pull well until about 4k and it just falls flat until it decides to shift again and then pulls well until about 4k then falls flat. The more I think about it, the more I think I need to put the 750 Holley back on now.
 
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Sounds lean to me at high RPM, secondaries and or accelerator pump cannot deliver possibly…..fuel pump as Bear noted cannot deliver adequate fuel…or as Anomaly said fuel filter crud died up…

you opened up the exhaust flow improving the flow and therefore the power…..but now the same level of fuel is not enough…..

yes put the 750 back or put a AFR meter in the tailpipe, watch it when it bogs…..bet it goes lean…..bogs…and then pulls back….

lean at speed….first look at those things…..
 

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army - I guess running lean is better than running rich... But how lean? I don't think it takes much either way to affect performance, especially with a larger carb like that. Also, which heads do you have? I understand there are significant flow differences across the five different Ram Air heads.
 

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Discussion Starter · #12 ·
My vote is lean. But I would verify with a AFR.
Are you going to run open headers?



Currently plan is a set of these turned down before the axle:





I got them for $100 off a friend of my dad's. I'm running 2 1/2 inch collectors and pipe to them and welding another collector to the end of the mid pipe so I can take them off and leave the mid pipe if I like or I can take it all off at the header...



I'll probably never take them off, just a cool option to have IMO...



And they're chrome...:cool:
 
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army - I guess running lean is better than running rich... But how lean? I don't think it takes much either way to affect performance, especially with a larger carb like that. Also, which heads do you have? I understand there are significant flow differences across the five different Ram Air heads.
My car is on the lean side now, because of the dense winter air in Jersey. Although I do prefer to be on the lean side anyway, but most around here would recommend that I went a full point richer with my mixture. Which is why I love the Edelbrock carbs so much. I could easily swap out needles, springs, mains, and secondaries, in under 5 minutes, without draining fuel.

The heads are the original 670's.
 

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army - Just a thought (and this could be a good thing) perhaps your suspension is just dialed in that well? I have seen cars that just hook and go if everything is perfect.

Otherwise, I assume you're running premium. Having traveled the continental US coast-to-coast driving trucks, as well as knowing someone who lives in Washington state, I know that certain locations require different octane ratings for altitude (85 octane for example), which affects the oxygen content of the intake air. Perhaps some octane boost or racing fuel would give that extra oomph that is missing?

I wonder if this might apply to predominantly cooler / colder climates also regardless of altitude. Say, for instance, your engine might do everything expected on 93 octane at say, average temps of 70 degrees, but perhaps average temps of 50 would stifle it somewhat. Also, I found some interesting info on the 670 heads you mention. Maybe all this was already done to yours, but might be worth a read.
 

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Discussion Starter · #15 ·
My car is on the lean side now, because of the dense winter air in Jersey. Although I do prefer to be on the lean side anyway, but most around here would recommend that I went a full point richer with my mixture. Which is why I love the Edelbrock carbs so much. I could easily swap out needles, springs, mains, and secondaries, in under 5 minutes, without draining fuel.

The heads are the original 670's.
I cant decide between a 750 edelbrock or a 750 summit... i already have a 600 summit (knock off of the holley 4010) and ive been pretty happy with it on this car thus far so i might go that route...

just like the4800 vs 4801 cam, i cant decide summit vs edelbrock...
 
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I cant decide between a 750 edelbrock or a 750 summit... i already have a 600 summit (knock off of the holley 4010) and ive been pretty happy with it on this car thus far so i might go that route...

just like the4800 vs 4801 cam, i cant decide summit vs edelbrock...
Well, if you go with the Edelbrock, you'll want the AVS2, which is only available in an 800. It has dramatically improved fuel atomization, for better response, etc.

Obviously, @PontiacJim and I are going to push these, because they're very easy to tune and they just work... That being said, I don't need to tell you that aside from us, Earth will tell you to get a Holley.

One thing I will say is that in order to compare apples to apples, always include the price of fuel lines, gaskets, regulators, pumps, and jet kits... IF necessary. The Eddy carbs have unique fuel inlets, as do Holleys, and they don't like more than 6 psi of fuel pressure, so you'll either want a regulator or the Edelbrock fuel pump.

The advantage to the fuel pump is that it's a high performance, clockable, rebuildable unit, which many of us use with or without Eddy carbs, just because it's great.

And... Jets. Unless you're planning on luck, might as well get the jet kit, too.

FYI, if your heat crossover is active, Edelbrock also makes a heat insulating gasket. Which works well.
 

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Discussion Starter · #18 ·
Well, if you go with the Edelbrock, you'll want the AVS2, which is only available in an 800. It has dramatically improved fuel atomization, for better response, etc.

Obviously, @PontiacJim and I are going to push these, because they're very easy to tune and they just work... That being said, I don't need to tell you that aside from us, Earth will tell you to get a Holley.

One thing I will say is that in order to compare apples to apples, always include the price of fuel lines, gaskets, regulators, pumps, and jet kits... IF necessary. The Eddy carbs have unique fuel inlets, as do Holleys, and they don't like more than 6 psi of fuel pressure, so you'll either want a regulator or the Edelbrock fuel pump.

The advantage to the fuel pump is that it's a high performance, clockable, rebuildable unit, which many of us use with or without Eddy carbs, just because it's great.

And... Jets. Unless you're planning on luck, might as well get the jet kit, too.

FYI, if your heat crossover is active, Edelbrock also makes a heat insulating gasket. Which works well.
I think you've talked me into the Edelbrock...
 
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Discussion Starter · #19 ·
Is the factory fuel pump going tp be ok with the 800 eddy? The 600 handles it just fine.
 

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Is the factory fuel pump going tp be ok with the 800 eddy? The 600 handles it just fine.
It will probably be fine. I've run their 600 carbs on a couple cars, both with stock fuel pumps and never had a problem. I think the issue comes on high HP applications where a super high volume pump is used, with the increased flow capabilities comes higher fuel pressure. Then a regulator is needed to step down the pressure. If you look, Edelbrock sells two different pumps for the Pontiac. You would need to lower GPH pump. If your 600 ran fine using the stock pump, I can't think of any reason that the 800 wouldn't as well. That all being said, an 800 cfm carb on a 350 may be too much for it. Like others have said, your fueling issue could be further up the line and it just came to head when you installed headers and open exhaust.
 
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