I need some help here guys. My car accelerates very choppy and flutters. It starts at approx. 4000-4500rpm and continues until I shift it(usually around 6000rpm) The problem occurs in either second or third gear... not first. There are no vacuum leaks and the carb is dialed in. The ignition is a new HEI MSD. So, what do you guys think? I recently discovered the problem when I was on the freeway doing 75mph (3000rpm) and floored it. The car accelerated but not smoothly- like it does in first. I had new gears, a locking diff with aftermarket axles put in a few weeks ago, and this was the first time I stomped on it. Im stuck! help.

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70 Chevelle 350ci/th350 10bolt Go Earnhardt Jr.!

Couple of things come to mind:

1)Fuel delivery ie-fuel filter, fuel pump

2) Do you have 12-volts going to the MSD? If you are using the original distributor wire, your not getting a full 12.

3)Plugs and/or plug wires

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-Mark "Some of us got it and some of us ain't." -Deputy Sheriff Barney Fife
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1975 Corvette 396/425 (http://www.chevelles.com/showroom/1BadRat1.jpg) "Wow, that's a mighty strong 350!"
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yeah, I checked the voltage at the coil and its only 11.3. battery voltage was 12.0. so thats a .7 voltage loss. whats the best way to hook up the coil to a solid 12 volt source. I hooked up a fuel pressure gauge today but the gauge leaked inside so I have to replace it tom and then test. theres a reason why i dont run Sunpro gauges. Im also swapping out the plug wires because I think the SUper Stock Accels are not up to par. they are only solid cores. Ive got a set of 8.5 MSDs on the way. And this time Im going to separate each wire by a .5 inch to keep them from crossfiring. I think the ignitoin is either crossfiring or the coil is laying dowm because the poor voltage source. where do I plug in to get a good 12 volt source?

I don't know about a 70, but a 69 has a nice big red wire coming through the harness plug on the firewall. You could tie into that if it is dead with the key off. Mine is hot with the key in run and start positions.

You may also want to check your float level.
If the level is low, it usually does not show up until you hit 2nd gear.

dave

Green70, Here's a few things you can check before you spend any money. They may seem too simple but, without knowing all the details of your set-up, these are just suggestions for things that can cause your situation.
Your ignition system is probably just fine. It's normal to see a slight difference in the voltage at the coil positive terminal and the battery direct because the coil itself applies a small resistance to the ignition circuit with the ignition on. If you disconnect the positive wire from the coil and check the voltage at the wire (not the coil terminal), you will probably see voltage closer to that of the battery. You mentioned that you have an MSD HEI distributor so I'm assuming you don't have a separate ignition module like a 6A or 6AL. If that were the case, you wouldn't read any voltage at the coil until the engine was running, then you would get bit by 450 volts. I believe you have enough voltage at the coil.
Your ignition timing could be over-advanced. Check the timing at idle. Retard what you see at idle by 6 degrees (less timing) and test drive it. It may feel a little sluggish at low rpm but you want to see how it responds at 4000 to 4500 rpm, where your mis-fire is occurring. If the problem goes away or it runs to a higher rpm without mis-fire, then you need to reduce the mechanical advance in your distributor enough so that you can add the initial timing at idle back in but have less timing at high rpm.
Check your spark plug gaps. They should be no more than .035" for your ignition system. The spark plugs should be the correct heat range also. Cross-reference whichever brand plug you use to an NGK '6' heat range.
Your plug wires are NOT cross-firing. If so, they would cross-fire at any rpm so long as you were at or near wide-open-throttle. If you suspect that your wires are cross-firing, open the hood at night, turn off all lights, and, with the engine idling, look for sparks. With someone holding their foot on the brakes and the car in reverse, STAND BESIDE the car and look for sparks. Lightly touch the throttle and look for sparks. If you don't see any, your wires are fine.
Valve-float can cause this exact symptom. Valve-float is absolutely mechanical though, which means that it will happen at the same rpm each time regardless of whether you are at part-throttle or full-throttle. If you leave the car in first gear and slowly accelerate up to the point of the mis-fire and then do the same except start out with your foot down to the floor, you can determine whether it's valve-float or carburetor problems. A lean carburetor will usually run higher rpm before mis-fire at wide-open-throttle than it will at part-throttle. Valve-float always occurs at the same rpm regardless of any other changes you make. Did you change to a different cam and still have old or stock valvesprings? Hydraulic lifters can 'pump-up' and cause this problem but it's rare to see this happen below around 5500 rpm.
1BadRat was correct to suggest checking the fuel delivery. You can troubleshoot this by accelerating at wide-open throttle versus accelerating at part-throttle. Wide-open throttle requires more fuel sooner than part-throttle so the rpm point that the mis-fire happens will change with the amount of throttle applied. A poor fuel delivery system will cause the same problem but at a lower rpm if you are climbing a long hill than it would on flat ground.
However you go about checking these things, change only one thing at a time and then re-test. DON'T CHANGE TWO THINGS AT ONCE! You'll never figure what the problem is if you do.
Don't keep us all in the dark now, we'll all be curious to know what fixes it. That's how we learn and that's why we write.
Good luck,
Louie Hammel