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Old 07-05-2008, 02:45 PM
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Popping & Banging Under Heavier Throttle...

Hey guys I recently picked up a '69 C10 SWB for a little truck project that me and the better half can do together.

Anyway, it has a late '70's 350 engine in it (junkyard special I am sure) and it idles and drives normal very smooth. However, anytime I get into the throttle past half way and the engine speed goes up it starts missing and popping/banging through the exhaust. I can feel the loss of power as well.

Its got a HEI distributor already, but I went ahead and changed the cap, coil, rotor, plugs, wires, etc. and I played with the timing (10* initial). I also swapped the carb out for another one and still nothing has improved. I haven't pulled any valve covers yet, but I don't hear any unusual valvetrain noise.

Ideas?

Thanks guys!!

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Old 07-05-2008, 02:52 PM
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Check the firing order again, pay special attention to 5 and 7 they are real easy to mess up as they are next to each other on both ends. You could also have tight valves or something wrong in the ignition system. A bad module can wreak havoc. I would also throw a vacuum gauge on it and check for at least 18 at idle.
Does it only do it when under a load, if so you could have bad wires.

Chet
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Old 07-05-2008, 03:02 PM
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I have 21" at idle, I ohm checked the wires (all good), and I guess I can check the wire order again, I only pulled them one at a time when I was testing them.
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Old 07-05-2008, 03:04 PM
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as tbucket 23 said a bad module can wreak havoc. sounds like a module to me
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Old 07-05-2008, 03:09 PM
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21 is great, is it steady. An OHM test wont show a leaky wire or a cracked plug they usually show up only under load. If the vacuum is steady I dont think you have tight valves. Have you checked the plugs.


Chet
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Old 07-05-2008, 03:11 PM
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Quote:
Originally Posted by 1drwgn
as tbucket 23 said a bad module can wreak havoc. sounds like a module to me
I have another module so I'll swap them out.

Quote:
Originally Posted by T-bucket23
21 is great, is it steady. An OHM test wont show a leaky wire or a cracked plug they usually show up only under load. If the vacuum is steady I dont think you have tight valves. Have you checked the plugs.


Chet
I haven't checked the plugs because I just changed them AFTER the popping was already present.
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Old 07-05-2008, 03:13 PM
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You got a leaky spark tube...
 
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Have you checked your timing?
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Old 07-05-2008, 03:18 PM
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Quote:
Originally Posted by Blazin72
Have you checked your timing?
Quote:
Originally Posted by Ford_Assassin
.....and I played with the timing (10* initial).
Thanks anyway!!
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Old 07-05-2008, 03:49 PM
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I personally have never seen a bad module do that I have however seen pickup coils do that. It might not be a bad idea to check that as well as fuel quality...
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Old 07-05-2008, 03:50 PM
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Quote:
Originally Posted by HalfOunce
I personally have never seen a bad module do that I have however seen pickup coils do that. It might not be a bad idea to check that as well as fuel quality...
Either have I. My experence with modules is they work or they don't. 91 octane in the tank, all the time.
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Old 07-05-2008, 07:26 PM
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You got a leaky spark tube...
 
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Quote:
Originally Posted by Ford_Assassin
Thanks anyway!!
Oops, my mistake. And to think I actually read the thread twice to make sure I didn't ask a question that was already answered.
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Old 07-05-2008, 07:58 PM
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Valve springs are toast.
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Old 07-05-2008, 10:16 PM
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Quote:
Originally Posted by techinspector1
Valve springs are toast.

What he said or the cam has some flat lobes.
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Old 07-05-2008, 11:55 PM
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Okay pulled the valve covers and had my girlfriend crank the engine to check to see if all the rocker arms were moving up and down like they should. They don't, or at least #5 exhaust valve isn't. So I got a flat lobe which crossed my mind before, but really was hoping it was something cheaper and easier.

But I guess it isn't all bad, I really didn't like the heavy grease and grime caked all over the motor (a pet-peeve of mine). So I guess I'll be yanking the engine next week and changing a cam and valve springs/retainers/locks/seals/etc. While the motor is out and partial apart I am going to clean the motor inside and out and then paint it a nice orange (its currently Chevy late '70's blue). I figure for good measure I might as well change the oil pump and the timing chain set too.

As far as cam selection I think I am going with the cheap and easy route and buying a Summit cam kit 1102 (.420/.442" lift, 204/214 dur@.050" 112 lsa) for $90. I heard several guys running 1102's in Target 350 crate engine with great results.

I am keeping it pretty mild considering this engine is a bone stock late '70's SMOG era 350 with maybe 8.0-8.5:1 compression with unknown amount of miles.

I've ran the Summit 1103 cam in a 355 with 9.5:1 compression and it did well. I figure a step down with less compression and it will still do pretty well.

What do you guys think 1102 okay?

Thanks again.
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