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Discussion Starter #1
My buddy has a k20 that I'm looking at buying. Its got a 350 with aluminum heads, a Comp 4x4 cam, lifters, springs pushrods, longtubes, carb, and I'm sure some other things that I'm missing. The only issue is the motor just doesn't seem to run right. Its got low power and backfires. The cam is flat tappet, and he used stock length pushrods, which is what I think might be the issue. Anyone got an idea what the issue might be?
 

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Just some fuckin guy
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did he measure before he just threw the pushrodes in? could be alot of shit.
 

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Backfiring would be timing?
It can also be from the valvetrain. I was building a 327 for a friend when I was in High School. While I was out of town for a couple days he decided to finish it up and drop it into his blazer. Damn thing would throw 3-4 foot tall flames out of the carb... He thought you just bolted the rockers down....
 

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Discussion Starter #7
Backfiring would be timing?
Yeah it definitely could be timing, it idles way tougher than it should. I’m not really familiar with 350s so I’m kind of going into this blind. I know enough to work on them without messing stuff up but I’ve never owned one before. I have to swap the aluminum “Vortec” heads back on so when I do that I’ll verify that everything’s correct. Is there a good resource to learn how to adjust timing?
 

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n. fil-dert.
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No there is nothing on the internet about adjusting timing. It's a relatively new concept.
 

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No there is nothing on the internet about adjusting timing. It's a relatively new concept.
lolol. I was just wondering if there was a resource that was better than others. I'm so new to this I just don't know where's best etc. The simpler the better.
 

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What year is this for? are you running a carb or efi? What distributor? Now you are talking about putting aluminum vortec heads "back" on. Vortec heads aren't usually aluminum stock, in fact I was pretty sure they never were.
 

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What year is this for? are you running a carb or efi? What distributor? Now you are talking about putting aluminum vortec heads "back" on. Vortec heads aren't usually aluminum stock, in fact I was pretty sure they never were.
Sorry I should have made that clear. My buddy originally put the original ported heads back on because he was going to sell the aluminum ones separately, but as part of the deal I'll be getting the aluminum vortec style heads. And they're not true vortec heads, but they are according to him the same style.
 

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That makes sense, they are just aftermarket heads. If you do put them on then you will need a new intake manifold too. They don't interchange.

You should also check that the advance mechanism in the distributor is working properly. You will need to disconnect the vacuum advance hose from the distributor and plug it with something. Check the base timing, you should be around 8 degrees at idle, then rev the engine up to around 2000 rpms and the advance should be closer to 26-30 degrees. Once that is done, plug your vacuum advance hose back in. There are tons of things you can do to optimize timing for better power/response, but if you are close to this then it won't cause problems.

A basic google search for small block chevy valve lash adjustment, should give you plenty to read through. You will need to know if you have hydraulic lifters or solid lifters. if you can set the proper valve lash without throwing the rocker arm at extreme angles then you should be fine. The beauty of adjustable valve train.
 

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Discussion Starter #14
That makes sense, they are just aftermarket heads. If you do put them on then you will need a new intake manifold too. They don't interchange.

You should also check that the advance mechanism in the distributor is working properly. You will need to disconnect the vacuum advance hose from the distributor and plug it with something. Check the base timing, you should be around 8 degrees at idle, then rev the engine up to around 2000 rpms and the advance should be closer to 26-30 degrees. Once that is done, plug your vacuum advance hose back in. There are tons of things you can do to optimize timing for better power/response, but if you are close to this then it won't cause problems.

A basic google search for small block chevy valve lash adjustment, should give you plenty to read through. You will need to know if you have hydraulic lifters or solid lifters. if you can set the proper valve lash without throwing the rocker arm at extreme angles then you should be fine. The beauty of adjustable valve train.
Okay thank you for the info that really helps. And I do have a manifold etc. that works with those heads. Hopefully by next week I'll have it done.
 

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The numbers on the distributor won't be needed. Just was curious if it was an electronic ignition vs points style. Most likely I would suspect it is an HEI distributor.
 

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lolol. I was just wondering if there was a resource that was better than others. I'm so new to this I just don't know where's best etc. The simpler the better.
Timing came to my mind , too . Vheck YouTube videos .

I would think you could loosen off the rocker arms & get some rough measurements ?

Wyr
God bless
 

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My buddy has a k20 that I'm looking at buying. Its got a 350 with aluminum heads, a Comp 4x4 cam, lifters, springs pushrods, longtubes, carb, and I'm sure some other things that I'm missing. The only issue is the motor just doesn't seem to run right. Its got low power and backfires. The cam is flat tappet, and he used stock length pushrods, which is what I think might be the issue. Anyone got an idea what the issue might be?
It is most likely valve lash to tight, you haven't mentioned anything that would change push rod length much.
 
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