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Discussion Starter #1
I'm running a Holley SA 670 on my 383 that someone gave me. Like a lot of "gifts" ... well, lets just say I have never stopped fiddling with it. It runs OK up to about 4K but after that there just isn't much. I spent a lot of time yesterday fooling with the ignition and I am pretty sure it is OK, but I don't think the vacuum secondaries are doing much. I pulled the spring out of the vacuum thingy just to force it to come on and it really fell on its face at about 4500 RPM.

I pulled the bowl and the phony metering block off and cleaned them up, and put a purple spring in the vacuum dingus (that's another technical term!:turn:) and it seems to be running a little stronger but not really thrilling if you know what I mean. The jets, by the way are 68s. Let's just say that I sure don't need to worry about over-revving it!:bored:

So finally I get to my question(s).....................

Am I wasting my time with a Street Avenger? What I want is a moderately hot street thug, not a car that I would ever race. So from a user perspective, would I be happier with double pumper?

Someone at a cruise-in told me that the Street Avenger carb is nothing but a 4150 with a fixed metering block on the rear bowl. If that is the case, can I just replace the metering block to get a double pumper?

What do you think?

Dave
 

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I'm thinking if you can't make a Street Avenger work, you aren't going to have any more luck tuning a double pumper. SA's work really well right out of the box--I'd run a 770 on a 383, but the 670 should be fine unless you have a pretty nasty 383. Maybe there's a reason some guy gave it to you! It could have been screwed with and how will you know?

the phony metering block
What's phony about the metering block? It's the same old kind used on millions of other Holley's for many years. Maybe you should give it to someone that knows what they are doing before you make it worse?

And the jets aren't going to have much effect on RPM either.
 

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Discussion Starter #3
Yes, thanks Bowtie. I know there are many folks who know more about how to tune these carbs than I do. I appreciate the advice. However, I am hoping to learn more about how to tune these carbs...maybe from others who have more patience. I am sure there are many on SNS who can help me out with this problem.

Dave
 

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well there are a number of things you might want to look at first one of them is timing. you did say that you got it from a buddy what did he do to it did it work on his car but not your car. and one of the biggest problems is you have to do one thing at a time or you will never know where your at. so lets start from there:
1) check your timing make sure its where you set it if you got a 383 i would set it a 17 degrees inital ( idle ) and then 36 at 3000 rpms ( hopefully you gotta tach )
gonna have to adjust the idle to get it to where you want it

we need more info on your motor cam specs , compression ratio, heads , manifold , ignition system you know all the nitty gritty
 

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Can you just replace the rear metering block and get a double pumper??? No.:no:

Are you still running vacuum advance?

We definitely need more info an your combination. Your problem may not even be your carb. My be weak valve springs.:rolleyes:

Have you checked your throttle position at WOT? Get someone to sit behind the wheel (While it's NOT running) and tell them to floor it and hold it while you look to make sure you're actually getting WOT. Maybe a simple adjustment will fix it?:yes:
 

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my buddy put a 870 SA on his 472 hemi and it runs great out of the box, if the holley is not easy for you then i would switch to a 750 eddy thunder series. from what i understand it like a tuneable square bore Q-jet.
 

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I'm running a Holley 870 SA on my 383 and it runs very good.
 

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Discussion Starter #8
Thanks for the tips guys. Here is some more information on the car.

>'71 Nova coupe so it probably weighs around 3300 lbs
>short block is a 1990 L98, bored .030 and stroked 3.75 with 16 cc dished pistons. CR is about 10.0 and I do have a problem running it on California's 91 octane gas.
>Heads: Scoggin-Dickey stage 2 vortec heads
>Timing: I set it at 35* total then backed off until it stopped knocking. Right now it is about 9* at idle, not the 13*-17* recommended at idle
>Cam: GMPP Hot Cam - 218/228 @ 0.050, .495/.495 lift (w/ 1.5 rockers which I am using), w/112* LSA
>Ignition: Mallory HEI 8548201 - their equivalent to the GM factory HEI...nothing special

So as you can see it is a fairly mild build. I don't know what spring SD uses in their vortec heads, but even the stock GM springs should be able to do better than what I am getting.

Could this be caused by having retarded the timing to stop the knocking on our 91 octane gas?

Thanks again for your thoughts on this...

Dave
 

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Could this be caused by having retarded the timing to stop the knocking on our 91 octane gas?
The lack of timing is going to hurt power, but I don't see why you have trouble running on 91 even with the correct timing. I have just under 12-1 and use 91.
How's the cooling system? If the temperature is well controlled it should be fine on 91--retarded timing will cause it to run hotter, which could make it knock more.
 

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Here's a few suggestions.

Get a fresh set of plugs. Drive around a bit, shut it off (without idling) and get a good reading on the plugs.

Try using one or two steps colder plugs and putting the timing back in a little at a time.

Take the car to a chassis dyno so you can get a wide-band reading on it and verify the secondaries are opening. No matter how hard you rev it in park or neutral, the secondaries will not open unless the engine is under a load.

You may need to jet up the primaries a couple jet sizes. Lean is mean, but on the raged edge you'll find it can be more headaches than added power. You may also need to replace the rear "jet plate" with a metering block so you can actually "Jet" the secondaries as well.

Just a small added note...If the secondaries aren't opening, at WOT and higher RPM levels, the engine will again start to produce vacuum and with a vacuum advance it will start to pull more timing in and cause detonation as well.:yes:
 

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your having trouble running 91 octane on 10 to 1 compression :eek: im running 11 to 1 compression have 36 degrees total timing and no signs of detonation. is your distributer in right or is it 180 out i would pull the cap and bump the motor over to see if it is close to number one and not the fire wall :yes: something doesnt seem to add up just my opinion
 

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Yes, thanks Bowtie. I know there are many folks who know more about how to tune these carbs than I do. I appreciate the advice. However, I am hoping to learn more about how to tune these carbs...maybe from others who have more patience. I am sure there are many on SNS who can help me out with this problem.

Dave
hey PM me and I can help you out. In in the south bay area.
 

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Discussion Starter #14
I thought it was strange to be knocking so bad, too. It was running OK before I tore it down to fix a problem with the rotating assembly. When I did I never pulled the heads or the pistons...just shoved them up into the cylinders. After I put it back together it was detonating like crazy. I figured the gas went bad after sitting for 3-4 months, and it did get a little better when I ran that tank out and refilled it.

I know the dist is in right and not 180 out. I've actually had it in and out 1/2 dozen times checking on things and trying a different dist to see if it made a difference.

Last time I pulled the plugs they looked about right...maybe even a little cleaner than I would expect. I have had trouble with the electrodes getting mashed, so all of them are indexed.

Yeah, the rear "metering" plate has jets, but doesn't have a power valve or individual idle mixture screws. I should have called it a fixed metering block instead of a phony metering block.
 

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I have had trouble with the electrodes getting mashed, so all of them are indexed.
If you're having trouble with "the electrodes getting mashed", it must have domed pistons, Or you have spark plugs that are much longer than those heads require. What plugs are you running? Vortec heads don't have many choices when it comes to plugs in the correct reach.
 

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D-Man, those carbs have jets not the plates.
Too shay. I've been through more Holley's than I'd care to remember, just not as many SA's. I was thinking 3310 series.:rolleyes: Good catch.

Last time I pulled the plugs they looked about right...maybe even a little cleaner than I would expect. I have had trouble with the electrodes getting mashed, so all of them are indexed.

Yeah, the rear "metering" plate has jets, but doesn't have a power valve or individual idle mixture screws. I should have called it a fixed metering block instead of a phony metering block.
Sounds like Bowtie is on to something here. I'd bet there's a 90% chance you've got the wrong plugs in there and the pistons or exhaust valves probably have the witness marks of an unfortunate meeting.:yes:
 

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Discussion Starter #17
You guys are about to convince me the problem is not with the carb or the timing. I'm thinking I must have done something when I rebuilt the engine last winter, especially since I did not have this problem before the rebuild. Especially the detonation! I had 35* total advance before the rebuild with no problems and the car ran just fine. Somehow the detonation and the lack of power must be tied to something else.

Indexing the plugs was because the deck was zero'd and I first used the large gap plugs GM recommends for vortecs. I switched to .035 gap plugs but just kept on indexing them because it was easy to do once I got those shims. Also the pistons are dished, not domed.

Back to the rebuild...I never pulled the heads. Just rolled the engine over on the stand, pulled the rod caps and pushed the pistons up (down!) into the bores. When I went to reinstall the crank I just pulled the pistons back up and torqued the caps down. These are KB 16 cc dished pistons, with a D-shaped dish on one side and the squish on the other. If I happened to rotate a piston 180* in the bore, so the squish was on the wrong side, would that be causing this detonation and lack of power?

Dave
 

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If I happened to rotate a piston 180* in the bore, so the squish was on the wrong side, would that be causing this detonation and lack of power?
That could cause some issues--did you have to index the plugs before you worked on the bottom end? There is no reason the plugs would hit anything unless there is a dome in the way, or the plugs are wrong.
 

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Discussion Starter #19
That could cause some issues--did you have to index the plugs before you worked on the bottom end? There is no reason the plugs would hit anything unless there is a dome in the way, or the plugs are wrong.
Yes I did. No dome and the plugs are correct.
 

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What head gaskets are you running?
 
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