650 double pumper - Team Camaro Tech
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post #1 of 16 (permalink) Old Jul 20th, 03, 07:25 PM Thread Starter
 
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Hey Guys,I've got a question. I'm runnig a 650 Holley double pumper on my '68 RS/SS. The engine is a LT-1 from a '70 Vette or '701/2 Camaro. It's got a Edelbrock Performer RPM intake and a pair of 202 turbo heads, which I think are like the first generation Bowtie heads today. Running a set of Hooker Supercomp 13/4 headers. Ever since I've had this car the carb has idled very rich. I mean the exhaust will burn your eyes. I checked the vacuum but don't remember what it was. Anyway, I was told I could get a power valve with a lower number and it should clean up the idle. If I remember right, the idle cvacuum was like around 6 inches. I'm running a power valve that is stamped 52. Meaning 5.2 inches of vacuum before it will open. Should'nt that be a low enough number on the power valve to keep it from opening at idle? Is there something else to check? Thanks, Matt. P.S. It also has a M21 and 410 12 bolt posi.
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post #2 of 16 (permalink) Old Jul 20th, 03, 08:22 PM
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Holley recomends at least 2" lower than idle vacuum in a performance application and half the idle vaccum in milder applications.

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post #3 of 16 (permalink) Old Jul 21st, 03, 04:43 PM Thread Starter
 
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I'll try it. Thanks DjD. Matt
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post #4 of 16 (permalink) Old Jul 22nd, 03, 03:03 AM
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Your vacuum reading sounds pretty low for a stock LT1 engine. It would be a good idea to swap in a new power valve but I would set the idle fuel/air mix, float levels, and idle speed first.

Adjust the float levels first, then set the A/F mix screws for the highest vac reading. Your idle speed will probably increase so you will probably need to reset the idle speed. Once you have the idle all set, re-read your idle vacuum and divide by two --- that is the number of the PV you need to get.

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post #5 of 16 (permalink) Old Jul 23rd, 03, 12:56 PM Thread Starter
 
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Thanks Eric68, I'll try it. That vacuum reading was off the top of my head. I'm going to check it tonight. Matt
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post #6 of 16 (permalink) Old Jul 24th, 03, 02:53 AM Thread Starter
 
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Well, I was able to recheck my idle vacuum. It's between 12 and 15 inches depending on idle speed. I have about a #50 power valve in the carb so I would think it would be ruled out. I have my base timing around 10 degrees with an Accel dual point. Does that sound right? Any less timing and the idle goes down and I would have to screw the idle needle in more. If there's a posibility I'm running on the primaries, that would make it worse. Matt
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post #7 of 16 (permalink) Old Jul 24th, 03, 03:52 AM
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Do you know what your fuel pressure is? Holley's should be less than 8 psi or you can push fuel past the seat. I had that.

Also, I had a loose power valve that was allowing gas to flow past it. Can you see fuel dripping down the carb throat when it's idling?

My experience was on a 700 DP.

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post #8 of 16 (permalink) Old Jul 24th, 03, 10:10 AM Thread Starter
 
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I haven't looked for fuel yet but I will. My fuel pressure was 6 1/2 psi. I dropped it to 5 just to make sure. Matt
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post #9 of 16 (permalink) Old Jul 24th, 03, 01:23 PM Thread Starter
 
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I haven't looked for fuel yet but I will. My fuel pressure was 6 1/2 psi. I dropped it to 5 just to make sure. Matt
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post #10 of 16 (permalink) Old Jul 25th, 03, 09:43 AM
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I liked 6-1/2 psi better 50 for a power valve doesn't sound right to me . . . you read the numbers clockwise and the number will typically end with a 5. Like this "O 6 5" means you have a 6.5" power valve. Which BTW is what you want for an engine with 12" minimum - a 6.5" er

Good luck.

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post #11 of 16 (permalink) Old Jul 25th, 03, 04:44 PM Thread Starter
 
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I think it read something like 50 or 52. Don't remember. I'm gonna pull the front bowl off and put a new power valve anyway. I think my carb kit came with 2 6.5's and another one that I can't read the number on. I think it started with a 5 though. I'll try a new one. If you think the 6.5 will work I'll try that one. Matt
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post #12 of 16 (permalink) Old Jul 26th, 03, 07:06 PM
 
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Its just the nature of the beast with a Double Pumper that it will idle rich since they are meant for big, loopy cams and when you put them on mild engines they always seem to run a little rich.

If ya get a chance take off the metering block and compare it to say a 750 Vaccum Secondary carb. I did and the passage ways are a lot bigger on the DP and if you look at the Idle Feed Restrictions holes they are nearly twice the size. You could always epoxy them up and drill them smaller to keep it from running rich at idle or do what i did: I installed a 750 VS primary metering block on my 650 DP and the idle cleaned right up and the car is much more responsive and doesn't dump as much fuel in it. I have a 350 with a very mild 203/212 cam and that carb was running dead rich on idle before no matter how much I played with the idle mixture screws.
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post #13 of 16 (permalink) Old Jul 27th, 03, 06:14 PM Thread Starter
 
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Hey guys,
I really appreciate everybodys help. I think I've got my carb adjusted about as good as I can hope. I pulled the front bowl off yesterday and changed the power valve. The one I had in it before had a 5 and some other number on it. Can't really remember which one I had in it. Anyway, I took Eric 68's advice and put a new 6.5 in it.
I replaced the plugs with new R44TS's. I sanded th epoints and checked them. They were about .018. I set the base timing at 10 degrees. Ran the valves and adjusted to .018 on the intake and .020 on the exhaust.
The idle has cleaned up quite a bit and is tolerable.
Took the car for a nice little ride and it feels pretty strong!! I get a small stumble after a shift so if ya'll have any suggestions, I'll listen.
Also, any comments on my valve clearances would be appreciated. It's the stock LT-1 cam from 70 Vette's and 701/2 Camaros. I using Erson roller rockers at 1.5 to 1.
Thanks for everyones help. Matt
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post #14 of 16 (permalink) Old Jul 27th, 03, 06:17 PM Thread Starter
 
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P.S. I checked the primary jets, their 67's. Matt
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post #15 of 16 (permalink) Old Jul 28th, 03, 02:04 AM
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Chilton's, copyright 1973, states "Int .024", Exh .030", goes for all except Z/28 302, 30/30 for both.

AllGo has the right idea. You might search the Class ads, garages, etc. for a junker Holley 3310 to swap the primary block.

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