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Old 04-08-2017, 01:20 PM   #1
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383 big cam will not idle

I have a 383 with 3/4 cam edelbrock aluminum heads roller rockers and 30 over pushing 365 horsepower on the dyno at rear wheels . It has a performance intake with a Carter 650 or 600 carb. I have had 2 people go over the carb adjustments timing etc , it has electronic msd ignition and distributor has new msd wires. it runs great besides at idle it is high 1200-1300 rpm and drops to 800-900 when put in drive. It has a 2800 stall . We tried new metering rods and different colour springs in carb., and cleaned it up . I have spent $400 at each shop because I don t do carbs and one shop said put a Holley 750 on it . The second guy claimed he could set it up and the result was similar try a bigger carb. I am half way into a fuel injection conversion at this rate and need help before taking it back to a shop to spend more . What could I try next I guess any ideas.
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Old 04-08-2017, 05:03 PM   #2
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Your second guy hit it right on the money... Needs more carb...
I found the 780 CFM Holley work best for me...
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Old 04-08-2017, 05:07 PM   #3
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easy -

Can't see it from here, but what you're describing is a vacuum leak.
Also, there's no such thing as 3/4 cam... without the actual specs, it doesn't really tell us anything.

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Old 04-08-2017, 05:22 PM   #4
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Quote:
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easy -

Can't see it from here, but what you're describing is a vacuum leak.
Also, there's no such thing as 3/4 cam... without the actual specs, it doesn't really tell us anything.

Archer

Just an old school term for a 0.375 lift cam... like the old Isky .375 or 0.400 lift cam... OR 3/4 track cam.

It was a cross between a hot street cam and just short of a race cam...

Cool old hay day stuff... Sounded really tough.... I still have one for a Chevy engine...

Last edited by RacerHog; 04-09-2017 at 05:38 PM.
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Old 04-08-2017, 05:26 PM   #5
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3/4 Race Cam Reading... :)

This article was based of the Fords.... But the concept is still the same....

http://www.tildentechnologies.com/Ca...rformance.html

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Old 04-08-2017, 07:57 PM   #6
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I have got to say that I have not heard the term " 3/4 cam" in a long time. Brought back some good memories. Check for vacuum leaks. If your running power brakes, plug of that line and see if it changes the idle.
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Old 04-09-2017, 05:57 AM   #7
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Bob -

I know the term, but like I said, today, it's pretty much meaningless. Actually, a lot of people thought it was meaningless 40 years ago! Think about it, 3/4 of a race cam? Does that mean it's missing 2 sets of lobes

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Old 04-09-2017, 06:36 AM   #8
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Sounds like you have a vacuum leak, I would go with an Holley 750 dp. I use cams in the 280+ @ .050 range in my 440s and can get a cleen 950 rpm.idle, drag RACE CAMS.

Last edited by Iowan; 04-09-2017 at 06:50 AM.
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Old 04-09-2017, 08:55 AM   #9
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Quote:
Originally Posted by Archer View Post
Bob -

I know the term, but like I said, today, it's pretty much meaningless. Actually, a lot of people thought it was meaningless 40 years ago! Think about it, 3/4 of a race cam? Does that mean it's missing 2 sets of lobes

Archer

Agreed.... Hahahahahahahaha
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Old 04-09-2017, 10:11 AM   #10
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Maybe it's a flathead cam from the 50s.
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Old 04-09-2017, 12:53 PM   #11
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3/4 cam? wtf happened to the rest of it? As stated no such animal just a foolish backyard/gas jockey term we need specs ie... Lift,duration overlap etc... I agree for 383 cubes way under carbureted as mopars like fuel
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Old 04-09-2017, 01:45 PM   #12
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thanks I will try a bigger carb maybe a 750 quick fuel /holley , I have checked the vacuum leaks and put a vacuum reservoir on for my brakes to work better.
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Old 04-09-2017, 05:31 PM   #13
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easy / Guys -

Quote:
I have checked the vacuum leaks and put a vacuum reservoir on for my brakes to work better.
If you have too much break travel, it again points to a vacuum leak or WAY too big a cam. In either case, I can't see a bigger carb fixing the problem. Unless something is really off, a slightly small carb will just rob mid/high rpm power. It should purr at idle.

Still no idea on the cam, but 440 Magnums (and Commandos for the Plymouth guys...) came with a 600 cfm Holley from the factory, and IIRC there were a few guys here turning in some pretty good times with a 600 atop a well built 440.

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Old 04-09-2017, 05:40 PM   #14
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Would help if you gave specs on cam
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Old 04-18-2017, 10:10 PM   #15
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still idle issues

So before I spend more money on a carb I would like to know why a rebuilt carb that is too small for my engine doesn t get me idle properly at 800 rpm and soon as I put it in drive it drops and stalls , I also notice my car doesn t hold vacuum and wondering if that could be my problem at the brake booster or something. I hooked up the comp cams reservoir and helps with brakes a bit I think. I still notice the idle changes periodically higher and noticed some fluid under the master cylinder too. Could there be a vacuum leak in booster that I can not locate and how can I narrow this down without a guage. Uuhm a friend said block the vacuum at manifold and see how it runs then too!!! Any help here on my un resolved issue to pin point this guys??????
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Old 04-19-2017, 03:26 AM   #16
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specs please, possible the cam is to big and the converter is locking up to early for the cam, we really need specs
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Old 04-19-2017, 06:06 AM   #17
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easy -

Yes, a vacuum leak can be anywhere, including the intake manifold gaskets (don't ask me how I know that...) If you think it's the power booster, just pull the hose and seal that port.

If you're willing to do it, you can get the cam specs with a dial indicator and working off the rockers or push rods.

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Old 04-19-2017, 07:22 AM   #18
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The guys you've had look at it should have been looking for vacuum leaks but you can clamp off or plug the brake booster and see if the idle goes down. Next try spraying carb cleaner around the base of the intake manifold with the motor running, if the gaskets are leaking the rpm will go up. Try this on the distributer if vacuum advance also. Don't go crazy with the carb cleaner it's flammable and you want to isolate the location of the leak.

As far as the cam goes the cam compans sell " pro street cams" that have alot of duration and not much lift for the big motor sound but can be driven on the street for the showcar guys. You could have something like that in your 383 never know.

Have fun and let us here what you find.
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Old 04-19-2017, 07:27 AM   #19
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If you have one of those BIG cams something with 220 duration @ .050 and less than .500 lift would work in your 383 .

Last edited by Iowan; 04-19-2017 at 07:32 AM.
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