pj_corvette

Hello
Got a 383 Crate from Derebery Performance.

I am having problems getting it to idle well. It wants to idle at around 1300-1400 rpm, and when I put it in drive, the rpm drops to about 500 or so, and wants to die. I have to play a lot with the brake and gas pedals to keep it alive.

What should I look at or try to do? Already checked for vaccuum leaks and found none.


Here are the specs:
Model: CH383PC40
450HP/475TQ
Aluminum heads
Camshaft:
Cam Lift: 543/545
Cam Duration: 234/240
Transmission: 200-4r from Bowtie Overdrives with 2600 stall converter
Exhaust: Dual 3" exhaust.
Carb: Holley 850 CFM - Mechanical Secondaries

http://www.who-sells-it.com/cy/napa-...2/page-13.html

cv67

How much vacuum is it making?

Id be suspicious of (know you checked)

-vacuum leak
-Too tight of a converter

Dantana

i had this problem on a crate and it was my MSD-6AL box. I sent it to MSD and they fixed it up for me. Not sure what ignition you are running. Mine also ran rough through the entire power curve, in fact it pretty much eliminated the power curve.

Fishndude

My 355 is making about the same power (just not as much torque) and I had the same issue. Mine ended up being my power brake booster was leaking (vacuum leak).. I contacted alot of different companies at that time and they all said it was probably vacuum related and they were right. What type of vacuum are you pulling at idle? Was the motor put on a dyno and tuned before you received it?

Edit: After looking at the link, I assume you had to install the carb and dizzy? If so, what is your timing curve set at? When I tried running mine at 14/34 initially it ran and idled like crap so a vetran drag racer said my set-up would prefer it locked out at 36-38 degrees and now in runs/idles like it was meant too. I also had to make some minor card adjustments due to the large cam to get rid of the off idle stumble and rich idle.

pj_corvette

I am not using an MSD box. Just the HEI distributor.


My friend measured the vaccuum for me earlier, and said it was making 10hg at idle, though i'm not sure what rpm he was calling "idle." The engine was dynoed before I got it.

Fishndude

Mine idles at 1100rpm and drops to 900 when put in gear with a 3000 stall. I would call the engine builder or whomever dynoed the motor before trying to make any major changes because that is a huge loss in RPM. My vacuum will also run around 10hg at 1200-1300 but only 8hg at 900-1000rpm idle.

RobbSalzmann

pj_corvette, Have you resolved this? I'm having similar symptoms in my 383 and would like to know what you did to correct yours?

woodlandcorvette

Had same problem with my 383. Check the vacuum at idle in gear, mine was at 6 and my power valve on my 770 was a 6.5. Changed the power valve to a 4.5 and it not only cured my idle problem but also my off idle stumble when I pushed on the gas.

Good luck with your new motor.

OzzyTom

I had issues getting my new crate to run smoothly too.
My cam has 242/240* I/E duration at 0.050" with 0.594" lift with an LSA of 112*.

After plugging all vac lines, idle was still erratic and would cough and splutter when on the road.... Found a crack in distributor cap which was probably caused when engine was installed... I remember the dizzy making contact against the firewall as we were dropping engine in.

Carb also caused a few concerns.... it was the supplied Edelbrock 800cfm AVS .... just could not get an off idle surge/cough eliminated.
Put on a 4150 750cfm Holley and that solved that.

Getting carb dialed in will most likely sort your issue... although I'd think an 850cfm mechanical carb is not ideal with an auto.

I'd love to hear how you go with this engine when it's setup correctly.
It was the initial engine I wanted to buy, but I eventually went with the engine factory, as they had a local Australian import agent.

Love to see any dyno or track data you get with this motor.

cheers

76 sting

As a few others have said, carb is too big for the car.... what PV is installed?

RobbSalzmann

Power Valve, doh!

Now that you mention it, mine is acting like it might have a raptured diaphragm. I can't imagine what else it could be.

And I bet everyone here has recently gone through the initial timing routine, which can be rough on a PV. I got lucky and had no backfire issues - just primed the primary bowl, cranked the curb idle screw to 11 (think Spinal Tap), and she fired up, but the carb is bought second hand.

It wasn't until the break in period was over and I started to tune the carb that I encountered this problem.

I ordered a 5.5 and a 6.5 just in case. I'll update when I get it in.