Corvette Forum : DigitalCorvettes.com Corvette Forums banner
1 - 11 of 11 Posts

·
Premium Member
Joined
·
115 Posts
Discussion Starter · #1 ·
Here's the facts....350/300hp crate engine with a Holley 670 SA.

When I first start my engine in the morning, it idles at about 1100 rpms (in park)for about 5-10 minutes. After that I "blip" the accelerator, it drops to 800. Then when I put it in Drive (before the engine hits operating temperature of 200*), the engine wants to die (drops below 500 rpms). The electric choke is adjusted as far as it can (counter-clockwise).

During this per-operating temp time, if I come to a redlight or stop sign, I have to put it in neutral so the engine won't stall out. Now after the engine gets to operating temps, it idles just fine (750 rpms in Drive & 900 rpms in Park). And runs real strong without any problems or misses.

What could be causing this? Timing? A/F Mixture? (the A/F screws are turned 2 1/2 out for both sides and she's not running rich). Float bowls are adjusted correctly. So what could it be???? :bang
 

·
Registered
Joined
·
2,948 Posts
Raise your idle a touch so that in park it's around 900, and 600 in drive. See if that changes anything for the better. If it works, drop it back down another 50 and retry.
 

·
Registered
Joined
·
152 Posts
Exact symptoms of a vac leak.

While in park and engine running try this:

Carb cleaner spray around base gasket, attached hoses etc. If idle rpm increases, you have a vacuum leak.

Spray carb cleaner on any vacuum plugs you may have installed on the manifold. If idle increases bingo.

Another place to look is your distributor vacuum advance.
Pull the hose from the carb and see if it holds vacuum. Yes suck on it. ;)

Check your pcv valve also. Sometimes they can get goopy and you will have that issue. To test pull the pcv valve from cover and plug up with your hand and see if your idle increases.

if you have a base gasket leak:
If you are using a dual plain intake make sure you use the heat insulated base gasket with the single rib across the middle.
Holley and edelbrock both sell them. They are about 5/16 in thick and will absorb any bent tang imperfections your carb may have and usually do.

I don't recommend using the four hole felpro gasket it doesnt swell very well around the base of the carb.
 

·
Premium Member
Joined
·
115 Posts
Discussion Starter · #6 ·
Exact symptoms of a vac leak.

While in park and engine running try this:

Carb cleaner spray around base gasket, attached hoses etc. If idle rpm increases, you have a vacuum leak.

Spray carb cleaner on any vacuum plugs you may have installed on the manifold. If idle increases bingo.

Another place to look is your distributor vacuum advance.
Pull the hose from the carb and see if it holds vacuum. Yes suck on it. ;)

Check your pcv valve also. Sometimes they can get goopy and you will have that issue. To test pull the pcv valve from cover and plug up with your hand and see if your idle increases.

if you have a base gasket leak:
If you are using a dual plain intake make sure you use the heat insulated base gasket with the single rib across the middle.
Holley and edelbrock both sell them. They are about 5/16 in thick and will absorb any bent tang imperfections your carb may have and usually do.

I don't recommend using the four hole felpro gasket it doesnt swell very well around the base of the carb.
Thanks! I'm going to try all those idea!:thumbsup:
 

·
Registered
Joined
·
1,524 Posts
It's about 5-7 years old.
Oh ok. The new 670 SA'a are having casting problems. I just went through two of them as they have casting problems, and this occurs only on the ones that have been made within this past year. One leaked at the body to base plate, and the other would idle in park but died as soon as it was put into gear either hot or cold (engine temp).
 

·
Registered
Joined
·
152 Posts
Oh ok. The new 670 SA'a are having casting problems. I just went through two of them as they have casting problems, and this occurs only on the ones that have been made within this past year. One leaked at the body to base plate, and the other would idle in park but died as soon as it was put into gear either hot or cold (engine temp).

how do we find out if we have one of those? is there any sort of recall?

my Avenger is pretty new. and has some finicky issues also
 

·
Registered
Joined
·
1,524 Posts
I sprayed it around the main body and found the leak. As far as the second one goes I tested everything and went through all the required adjustments and when nothing solved it I put on a Demon that was known to run good and the problem disappeared. I don't know of any recall, but my old manager at the parts house told me a customer had a similar problem and went through three of them before one functioned correctly and I went through two, and the old 670 SA (7+ years old) we had didn't have any problems.
 

·
Registered
Joined
·
152 Posts
I sprayed it around the main body and found the leak. As far as the second one goes I tested everything and went through all the required adjustments and when nothing solved it I put on a Demon that was known to run good and the problem disappeared. I don't know of any recall, but my old manager at the parts house told me a customer had a similar problem and went through three of them before one functioned correctly and I went through two, and the old 670 SA (7+ years old) we had didn't have any problems.
Thats a good thing. Those holley base plate are notorious for bent tangs and distorting.
 
1 - 11 of 11 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top