Dante DiJirolanio

Recently purchased a blueprint 355 with aluminum heads. After getting the motor I took it to local engine shop to be broken in and run on the dyno and to have the timing set. Upon going to pick it up the guy at the engine shop stated he believed the carb needed rebuilt due to the motor not wanting to idle.
I purchased a carb from Holley performance a 600cfm like the engine manufacturer recommended. After getting everything hooked up I am having a terrible time getting the car to idle properly. The distributor was never removed when the engine was installed so the timing should still be dead on from when it was set by the builder.

Problem I am having is with the vacuum advance I believe. If I start the car with it connected it will idle very high 2000-1800 rpm roughly and if I adjust the idle screw the car will die. Now if I unplug the advance and cap the vacuum line the idle drops down to about 800 and it runs perfect except when I put the car into drive it only had about 600 rpm and wants to die. This is using the timed vacuum port on the Holley carb.

Now if I try hooking the vacuum advance up to full manifold vacuum I get a great idle that I can adjust just about anywhere I want. Car starts fantastic as well. Only problem is as soon as I try to put it into gear it stalls. I have tried adjusting the idle up to about 1,200 rpm and still when I put it into gear the car dies. Looking for suggestions I really want to get this car on the road.

cv67

What cam is in that thing?
Surprised a dyno operator said new carb needed to be rebuilt if I understood that right-

Does he understand distributors and carburetors?
Do you have a stock torque converter?

Dante DiJirolanio

Sorry for the confusion. When it went to the dyno I had the old carb on it. He stated he had issues with getting it to idle and believed that it needed rebuilt. After putting the motor in I ordered the new carb when I was having issues with the idle as well. Which the new carb did help a lot. Flat tappet
Cam is .480 intake .486 exhaust
.229 intake .230 exhaust duration
@ .50

Right now it looks like my timing is set at 8 degrees btc with the vacuum advance plugged and the car idling about 750 rpm. When I plug the vacuum advance in the idle jumps up to about 1,850 and it appears like 24 degrees total. When I rev the engine I get to a total of about 32-34 advance.

Dante DiJirolanio

Transmission is 200r4 with I believe a 2,200 or 2,400 stall. Can not remember

Jebbysan

It should be hooked to full vacuum.
Have you adjusted the mixture screws with a vacuum gauge and the float levels on the new Holley?

Jebby

94LT4

Vacuum leak somewhere? Intake, unplugged fitting on carb, etc?

maverickmk

This is where I would start.

REELAV8R

Timing is too retarded. Should be a base timing of around 15* to 20* with a cam like that.
Also could be your vac advance can is falling off when you put it into gear. You need the vac can to be advancing the timing at a low vaccum, something that is still advancing at 8 to 10" of vacuum.

What it sounds like is happening is that with the vac advance plugged in out of gear you have sufficient advance to get a good idle. But as soon as you put it into gear the rpm and vacuum drop off enough to drop the vac advance and all you get then is your base 8* of timing. With the drag of the torque converter that makes the idle and vac drop further and the engine dies due to lack of sufficient timing.
See where your vacuum is at 700 rpm, or in gear idle range, that is where the vac can needs to still be working to use manifold vacuum.

My 219/219 @ .050 roller cam has 19* of base timing. With vac can plugged in it rises to 36* at 800 rpm idle. Total timing is still 34*. 51* at cruise.

Modifying/limiting the travel of the vacuum advance and the mechanical advance may be required to get best results and not exceed 36ish* total and 52ish* at cruise.

0BluePrint Engines

Hello Dante

We saw your post here and wanted to jump in to offer our assistance in getting your engine running right so you can enjoy your Corvette this summer.

Give us a call, or an email us, and we can help you figure out what is going and get you going again.

Scott Liggett
BluePrint Engines
1(800)483-4263
info@blueprintengines.com
www.blueprintengines.com

maverickmk

Nice! This is why I love this site