Hot Rod Forum banner

1 - 9 of 9 Posts

·
Registered
Joined
·
122 Posts
Discussion Starter #1
im in the process of restoring my nova. it has a new motor (350 bored .60 over) and a 700r4 that just came out of the shop. the engine strains when i put it in gear...like it wants to die. sometimes it will. now im pretty sure its not the tranny... because the th350 that was in there a week ago did the same thing. its possible the motor isn't tuned all the way it could probably use some more advancing. but even so why should the engine be strained by me just putting it in gear? the stall is somewhere around the 2000-2500 range. everything in the drivetrain is new and the engine pulls 13'' vaccuum.

Specs:
350 4 bolt main bored .060 over
Comp cams XE268
10.5:1 compression
Dart Platinum 200cc
Edelbrock RPM Airgap manifold
Barry Grant Speed Demon 650.
Pertronix FlameThrower II Ignition
Flowtech Longtube headers /w 2.5'' exhaust.

700r4 tranny
Beast Sunshell
Z-Pak, Corvette servos, stage II shift kit.
Bowtie Overdrives custom crossmember and TV cable setup.
 

·
Registered
Joined
·
122 Posts
Discussion Starter #3
well.. like i said im thinkin its not advanced all the way yet anyway. i would expect 15'' tops. and yea...its steady no leaks.
 

·
Registered
Joined
·
39 Posts
Have the same problem w/ a 440 in a road runner. The drop in vac. and rpm when in gear makes it want to die. I think if you lock your timing and use an ignition control like msd w/ a timing retard for starting it would help your problem, plus give you added beniffits. I couldn't get the kid w/ the 440 to install the msd yet so I'm not sure if it will solve the problem but I have check everything else out and advancing the timing it smooths out and idles great in gear, but then it starts hard. Good luck.
 

·
Chasing dreams with a ball bat
Joined
·
545 Posts
What are your initial and total timing settings????

Does your distributor have an easy way of changing the amount of mechanical advance (not the rate)??
 

·
Technical Support Barry Grant
Joined
·
1,500 Posts
Sagacious,

Most likely you’re carburetor is out of adjustment, and you have too much of your transfer slots exposed. When you put the car in gear the extra load from the torque converter isn’t allowing the engine to burn the additional fuel coming out of the transfer slots and is causing the engine to lug down and even die. If you don’t have enough initial timing in the engine it won’t create enough vacuum to draw the air and fuel it needs causing you to open the butterflies further and exacerbating the situation. The Air Gap style intake manifolds run more like an open plenum, and require more initial timing in order to run cleanly and properly. You’ll most likely need 15 to 16 degrees initial timing with a combination like this.

First reset your timing, and then from there you can go back through the carburetor settings.
 

·
Chasing dreams with a ball bat
Joined
·
545 Posts
vacuum advance

Remember as well, that you may find using a full manifold vacuum source to your vacuum advance will make the idle much stronger as well.

A side effect of that is that the motor will sound much tamer at idle (since you'll likely be running 30 deg adv. at idle, while the vac advance is on) - and that can be good and bad depending on the situation.

But like [email protected] said, you will need some healthy initial timing to make it work - I run 20 deg initial, with a total of 36, and it works very well (but the cam is larger, which explains the need for the larger amount of initial advance).

IIRC, the explanation is that at idle, with a largish cam, the mixture is not ideal (hence the rumpity rump sound), gets diluted with exhaust, plus some of the misture gets spit back into the intake before the intake valve closes. What that means is that the extra advance allows the engine to better burn that less than ideal mixture that occurs while at idle.

If you try just messing with the timing, I bet you'll find it actually like around 24-28 degrees initial timing - and that can be accomplished using the vacuum advance like I said earlier.

Hope you have some ideas to try.

- are your secondaries cracked open a little on the carb? that may help you close the Primaries a little and get things under control as well.

good luck :D
 

·
Registered
Joined
·
8 Posts
most likely a timing issue

Looks like you've done some mod work to the engine and your not sure what to put in it for timing. You should be safe for starters with anything from 16 to 20 degrees initial timing with out vacuum advance. Most of my modified sbc's wind up with about 18 degrees intitial advance and 34 to 38 degrees total mechanical. All the engines, including the big blocks I've worked on will fall flat on their face and die when the timing is not advanced far enough and the automantic tranny is put in gear.
 

·
bobs77vet
Joined
·
1,206 Posts
i have a very similar set up on my vette...speed demon,xe268h, 700r4, 2500 stall......i think yur problem is in your vacum advance cannister....you need to install the one that pulls full advance at low vacuum and run manifold vacuum to it...this way when youput it ingear the reduced vacuum does not effect the timing like it is now. the cans cost about $14 at napa




 
1 - 9 of 9 Posts
Top