Car stumbling and dying
 

Hey Guys
I just put a new small block 434 in my car with a Pro-systems carb built specifically for my application. I've got just over 450 miles on the motor so far, but am having issues with the idle.

The car takes awhile for it to "warm up" until it will idle on its own, then seems to run fine for ahile where it will come to stop and idle but then after I drive it for awhile, when I come to a stop it wants to die unless I feather the throttle to keep it running...

For example....yesterday i drove it to work. When I first leave my house I need to keep tapping the throttle to keep it idling. The I get a couple of blocks, it idles fine. Get on the freeway for about 15 minutes, then off and through town... a couple of stop lights through town it wont idle when I come to a stop....it wants to stumble and die unless I feather the throttle.....

I havent pulled the plugs yet, but that was next.

I plan on getting it dyno tuned to really get it set up right, but want to put some more miles on the new motor and clutch etc before I really beat on it. For now I just want to get it to idle around town...

So any suggestions on what to try first ??

sounds lean. I'd check the carb adjustments first, starting with the mixture screws. Sounds like they're in too far. Float level, etc. should also be checked.

Jody

call patrick even on a weekend, he has some of the best tech support out there.
also i am with jody, try idle mixture screws, try 1/2 turn out and take for ride, also verify float level

Float level is good... thats what I checked first......

Its just wierd that it runs fine and then after awhile it starts trying to die at a stop.

So mixture screws all the way in and then back out 1/2 turn ??

no go out 1/2 turn from where it is now, however screw them in so you know where they are now and can reset it if it does not help any

Ned, screw them in slowly watching vacuum or rpms; the vacuum will drop and the rpms will drop as it leans out. Start screwing them out until you get the best vacuum and/or highest rpms at idle. If you go too far out the rpms and vacuum will drop again. Find the happy medium, highest vacuum or rpm. You'll probably end up 1.5-2 turns out, sometimes a bit more.

Do both sides a couple times. If they're way off the idle speed may go up enough that you need to drop it back with the idle speed screw, that's fine. Also, if that carb has four corner idle circuits (idle mixture screws on the secondaries also) then do the same with them.

Jody

the pro systems hp1000 i got for the 496 in vins car, the mixture screws are only 3/4 a turn out from seat, i messed with it but it just messed carb up, put them back and have never had a problem.
you should really call pro systems(patricks) tech line

that's true Jake, with a modded carb like that the correct setting could be anywhere. Give it what it wants, try adjusting it but don't get hung up on exactly how many turns that ends up being.

Jody

exactly jody, if i were ned and did not want to get to into it to deep with tools,
i would turn the idle mixture screws all(4) out 1/2 turn, go for ride, if it got better but not perfect go 1/4 turn more out.

just before doing that turn them into seat so you can return it back to how it was originally.
on vins car when we turned them out, it made it pig fat, on just off throttle and idling.
so it may help yours, try it, but call patrick also

Idle speed is very important as well. Carbuerators are notorious for variation in idle speed. Depending on your camshaft shoot for 800-1000 minimum. That is where you want to start adjusting your idle mixture. After your mixture adjustments then re dial in your idle speed. A little to fast is better than slow. It gives your carb some room to wonder with varying conditions. All the adjustments should be made at operating temp.