ding56

Hi,

i have a 68 289 with a c4 transmission. I just swapped the old 2v stock intake and and carb and installed a Edelbrock Performer intake and a Holley 600cfm carb. When i start up the car the idle is much faster than it was originally(but still smooth not jumpy) and i have turned it down as far as the carb will allow. I sprayed carb cleaner all around the the intake seals and i did not notice any change in the engine so i dont think its a leak there. Also when i shift into reverse the car jumps a lot more than it used to(can actually hear the tires squeek) and there is also a very noticeable hiss. When i put it in drive i was doing about 25mph with my foot off the gas which is very different than how it was. Any ideas as to what happened in the swap?

Thanks

racer_dave

You turned down what to change the idle? The idle mixture screw? the linkage adjustment? Are the floats set correctly?

ding56

sorry for being unclear, what i meant was that i turned the idle mixture screws on the side of the carb all the way down. i just went out and checked the bolts on the intake and carb and my fittings and found that there was a small leak in the line for the brake booster hose and i fixed that. Then i started it up and it would not hold idle so i had to give the mixture screws a half turn out and that fixed the problem. With it running i used my hand to cover the carb and it took 15-20 seconds of sputtering but she eventually died so it does not seem there is a leak that is at least letting in enough air to keep it running. When i shift into reverse or when i drive i still hear a pretty loud hissing noise that i cant identify. Also to note i don't have the air cleaner on right now as i need a shorter screw to secure it, could that just be the issue? I don't see why going from park to reverse or drive would cause a louder hissing all cause the air cleaner isn't there.

When i am in park i can rev the engine and i don't hear the hiss, just when i shift into reverse or drive. Also when i shift into reverse or drive the car has a pretty big lurch (wheels squeak a little). I do have a shift kit installed so i dont know if this is the cause but it did not lurch after i installed the kit but before i swapped the intake and carb. The transmission fluid level is not low, actually i think i over filled it so i need to drain a little out. Is there a way to do that besides dropping the pan?

Gun Jam

ugh.....I guess ill be the one to ask.

Did you try adjusting the curb idle speed screw....you know the one you use to increase or decrease idle rpm?


Oh I see in your 2nd message it looks like you got it figured out

As for the hissing noise you'll have to check all vac lines

might not be a bad idea to replace them all anyhow

-Gun

Diputado

Like Gun jam says...I'd replace all those old vacuum lines since you've already gone to the great expense and trouble of the new intake/carb.

Get a good vacuum gauge and use it to tune the carb to the highest vacuum you can get at idle. Just follow the instructions that come with the gauge. On that 600 Holley (I assume it's a model 1850?), you should turn the idle mix adjustment screws all the way in (clockwise) EASILY (not too tight)...and then back out 1.5 turns for the initial starting point. Once you get the best vacuum level possible via the idle mix, then readjust your curb idle speed.

ding56

I think i found the issue, the carb needed the idle speed turned down and the throttle linkage was getting hung upi installed an aftermarket tach and now im idling around 1000 rpm. The car still has a decent lurch when i put it in reverse through, any thoughts?

barnett468

remove the throttle linkage.

what carb is it exactly?

is it new?

make 110% sure that the idle screw on your choke linkage is NOT touching the little metal "cam" as suggested earlier. if it is, your regular idle screw will not work.

Disconnect ALL vacuum hoses from the carb and plug the ports at the carb.

you can also do them 1 at a time to see if the hissing stops and the idle lowers.

you might have a leak at the lid for the diaphragm on the vacuum pod for the secondaries.

your secondaries may not be fully closed, make sure they operate freely and are closing. to do this look at the little stop on the passenger side and make sure the arm hits the tip of the screw stop..


if the problem still exists it is an air leak at your carb base or intake at the cylinder head.

the intake might be leaking on the bottom side. if it is you can not test for that. you need to remove it and try again.

take a can of brake cleaner that says FLAMMABLE on it. stick the long plastic nozzle on it and GENTLY and SLOWLY spray for leaks.. if you have one you WILL find it using this method.

most brake cleaner is NOT flammable these days.