my car is hard to start, and when it does start it idles rough between 300rpm n 500rpm and slowly gains rpm over 30 seconds to 800 rpm thne is fine. if i punch the throttle to the floor the car trys to die, or sumtimes falls to bout 300rpm and then rapidly picks up to 4k rpms or higher. if i slowly put my foot into the throttle it piks up fine. is this a mixture screw problem with my carb or something else?

i have no vacuum leaks that i can tell, my vacuum advance is set up on driver side port for FULL vacuum. i have a cheap off the shelf inline fuel pump that puts out about 7lbs of pressure, i have a regulator set on 4 1/2 lbs of pressure. i was told not to set it over 5lbs of pressure. anyone have any ideas?

 

I think you would want around 6 lbs of pressure for a carb. Is it the factory carb still?

 

naw its a new edelbrock 600. but a mech tryed helpin me with my hesitation issue, he adjusted mixture screws, idle screw n distributor n vaccum advance then he said, WELP idk! Good luck have a nice day no charge... lol wow. so now here i am with all that readjusted to non factory settings and i gota figure out wth to set it at. and i still got hesitation and its hard to start. when it does start it roughtly and slowly idles up to 800 to 1000 rpms and then idles good. but i cant give it gas or it trys to die, if i slowly rev it up it does fine

 

I am thinking you might have too low of fuel pressure and it's starving. Try upping the pressure to about 6 psi and see if that helps when you give it gas. The mixture screws can always be set, but you got to get it running good first. If I am understanding you correctly, you have an adjustable vacuum advance and the mechanic adjusted it?

 

ok ill up my fuel pressure but my regulator only goes to 5lbs lol.. n i know if i remove it my plugs fowl out after a day or two running it. its set at 4 1/2 so ill up it to 5 n see. also yes the shade tree mech took a small allen wrench and truned the interal of my vacc advance on my distributor both directions bout a turn at a time plugin the hose back on and me patting the gas a bit to see any change. no change. still hesitates like starving for gas maybe. but i know before i ever had my regulator on it did the same thing. with all 7lbs of pressure my pump puts out straight to the other carb i had on, it still hesitated. i did have a 750 carter on it, i baught the new 600 thinking that was my problem for the fowled out plugs. but the 600 fowled them out too. black chalky equals too much gas? put the regulator on n set it at 2 and the car whouldnt idle at all. set it at 3 and it idle rough, so i set it to 4 1/2. now fowl out yet. ive gone through 3 diff sets of plugs. first where the autolite cheepos, then i baught NGK (No good kinds so i hear) and now i have boushe platnum 4 prong plugs. it even fowled those out but i cleaned them up really good like new again and put them back in. no fowling out so far but car still hesitates

 

well, the thing shouldn't balk at the fuel pressure from the stock pump, so that's odd. As for the vacuum advance, at idle, it shouldn't affect it at all, only when there is a demand on the engine. A good rule of thumb is to turn the mixture screws all the way in (to the right) and then back them out 2 to 2 1/2 turns, that will get you in the ball park to run good. As for the plugs, I assume you are putting in the correct heat range?? Also do you have any other mods like a high rise intake or carb spacer on the motor?

 

well its not a stock fuel pump. its a off the shelf from autozone 50$ inline pump. the plugs i have tryed different brands and recommended gaps (Double checked gaps) and now im running the hottest burning plug u can get the 4 prong bocshe plats and yes my intake is a vortec intake with 4 1/2 inch rise and i have a 2 inch carb spacer in. i just put the spacer in 2 weeks ago, car was still hesitating before the spacer was installed. also i was tinkering with my car yesterday and if i rev it up to hi rpms it backfires thro the exhaust once or twice. im being told thats normal. but once in a while if i rev bout 4 or 5 times, once out of those 5 times it backfires out the carb. its rare but it does after a few trys it will back fire thro the carb. wats that about? slightly out of time? or valves not seating rite? i have good compression on all cyls they have about 65-70lbs of pressure. kinda hi i think. but i have hydo lifters all push rods are good. so y a back fire everytime out the exhaust and y a rare backfire thro the carb??? guess i should double check timing, needa buy a timing lite but my harmonic balancer has only a barly visable line on it. no numbers and i have a chrome chain cover that has no markings either. so id have to find TDC mark both the barely visiable line and timeing cover with like chalk or white out or sumthing im guessing to use a timing lite rite? (can u tell im still a newbie, this is my first engine, im still happy at the fact that i put it together and the dam thing actually fired up, bahaha)

 

1) Set your timing right. Initial timing should be somewhere around 8deg. Make sure you have the correct timing mark for your damper diameter. You don't know how many times I've seen people tinker with their carbs thinking its a fuel problem when it's only a timing problem. Also make sure you disconnect the vacuum hose from the dist. and plug it while you're setting the time. A symptom that timing is off is that when neutral the engine revs up fine, but when you put it in Drive, there's no power and engine wants to die.

2) If you get timing right and still have like a bog down when flooring it, find how to set the accelerator pump on your carb. I don't know carter style carbs, so can't tell you how to do it.

Hope this helps.

 

I concur with Blazer79, make double sure your timing is right on. It should never backfire if everything is right, you could have a bent or burnt valve, but usually a burnt valve is a dead miss. A bent pushrod is possible too, although you have checked them, it could still happen. Take a piece of chalk or a white crayon, or white paint and make the balancer line visible and then go to the local Autozone or equivalent and buy a timing tab and bolt it on, then set you timing and take the guesswork out of it.