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Old 04-23-2012, 09:34 PM
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idle issue with a new engine

new 350 bored .030 over, proform 4150 conversion main body with a quick fuel baseplate, vacuum secondary. the cam is a thumpr from comp cams with .520 lift and 283/303 duration. 107*lobe sep. just a basic run of the mill sbc really. problem is i had the carb on another 350 before this one and i ran fine. the first engine was milder with a small cam(480 lift 238/242 duration flat tappet). the jetting is 80's up front and 74's in the back i think, thats what it liked on the dyno anyway. so i left the initial jetting alone thinking it couldnt possibly run too bad on a bigger motor.....wrong. cant get this deal to idle worth a darn and the vacuum sucks even tho i was told thumpr cams will keep good vacuum. it will idle at 800rpm but vacuum will be 10"Hg and drop to 5-0 and try to kill unless i bump the throttle. if i manually idle it to 1200 rpm the vacuum jumps to a steady 20"Hg and i'm sure i dont have vacuum leaks but then again all i did was the carb cleaner test. so i'm lost as to what to do next. any ideas?

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Old 04-24-2012, 09:06 AM
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What's your timing set at?
With that much cam you might need up to 20-22 degrees initial.
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Old 04-24-2012, 10:17 AM
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it might be a intake gasket issue.
I just had an issue with miss at idle and pinging under load and found the intake gasket shifted and 1&3 inlet ports were sucking off each other.
my vacum was reading 17to 19 and no external vacum leaks, BUT i had a leak internally under 1&3 which was suckin in a bit of oil aswell.
was a pita to find this!!!!
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Old 04-24-2012, 09:46 PM
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dawg-i think i'd have thrown a wrench through the windshield before i figured that one out. f-bird thanks! i called comp cams tech and never thought about the power valve. its gotta be dumping at idle, its a 6.5 now and the tech guy said a 4.5 is what i need. unfortunately my fuel pump seems to have air bounded itself somehow now. fuel bowls ran dry randomly. guess its time to relocate it closer and lower than the tank. any thoughts on electric fuel pumps? mine is a mr gasket from the zone. doesnt suck very well, pushes fine....usually. should i spend the cash on a rotary vane or will this one work fine?
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Old 04-25-2012, 05:54 AM
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you are going to need more fuel pump than an autozone mr.gasket pump.

rotor vane pumps suck also. expensive, loud, and the motor brushes wear out quickly.

I recommend using a msd 2200 efi pump with a return style fuel pressure regulator for a carb (low pressure). This pump is cheap, brushless, quiet, and very durable. The pump cost $100 and the fuel pressure regulator around $100.

Mount the pump by the tank as low as possible and install the regulator in the front (ideal) or the back (if easier). But the regulator requires a line back to the tank (at least 5/16" diameter).

Yes, I know it is an efi pump, but it works great on a carb engine if you use the right regulator and return line.
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Old 04-25-2012, 07:10 PM
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ok i was wrong. not the power valve. eyes still burning. and the jets are 78 front/80 in the back. car idles fine at 1100 rpm's once its warmed up a lil. still waaaaaay too rich @ idle. plugs are fine and gapped correctly. cd ignition box says to gap em at 60. still digging for the problem....
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Old 04-26-2012, 07:00 AM
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not enough timing at idle.

after turning up the timing, turn down idle speed (which closes the throttle blades) and readjust the air mixture screws for best idle.

Its running to rich at idle because the throttle blades are open past the idle transfer slots at idle.

if more timing doesn't do it then you will need to let more air into the engine somewhere else. May need to crank open the secondaries or drill a small hole (0.08") in the front throttle blades
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Old 04-26-2012, 01:25 PM
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Advice on my unknown 350

Hey guys. So I bought this 65 Nova. It's got a 350, TH350 with a shift kit, rear end is a 10 bolt Posi with 3.73 gears.

This is what I know just from a visual. The engine is running an Edlebrock RPM airgap, Edlebrock 600 carb, I installed an Accel HEI distributor, it's got Headman shorty headers into 2 1/12" exaust and 40 series Flowmasters. No x pipe. The heads are 882s.

Engine runs well. Sounds like it has a bit of a cam in it. Although its a bit of a dog off the line at WOT. But when it it's about 2500 3000rpm it pulls hard and chirps 2nd gear pretty hard. I'm trying to Discribe it the best I can because I would like some thoughts as to what I might have inside this engine. Maybe it's impossible to tell at all without tearing it down. The previous owner was a young guy just out of the military. He bought it off his buddy who just shipped out to Afghanistan. He had to sell it because of a nasty divorce/custody. But he didn't know all the details of the build. I asked him to try and find out but he never got back to me.

The car was set up for the track. Heidts subframe, gutted with a single racing seat, Fuel cell in the trunk. Batt in the trunk. All new fuel lines and steel braided stuff. They dumped some money into this car. Oh to be young!

Anyway I'm trying to figure out how I can improve my bottom end without totally taking it apart. Maybe it needs a stall? Wondering if the heads were worked? Any way to tell without taking them off? I'd like to get the Edlebrock RPM cam to match the intake. But if the heads are not worked they will need to be.

How would you guys go about this? Just start taking it apart? Or are there things I could look for to give me hints on what I'll need to do? And how do you think this setup will run with the intake and cam with the 882 heads? I have an extra set of those heads in my garage. And a very good shop in my area who's has been there for 50 years quoted me 335.00 to work them for the RPM cam. That's a rebuild with a 3 angle grind. Stock valves. If I did that should I go with 2.02s? Of would I not see the benifit with this setup? I'm on a budget and am trying to use as much of the stuff I have already. Much of it looks newer. Any advice will be welcome.
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Old 04-26-2012, 02:56 PM
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Sorry. I have no idea how my new post ended up here! Can a mod please move this? Or just delete it? I can't even edit it!

Last edited by Localboy808; 04-26-2012 at 03:10 PM.
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Old 04-26-2012, 08:16 PM
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need a 10" 3000 stall converter, better heads, a bigger cam, and lots of initial ignition timing.
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Old 04-30-2012, 07:53 PM
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mmmkay if i advance the timing anymore it idles way too high with the fast idle screw backed all the way out. timing is about 28*adv right now. air bleeds are whatever came in the carb body, its a proform 750 upgrade. the old carb was a holley 600cfm straight leg booster vac sec 300 dollar from azone. i'm not privy to drilling throttle blades when air bleeds are meant to be changed. just dont know how to size em. throttle response is great and i can roast the tires at a dead stop just fine. i gave it a "vacuum leak" and it leaned out a lil. sound like air bleeds to y'all?
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Old 04-30-2012, 09:52 PM
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guess i should have mentioned the throttle plate and the metering blocks are both billet quickfuel parts. afr on my other 350 with this same carb was 12.8 on the dyno. that engine made 309ft/lbs and 240 horse with the jets that are still in there. i realize two different engines are two completely different monsters but the last engine was milder than this one. i figured the carb tuning couldnt be tto far off. i actually expected this deal to be on the lean side. think i should mess with the tiny jets in the metering block? the block came with some extra jets i think for the well.
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Old 04-30-2012, 10:04 PM
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bird, you mention the pcv sys. the valve works fine, hose from manifold vac to valve to valve cover, standard setup. the other valve cover has two breathers. sound about right? the carb base is manifold vacuum so it shouldnt matter so long as its manifold vacuum sourced right? the cap and rotor are fine. accel super coil, cd ignition box, and the .060 gap is what was told to me by a tech line at msd cuz until i re-gapped the plugs i was burning them up and detonating, an extra .030" shouldnt make that much difference with a 60,000 volt coil right? oh and i converted to a secondary metering block so the carb has a quick fuel baseplate, a quickfuel primary and secondary metering blocks, pform 750 body, holley 4160 style side hung fuel bowls. i'm curious if the combination of parts allows four corner idle? if i back out the secondary blocks "idle" screws it runs worse. i always left them closed, dyno mechanic siad the last setup was pretty dead on. i think i'm at the point where i should leave it be for awhile cuz now i'm thinking of all kinds of ideas instead of keeping it simple. think ima save up for a wideband. vac gauge and timing light only help so much

Last edited by gonzo08383; 04-30-2012 at 10:19 PM. Reason: xtra info
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Old 05-01-2012, 09:41 PM
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carb is tuned now. 78 pri/80 sec. never changed the air bleeds. 38*total timing, 26* @ idle. problem was electrical. there was a short between the steering wheel and the gas pedal(points to self). thank you bird for the info, starting over put me in a spot where i was forced to tell myself that what i already know isnt always fact. at one point in time when i first installed the carb the sec throttle blades were open. they somehow closed. i guess the allen screw backed itself out somewhere along the line. i also noticed the screws holding the baseplate to the main body were loose. a quick reset and no more burning eyes @idle. see, never a bad idea to doublecheck things. thanks all for the input. cheers.
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