I'm new to this place, and after browsing the carb section, it seems like the word EDELBROCK, is a sin. lol. But anyways, i just finished breaking in the engine in my sig for my iroc, and we took it to the track on saturday and turned the time in my sig. That was with a hesitation when i stomped on the gas even at stall speed (1800rpm) We already dropped two primary jet sizes, and two metering rod sizes, but kept the stock metering springs. Tried different springs on sunday, but got a headache real quick, and ended up puttin it back the way it was and put it back in the garage. I haven't tried anything else since then, but just to help my thought process out, what would you change next to try and get the hesitation out? we changed the jets and rods b/c at first, there was a HUGE fireball that came out of the carb when you'd stomp on the gas. But we've got it down to a hesitation. I'm thinking metering rods?

 

What is your ignition timing at idle and high rpm (Vac adv disconnected) should be 12-16 idle and 32 to 36 at high rpm.

Sounds like an accelerator pump problem move the linkage to the inner hole. Get some accelerator pump shooters like .035 or .043" . Your motor should run fine on the stock out of the box
jetting. What cam are you useing? Do you have a vacuum leak?

 

The timing is really advanced. everyone tells me for my vortec heads that 32 degrees total is the best bet, but i can't get the engine to run without alot of unpleasant roughness at 12-16 degrees base. Now my edelbrock owners manual points to my cam being a long duration cam, the cam is the only thing in the engine i don't know about, and it will more than likely get changed out this winter. There aren't any vacuum leaks, its pulling about 18inches through the port in the back of the intake, which is more than enough to run the vacuum advance. the pump is set at the hole closest to the carb, which is the richest, and if we move it out, the problem gets worse. I did not know you could change out the size of the accelerator jets. I'll look into that. Thanks

 

do a compression test. you may have a bent valve.

 

don't make the problem larger than it is. The engine starts fine, runs fine, except for the sudden wot that happens at the track. There is no missing throughout the RPM range, and there are NO symptoms of a bent valve here, I've worked on engines with bent valves before, i know what the symptoms are. Edelbrock carbs are also jetted severly rich from the factory, to keep edelbrock safe from frying someones pistons b/c they were too lean. The carb right out of the box fouled 4 sets of plugs within 4 weeks. Carbon fouled, not oil fouled. Also, there is a large carbon spot on the floor of my garage from the exhaust. Which throws out the big fat signal that its too rich. So i've dropped two jet sizes and two rod sizes but retained the stock springs. On the stock jets and rods, the car did not like any hard acceleration at all. I've changed out the springs and it only made things worse, either going to a stiffer spring or a softer spring. I think i'll go at it myself, trying different metering rods and see if i can get it to stop myself. IF anyone else has suggestions, lemme know if not, don't worry about it

 

"but i can't get the engine to run without alot of unpleasant roughness at 12-16 degrees base."

This combined with the back fireing out the carb
sounds like an internal problem (valves).

I have the same manifold and carb. It works fine right out of the box. You have some other problem .

Edelbrock carbs are a little rich out of the box but not near enough to cause fouled plugs. 99% of the time you can bolt these carbs on and not need to even adjust the idle screws.
The first place to look when troubleshooting a motor that won't run right is a compression test. Takes a few minutes and will save you hours and hours of pissing around trying this and that
endlessly only to find you have a valve problem or leaking head gasket.

 

I believe you when you say you can just bolt it on. I had a performer intake on my 350 chevy truck, and a 750 edelbrock carb. I dind't have to touch the carb. But on this engine, jets were needed. The compression is fine, The lift of the cam does not exceed the limits of the vortech heads. I'm simply asking about metering rods here, but i obviously can't get a simple opinion.

 

From the way you describe things, it sounds like you may have one of a few problems Ive encountered with the same symptoms.

Simplest of which would be that your pump shot is lacking. There are several ways to go about fixing this the first thing would be to move the linkage rod up like the poster above suggested maybe even to the last hole. This might not do the trick and if it doesnt its time to step up the shooter size which can be accomplished by drilling the stock shooter with a pin drill set.. course its always good to start off with less and work up to what will do the trick.

course the Doomsday proffessor in me believes it sounds to me like something to do with your timing is out of whack. Retarded timing will cause those same problems especially the intake backfires. You wouldnt happen to still be using the stock computer controlled hei would you? it almost sounds like when someone adjusts the timing without disconnecting the est line and you end up inadvertantly retarding the timing. Try the simple stuff first though.

and as far as edelbrock jetting goes, i think saying they are rich or lean as a blanket statement is innacurate. There are so many factors, and so many carbs really. Heck, the 1406 and 1405 have different jetting out of the box.. it wouldnt make sense to produce a rich carb and then an Extra rich carb and call it a performance setup. I run a 1405 on a 30 over 305 with a single plane and mildly large cam and im running like 104 primary jets and 98 secondary jets which is quite a few steps above stock and neccessary for best (ok.. better, i dont have totally conclusive evidence) performance

anyways.. forget about the rods and jets for now, any hesitation when you stomp on the gas is going to be your accelerator pump

 

Pablo, did you get rid of TBI???

 

i'm getting the sneakin suspicion its all in the cam we've got, we know nothing about it, and when we sent the engine to the machine shop, they spec'd it and said it was the same as what they offered for their highperformance engines. The distributor is a 1975-1979 model, so its not computer controlled. I do disconnect the vacuum tube to the canister when i time the engine, and setting it at 32 total just don't cut it. The cam will more than likely get swapped out over the winter. The accel pump is set to the richest setting. There was one thing at the track i neglected to try though, in the owners manual, it says to shut the choke about halfway and either close or open it until it runs right, with long duration cams. We had the 600cfm running pretty well, but it only let the engine turn a 15.19, with the poorly tuned 750, it turned a 14.7. I'll play with it some more and get it worked out. thanks for the realistic ideas pablo.

 

I agree. According to an exhaust gas analyzer, my WOT mixture was right on right out of the box but I needed to richen it up a bit at cruise.

 

No

 

[QUOTE]Originally posted by Blueirocz28
i'm getting the sneakin suspicion its all in the cam we've got, we know nothing about it, and when we sent the engine to the machine shop, they spec'd it and said it was the same as what they offered for their highperformance engines.

that sounds pretty far fetched to me (the cam being the problem that is) if the cam was iffy the car would likely run crappily all the time and from what it sounds like it definately sounds like a tuning issue.


The distributor is a 1975-1979 model, so its not computer controlled. I do disconnect the vacuum tube to the canister when i time the engine, and setting it at 32 total just don't cut it.


What do you set total to then? what sort of advance curve do you have? a lazy advance curve will make the car unresponsive even though total timing is close.. Even so.. >

The accel pump is set to the richest setting.

What do you mean by richest setting? the edelbrock carb has many variables as far as pump shot settings. If you set everything up to be as rich as it can be, (eg. bending the linkage rod for the most upward plunger travel, connecting it to the top hole (or drilling even more holes) , and putting in the biggest shooter) I dont think your car would be very driveable at all. It would be rediculously rich when you stabbed the throttle. From what i gather it sounds like you just put the linkage on the top hole. Believe me there is more youll have to do beyond that in many cases. My own car (305, single plane, moderately large cam, edelbrock 1405 ) does not have even close to enough pump shot with just the linkage rod in the top position and everything else stock. Course I could be assuming wrong in that you havent tried experimenting more with it but if you havent you should definately look into it some more.

glad to help,
Pablo

 

Sounds like your valve timing is off. If you can't get 'normal' timing to work for ya on your motor,something more than your carb is off.

Is your distributor a points distributor? or HEI?
check your dwell angle.

verify spark to all your cylinders and take a look at your plugs.

 

I happen to like my Edelbrock!!!!!!!! It does pretty good A Holley would probably better for racing for me though!