Constant Miss-Fire

[rich weyand]

He's probably running the stock distributor with 20* of centrifugal advance.  If not he should set the total advance to 36* once all the centrifugal advance has come in.

[LTZ C20]

Ok I'm confused about everything Rich just said. I don't know how many miles are on my carb but it was professionally rebuilt 1 year ago, it's a 1400 edelbrock performer, it's not a 1401 or anything, it's a straight 1400, I also have the matching performer dual plane intake and long tube flow tech headers. Rich if you could give a more "watered down" explanation. Not that there's to many fancy words just info overload. And from what I've heard you don't wanna run really any higher than 12* BDC?? My vaccum advance only has vaccum when pulled open by the carb, it's labels vaccum advance port. I'm also not sure what you mean by upper and lower vaccum ports, all the ports on my carb at at the bottom, none are near the top, all are under the throttle plate, which is the same as the butterflies at the top of the carb right?

[rich weyand]

OK, you got the Edelbrock, so I can help you a bunch, that's what I have.

The plate at the top of the carb is the choke plate.  The throttle plate is down in the carb venturi.  See this page for the explanation if you want, but mostly for the pic.  You want the vacuum advance connected to the 3/16" manifold vacuum (driver's side port), NOT to the 3/16" timed vacuum (passenger side port).  See in the pic how one is a little lower than the other?  http://chevellestuff.net/tech/articles/vacuum/port_or_manifold.htm

Do you know what metering jets and rods you have in the carb?  It should be something like: seondary jets .094; primary jets .094; rods .068/.052.  Do you have those numbers, or can you ask the rebuilder which ones he put it.  I will tell you that the Edelbrocks come from the factory set richer than heck.  You are supposed to tune them on the car, but most people don't, so the factory has to tune them so they won't run lean (and burn the valves under load like pulling a trailer on the highway) and burn the valves no matter what engine they are in.

I can tell you what jets and rods will work on your setup, because it's the same more or less as mine, but I want to know what's in there first.  I may be able to set you up without having to split the upper and lower halves of the carb.

[rich weyand]

That's also the EGR carb.  Is the EGR set up on your engine?

[LTZ C20]

Ok lemme go over this and try again.

[LTZ C20]

I just looked at the picture and realized they are slightly higher and lower, I also just realized thanks to Rich that the right is for emissions and I don't have any emissions. So I should switch ports. As to what metering rods and such I have no idea and they guy who rebuilt it probably doesn't remember haha. So today I should try switching vaccum ports, advancing timing to 16 and then drive around and romp on it to see if it stumbles?

[74 C-10 Shorty]

He's probably running the stock distributor with 20* of centrifugal advance.  If not he should set the total advance to 36* once all the centrifugal advance has come in.

Yes, 36* is a good number and should be all in by 2800-3000, if it can handle it 2500 is even better.

[rich weyand]

I just looked at the picture and realized they are slightly higher and lower, I also just realized thanks to Rich that the right is for emissions and I don't have any emissions. So I should switch ports. As to what metering rods and such I have no idea and they guy who rebuilt it probably doesn't remember haha. So today I should try switching vaccum ports, advancing timing to 16 and then drive around and romp on it to see if it stumbles?

Not stumbles.  Knocks.  Sounds like there's loose ball bearings banging around in the engine.  But otherwise, yes, you've got it.

Also, you probably have the stock jets.  You should pull the rods and get the numbers off them.  Take off the air cleaner cover.  Put a rag in the bore of the carb so you don't drop any parts into the engine.  In the top of the carb, on either side, are two torx screws.  Back them out about two turns, and the little metal plates rotate out of the way to expose the rods and step-up pistons.  They'll jump up in the holes when you rotate the plates out of the way.  Pull the rods and pistons out and use a magnifying glass and strong light to read the numbers stamped on the rods.  Should be four digits, like "6852".  Put the rods and pistons back, hold them down while you rotate the little plates back into position and snug down the torx screws.   DO NOT OVERTIGHTEN THESE; stripping the holes would be bad!

Tell me what those numbers are and I'll tell you if they sound close or are way off for your engine setup, as well as what to replace them with.

[74 C-10 Shorty]

If it's a 1400 it's calibrated for economy, if it's all stock it comes with the Metering Jets - Primary .098, Secondary .095; Metering Rods - .073 x .047; Step-Up Spring - orange (5" Hg)

[rich weyand]

If it's a 1400 it's calibrated for economy, if it's all stock it comes with the Metering Jets - Primary .098, Secondary .095; Metering Rods - .073 x .047; Step-Up Spring - orange (5" Hg)

If he has those settings, I'm running slightly richer in the cruise circuit and quite a bit leaner in the power circuit (.092 with .065/.052).  With .095 stock jets, the better rods would likely be .070/.057 or .068/.057, given his setup is so much like mine.  And 8# springs with the vacuum he's likely pulling, or the power circuit will come in too high.

I wonder how well his idle mixture is set up?  You have to be pretty rich to turn the oil black.

[74 C-10 Shorty]

If it's a 1400 it's calibrated for economy, if it's all stock it comes with the Metering Jets - Primary .098, Secondary .095; Metering Rods - .073 x .047; Step-Up Spring - orange (5" Hg)

If he has those settings, I'm running slightly richer in the cruise circuit and quite a bit leaner in the power circuit (.092 with .065/.052).  With .095 stock jets, the better rods would likely be .070/.057 or .068/.057, given his setup is so much like mine.  And 8# springs with the vacuum he's likely pulling, or the power circuit will come in too high.

I wonder how well his idle mixture is set up?  You have to be pretty rich to turn the oil black.

I have the 1400 on mine and it's out of the box and it's right there wouldn't want to go any leaner but pulls very hard, but of course every motor is different and requires different tune up. But to pollute the oil like his you'd have to be dead fat from idle all the way up. One thing that'll make them run real fat is if the rods are sticking.

[rich weyand]

Well, you'd have to be rich from idle on up at least  through the cruise circuit.  Depending on how you drive and what the commute is, that might be enough.  But he's not rich in the cruise circuit, so I don't know where the black oil is coming from.  You could be right about the rods sticking, as long as they were sticking in the up position.  That would run richer than a cob at cruise.

Kevin: you can check if the rods are sticking by opening up those little plates and seeing if the pistons are free to move up and down freely.  You should be able to bounce them up and down with you finger (once you get the rod through the jet).  If they're sticky, a shot of carb cleaner into the pistons may be enough, or you could pull the pistons out and clean them off, and clean the cylinders with Q-tips wetted with carb cleaner.

[74 C-10 Shorty]

Edde's are just a glorified Carter and I remember way back in the day it was common for rods to stick open, had to filter the fuel real good. Only other thing I can think of at the moment would be floats sticking open???..

[LTZ C20]

Thanks for all of the info guys! It's alot for my brain to take it but I think I got it. Today I will set the timing to 16* and switch ports, tonight or tomorrow if I get a Lil time I will pull the rods out, get the numbers, clean everything and put em back in. Ide love to have this running alot better. Hopefully should be a big up in horse power right? Plus it seems like lately, past month, I've been goin thru alot of fuel, that should be due to all my parts being way out of whack?? Thanks again, I've learned alot

[rich weyand]

If the rods are sticking in the up position: 1) it will run crappy, 2) it will turn the oil black with carbon, and 3) mileage will suffer.

Sound familiar?

And they do gum up.

So that's certainly something to check on.  I was surprised how gummy mine were after just a year when I recammed the engine and switched rods to get the mixture right.