mcgruff1

A couple days ago I found a small tear in the airhorn gasket of my edelbrock 600cfm 4 bbl carb, so I took the airhorn off and took the old gasket to a carb shop to get a new one. They didn't have the exact one, but he made one to work by doing a little trimming, and it looks like it should seal. So while I had the airhorn off I adjusted the floats to spec: 7/16", and 1 1/4" at full drop and replaced the airhorn with the new gasket. With nothing else altered, the engine would take some persuading to start and once it did it would choke and die with an inch of fuel on the primary throttle blades and some on the secondaries too. I tried it again thinking the gasket wasn't sealing with a little silicone around the fuel bowls (I know, horrible idea) and that didn't help. Next I took the airhorn back off and cleaned all the silicone off everything and out of the fuel bowls. I brought the gasket back up to the carb shop and they said by the pattern on the gasket it was sealing fine. So again I tried it but this time without the electric fuel pump wired and the motor started and ran perfect for about 2 minutes, then when I saw it was running out of fuel I quickly plugged in the wire and even with the least amount of fuel alotted from the regulator it flooded rather quickly. Even with me pinching the fuel line to the carb and plugging/unplugging the fuel pump wire to limit the fuel it still floods. It seems like an actual carb problem as opposed to a fuel pressure issue and i was thinking maybe airhorn gasket is somehow bad or the needles and seats need replacement. This reman carb is pretty new, please give me some advice.

Pablo

iTrader: (1)

you need to know your fuel pressure, electric pumps can easily far exceed what that carb needs, pressure should be around 5.5 psi. Any more than that and youll experience flooding.

If that isnt the case I would then ask you how you adjusted your floats, if you did it incorrectly you could have damaged the needle and seat and also cause flooding

Pablo

iTrader: (1)

btw the airhorn gasket has very little to do with anything. The only thing a bad gasket would affect would be your metering rods not being pulled down because of a leak between the airhorn and the carb body in that area and since your primary boosters are not in use at idle it has no bearing on a problem that occurrs at idle

mcgruff1

The fuel pressure was set at 5 psi and wasn't changed. I found out what the problem was, my dumbass installed the needles backwards (the rubber needle pushing on the floats). They don't look damaged so Im gonna try to reuse them, unless that's a problem?

Pablo

iTrader: (1)

if they arent damaged then go for it.. its hard to screw these carbs up

mcgruff1

Pablo, you seem to know alot about this carb. Have you ever considered taking the airflow valve on the secondary side out or reducing its weights? I have found mine doesn't open up until around full throttle and definitely chokes its power. I was experimenting with it and if I peg it open at the weight there is much more power all over. I was going to try running without it because it comes out so easy, but Id like to hear some opinions first. Like is there anything I can do to avoid a lean spot if I take it out?

Pablo

iTrader: (1)

you can try removing it but I doubt youll like the results unless you have a specific set of circumstances that would make this beneficial (depends on your combo)

Your airvalve will only open at near WOT regardless, the airvalve opens with airflow through the secondaries, and the only way to get airflow through the secondaries is by opening the secondaries. The secondaries are not at a 1:1 ratio with the primaries the secondaries open at like the last 30% of pedal travel (around there). So for all intents and purposes you pretty much are at WOT.

As such, the only time you will notice a difference from removing or changing the airvalve is when you are in that last 30% of pedal travel (again im not sure of the actual %, im estimating)

These carbs are calibrated with a very generic and probably mild combination when edelbrock decides what cal. settings they will send their carbs out with. The airvalve is then weighted accordingly to deliver satisfactory performance on this combination. If you have a lighter car with low rear end gears you could probably get away with lightening the airvalve. I myself have installed a lighter airvalve in mine but the lack of a secondary pump makes things boggy if I slam on it. Ive even increased the amount of aux secondary transition fuel, and no fiddling with the front squirters or pump shot will fix this problem. If the carb were smaller relative to my engine or my car was alot lighter it would probably be better but I would say that it would never be really right, esp. on a 5 speed, on an auto you can get away with it just fine

If the carb were a holley you would have to make a big pump cam change to accomodate for the opening of the secondaries at the last bit of pedal travel it would have to ramp up right at the end. With the edelbrock the best you can do is ensure the shooter is delivering just enough on the low end of the pedal travel spectrum so that at the end it is still delivering some of the fuel from the pump well. Why? because you have no way of tailoring the pump curve really, you can maybe affect it slightly by bending the pump rod and changing the pump lever at rest. Even so, its too little too late to compensate for an engine setup like mine when the secondaries open. Carter didnt design the carb with this in mind which is why the airvalve exists in the first place.

Long story short, if you have an automatic with a decent stall you are in luck, you can probably get awya with removing weight off the air valve and may even try removing it entirely if its one of those combos with high stall, low gears, and low weight.

You can tune how much fuel gets delivered slightly by enlarging the feed tube and altering the airbleed size for the aux secondary fuel circuit. I did this too and saw gains.
Still, for a manual transmission car a vac. secondary carb or air valve carb is not the best choice.

mcgruff1

I have a 266ci v6 with a 2000 stall, 4.10 gears and 31" tire. Weight is probably around 3800lbs. I don't know if there is enough airflow to open the airvalve properly with that big of weight since the carb was calibrated for a small block v8 in mind. I put a 1/4" L shaped allen wrench in the drivers side hole where choke provision use to be and set it to hold the weight up so the valve is always open. I noticed a great bit of extra power that way and haven't noticed a bog, but its only been like that for a short time and I haven't seen much full throttle. BTW the secondaries open mechanically at 65% throttle. Would I need to add richer secondary jets if I removed the airflow valve because of less air restriction? If that doesn't work, where did you find the smaller airflow valve?

Pablo

iTrader: (1)

hmm, I would say that on a combo like yours that lightening the airvalve wouldnt have a positive effect but Ive never dealt with anything like that, there are alot of things there that sort of make it hard to say.
A 6 is gonna have alot less manifold area and when you consider that the pump, transition circuits are calibrated for alot more manifold it kind of makes for a weird situation I guess

It isnt hard removing the airvalve at all, would take you ten minutes tops, if you want to try it just remove it and go for a spirited drive just remember the only difference youll see is at 65% +

I would say that you would definately be leaning out the mixture some by removing the airvalve just because it allows more are to travel around the boost venturi and that sucker is calibrated under the assumption that x amount of flow is occurring in the barrel around the boost venturi.


I got my lighter airvalve from an old AFB dual quad setup, the airvalve seems like its probably half the weight of the original which brings up an interesting point, with two carbs, the airvalves were made lighter. Which would make sense in one vein being that it would require aLOT more rpm to open the airvalves on a dual quad setup if the weights were held constant, but at the same time the AV should only open at an airflow that can provide satisfactory booster signal.. then again, Im sure those carbs were rated at considerably less CFM

I still think the gains from a lightr AV would only be felt on a car with a loose converter, light weight, low gears, or some combination with those factors. It wouldh ave to be something that didnt load the engine down enough that accelerating through the rpm range would be slow especially at low rpm (where a loose converter would erase)