I've got one of those reverse-idle system Holleys (6619) on my big block that has been giving me headaches lately. It likes to run very rich at idle. If I understand these carbs. correctly, turning the idle screws OUT will LEAN the engine, correct? Turning IN cuts off air, thus increasing the ratio of fuel in the system and making it run richer. Of course, all the way in the car runs but is dead rich. I have them basically 'hanging' at the edge of falling out of the metering block and it is still rich. Not as rich as all the way in, but still too rich at idle. Since this system does not adjust the amount of fuel at idle, only air, how can I adjust the amount of fuel at idle then? It seems I need less fuel somehow because I have the maximum amount of air entering the idle circuit and it is still rich! I really like this carb., it outperformed my 750 V/S by a lot after much tuning and I get 13-14 MPG with it, so I don't want to ditch it! Help!

Oh, BTW, what kind of idle mixture screws should this carb. have? Mine look like regular idle circuit ones, I have heard that these carbs. had different ones? Would that cause a problem and where would I get the right ones since this is such an old carb.?

I don't know how big of a cam you have, but I had the similar problem with a 6619 in my 327. The reverse idle just isn't capable of delivering the required amount of air/fuel.

Now that I think about it, mine ran too lean at idle. Is it possible that your floats are adjusted incorrectly?

I found that an out of the box Qjet will get up to 2 mpg better than the 6619 with no loss of performance.

Yeah, the floats are correct. I've had the front bowls off numerous times to check that. Could I swap the metering block from a conventional idle circuit carb.? The cam is smallish - idles really low.

Can anyone post pics of what the reverse idle circuit idle mixture screws should look like? I think mine has the conventional ones. What type of problems would that cause? I can take the screws OUT of the carb and it still runs rich.

sounds like you have a leaky power valve to me. that why it's rich even with the screws all the way out. if you have a mild cam the is the best Holley 600 available, IMHO. there's two ways for the PV to leak, one is though a hole or crack in the diaphragm and the other is when the front of the main body isn't flat, some are low around the PV chamber and let fuel leak in from the main circuits. this usually caused by guys getting aggressive tightening up the bowls screws. this problem got a lot more common after Holley started using bolts with hex heads to hold the bowls on. most likely is the PV itself. get a new Holler brand PV with the correct gasket and install it.

Well, I know the PV is good - it's been replaced with a Holley brand name PV. I will check for the trueness of the main body tomorrow. What can I do if the main body is warped? My bowl bolts are the straight blade type - pretty hard to overtighten. I know what you mean about the hex head ones though - very easy to overtorque them.

Reverse idle? Please explain how this works. Steve

In a conventional idle circuit, you adjust the amount of fuel entering the mix at idle by turning the screws. In a reverse idle system, turning the screws only adjusts the amount of AIR entering the idle mix. This is a feature on some emissions carbs. from the 70's. You are not adjusting fuel in a reverse idle circuit carb. Also, turning the screws IN on a reverse carb. will cut off the amount of air entering the system, and have the effect of richening the mixture. Turning out allows more air in and leans the mixture. My problem is that even when all the way out I am too rich. It would be like a conventional carb. still running rich with the screws all the way in - it's getting too much gas from somewhere . . .

In a conventional idle circuit, you adjust the amount of fuel entering the mix at idle by turning the screws. In a reverse idle system, turning the screws only adjusts the amount of AIR entering the idle mix. This is a feature on some emissions carbs. from the 70's. You are not adjusting fuel in a reverse idle circuit carb. Also, turning the screws IN on a reverse carb. will cut off the amount of air entering the system, and have the effect of richening the mixture. Turning out allows more air in and leans the mixture. My problem is that even when all the way out I am too rich. It would be like a conventional carb. still running rich with the screws all the way in - it's getting too much gas from somewhere . . .


Gotcha. I've rebuilt hundreds of Holleys, but never the emmision type. It's metering the air from the idle air bleeds. I'll have to make a note of this in the event I receive one for rebuild! Steve

I just discovered something interseting when taking the carb apart for the 5th time . . . the secondary well for the power valve was full of gas. I have a secondary metering plate with the thin plate over the gasket, then the metering plate. This doesn't seem right that it would fill with gas? Would it act like a bad power valve?

I just discovered something interseting when taking the carb apart for the 5th time . . . the secondary well for the power valve was full of gas. I have a secondary metering plate with the thin plate over the gasket, then the metering plate. This doesn't seem right that it would fill with gas? Would it act like a bad power valve?


The rear vacuum well should not have a vacuum hole drilled through, so the fuel would have to pull past the threads on the baseplate screw. It very well may be pulling enough fuel to affect idle, and probably is. Was there a gasket between the metering plate and the backing plate? Does the metering plate appear cracked? Could just be gasket failure.

If you need only the two rear gaskets, I could mail them to you. I have dozens of extras I'll never use. Just let me know.

Steve

I took the rear metering plate and the thin plate that mates to it off and cleaned them up really good. I think that when I put it together last time, I put the thin plate on inverted. It still fit, but it didn't really fit as tight as it does turned around. I was looking at the paths in the metering plate and think I found a few places where it was sucking fuel into other passages and filling the secondary well. I think that the reason I didn't find this before was because I always disassembled the carb. when it was level, so when taking it apart gas ran out and I couldn't tell exactly where it was coming from. This last time, I didn't have the bench space available to do that, so I set the carb. on the primary bowl as I worked on the secondary, so the gas stayed pooled up in the well when I took the bowl and plate off. The gasket looked good, but there is a hole in the gasket that leads to the secondary well that I think gas was getting to with the plate on not as tight. I just got it together and set everything the way it should be (floats, idles screws) and it ran perfectly. I was able to adjust the idle screws to lean it out and richen it just like I could before. I guess this is a lesson to always check the secondaries and not just primary bowls!