Ok, I put a rebuilt my carburetors, and now I'm having problems getting them just right. I can't get the mixture just right. I can set the air flow with my unisyn, and I can drop the idle down to under 1000, but the mixture I can not get right. I have set the mixture nuts to 2 1/2 turns, but the car will bog out when I lift up on the lift pins, like it is going to die. No matter how much I turn the nut out, the car backfires out of the carburetors, which I am assuming is a lean situation, since it is mixed with the bogging out when I push the lift pins. My carburetor dampers are good, I have SU fluid from MSA in them, and I might end up using Marvel Mystery Oil to see if it makes any difference. When I have my choke on, the car runs good, but when it is off and the car is warmed up, it stumbles when going from idle, and can die if the throttle is not feathered just right. The nozzle and needle are not stuck, because when I lift the piston/dashpot, and I drop it, it slides down fast and makes a distinct clunk noise.

What could cause this issue? I don't believe it to be my float settings, because I replaced them with another float that I have from another set of carburetors, and it didn't make a difference.

If you want more information behind the matter, and what I've tried, see my thread at Zcar.com

Any help is appreciated, I just finished rebuilding the engine, and I'm eager to get her back on the road and driving again!!

The oil in the dampner will not effect idle or mixture.

Thanks for all of the help guys, I'm trying to trace this problem down.

You are totally right, the oil in the dampner will not affect mixture or idle speed at idle, but will affect mixture when accelerating, but I'm sure you knew that :laugh: , I was just thinking that the velocity of the air pulling on the dashpot might have to correlate with the dampner oil.

I think you can try again at raising the fuel level in the bowl by bending the float tab so the float is closer to the lid. This will give the bowl a high fuel level and in turn it will also raise the fuel level closer to the top of the nozzle in the bottom of the carb. Then again start the adjusting nuts at 2 1/2 turns open and start the car. Hopefully with the choke off, or closed.

When you pull the choke, the cable will pull the nozzle jets down and this raises the fuel level at the tip of the nozzle allowing for alittle more fuel on cold starts in the morning, gives little more fuel to get the cold blooded animal going, until it warms. This is what Arne is saying about proves the theory of float level still off, too low.

yeah, mine are the stock 3 screw carbs from my 240Z. Why do the drain plugs make a difference, out of curiousity?

Just to make sure I read what he said right, put the clear line on the bottom of the float bowl, turn the motor over until the fuel inside of the plastic line stabilizes (air is bled out), and the put the line up to the mark I made on the float bowl, and adjust the float setting until the fuel in the plastic line is at the same height as the fuel in the float bowl?

Oops! I didn't see that part. I was assuming he was having you connect to the float drains like the ZTherapy kit. If you are connecting to the bottom by disconnecting the hose to the nozzles it shouldn't matter which style float bowl you have.

And no, you want to adjust the float level until it matches the line you marked at 23 mm from the top. The level in the clear hose will always match the level inside the bowl.

oh, okay, I feel dumb now, , I'll try that out tomorrow and see what happens. Thanks!

quick question, when setting the float adjustment, and the float bowl top is upside down so that the adjustment can be made, is the float supposed to sit at 9/16 under it's own weight, or am I supposed to hold the float until it just touches the needle, and go from there?

It's been several years since I've done this. (Haven't got SUs back on the Z yet. Last time I did this was on my MG.) But it seems to me you want to measure it with the weight on it - that way the valve will be closed.

If you have the standard needle and seat setup with the internal spring, turning the lid over will give a setting where the float will be way too low. You need to hang the float vertically while blowing gently into the fuel inlet tube. Move the float toward the lid and you'll feel when the shut off happens. Not allowing for that internal spring will screw things up to the point you will be found whimpering in the corner.......

Question: How does the car run with the carb nozzles set at 2 1/2 turns from the full up position? I don't think you were that far off from the start, that you could not have adjusted your way out of it by adjusting the metering nozzles. What needles are you running? Where ever you end up with the nozzle you're going to want the fuel level in the nozzle (float bowl) 1/16" or so below the top of the nozzle.

If you have the standard needle and seat setup with the internal spring, turning the lid over will give a setting where the float will be way too low. You need to hang the float vertically while blowing gently into the fuel inlet tube. Move the float toward the lid and you'll feel when the shut off happens. Not allowing for that internal spring will screw things up to the point you will be found whimpering in the corner.......

That would explain a whole lot. Thanks for the insight, Bruce!

If you have the standard needle and seat setup with the internal spring, turning the lid over will give a setting where the float will be way too low. You need to hang the float vertically while blowing gently into the fuel inlet tube. Move the float toward the lid and you'll feel when the shut off happens. Not allowing for that internal spring will screw things up to the point you will be found whimpering in the corner.......

Question: How does the car run with the carb nozzles set at 2 1/2 turns from the full up position? I don't think you were that far off from the start, that you could not have adjusted your way out of it by adjusting the metering nozzles. What needles are you running? Where ever you end up with the nozzle you're going to want the fuel level in the nozzle (float bowl) 1/16" or so below the top of the nozzle.

I was off by something, because when I went to set my adjustment, nothing happened. I was running extremely lean, causing a lean backfire out of the carburetors, and the car would only run right when the choke was all of the way out.

That's why when you pull the choke on to get it to run it's like screwing the nozzle down at least a couple of turns. Get those nozzles cranked down a couple of turns and see what happens. We send everything out of here set at 2 1/2 turns down and I'd be interested in knowing how many cars are out there never haveing been moved from there. Just a good square one position for most applications. A tweak up or down is about all that is needed in most cases. Any major tweaking is often an indication of something else amiss......

When using the 23mm mark as suggested, where is this measured from? The top of the float bowl, as in the line between the float bowl cover and the bowl itself, or the top of the cover?

I just ordered one of Bruces's rebuild kits so I'm going to be doing this myself in a week or so.

I have had the same problem as described in the firsts post. I thought my problem was float level. My mechanic sets the floats by blowing into the float jet (when remover from car) and closing the float as you blow. He sets the float so that it is just past level with the float lid (closer to it) as that is when it is shuting off the valve. This seems to work too.

My problem however is that I have been testing the car with no air cleaner on it and it hase been backfiring when warm with the choke off and stops backfiring and runs pretty good when the choke is pulled abit. I have re-installed the air cleaner and will test it in the morning (my eyes are closing at this time of night). It is cold here now and I think the cold air could be my problem.

I guess I will see.