SU and vacuum adv

[dcraigbrown]

Hi,

I'm new to the forum and would appreciate any one willing to help a nubie.

I just bought a 73 240z for a restore project. This car seems to have all the common problems early Z's are known for, rusted out floorboards, kinked choke cables, runnig rich , etc. I've used the current threads to get me through most of the problems but I'm having a lot of trouble with the SU's. They're round tops, I assume they were swapped out in lue of the infamous flat tops by the previous owner- unless early 73's came with round tops. They'e running extremely rich. While attempting to adjust the mixture I noticed that turning the mixture nut on one carb all the way in made little to no difference in idle speed. Also, while reading a ztharepy article I read (or maybe mis-read) one way to check if the needle is properly seated in the horn to turn the mixture nut in, thereby lifting the horn into the needle until the needle piston moves up slightly and then back down slightly. If this is true then my needles are way out of whack with the mixture horn as they never bottom out. Its also plausible that this would cause a very rich mixture, right?

I also discovered the vacuum (not mechanical) advance isn't working. After pulling it and giving it the suck test I couldn't get it to move. I can get the arm to move with some force but the spring on the arm is so stout I don't know how the diaprham could ever move it. Is this normal?

Any help would be much appreciated.

[Bruce Palmer]

To fully understand the inter-relationship of things on Hitachis, I'm suggesting the JUST SUs Video or DVD would be a real asset in helping to go thru these carbs. At this point it's impossible to make suggestions about what may or may not be causing the symptoms, at least for me.

[Curtis240Z]

You mentioned kinked choke cables. Make sure the choke aren't already engaged. Loosen the hex head screw on each carb securing the cable to it's respective choke lever. Then check the position of the choke by seeing if you can push the choke levers down further (thereby fully unchoking the carb).

[dcraigbrown]

I was able to get the kinks out of the cables and oil them so they operate smoothly. To make sure I didn't get the cable too tight I kept my eye on the nozzles and tightened both cables as tight as they would go with the nozzles still seated. There's quite a bit of play in the choke levers so if the cable is tightened with the choke levers as far as they go in the unchoked position the chokes never engage with the choke (cockpit) lever at the end of its play in the choke position. Sorry, sounds very wordy and confusing after re-reading this post but its hard to explain. Bottom line is that if the nozzles underneath the carbs being completely seated is a good indication that no choke is being applied then a partialy open choke isn't the problem.

[beandip]

Brown, I think you have the idea on the choke adjustments. you just need to adjust the length of the ''cable'' with the hex nuts so the lever all the way froward the nozzles are all the way up. for the vacuum pistons, with the engine not running lift the piston with your finger and let it drop. It should fall and bottom with a klunk. By the way are these 3 screw or 4 screw SUs? If the pistons do not fall freely there either dirty or the needles are misaligned to the nozzle. If the pistons fall freely. Start then adjusting the fuel mixture. Turn the mixture up, counter clockwise, all the way to the stop, on both carbs. Then turn them out, clock wise, 2 1/2 turns. This should let the engine run. Providing the timing and ignition is OK. After the engine is fully warmed you can set the idle at about 700 or 800 rpm. When adjusting these carbs , you disable one carb and adjust the other one. You disable the carb by lifting the vacuum piston. Now with the engine at idle, use your finger and lift the vacuum piston on one carb. If the engine dies it means the carb that is NOT disabled is too lean. Now if the engine runs smoothly the carb is too rich. Adjust accordingly in 1/4 turns. Then you need to adjust the air balance . For this you need a uni-sen or similar tool to balance the air of the carbs so that they are drawing equally. After this recheck the mixture , lifting the piston. and so on. When the mixture is right , the engine should stumble but continue to run when the piston is lifted. When this is accomplished I then ''blip'' the throttle to wide open and close , quickly. If there is a backfire out of a carb then this is a lean pop. Richin the mixture of that carb 1/8 turn. When this is done, set the idle where you like it . 600 rpm or so. This should do it . And No the '73s all came with flat top carbs. The Zs didn't' run all that well and if the new owner bitched long and hard enough they installed round tops at the dealer, to cure the problem. Keep us in the loop on how you are doing with this. hope this helps. Gary

[dcraigbrown]

Thanks for all the suggestions. These ar 3 screw SU's. The prior owner gave me an SU tuning manual, "SU-HITACHI Carburetors", Carbooks, inc. There's a hand written note in the back with the words "HS6 1 3/4", same as 1968 Volvo". I did notice that one carb, front, smelled strongly of fuel, there was a small amount of fuel leaking out of the jet nozzle on the bottom, the black plastic fitting that holds the jet nozzle was wet to the touch with fuel. I surmized that the float is possibly adjusted to allow to much fuel into the jet nozzle. Currently I'm trying to figure out what he float adj should be. The SU book I have lists 1/2" for seperate floats and 1/8" for nylon floats with no explanation concerning which one I might have. I can't find specs specific to the HS6 just general specs for SU's varying from 1/2" to 1/8"- very frustrating. As soon as I get the floats right I'll reassemble and go through your recommendation of disabling one carb, etc.

[Bruce Palmer]

Thanks for all the suggestions. These ar 3 screw SU's. The prior owner gave me an SU tuning manual, "SU-HITACHI Carburetors", Carbooks, inc. There's a hand written note in the back with the words "HS6 1 3/4", same as 1968 Volvo". I did notice that one carb, front, smelled strongly of fuel, there was a small amount of fuel leaking out of the jet nozzle on the bottom, the black plastic fitting that holds the jet nozzle was wet to the touch with fuel. I surmized that the float is possibly adjusted to allow to much fuel into the jet nozzle. Currently I'm trying to figure out what he float adj should be. The SU book I have lists 1/2" for seperate floats and 1/8" for nylon floats with no explanation concerning which one I might have. I can't find specs specific to the HS6 just general specs for SU's varying from 1/2" to 1/8"- very frustrating. As soon as I get the floats right I'll reassemble and go through your recommendation of disabling one carb, etc.

These Hitachis are a metric version of the SU 1 3/4". They were made under license from SU by Hitachi. Instead of saying they were the "same" as 68 Volvo, it would be more precise to say they are "very similar" to the HS series SUs used on MGs, Tirumphs, Jaguars, etc. etc. etc.

Before assuming the float level has somehow magically changed, assume for a moment that the nozzle is too low allowing fuel to stand on top of it thus leaking down onto the nozzle heads. It's easier to achieve "tune" by adjusting nozzle up and down than it is to chase the float level around. Float level does not adjust the amount of fuel into the jet nozzle.... it raises and lowers the fuel level in the nozzle tube or in the case of a too high situation allows fuel to puddle on top of the tube.

As far as the 1/8" float setting is concerned, you think you have fuel drooling out now?? Any and all SU float settings will be give or take 9/16" and when the nozzles are set correctly the static fuel level will be about a 1/16" below the top of the nozzle.

[dcraigbrown]

I'm making progress. Followed your suggestions and the z runs much better. I am still concerned about the float levels. Holding the bowl cover upside down, should the float level be measured at the front, middle, or back of the float. The reason I ask is because I checked the measurement and they're right at about 1/2" at the front. As you move towards the rear of the float the hight decreases significantly due to the angle the bowl rests on the needle. At any rate thanks for the suggestions and information, I'm getting there.

[Bruce Palmer]

Checking float level should be done with the float hanging down and the pivot pin at the top. Blow gently into the fuel supply tube qhile moving the float toward the lid. You feel the pressure change when the needle and a seat closes. At that point the distance at the far end away from the float pivot pin.....

With the lid inverted, you'll automatically over-power the tiny spring inside the needl and seat giving an erroniouse reading.

Sounds like you're getting close. We have a lot of customers who start messing with floats without stopping to ask, why would the float levels change? Fiddling with float levels often times cause more problems than they solve when it often comes down to nozzle being incorrectly set or choke cables being too tight or any one of a number of other adjustments being hay wire. Believe me we see them everyday.......

[dcraigbrown]

Bruce,

I hadn't thought about or touched the floats until I saw the front carb dribbling fuel. The front float was noticably higher, or lower if measuring inverted. Thats when I started messing with the floats and digging to get a correct measurement. The car does run 100% better with the floats at least close, I didn't take the precautions you mention to not overpower the needle spring- which I'll do eventually. I've also been yakking in another forum about a bad vacuum adv just too find out my dizzy is only a spinning rod, bearings crunched and mechanical advance rusted and frozen, etc. Oh well, its a project car :-)

Craig

[Bruce Palmer]

I'm taking the counter position. The dribbling gas is due to a correct float level and a fuel nozzle is set too low allowing gas to pool-up on top of the nozzle. It may have already been mentioned here but I'd say run both nozzles all the way up and then back them both down 2 1/2 turns and start your tuning from there. At 2 1/2 turns down, if you still have gas pooling, hence leaking by the tube onto the nozzle head (and the exhaust manifold) then you may have a float level issue.

It's a bit of the chicken and egg thing.