1,000 rpm

[Gary in NJ]

I purchased and watched the ZT DVD Friday evening. That DVD is very informative and thorough. I felt very confident disassembling my carbs and getting them up to spec. The float bowls were very dirty and the floats tabs had the floats sitting at the very top of the cover (no wonder this car was barely running). I had them completely cleaned, adjusted and running in about two hours.

I followed the sync instructions which is the same procedure as I used 25 years ago. I also got the same result that I got 25 years ago; I found that the engine runs smoothest at an idle rpm of 1,000.

I started with the mixture knobs set at 2-1/2 turns out and the high-speed balance screw on the RH carb out (not touching the tab). I had the similar screw on the LH carb out as well (I believe this is the idle recovery screw for the emissions system). I started the engine and proceeded to adjust the Throttle Adjustment screws to get them in sync. From there I adjust the mixture knobs to get maximum rpm (still set at about 2-1/2 turns). When all was said and done, I was at 1,000 rpm.

I know I should adjust the Throttle Adjustment screws (turn-in) to achieve 750 rpm but it idles much smoother at 1,000 then 750. Should I readjust the mixture knobs (again) once I turn-in the Throttle Adjustment screws?

Edited May 2, 2010 by Gary in NJ

[tlorber]

Sometimes when you lean out the mixture at idle, the idle will increase. Therefore if you do lean them out you could back out the throttle plate adjustment to lower the idle speed. The "problem" with SU's is that they tend to run richer at idle than at speed (say @ 3,500 rpm). You sort of need to pick where you want the performance-at higher rpms or at idle around town.

Obviously selecting the correct profile needle will minimize this compromise. I'm sure Bruce Palmer will have more to say here. At the end of the day, idling at 1,000 won't hurt anything, (in fact it will keep the oil pressure a bit higher) it will just use a bit more fuel and you'll have to be on the brakes a bit more to slow down.

[Gary in NJ]

Yeah, I'm gonna have another go at setup. I'm 95% in the ballpark right now. I'm going to do a full tune-up (plugs, wires, points, timing) onthe engine, and then dial-in the carbs.

I think I can go leaner on the nozzle mixture adjustment. I left the nozzle adjustment locking tab in place while making my fine mixture adjustments. The problem is, I think the mixture nut wanted to be where the locking tab and the elongated part of the nut come together.

Do most people remove those tabs? If I leave them off will the mixture nuts move over time?

[ChrisZ]

You are better of by getting your ignition in order first, what is your setting of the timing.

Have you tried to lift one dome piston a ½ inch at idle, that will give you an idea of if you are running to lean or to rich, ill say you are only half way there by now.

Chris

[Gary in NJ]

Have you tried to lift one dome piston a ½ inch at idle, that will give you an idea of if you are running to lean or to rich

Chris,

When I lift the piston in the dome, the engine stumbles and recovers. I believe that is an indication of correct mixture.

[ChrisZ]

It does sound just about right, what is your timing set at

[Gary in NJ]

It does sound just about right, what is your timing set at

I'll know later in the week when I get my light on there (this Z is new to me). I know the value is 17 degrees BTDC with the vacuum advance disconnected. I haven't found a high-speed figure. I'd like to know the maximum advance and at what RPM that advance happens. My timing light has a feature to check the high-speed setting.

[Walter Moore]

17 degrees static timing is only for the "Euro" spec points distributor, part number D606-52. (Which unfortunately is the unit listed in the dreaded Haynes manual...)

If you are running the early U.S. spec points distributor (D612-52) the static timing is 5 BTDC. That distributor has 24 degrees of centrifugal advance and setting it to 17 degrees of static timing will cause major spark knock.

Most of the electronic first generation distributors were set to 7 or 8 degrees static timing, while the ZX distributors nearly all are set to 10 degrees.

Go to Xeons30 and download the real factory service manual for your car:

http://www.xenons30.com/reference.html

That is the real source of information.

[Gary in NJ]

I have the FSM but it looks like I interpreted the data incorrectly. The FSM says 17 degrees without emissions equipment and 5 degrees with the equipment installed. Since the air pump has been removed I assumed that the 17 degree figure applied. Thanks for pointing that out.

Regarding the 24 degrees of total advance, do you happen to know the rpm that the distributor reaches full advance?

[Gary in NJ]

I played with the carbs tonight. I got the idle down to 650-700 rpm. I leaned out the mixture but need to get them richer again. I have "wide-tab" three screw SU's, so I have the pesky locking tab on the fuel screws. That tab just makes it impossible to move the fuel screws smoothly. So they're coming off.

I should have it all sorted out tomorrow evening. I really love working on these SU's.