Loss of Power > 5K RPM under load

[beandip]

I am running the stock 240 tach as well with the ZX ignition. back to the carb problem . What about the shut off valve on the float on the rear carb ? could it be flooding the rear carb and there by adding fuel so you cannot adjust the needle to lean it out ? It is not wise to swap parts with these SUs , you might get by with a 4 screw but don't do it with a 3 screw. The domes are fitted at the factory and should not be interchanged . Since you have another rear carb , give it a try , swap out the needle so those are the same. I also have a color tune but find that it indicates proper mixture when actually it is lean . It is a great tool though. When I set the mixture with it , I get a lean pop when I blip the throttle. I find the color tune to be a good indicator at 2500 to 3K when trying different needles.

[jrusso07]

Thanks for the info on the ZX dizzy and carbs. My search for a ZX dizzy beigns today! How much for a new one????

I also found the colour tune tends to create a too lean condition, I always back it out a bit - no burnt valves for me!

I must say, there are a lot of great old Z cars (and owners, err, not old owners but great owners...) in the great northwest! Oregon especially! Must be nice slice of Datsun heaven !! The east coast has not been kind to the japanese steel. It's a rare occurance to catch a Z on the road - but if you look hard you will find then tucked away in some nice dry garage...we have learned the hard way!

I will let you know the secret of my mystery condition - this weekend (positive thinking now).

Thanks again!

[jrusso07]

I found the problem - it was with the rear carb.

At first, the gas puddled at the jet nozzle with the choke on and I could see it in the nozzle with it off. It is a new nozzle and needle.

Then I put the dome and piston back on and got the same crappy result. I took it off – and no gas at the nozzle. Checked the fuel delivery to the rear carb – it is fine. I took the fuel bowl cover off – dry as a bone. The needle valve was stuck closed, the edge of the tang on the float got caught up on it. I reshaped the tang so the needle contacted the arc of the tang. Put it all back together and TA-DA – she’s back!

She set right up, leaned her out and she idles like a champ – pulls hard all thru the range and in all gears (big smile!).

Thanks!

[kenz240z]

Glad to hear you found the problem. I'd also recommend changing the dizzy. The dual-point dizzy for the AT equipped cars uses one set of points for normal operation, and the second set is used after the temperature exceeds a certain point. IIRC, the second set retards the timing. So, I'd say either replace the dizzy with one from a manual car (single points), or do the ZX dizzy upgrade. It will be one less thing to worry about.

One other thing to check is the fuel line from the tank to the fuel pump, and from the pump to the carbs. Make sure there are no cracks or splits that could cause leaks or allow air to be sucked in. I always like to replace the fuel hose on an older car as it can get brittle and cause problems.

[jrusso07]

Good Advice Kenny. I found a rebuilt 280ZX dizzy today for $150 with the

e12-80 module. I bought it and I am making the switch!

I do have a couple of single point dizzy's in my spares but think I should go for the top of line!

Z car owners can't be wrong!

Thanks!

[2k2wickedspecv]

I found the problem - it was with the rear carb.

At first, the gas puddled at the jet nozzle with the choke on and I could see it in the nozzle with it off. It is a new nozzle and needle.

Then I put the dome and piston back on and got the same crappy result. I took it off – and no gas at the nozzle. Checked the fuel delivery to the rear carb – it is fine. I took the fuel bowl cover off – dry as a bone. The needle valve was stuck closed, the edge of the tang on the float got caught up on it. I reshaped the tang so the needle contacted the arc of the tang. Put it all back together and TA-DA – she’s back!

She set right up, leaned her out and she idles like a champ – pulls hard all thru the range and in all gears (big smile!).

Thanks!

Hi, My car is doing the same thing...could you by any chance do a how to do with pictures of what you did. my car wont rev past 5k either... and in 3-4 it wont rev pask 4k.

Im kinda of new to the 240z stuff, although i have had it for over a year already. thanks.

p.s. what is the fuel bowl cover... or best can you take a pic of it.. thanks.