Flat spot under light throttle application.

[azriel_strife]

hi guys, I have a 2.9 stroker motor in my z. I have a flat spot under light throttle with load, it sings under WOT and idles and revs perfectly fine. the problem is a consistent flat spot where the car feels like it doesn't want to go any faster, it lacks response and torque unless you push the pedal through the trouble area. unfortunately, this flat spot is almost exactly where the car cruises on the highway, so it hates highway trips unless i'm climbing a hills and use more pedal than normal cruise.

-Upgraded 240z dizzy points to electronic pickup, running stock 240z coil at 9v

-F54 block with flat top pistons

-N42 head

Timing is set to 36 degrees total with vac advance disabled. Total advance is all in at 2800rpm. initial is 10 degrees.

-z therapy SU's

-I have synched and resynched the carbs

-checked float bowl levels

-seated the needles against the seats

-atf oil in the dampers

Highest idle achieved at 3 turns out on fuel screws.

I read somewhere that the stroker motor is supposed to have a different needle profile? is this true? if the problem is just the needles i'l happily buy a pair. I have no idea what needles are in the car now.

Edited August 21, 2014 by azriel_strife

[madkaw]

Assuming SU's?

[azriel_strife]

yes sorry, fixed original post.

[beermanpete]

Try thicker oil in the carb dampers.

[azriel_strife]

I am running ATF in there now. the problem is a consistent flat spot where the car feels like it doesn't want to go any faster, it lacks response and torque unless you push the pedal through the trouble area.

[siteunseen]

When you say a stock coil do you mean a stock ZX coil? or your stock 240 coil? There's a difference.

[madkaw]

The needles should be labeled . You need to pull them off the piston because they are stamped around the head.

[madkaw]

'Running stock coil at 9v'????

[siteunseen]

Yeah when you swap to the electronic dizzy it does away with the ballast resistor giving it 12V.

[Bruce Palmer]

Your paperwork from us (ZTherapy) will tell you what needles were installed. More than likely SMs.

[azriel_strife]

Sorry guys, its the stock 240 dizzy with an electronic conversion. it's also a stock 240 1.5 ohm coil with the ballast resistor in tact from what I can tell, but i don't know where the resistor is, the engine bay was cleaned up.

I don't have the paperwork for the carbs because I bought the car from someone else, but I do have the "just SU" dvd.

Edited August 21, 2014 by azriel_strife

[Zed Head]

So the comments about the needles and the damper oil are about richening the fuel-air mixture, right? On an EFI engine with a potentiometer on the coolant temperature circuit you would just turn the knob to add resistance, leading to more fuel, if you had this problem. Of course, that would add fuel everywhere.

Anyway, if it sings under WOT and idles and revs fine, it's not likely a spark problem. Timing looks about right too, doesn't it?

So, change needles to a set that add fuel at part-throttle? Just trying to learn a little carb stuff.