Running very poor up high

[datto_240z]

Hi all

Now after i put my Z back on the road it is running like a POS! Stock everything L26 Auto.

Me(apprentice mechanic) and my Dad(Mechanic) have been trying to tune/sort this problem out all last weekend! Down low its pretty good, maybe a little rough but once it reaches 4k?(my tacho doesnt work) it will backfire and die and splutter. Sitting at 100kmh it is a struggle in increase revvs. It surges and carries on like above.(very annoying when comodores are screaming past you!)

What ive done is...

Tuned carbies as well as i can

tappets

timing

new BOSCH plugs (i know bosch plugs are $^!#)

new leads

new dizzy cap/button and points

newish coil

new fuel filter

although, i had it running pretty good then i tinkered with the points gap(tiny adjust so in the middle of specs) and maybe the timing, all fine, then found out the choke was stuck on on the rear carb so tied that open and then it started backfirng etc!

got me stumped! Why would it even backfire? It seems to run the same between 5btdc and 20btdc

please help!!!

[2-4-T-Z-MAN]

The "newish coil" would be the first thing I would look at with a NEW coil.

You noted 'tappets. Does that mean that you adjusted the valves?

Tuned the carbs, did you do so with and air flow meter?

A backfire could mean too lean, check the plugs. Black is too rich, white/gray is too lean.

Check the resistance on the new plug wires.

All I can think of for starters.

Good luck

[Mr Camouflage]

is the vacuum advance working?

[speedyblue]

Could be too lean. Mine ran OKbut struggled when the revs got much over 3500. Made it richer and it fixed it. Also as stated, Vacuum advance? And ditch the points for an electric dizzy. So much better.

[datto_240z]

Its not vaccy advance. the diaphram is all good and the outlet from the inlet manifold has neg pressure. Plus that shouldnt stop it revving! My old 1000 ute never had the vac advance conected up

tappets... tappets are tappets, cam-rocker clearance

tuned the carbs with a AFM? hey? I havnt got vac guages and was balancing by eye.

Coil should be fine

I stated that the plugs were coming out black, ie rich

I am now taking the carbs apart and cleaning them and hoping for the best when i put them back on! Will also invest in some vac guages to balance them properly

[beandip]

Are these SUs ? I have tried to balance SUs and found it nearly impossible with out a Uni-sen or equivalent . In the USA the auto equipped early Z have dual points. the second set takes over after warm up . Cumbersome at best . As to advance , the vacuum advance is only for lower RPM and the centrifugal advance is at full before 4K . What is the timing set at at idle . Set it at 10 BTDC . Hope this is of help. Gary

[Curtis240Z]

Make sure the vacuum pistons in the carbs move freely throughout their full travel.

[datto_240z]

Yeh twin Hitatchi flat tops, standard 260Z fitment.

AUS didnt get the crazy double point setup... thankfully!

Ive since pulled both carbs apart and cleaned everything with carby clean. Lots of carbon! The pistons move nice and free in their bores(always did). Now i just have to put the carbs back on and see what its like!

[datto_240z]

Well she's all fixed!!!

Put the cleaned carbs back on and no difference!

So i was mucking around a bit more with it and ended up advancing the timing to about 20btdc. Was better! Still not good but better! So i retested the vac advance and it does have a slight leak. So I put the one off my other dizzy on it. better again! I had it pretty good at that stage so i thought why not try a NEW coil(BOSCH GT40R) and some NGK plugs. Put them in and BEAUTIFUL! as if it were straight out of the factory!

Well it could have been that or the loose connection on the ballest resister:knockedou

thanks for the help guys! Im happy again now!