Locating the needle

[VaGuS510]

I am on the hunt for a rev limiting problem (stops pulling at 4.5k)... Seems many others have had this problem, currently I am just eliminating possibilities one at a time.

I doubt this is my problem but I just want to check...

I can't seem to find good documentation on how far the needle is supposed to be protruding out of the piston... Currently the lip on the needles is about 2-4mm out of the piston. Can someone point me in the right direction or tell me how to check that mine are correct?

Thanks!

[240260280z]

The needle's thick end/shoulder (where the needle taper stops and the flat cylindrical part of the needle starts) should be on the same plane as the bottom of the piston. (it should not be flush with the counter sunk groove that runs through the piston).

Edited April 23, 2011 by Blue

[240260280z]

To set the needle depth there are two methods I have used.

1. Hold a flat edge across the bottom of the piston and push the needle's shoulder against it then tighten the locking screw.

2. Screw Jet all the way up. Pull needle shoulder out slightly so that it is lower than piston's bottom. Ensure the screw that locks the piston is loose so that the needle can be pushed in and pulled out with gentle pressure. Place piston on carb (with no bell on) and let piston rest in place. The jet will then push the needle's shoulder to the correct depth. Carefully lift piston and tighten locking screw.

Edited April 23, 2011 by Blue

[240260280z]

http://atlanticz.ca/zclub/techtips/carbs/su/index.htm

[Bruce Palmer]

What needles are you running?

What distributor setup?

I don't think worrying about the needle setting in the piston is going to affect anything because at the end of the tuning phase you will have run the nozzle up or down to get to the sweet running spot anyway..... Set the shoulder flush and tune from there. Just understand you aren't doing any tuning with the needle depth.

Edited April 23, 2011 by Bruce Palmer

[JLPurcell]

Possibly an ignition timing issue???

[240260280z]

I had a points distributor on an early Z that had a fuel bog/wall at high rpms/load. Symptoms seemed like fuel. I even rebuilt the carbs and swapped fuel pump to no avail. Swapped the points distributor with a spare and problem solved.

[Arne]

In my experience, this is ignition, not fuel. BTDT. Fought mine for a long while. What ignition are you running? Points, ZX, Pertronix?

[240260280z]

It is still good to set up your carbs properly regardless of the other problem

[Arne]

It is still good to set up your carbs properly regardless of the other problem

Yes, but it is generally best to not make too many changes at once while troubleshooting. Make one or at most two changes, test and repeat as needed.

[Bruce Palmer]

We are finding that the gremlin in a lot of the problem situations we counsel end up being distributor related..... Not most certainly, but enough to say get a light on things before adjusting floats...... That outfit in Portland build a dandy distributor.

[VaGuS510]

I just posted a thread to specifically deal with my rev limiting problem...

Please chime in here: http://www.classiczcars.com/forums/showthread.php?42073-Rev-limiting-problem-at-4000-rpm&p=362040#post362040