SU carbs and high revs

[2ManyZs]

Since you seem to have checked almost everything already on the fuel side... maybe it's time to step back and look in a slightly different direction.

Have you checked the air gap on the ignition? Have you replaced the plug wires recently? Then there is always the slight possibility that the charging system is not charging at it's full capacity and the ignition is performing 100%...

Kyle might have hit on a key here as well, it could just be tired, weakened valve springs.....

I'm still somewhat baffled by the way it acts with the air filter housing in place....

[240ZMan]

Thought I'd share the latest. I only had a little time this morning so I moved the cam gear to the #2 position. The Nissan book says this results in 4 degrees of cam advance. I had expected to feel the power peak move up the rpm scale. But interestingly the point of maximum revs moved down from about 4800 rpm to 4500 rpm. And just to clarify, when the engine hits the max rev point, it just stops increasing in revs - period. If you're not ready for it, you almost fall forwards as the decrease in acceleration is that sudden. I think I can rule out valve float now, and my instincts point towards air intake, not fuel. I'm going to look at the little bit of smog control that's still on the engine. I'm wondering if at the max rev point if something is opening up enough that the engine is going too lean to rev any higher? Just a thought.

[240ZMan]

<b>SOLVED!</b>

This morning's clue that advancing the cam timing resulted in the max revs occuring sooner made me wonder about the overall cam timing. So I tried a few combinations of retarding the cam gear and found out that the best case occured when I had the cam gear on the #1 setting, but moved the chain one link to the right (retarded). This resulted in the notch ("V") on the cam gear being centered on the oblong mark. Before the notch was to the right as Nissan shows in the book.

Now it pulls to past 6k rpm, albeit there's a fair amount of vibration above 5k. Also, the idle is more stable now. I've gone through the carb tune-up steps again and what an overall difference in the engine!

So in the end it was all about the cam being too far advanced. What's so frustrating about this is that book shows the original setting I had (notch to the right of the oblong mark) as being desired, but clearly that's not the case.

Many thanks to everyone who made suggestions. The good news is that in the process of getting this resolved I think I've gone over just about everything else possible, and overall this is probably the best the engine has run in a long time!

Now on to the clunk in the rear, the pulling brakes, etc.... :classic:

[Chino 240Z]

That's awsome! It's such a good feeling when you do find the problem and all the other things you did only made it run that much better when you did find that gremlin!

Now don't you feel smarter, especially since you did it yourself? I do!

Cool deal, Craig

:classic:

[Kyle]

That's awesome!! Congrats on getting things running...

The clunk is your rear trans mount, about $35 last time I bought one...

Try adjusting the rear brakes so they drag the same and bleeding the brakes all around. If that doesn't help the pull, then you've probably got a stuck piston on one or both of your front calipers.

Just trying to bring closure to the thread:-)