Z revs slowly

[Patcon]

I am working on a 240z with an engine that has very few miles on an old rebuild. I have new Z therapy carbs and have them fairly well sorted now with Scotts's help. I also have the 280ZX dizzy conversion. The engine will rev but not real snappy like I remember. Ideas? Where to start? I will have to double check my initial timing advance but believe it is in the 12-15 degree range. The centrifugal advance is wroking and the vacuum advance is disconnected.

Thanks, Charles

[Zforce]

Are you talking about accelleration or revving in nut nuterual ? If you ignition timing is ok and the exhaust in not plugged it could be the cam timing in relation to the crank.

[Patcon]

I don't believe it is a cam timing issue. Possibly valve train but the car had Weber DGV's on it a couple of months ago and seemed to rev much more freely. I am running ATF for dashpot oil. Possibilities that come to mind were timing, not advancing fast enough. Weak spark, mixture, dash pot oil. I just wasn't sure of the best direction to start or most logical. I would expect the 280ZX dizzy to spool pretty quickly because of the full voltage coil and hotter spark. Just looking for ideas and a point in the right direction.

Charles

[Zforce]

A good way to tell if your mixture is right is to disable one carb and see if the engine will continue to run on 3 cylinders if it does your mixture is good if it stalls richen it up a little. Atf is not always the best solution, yeah it makes the piston rise faster but that cuts velocity through the venturi which in turn cuts the amount of fuel drawn out of the nozzle effectively leaning out the mixture.

[jmortensen]

Your initial timing seems a bit light too. I'd put it in the 18 range + or - a few. You want mid to high 30's when it's all in, and depending on what ZX yours came out of, it will have 17 or 18 degrees mechanical. Zforce is right in that the ATF will lean your mixture on accel, so might try some heavier oil. I think recommended is 20 wt. My Z ran much better with ATF, I put it in a friends and it sputtered and popped and would barely run. There are variables there, needles and nozzle profile and condition, tolerances in the carbs themselves, etc.

[Patcon]

Thanks,

That gives me a direction to start in.

Charles

[Gary in NJ]

Slow to rev makes me think vacuum advance issues. Have you tried disconnecting the vacuum advance to see if there is any difference?

[Patcon]

The vaccum advance is disconnected as most people find that total advance is too much on the 280zx dizzy conversion

Charles

[tlorber]

Other than pinging, what are symptoms of too much total advance?

[Patcon]

I got to messing with this again. I rebalanced the carbs and checked advance. At 800 rpms there is 18-19 degrees of advance. I can't get it to run much below that. If I lift the rear SU piston there is no change. If I lift the front SU piston it starts to stall and will if I don't set it down quickly enough. Is this a rear fueling issue or spark.? Thoughts?

Thanks, Charles

[beermanpete]

It sounds like the rear carb is not working properly. Check the float level, fuel supply to carb, etc. Not likley it is ignition related.

How the plugs look?