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Old 10-26-2004, 02:27 PM
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Timing Question on ZZ4

Ok.. so Ive been having some issues with dieseling with my fairly new (7k miles) ZZ4 crate engine. _Its got a Barry Grant zz4 crate carb on it.

So after flogging the distributor back and forth trying to find a spot where it wouldn't ping so bad and not diesel and simply not finding it I figured I better do it the right way.

So with the engine at operating temp I set the timing to 12 degrees.. The engine runs good at that but still diesels. _So I figured maybe there's something wrong with the vacuum advance. _So I disconnected and plugged the vacuum line and set the base timing to 4 degrees. _As soon as I plugged the vacuum line back in it jumped to 23 degrees. _To me that just doesn't sound right. _

The vacuum advance is connected to straight vacuum not ported.

Any suggestions? _


DUH - I figured it out after thinking about it..

I set the base timing with the vacuum disconnected to 12 degrees. Total timing 36 degrees at 3500 rpm.

THEN connected the vacuum advance back in Sometimes I wonder about myself

Last edited by JoeS; 10-26-2004 at 04:46 PM.
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Old 10-26-2004, 04:59 PM
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Glad to see you figured it out I think we all wonder about ourselves sometimes lol.
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Old 10-26-2004, 05:11 PM
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I`m pretty sure the vaccum advance is suppost to go to a ported vaccum source. It`s been a while since I used a vac. advance distrib. I could be wrong though. If it`s hooked up straight to vaccum, it`s got the full advance at idle. It`s not suppost to have full advance untill around 2500-3000rpms.
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Old 10-26-2004, 05:44 PM
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Ported vs Vacuum

Ok.. so I read about 10000 posts about the difference between ported and manifold vacuum advance. So it seems that everyone has a different opinion. Is there a definitive answer for a zz4?
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Old 10-26-2004, 07:03 PM
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Full manifold vacuum I beleive has been found to be optimal.
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Old 10-26-2004, 07:07 PM
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full manifold is the way to go!!!Ported vacuum was designed for emissions control.BM
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Old 10-26-2004, 08:31 PM
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I have always used ported vacuum, it stops the "tip in" ping that occurs under light loads and the engine generally runs cooler. I have experimented with both types of setups and have never found an instance where full vacuum outperformed ported...for street cruising or road racing.

Sorry guys, I have never seen an instance where switching back to ported vacuum and retuning the ignition timing to take advantage of running more initial advance didn't make the engine run better, stop run-on and drop coolant and exhaust temps. Dual diaphram distributors need both hookups with the inner diaphram getting full manifold vacuum. The proof is in the plugs, check them for signs of detonation and you will see the difference between the two methods.

Feel free to try both setups and determine for yourself, don't forget to recurve the distributor to have all your mechanical advance timing in by 3400-3600 rpm.

Just my opinion and I'm sticking to it.
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Old 11-07-2004, 03:50 PM
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OMG I cant get this right! help

Ok Still cant figure this out.. heres what Ive found:

14btdc Manifold vacuum = pronounced ping at tip in

14btdc Ported vacuum = Pronounced ping at tip in

12btdc Manifold vacuum = pronounced ping at tip in

12btdc ported vacuum = same ping

10btdc ported vacuum = not so much ping but there

Cant do manifold vacuum as rpms get up to high and cant idle below 900 in park

8btdc ported vacuum = ping going away but also power feels less

6btdc ported vacuum = ping there barely but definite drop in power. Also starting to diesel a lot when shutting off the motor.

So my guess is that the ping would go away at around 4 degrees but I also guess that 40% of the power would also be robbed by this setting.

I checked and with the vacuum disconnected from the distrib. advance I get around 32 degrees of total timing in around 3000k rpm.

What am I missing? Timing is not this difficult but for some reason I cant get this figured out. I tried emailing Barry Grant carbs but got no response. Could the pinging be something other than detonation? It starts pinging from a cruising speed to maybe 1/8th throttle trying to accelerate mildly. It doesnt ping at idle or at 1/2-full throttle.

Im going crazy, theres gotta be something Im missing

Thanks!
Joe
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Old 11-08-2004, 07:59 AM
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I also throughly checked for vacuum leaks and couldnt find any. So unless theres a leak under the manifold I think Im good there.

Joe
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Old 11-08-2004, 08:20 AM
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Joe,
call the people where you bought the motor.In my opinion you should have initial timing set at 8-10 btdc.Idle at 700-800 rpms and full manifold vacuum.Thats what I have my 67 setup as and it screams!!!!Good luck bm
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Old 11-08-2004, 11:09 AM
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Unfortunatly thats really not an option for me ;(

Theres gotta be a simple solution to this.. Could the distributor be bad?

Could the tip in pinging be caused by the idle mixtures not being set correctly?

Im beating my head against the wall
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Old 11-08-2004, 06:31 PM
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ZZ4

Yall are looking in the wrong place. There is too much air coming from somewhere. Usually the problem is when the idle screw is cranked down and the idle transfer slots are uncovered. Look to see if the carb has bleed holes drilled into the butterflies. Usually if you can uncrank the idle screw and get the idle back up by adjusting the idle mixture screws. Some old cars had a anti-diesel solenoid that dropped the throttle to nearly zero degrees when you shut off the ign. Just for kicks idle the carb way down to like 500 rpm. If you need to keep you foor on the throttle to keep it running than do so. Drive the vehicle as usual and then stop and shut the ign off and lift your foot at the same time. If this stops your dieseling than you have too much throttle angle at idle. If there is no way to adjust this out of the carb then you have a carb that is too lean on the idle circuit. If it's an aftermarket carb then you can install a smaller air bleed jet or pull the metering plate and enlarge the fuel jet NO MORE than .001" that will give you about a 7% enrichment in fuel flow at idle which should make up for the lean condition at idle.
OR...You could just try another carb!
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Old 11-08-2004, 07:47 PM
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The carb is a brand new out of the box Barry Grant crate engine zz4 carb. I suppose it could be a bad carb?
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Old 11-09-2004, 05:42 PM
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So when I plug in the vacuum line to the distributor I can hear a distinctive clunk. Could it be that the vacuum advance canister is kaput ?
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Old 11-09-2004, 06:24 PM
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That could be it.I never hear a Klunk from my distributor.bm
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