ZZ4 problems ?? - Chevelle Tech
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post #1 of 18 (permalink) Old Nov 9th, 13, 8:43 PM Thread Starter
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ZZ4 problems ??

Hello Felloe TC members. I have a GM performance ZZ4 350 cu crate motor, I replaced the factory Cam with a Comp Mutha Thumper cam
duration @ .050 235 intake 249 Exhaust installed straight up. Edelbrock Performer intake, Edelbrock #1406 600CFM carb. GM Hei ignition with light spring 12 deg initial timing and full 38 deg @ 2800 RPM 2200 Stall TH700R4 with 3:90 rear.

The problem I am having is RUN on at shut down. I put VOM on wire to distributor At the plug and it has no voltage on switch turn off. Read the plugs. there Light ( off white) have no signs of deposit.

I am thinking I need to fatten up the carb ( might have hot spots to ignite fuel ? )

Wayne
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post #2 of 18 (permalink) Old Nov 9th, 13, 9:19 PM
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Re: ZZ4 problems ??

What is your idle rpm? Very often run-on is the result of a high idle speed. In many cases, more initial will allow a decent idle at a lower rpm. In your case, you would need to reduce mechanical to allow more initial.
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post #3 of 18 (permalink) Old Nov 9th, 13, 10:19 PM
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Re: ZZ4 problems ??

Try to drop your idle to 750 and turn out your mix screws a 1/4 turn.I had a similar issue and it fixed it.
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post #4 of 18 (permalink) Old Nov 9th, 13, 10:29 PM Thread Starter
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Re: ZZ4 problems ??

Idle is at 800 rpm in gear around 900 RPM unloaded will tim the idle screws... I have no vac advance hooked up... ???

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post #5 of 18 (permalink) Old Nov 9th, 13, 10:31 PM
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Re: ZZ4 problems ??

First problem I see, the ZZ4 uses fast burn aluminum heads and total overall timing is only supposed to be 32 degrees. I'd agree with Jerry, bump the initial timing up to about 18 and limit the total to 32 to see how it runs.. The cam is some of the problem.

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post #6 of 18 (permalink) Old Nov 10th, 13, 8:26 AM
dt
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Re: ZZ4 problems ??

Use PREMIUM fuel, problem solved. My idle is set at 1,000.
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post #7 of 18 (permalink) Old Nov 10th, 13, 11:24 AM
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Re: ZZ4 problems ??

You may have to put a stiffer advance spring or two on to bring down the advance rate at idle. I had a similar problem on a friend's 66. One stiffer spring cured it. Good luck.
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post #8 of 18 (permalink) Old Nov 10th, 13, 8:31 PM Thread Starter
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Re: ZZ4 problems ??

I use 93 Sunoco gas, With 10:1 ZZ4 compression , and cam duration , higher compression, not crazy initial timing 12 deg BTDC. I read all the plugs today. all are about the same White insulator ( Slight tan hue on one area each plug ) there not indexed so the slight discoloration is not uniform to the electrode . Still going to jump up one metering rod size. will install ONE advance spring. I have no vacuum advanced can attached ( all mechanicial ?? )

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post #9 of 18 (permalink) Old Nov 11th, 13, 9:23 AM
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Re: ZZ4 problems ??

Quote:
Originally Posted by WayneK View Post
I use 93 Sunoco gas, With 10:1 ZZ4 compression , and cam duration , higher compression, not crazy initial timing 12 deg BTDC. I read all the plugs today. all are about the same White insulator ( Slight tan hue on one area each plug ) there not indexed so the slight discoloration is not uniform to the electrode . Still going to jump up one metering rod size. will install ONE advance spring. I have no vacuum advanced can attached ( all mechanicial ?? )
Interesting... I also do not have the VA hooked up. The 93 octane fuel solved my problem immediately, and this is with my idle set at 1,000. Plugs appear to be fine really. Lowering the idle doesn't help??
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post #10 of 18 (permalink) Old Nov 12th, 13, 2:42 AM
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Re: ZZ4 problems ??

metering rods don't affect the idle mixture at all. premium gas, lower the idle speed.

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post #11 of 18 (permalink) Old Nov 13th, 13, 2:28 AM
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Re: ZZ4 problems ??

Anyone besides me think that some vacuum advance might cool the engine a bit, and would allow the idle speed screw to be turned out?

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post #12 of 18 (permalink) Old Nov 13th, 13, 5:13 AM
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Re: ZZ4 problems ??

at least one does.

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post #13 of 18 (permalink) Old Nov 13th, 13, 9:38 AM
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Re: ZZ4 problems ??

Quote:
Originally Posted by Tom Mobley View Post
at least one does.
Make it two..

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post #14 of 18 (permalink) Old Nov 13th, 13, 10:08 PM
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Re: ZZ4 problems ??

Three, Proven in over 400 ZZ3 and ZZ4 engines.

BUT, you have to do it right, limit the amount of degrees the vacuum advance allows, and, 38 degrees total timing, way too many for any and all ZZ engines, 32 is right.
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post #15 of 18 (permalink) Old Nov 14th, 13, 12:17 AM Thread Starter
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Re: ZZ4 problems ??

OK was sub zero and going to pick up my 64 body today.
the metering rod was to fatten up the Air/fuel ratio. Plugs look to bright . I like a tan'ish color , Will try and lower the idle plum the vac can. it's an a orginial ZZ4 but I have limited the travel . ( I man's HEI info ) and back out the screw's 1/2 turn. calling for warmer weather Friday good day to get he street rod out.... I know it's not a Chevelle but it's a Chevy
1938 coupe and it's parked next to my 64 drop top

Want to thank everybody for there insight ..Drove my Chevelle or Elky most of the summer because of the run/ on nothing worse the pulling into your favorite ice cream stand and everbody looking at you ride and you shut it off and it go's in to run on chug chug clang sputrzzzzzzzzzzz

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