Detonating / Knocking When Floored Z24 Carb

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baseballguru44
Posts: 6
Joined: Tue Sep 10, 2019 10:55 am
Car: 1985 Nissan 720 King Cab ST 4x4

Detonating / Knocking When Floored Z24 Carb

Postby baseballguru44 » Tue Sep 24, 2019 6:09 pm

Hey y'all, figured I'd throw this out here and see if I could get any leads. 1985 720 King Cab 4x4 with carb Z24, 5-speed manual. Engine and carb were rebuilt around three years ago by previous owner.
When driving in any gear, if you give it a good amount of gas on an incline or floor it while flat, you'll get varying amounts of knocking/pinging/detonating/static, whatever you want to call it, coming from up front. Only happens when giving it gas. Sometimes it doesn't do it at all, but if you're in 5th gear on a slight incline at 2400-3000 RPM, it is pretty bad. It will disappear most of the time once you hit a certain RPM, around 3200-3400 I'd say.
I've done standard tune-up stuff, cap, rotor, plugs, wires, all good. I've read up a bit on detonation. Could be timing, compression, or something as simple as the gas, plugs, or lugging the motor.
Any tips would be great!


macgiver
Posts: 944
Joined: Wed Jul 04, 2007 10:21 am

Re: Detonating / Knocking When Floored Z24 Carb

Postby macgiver » Tue Sep 24, 2019 6:16 pm

Maybe carbon buildup increased your "effective / actual " compression high enough to need Hi-test gas??
What gas you runn'in ? Reg. ?

Go try Shell, Chevron , Mobil Premiun 94 , 93 , 92, 91? NOT lower than 91 - get the highest octane ,FILLUP
an empty tank - play with timing if need be AFTER several days runs, or a week whatever.

Is OK or better NOW ? :yesnod

baseballguru44
Posts: 6
Joined: Tue Sep 10, 2019 10:55 am
Car: 1985 Nissan 720 King Cab ST 4x4

Re: Detonating / Knocking When Floored Z24 Carb

Postby baseballguru44 » Fri Nov 08, 2019 2:25 pm

It is much better now. Changed the fuel filter and pump filter, and I've been running premium 93 for about a month. No pinging at all!


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