naps z 8 to 4 plug conversion

[Zfighter76]

i have a z20 naps z engine with a z24 8 plug head. its a fi head but im running dual 40 dcoe carbs. i am having trouble getting it to run perfectly, it seems that timing is off no matter what i do, it just pops and bangs and shoots gas out of the carbs sometimes, it runs and i can drive it but i sound like "old man jenkins in his jalopy", or a drive by shooter. i wanted to know if i could put any 4 plug dizzy on and make some plugs to screw into the head to block out the exhaust side plugs. at high rpms the fi z24 does that anyways so if im looking for a performance oriented engine (dont say anything about z engine not making any power please, ive heard it all, i get it) wont it work with just intake. i heard datzenmike say somewhere that the dual plug and single plug heads are the exact same except one was machines for four extra plugs. i just think 4 plugs would be way easier to tune, time, and be more reliable. any thoughts?

[metalmonkey47]

i have a z20 naps z engine with a z24 8 plug head. its a fi head but im running dual 40 dcoe carbs. i am having trouble getting it to run perfectly, it seems that timing is off no matter what i do, it just pops and bangs and shoots gas out of the carbs sometimes, it runs and i can drive it but i sound like "old man jenkins in his jalopy", or a drive by shooter. i wanted to know if i could put any 4 plug dizzy on and make some plugs to screw into the head to block out the exhaust side plugs. at high rpms the fi z24 does that anyways so if im looking for a performance oriented engine (dont say anything about z engine not making any power please, ive heard it all, i get it) wont it work with just intake. i heard datzenmike say somewhere that the dual plug and single plug heads are the exact same except one was machines for four extra plugs. i just think 4 plugs would be way easier to tune, time, and be more reliable. any thoughts?

 

Why not get an L head, matchbox dizzy, and have an LZ20?

[Wide14u]

yes you can just do the intake side that is how mine is

[datzenmike]

The Z24 heads were never FI equipped. Only the Z20 and Z22 had the injector notches in them. The Z24 head and intake has squarish ports with rounded corners. The Z20/22 heads and intakes were round port with a small injector notch on the top of the intake port near the gasket to the head.

 

Z24 head top (I cut the injector notches, normally they do not have them) Z22 below it.

 

 

If it is popping then you may have a wire on wrong. Check the order they are on. The top of the distributor cap has it stamped there.

 

I = intake

E = exhaust

 

The order counter clockwise on the cap is:

 

I 1

E 2

I 3

E 1

I 4

E 3

I 2

E 4

 

I would run dual plug any time over single. Dual plug needs less advance so be sure you set the timing around 3 to 5 degrees BTDC.

 

 

A blocked jet or a too small jet can cause a lean backfire through the carb too.

[Zfighter76]

the popping through the carbs is not consisteant. also some other factors to consider. at low end you really have to rev it and let go of the clutch or else it will have no power, you can step on it and it falls on its face if you dont preload the rpms and do a clutch kick. also i set the carbs to the factory setting and blew out every jet, tube, and every crevace i could find with carb cleaner. two of the wires have the outer casing exposed but the spark isnt arcing onto anything, except my hand once. and the less advance with the 8 plug setup is more performance oriented than the 4 plug setup? seems like there would be alot of options for performance 4 plug ignition systems whereas very limited for 8 plug. my dad agrees with you on that its a misplaced wire, he was saying that the mixture in one cylinder builds up and when the spark finally hits it pops, is that whats happening? honestly the engine sounds like a harley, exaactly like a harley, and it pops out the exhaust when i let off the gas and randomly out of the carbs. thanks for the quick reply

[Zfighter76]

and what jet sizes would you reccomend me running for a z20 with z24 head, dual weber 40 dcoe and hks manifold. stock header and two inch piping. and do you know which mark on the crank pulley is tdc? btdc?(thats bottom dead center right?) i see three little notches but that little plate on the block with the indicators is all rusty and i cant get to it to clean it off. i would love to get this running smooth and start an l20 build, i do have an l series block, deciding whether to sell or not. actually have an l20 head but its toast haha.

[Zfighter76]

The Z24 heads were never FI equipped. Only the Z20 and Z22 had the injector notches in them. The Z24 head and intake has squarish ports with rounded corners. The Z20/22 heads and intakes were round port with a small injector notch on the top of the intake port near the gasket to the head.

 

Z24 head top (I cut the injector notches, normally they do not have them) Z22 below it.

 

 

If it is popping then you may have a wire on wrong. Check the order they are on. The top of the distributor cap has it stamped there.

 

I = intake

E = exhaust

 

The order counter clockwise on the cap is:

 

I 1

E 2

I 3

E 1

I 4

E 3

I 2

E 4

 

I would run dual plug any time over single. Dual plug needs less advance so be sure you set the timing around 3 to 5 degrees BTDC.

 

 

A blocked jet or a too small jet can cause a lean backfire through the carb too.

 

so could my problem be an intake leak? im going to try replacing my o rings on the soft gaskets, what do you think about paper gaskets? would the gas resting in the bottom of the barrel on the side draft make it soggy? i know on my dads 48 ida downdrafts the gaskets dont matter because the air fuel mixture goes straight down and doesnt really have any chance to rest on the hgasket, so he uses paper gaskets.

[H5WAGON]

Yes, double check the o rings on the intake for the carbs! My Buddies webers were doing that...tightened a little bit, it went away.

 

Easy to pull them off.....never assume....lol

[datzenmike]

and what jet sizes would you reccomend me running for a z20 with z24 head, dual weber 40 dcoe and hks manifold. stock header and two inch piping. and do you know which mark on the crank pulley is tdc? btdc?(thats bottom dead center right?) i see three little notches but that little plate on the block with the indicators is all rusty and i cant get to it to clean it off. i would love to get this running smooth and start an l20 build, i do have an l series block, deciding whether to sell or not. actually have an l20 head but its toast haha.

 

Jets? I have no idea on those.

The Z24 head is identical to the Z20 head except for the larger ports. Won't have much noticeable improvement.

The tiny V notch on the rearmost rim of the crank pulley is the Top Dead Center mark but only when set against the O (zero) on the timing scale bolted to the timing cover behind it. When the notch and the 0 are lined up the piston is at the top of it's travel. When setting timing with a light the notch should be on or around the second tooth in the picture below. About 5 degrees.

 

 

'V' notch on crank pulley

 

 

Definitely check and set your valve lash, then timing then adjust the carbs. In that order. A too tight intake will backfire out the carb too.

 

 

...two of the wires have the outer casing exposed but the spark isnt arcing onto anything, except my hand once..

 

Listen to what you've just said. If you got a shock sparks could be jumping onto the wrong wire and firing the cylinder with an intake valve open... backfiring out the carb. Never assume. If the ignition wires are damaged... what about the ones you don't see? Get new wires on this first thing or we may be wasting our time chasing our tails.

.

[Zfighter76]

Jets? I have no idea on those.

The Z24 head is identical to the Z20 head except for the larger ports. Won't have much noticeable improvement.

The tiny V notch on the rearmost rim of the crank pulley is the Top Dead Center mark but only when set against the O (zero) on the timing scale bolted to the timing cover behind it. When the notch and the 0 are lined up the piston is at the top of it's travel. When setting timing with a light the notch should be on or around the second tooth in the picture below. About 5 degrees.

 

 

'V' notch on crank pulley

 

 

Definitely check and set your valve lash, then timing then adjust the carbs. In that order. A too tight intake will backfire out the carb too.

 

 

 

 

Listen to what you've just said. If you got a shock sparks could be jumping onto the wrong wire and firing the cylinder with an intake valve open... backfiring out the carb. Never assume. If the ignition wires are damaged... what about the ones you don't see? Get new wires on this first thing or we may be wasting our time chasing our tails.

.

 

the wire is definately not sparking to anything, because it doesnt sit close to anything, it shocked me because i touched it haha. i wrapped it in copius amounts of electrical tape. and when you say to set the v notch on the crank pulley should be at the second tooth, do youo mean the tooth in between the 0 and the 10? or the 10 and the 20? im assuming 0 and 10, but i want to clarify. also, my crank pulley has three of those v notched right next to each other, about a half a centimeter apart from each other. i got it to run good now actually haha, besides the timing and the valve lash, which i know needs to be done, thatlll be next. i made some rubber gaskets for the carbs to seat onto the manifold with, which seal really good, and the main problem was i had two wires out of place, and the rotor and cap needed a tiny bit of sanding to remove the corrosion from the contacts. thanks for all the help. i would have never guessed to set the timing at low advance haha. any thoughts on the three notches on the crank pulley? ill try to snap a pic of it and put it up tomorrow. thanks

[datzenmike]

Each tooth on the picture is 5 degrees so you want the one between 0 and 10.

 

First thing I said. It's almost always the simple things.

 

If it is popping then you may have a wire on wrong. Check the order they are on. The top of the distributor cap has it stamped there.

 

Just because it's running better don't put off checking the valve lash... important!

[Zfighter76]

Each tooth on the picture is 5 degrees so you want the one between 0 and 10.

 

First thing I said. It's almost always the simple things.

 

 

 

Just because it's running better don't put off checking the valve lash... important!

thats normally what i do first on my cars but i havnt gotten around to it yet, will do that probably in the next day or two though, im not driving it yet due to not having it registered or any exhaust. any clue on what to adjust the valve lash to? i know on the bug it was .06 thanks again for all the help. and any tips on what sites are good for weber tuning, or any shops i can contact about tuning? i like doing my own work but i feel that professional input (like yours seems to be) is very important.