Hi i am trying to chase a misfire
i have a 383 stroker
425 hp
I put 2 carbs on 2 diffrent distrubitors in
2diffrent new set of wires
4 set of plugs
Adjusted valve lash
compression all 8 cylinders with in 7psi
new set of intake gaskets
misfire is in all rpm range
Vacuum is low at 12-17

 

Have you determined which cylinders are mis-firing?

 

Like posted earlier, see if you can find the missing cylinders unless its sporadic.

Get 8 straight pins and a small jumper wire that can reach from the center carb stud to the 8 lugs on the distributor. Push the 8 pins into the tops of the 8 sparkplug boots at the distributor cap deep enough to hit the core of the wire. Hook the jumper lead to the carb air cleaner stud. Start the car then with a good set of insulated pliers touch the other end of the jumper one at time to each pin and notice if the engine seems the same or gets worse idling. If one pin makes no change then you've got the bad cylinder. Now figure out why that one isn't running. (You could just try a timing light and hook its inductive clip to each wire and see if it pulses but it wont tell you if its something other than the ignition).

Plug all of the vacuum related items even the booster if you have one and then check your vacuum. Plug them at the manifold and carb so you know you are not fighting bad hoses.

If its higher then take it for a ride remembering that the booster is disconnected. Keep in mind to hook up the vacuum advance or just set it to 36 for the test.

If its not higher then spray gummout around your intake gaskets and carb base while it running and see if the engine rpm increases to determine if you have leaky gaskets.

If your running egr (not likely if you've gone with a stroker) remove it and plug it off with a plate to see if its leaking.

 

Could your air/fuel ratio be too lean in spots causing 'lean' backfiring? Do you have a way of checking A/F?

 

No back fire up the carb
already pulled booster line and blocked off
the mis feels like it is across the board

 

No o2 sensors inthe system
but all plugs are filling with carbon no lean powder on any ofthe plugs

 

correct spark plug heat range? make sure there is at least 12+ volts at the distributor especially if you're using the oem wiring. just some ideas.

 

The plugs r e3.42 correct heat range
14.2volts at the distrubitor
no intake or carb leaks

 

I can sweep the dist.35to 40 deg. with out a major change in idle and still retain a mis that feels like i said across the board
and that is with both dis.in the car
and just running o.e. style hei
with 75000 volt coils in both dis.
wires r 10 mm
all. have the same resistance
diffrent caps and rotors
the timing mark on the crank holds steady

 

18436572 unless it has one of those cams that swap 7 and 2. You can ckeck for the miss fire similar to the above post, only, just use your test light. Ground it then stab through the plug wire boots at the cap, or if possible, pull all the boots back for the test.

 

I will post back to night i will swap 7 and 2 and see what she does

 

Thanks 75 u put me on the rt track
it is a 7/4 cylinder firing order swap
now she is a raped ape
idle and vacuum is perfect
no more jumping all over the board
thanks to all

 

Glad you got it!

 

7-4 or 7-2 cyl swap?

wow that's crazy, I would have never thought of that. How bad was it misfiring? Mine has a slight misfire that sounds similar, maybe I'll try this...

 

its a 4 / 7 swap.

http://www.competitionproducts.com/C...products/1980/