motor specs first

350 .060 over, 9:1 pistons, 441 heads, 500 lift cam, holley 4412 carb(71 jets, idle 1 1/2 turns out, 3.5 power valve), center dumps with 2 1/4" tubing running a locked disto at 41 degrees(this is a circle track race motor running turbo blue 110 octane)

i have an odd motor problem experienced between 4900-6000 rpm, the tach is very jumpy, motor seems to be cutting in and out at a very fast speed, more like a stumble. any ideas as to what this could be? I thought it possibly could be jet sizing, anyone have any recomendations?

thankyou in advance

Did you change valve springs to match that cam?

i have an odd motor problem experienced between 4900-6000 rpm, the tach is very jumpy, motor seems to be cutting in and out at a very fast speed,

Sounds like a Dist. problem to me...

the springs are fairly new z28 duals, It does not feel as though it is going into valve float

jets are 71 is that primary or secondary? is the fuel pump able to keep up? also the timing seems a little high try backing it down to 38. Are the valves adjusted properly? is your ignition getting 12 volts? your compression is low for the type of fuel try some pump gas the higher the octane the hotter the spark needed to set it off no answers really just things to consider:confused:

its a 2bl, there are only primary jets, im running a safe setup compared to some of my competetors, running 42-45 degrees, been running these 9:1 motors with 110 and 40+ degrees for awile, its not related to that, anyone have any other ideas?

Justin,
I am going to second the distributor / ignition problem. That is the only thing that would cause the tach to jump around and it would also cause the "jumpy" problem. What type of ignition ?

stock type Hei distro, accel unit inside, no vacuum advance, msd cap and rotor, stock type coil, prc plug wires, autolite racing 13 plugs at .40

Justin,
Check all of your wiring and especially grounds. I bet if you do whatever it takes to stop the tach from jumping, the car will run ok too.

Swap out the ignition module if you have a spare.
Squido

a new moroso durafire distributor cured the problem, thanks guys