[72 CONV]

just dropped a zz4 in the vette
on initial throttle the car dies/hessitates then it runs pretty good (after 1300 -1600 rpm)
it has a msd 8572 distributor w/ vaccum advance with a holley 670 street avenger w/electric choke
i'v tried no vaccum advance , full vaccum advance and ported vaccum advance with no change , the timing is set a 12 deg w/ no vaccum
the carb, dist, zz4 is all new, firing order is good, and have the msd box hooked direct to battery any ideas on what it could be ???? thanks

 

[craftomatic]

Fuel pressure, advance you distributor a bit more, or double check your grounds on the MSD box. Sounds like a fuel or firing problem. Maybe there's something wrong with the way your choke is set up. Does it still do this when the engine is warmed up?

 

[iburke]

Does it pop back thru the carb. Check to see if your accelerator pump is working. It may not be adjusted correctly.

 

[72 CONV]

yes it still does it when it hot or cold
msd is ground rus direct to engine
fuel pressure is good
has a constant 12v on electric choke

 

[72 CONV]

does not pop back though the carb

 

[72 CONV]

adjusted the accel pump spring helped alot but still not right

 

[craftomatic]

Cracked vacuum hoses? Fuel pump or fuel filter? Spark plug wires or routing correct? Fouled plug?

 

[iburke]

I would lean toward some thing plugged in the acceleration ckt. If its a new carb I would check for casting particles in these passage ways.

 

[basketcase]

Have the same issue with my ZZ motor, fatten up the idle by half a turn or so on each screw, fixed the problem for me.

Cheers

Richard

 

[Repo73Vette]

I have a friend who just put a new 350 HO in his 73 with the Holly 670 street avenger. His would die when he braked hard. It turned out his floats were out of adjustment and the floatbowls were too full and the rear one would dump fuel when he braked hard. I don't know if that could happen on accel, but its worth checking.

John

 

[willg1966]

adjustments

most of my chevies were 8 degrees btdc , full advance is another issue, do you have a timing light with the adjustment for full advance, the carb I assume is a Holley the accel pump should just start to mist as you move the linkage. use a vacuum gage to set the idle jets ... max vac per side and alittle tweak one way or the other. the tweek is subjective as to temp humiity altitude, aka density altitude but the gage is cheap and usually has instructions , you can also use a mighty vac for that if you have one, check for vacuum leaks. in hoses and manifolds. check the setting on the choke that can make it run plump. Back in the day we would use double pumpers that would overpower the engine, it sounded like it was gargling gas. Ahh the good old days , by the way I am looking for and l98 injection system and acc. drive for my 75, now that i have lernt da way to play with injection and yes it will fit under the hood. Have fun guys,, hope to see you in a few days I am heading down to the dirt track for a few.