Ok, i posted this in the tech boards but no one replied. Ok well this problem has been a issue for a while now. From about 3000 rpm to about 4000 rpm this engine sounds like a can of marbles its pinging so bad. The thing is, it clears up after 4k and is fine before 3k. When i give it about 1/2 to 3/4 throttle the car feels like its surging, like it has the power but somethings holding it back, it will like studder almost. Kind of hard to explain. The carb is a brand new Holley Street avenger 670 vacuum sec. The distributer is a new MSD hei with 6a box. I rejetted the carb to 68 primaries and 70 secondaries but it didnt help anything. The problem gets really bad once it gets hot outside. Is this a problem of recureving the distributer? Or are my secondaries not opening correctly? Help me here guys please

 

Maybe its getting too much fuel? If your secondaries weren't opening, it would just stop accelerating (the engine I mean) at about 4000, cuz its basically a 2bbl if they don't open.

 

I dunno, it pulls pretty hard from 4-5k, after it stops pinging. I have the timing set way back to kinda help it, it only helps a little.

 

I'm having the exact same problem, gets REALLY bad when it's hot...I've no past experience with pinging engines, this is a new one for me. It does seem to be running a bit rich, got the stock Quadrajet on there with different secondary needles and hanger, but it pinged way before i changed those. Could it be my timing ?

 

Try driving around with the vacuum advance canister unplugged and if that solves the problem then you need an adj. advance canister.

If that is not the problem then I would look to fuel supply. These cars are notorious for heat soak and surge issues.

 

isn't surging a good sign of running lean also?

and pinging can be caused by detonation correct?


isn't there some sort of valve that helps the switch from primary to primary/secondary operation


and then does it stumble only in first gear or every gear when accel or is it every gear it does this?

 

What was the original jet size on the 670?

 

Thanks for the quick replies guys! I appreciate it.

CamaroMike: I'll give that a try tomarrow and see if it helps anything. Do you mean like a restricted fuel line maybe? Because one of mine is kind of bent near the carb. I'll replace that just to make sure.

rx7speed: It stumbles in every gear. This engine is really underpowered. It just feels like its being held back. I mean, a 15.6 with all the mods in this car.. i was hoping for high 14s..

AM Racer: The stock primaries were 65 and the secondaries were 68. Now the primaries are 68 and the secondaries are 70.

 

Check the float level in the sight glass on a level surface.
Look into any kinks or bends you may have in the fuel line.
Only moving 2 numbers up in a jet is really nothing when you're trying to troubleshoot a big issue like that.
I'd look at the plug color myself though first.
You say the ignition is new.
What are you running for plugs and wires?
The problem may be here too.

 

Was the problem found?


Im having this issue out of no place right now.

If i apply vaccume to the vac advance while the engine is idling it stumbles and wants to die.

In park it revs fine, no problem.


while driving it bogs/pings.

 

Is your advance hooked to the ported source or a full vacuum source?

 

Its hooked to the ported source.

 

What degree did you set the timing to?
Did you check the total advance?
Does it change any if you test it without the vacuum advance?

 

14*


I didnt check total but the car has been running fine, it just started to happen out of no place.

I dont have a timing lite,i used someone elses. Ill try to use theirs tomorrow and see if it changes.

 

Kind of a late update, but I installed a Crane adjustable vacuum advance canister with new weights and springs and wow, what a difference. All pinging / detonation is gone, and the car actually runs MUCH cooler.