When he put his Holley 670 Street Avenger on the first time, it went sideways on him at the hit, well over 6000 rpm, with Z28 springs, set up with shims, and now it won't get past 5000. In the winter we did some serious intake port work on it, did both short sides, and checked and shimmed the hi-po springs. Now I told him to check the back barrels for opening. They were very lazy on the street. He put a lighter spring in, and they are comming in, but all the way? How do you check for that on a vacuum secondary carb? I also feel his distributor may be junk. I have a Craftsman dial-back, and will be checking that this weekend, but that would't check for a bad module. Any ideas. This street motor is more than mild, and it should fly. 15.2's at 94 miles per hour after the carb and porting, and 15.2's before at 96 mph. Something is wrong.

I don't know about fly,but should be running mid 13's with that mph. Something don't jive. It's possible you ported too much and lost all your torque. Why shim the springs if it ran fine before?

my chevelle's been doing that lately, but my secondary float sticks. maybe check the needle and seats? just a thought

shimmed the hi-po springs:eek: That'll about guarantee a malfunction right there, shimming those POSs. He's lucky they haven't broken yet. It's just a matter of time.

Get those stock springs out of there, and put something decent in there instead, AT THE CORRECT INSTALLED HEIGHT.

Mine will rev over 5k with stock springs, and I doubt they're z28 style either.

A Z-28 spring set, if needed with shims, at the correct seat pressure and the stock recommended install height will run an old 30-30 solid lifter stock cam up until you will get scared!!

Heck, my junk 301's, -097 Duntov solid cam would go above 7,000 rpm easy!!

BUT RB is right!! DON'T shim them EXCESSIVELY!! THEY will break as well as wear the lobes too quick!! heck, they might even coil-bind??? BAD, BAD!!!

pdq67

installed heght on them z springs on a small block should be 1.750 why if they worked you would shim them is crazy i think that is your problem for sure porting them mildly would if anything increase rpm unless you touched the valve seats with a grinder then you would loose made power and also the z springs are only good to a .510 max lift cam also i hope you removed the exhaust rotators from the springs if there still a problem comp cams makes the new tool steel valve springs that are goo to 590 lift and fit right in the factory hole

I'm also having a similar problem.I thought at first it might be a transmission problem but know i'm leaning more towards fuel.

Does it have a hot start problem?

No hot start problems. Difficulties started to manifest themselves after a first successful test drive. I believe the module is weak. He told me that this was the best distributor he could find in his collection. This does not give me a high degree of confidence. Also, with a 460 something lift cam there should be no coil bind problems, or undue fatigueing of the springs, although we will check for broken springs. No fuel delivery probs with a Holley high performance mech pump. It just won't rev. It's either springs or ignition, bottom line.

My truck has the same problem as you. It just won't rev!

Replace the module or hardwire an MSD to the pickup.