Rob 97 Z28

iTrader: (3)

Been fighting my '88 with its "backfiring" issue.

Long story short, car has a '72 350 .040 over , w/new Lunati cam, lifters and timing set. Everything was installed properly. The carb was just rebuilt lastweekend, thinking that that was the prob. My buddy believes that since we know nothing about the distributor that its junk. I put a new curve kit in it about a 2 months ago or so. The issue is that anything near 1/3 throttle or more it "pops" through the carb the more throttle the worse it gets. I went and retarded the timing today and it seems to really make no difference.

My '02 has to have the clutch bled so its "out of commission" til i can do that. But the '88 is really begining to **** me off.

If i do go and buy as new distributor (for like a 1980 Z28 we'll say just cuz its an HEI non CCC car like my '88) tomorrow at autozone along with a cap and rotor could this possibly solve my issue? Im USAF and am on stand by this weekend so if i get a call things are gunna get real crappy real soon...

Air_Adam

Sounds to me like its either running too lean, has one or more intake valves hanging slightly open (too tight on adjustment) or the timing is too retarded.

Under what conditions does it pop? loaded, steady cruise, hot, cold, what rpm...?

Whats the carb setup like (rods, hangers, etc)? Whats the engine combo?

Rob 97 Z28

iTrader: (3)

I adjusted the carb like the Edelbrock vid said to do it, and i have also tried adjusting it prior to the rebuild=no improvements

the timing has always read way off. We put the set up together this summer when i got back from the desert. Its always read like when the balancer says its at like 8 or 10* advance it'll barely run, obviously the more you advance it to run at what seems/sounds like normal timing, it'll read like 24* advanced.

The car does it anytime. wether its idiling, when its being driven. It "pops" no matter what.

The carb as far as i know has the stock Edelbrock 1406 carb jets and rods. It was given to me by another friend and worked fine on my 305. Thats why i was hoping that it just needed to be rebuilt but that didn't solve thye issue.

As far as vavle adjustment, i adjusted the about 2 or 3 months ago and i loosened them up till i heard clatter, tightened them just until they stopped clatering then gave each rocker an additional 3/4 turn. I know theres a rocker or 2 on the pass side that recently started making a tiny bit of noise but nothing that would cause and or be contributing to the issue at hand.


Engine:

'72 350 out of a '72 Monte

.040 over w/stock CR pistions
stock heads w/only 20k on them
Lunati: Valve spring, timing set, cam and lifters
SLP 3rd gen shorties, w/"true dual Y-pipe", Borla cat-back
Edelbrock 1406 carb & intake
stock Delco tr45 plugs

JohnyP

iTrader: (3)

theres your problem edlebrock carbs are junk....go get a holley with mechanical secondaries..i bet you wont have a problem again for quite some time....

Rob 97 Z28

iTrader: (3)

Well I understand not everyone likes Edelbrock carbs but I really don't feel thats the problem. Can't say for sure, thus why i keep posting about this issue...

89RsPower!

sure a lot of people hate edelbrock carbs, but theres no reason a car can't run just fine with one. I DOUBT throwing another carb at it will magically fix the problem.. sounds like it's probably a timing issue.. are you positive the chain was installed correct? How about the dist? Positive on the firing order?

Air_Adam

Exactly. I'm no fan of Edelbrock carbs, but it should still function just fine unless something is mechanically wrong with it. The Edelbrock sticker is not your problem.

The first thing you need to do is figure out whats going on with your timing. It sounds like you have either the wrong balancer or the outter ring has slipped. You need to correct this so you can set the ignition timing properly.

Rob 97 Z28

iTrader: (3)

Thanks for all the replies!

As far as the balancer, its the original stocker. Everything on the engine(excl. the cam, lifters, timing set, carb and intake) is what was on it when it was running like a top.

This morning driving it to work, popping/backfiring as normal, no power to speak. I noticed also once its warmed up it pops/backfires very subtuly and if its in drive after its warmed up it will stall out. Needless to say I had to nurse it here on base this morning

Im seriously just considering taking it to a garage. I HATE giving up, especially on such a simple set up on the car but Im runnin out of hope and ideas



LUNCH TIME UPDATE:


Went out to the car on my break fired it up and started on the driver's side and began to readjust the valves. This time backing off each nut til i heard "clatter" then slowly tightened them back til the were quiet, then went 1/4 turn as a final tightening.

Made to the No. 6 cyl exh. valve and began loosening the nut...no clatter...more...still no clatter. Began tightening it down and after plenty of turns when it normally would've been tight and notice the pushrod just sittin there doin' 360*s laughing at me =P

The good news is that theres no more popping/backfire through the carb!!
Gotta alittle bit of clatter where i need to go back and maybe "snugg" down a nut or two. Sucks that the lifter went dead on me though, those were all brand new Lunati lifters =(

89RsPower!

are you sure it's a lifter and not a missing cam lobe? Did you replace it and all is well? I'm a little confused, you said it's fixed now so I'm guessing ya left something out?

Rob 97 Z28

iTrader: (3)

Since its not backfiring anymore, im assuming that the rocker arms were tightened down a bit to far. This is all what i was able find out/do on my lunch break. I hope and pray it didn't grind the lobe to a complete circle! It doesn't pop at idle any more, that was a first of the good signs, then when i cracked the throttle a few times all it did was rev up with out anykind of popping/backfiring. I want to try and pick a a few lifters today on the way home so I can replace the one thats bad but I can't remember, on the Gen I small blocks; can I retreve the old/bad lifter by just taking off the rocker nut and pushrod OR do I have to take the intake off. I know if the intake is off it can be taken out that way, im just trying to do this the most time efficient way

five7kid

iTrader: (14)

You have to take the intake off.

Lunati will probably have something to say about you replacing lifters and not the cam.

Rayzor32

iTrader: (1)

.

Rob 97 Z28

iTrader: (3)

First off to all of you who took the time to read/reply to this thread


Five7 kid, thought so but couldn't remember. I know the Gen II & IV heads have to be pulled but couldn't remember from the lasttime i had the intake off on this one. Sounds like a good project for this weekend.

I already stopped by AZ today after work, got new intake gaskets, 4 new melling lifters (i know they're not Lunati, but its a pretty tame cam). I just hope the cam lobe is okay and by replacing 1 or (worst case 2) lifters things'll be okay...

1320_Guy

iTrader: (3)

Remember if the cam is fine you still have to break in the new lifters (flat tappet of course)

BASSETT IROC 85

iTrader: (2)

I hope lifters fix the problem but I would bet that the cam went south.keep us informed.

Rob 97 Z28

iTrader: (3)

Well worst case senario if it did, this gives me a good excuse to order/install the cam I originally ment to get the Lunati 60101

Advertised Duration (Int/Exh): 256/262
Duration @ .050 (Int/Exh): 213/219
Gross Valve Lift (Int/Exh): .454/.468
LSA/ICL: 112/108
Valve Lash (Int/Exh): Hyd/Hyd
RPM Range: 1000-5500

I hope I'd be able to reuse my lunati valve springs seeing as how the whole springs/cam/lifters went in at the same time. However if the lifters been under addtional pressure the springs have most likely endured the same added stress

Rayzor32

iTrader: (1)

that cam is TINY

Rob 97 Z28

iTrader: (3)

Yeah i know it is, however they're stock heads. Im not sure what the stock '72 monte heas flowed but i know its nothing spectacular; not the worst but...

The cam in it now is a 60100 which is alittle bit small than the 60101. Little less lift & duration but same LSA. Im just wondering it the valve springs are okay if doing a swap if fea$ible

Rayzor32

iTrader: (1)

they might be good find out the casting number

1320_Guy

iTrader: (3)

Might wana check the studs in the heads, if you overtitened the rocker arms the you could have started pulling the studs out.

Rob 97 Z28

iTrader: (3)

Will do, thanks. Didn't even think of that