d1rtyb1rd5252

Okay So I finally started tinkering with my '84 T/A this winter and am spinning circles trying to tune this thing.

SPECS: Chev. 355CID, 10.1 compression on cast GEN 1. 72cc heads with 1.94intake 1.6 exh., Comp cams P/N CCA-12-246-3....lift= .487in .490ex duration=230/236 @.050, weiand stealth intake, Quick Fuel 750cfm duel inlet single pump vacuum secondary on 2" spacer (P/N QFT-Q-750-PV), MSD pro billet HEI with accel supercoil and 6al box wired WITHOUT the module. Autolight "25" plugs at .050" and 8mm superconductor wires. Motor is at 10 degrees advance at idle with vaccum advance DISCONNECTED. I have 1 heavy silver and 1 light blue spring on the mech. advance with a black stop bushing.


PROBLEM Burns eyes at an idle and hesitates off the line. Cruising to WOT is sluggish and secondarys have no "umph" motor misses at high RPM. Does great burnouts and cruises ok just lacks performance with agressive throttle. If U keep on it the motor stalls severely at the end of 3rd gear (sucking floats dry??) Motor "diesels" after driving and is hard to start when fully warmed up. Also "Pops" on deceleration.


CARB SET-UP Motor pulls around 14" vacuum at 1000RPM. went from a 4.5 to a 5.5 power valve and it pucked black smoke so I went to a 3.5 and it seems better...mabey too lean. I have #75 jets in the primary and #80's in the secondarys. Idle mixture screws are 3/4 a turn out. I have a pink accelerator cam in the #1 position and a #35 nozzle. I adjusted the linkage to .014" with a feeler gauge. Fuel pressure is at 8psi. I have no Idea however which way is which on the vacuum secondary adj screw. It is about 21/2-3 turns out. Floats are also adjusted to the bottom of the sight hole.

Would appreciate some insight into this problem I hope I provided all the info you'll need

Sonix

iTrader: (1)

That's a good amount of info you gave. I'm impressed.

What cylinder heads are those?
Is that the compxe 274h cam?

Ok, I think .050" spark gap is a bit high for a 10:1 motor, but with that good ignition system, it might be ok. I'd try .040" or so, but that's probably not top priority.

Do you run vac advance on manifold vacuum or ported? 10* is not enough to run that motor, hence you're cracking the blades too far to get it to idle. That'll give you a nice rich idle alright, and might be part of it dieseling.

Try running ~20* at idle. Well, set your timing at 3600RPM to 36*. That's an easy way to remember. Then see what it is at idle. 16* might work, since that's probably what it'll be at. Black stop bushing - not sure what this does (the black part that is), how much mech travel do you have? If you have this much adjustability, get 36* at 3000 RPM or so, and 20* at idle - at least.

I'd swap the heavy dist spring to a medium - medium and light is a nice combo.

Did you try without the spacer before? The spacer (2", open?) is probably best for higher RPM, i'd try without it first. It gives less signal to the carb generally, almost like using a tall single plane intake.

I'd check the spark on each wire just to be sure it's not missing.
I don't think you've got enough power to drain the floats on that carb, assuming the floats are setup right. 8 psi pressure is a tad high, but should be good. Do you have a gauge wired up to it? I mean, can you check pressure as you're driving? That's what i'd want to know - my car did the whole "dieing at top of 3rd", turns out my mech pump was dying. I'd watch the pressure as I hit higher RPM to be sure it's still got 8psi.

That's my kind of car - beater early bird from the outside, very nice looking under the hood. Just like mine.

d1rtyb1rd5252

The heads are a mexican casting off a gen 1 crate motor. I port matched them to the intake and smoothed out the runners

The cam is the xtreme energy 274H

The vacuum advance is going to the base of the carb so I guess thats ported.

I was running 12 degrees advance at idle and backed it off to see what happens, what u say does make sence...unfortunatly Im using a crappy timing gun that won't let u time it back and MSD claims I have to buy there gun to work with the 6al box if I want to that anyways. I never have set intial timimg past 12* so mabey I'll try that I did have a friend that said 16* was good so I'll start there.

The black stop bushing just stops the mech. advance around 3500 rpm which now that I think about it should be higher....right? (6000 to 6500 red line)

I did run it withought the spacer and had the same problems and yes it is an open type.

I have been wondering about the fuel system. I have a brand new "Blue" holly pump (14psi) attached just under the tank and 3/8 OD hard line going to a canister style filter on the fire wall. From there is braided 3/8OD line going to a regulator - fuel cooler- gauge - carb. However the pump rattles and wines like no other. I have a none vented gas cap and left the Evap canister intact venting to atmosphere....and yes sleeper T/A's F*%king rule

Sonix

iTrader: (1)

oh ok, so like 993 heads?
How did you get 10:1 CR? Dome pistons? Just making sure you're spot on for the CR calculation.

Base of the carb is probably manifold advance. So when it's setup, you 10* base becomes ~30*. Which should work ok, but it's debatable.

No, you want all your mech advance in by about 3000RPM or so. The bushing probably limits the travel, meaning you only get 16* mech travel instead of 20* or so. The springs should set from when it starts coming on, to when it's all in. Medium and light should be 1200RPM start-2800 RPM all in- or thereabouts.

Fueling sounds good. You've got a gauge hooked up, so you can verify full pressure at redline, it doesn't drop to 1psi i'm assuming? I'm not wise to electric pumps and regulator setups, but I think you've got it right there.

I know there's a way to bypass your MSD stuff to check your advance, then you can just re-hook up the booster box or whatever. I think someone was just talking about that recently.

I'd go to ported vacuum advance. Using manifold can lead to dieseling from what i've heard. Find a port that shows no vacuum at idle, but increasing as you rev it up higher. Then swap to that one. I'd set up for

20* base
36* total
Ported vacuum advance.
Use timing tape on the balancer or something, and bypass the MSD booster to set your timing. Try that.

d1rtyb1rd5252

Yeah as far as the number on the heads I'd have to go look. I do know that they are 72cc and have been deck once by me. I decked the block to 0" with Speed Pro Power Forged flat tops....I used a program like engine Dyno Pro or something and it gave me around 10:1 static 9:1 dynamic(running).

Hooking up the vacuum advance does raise the advance at idle...so do I still want to set it at 16-20*?

I used to run the medium light combo springs and got away with It I just set it back to stock to get base reading but I was planning on probably upping the advance curve after I got the carb set up. So I'll do that

I only have a fuel gauge under the hood though so I have no idea what fuel press. is on the road.

And what ever I can do to stop the damn dieseling I'll do....so embarassing rolling into a parking lot all bumpata rum pa da rump and then turning it off and a big cloud of smoke comes out the air cleaner :-(

I've also heard 36* total other places so I'll give it a try...I'll have to see about bypassing the MSD..I don't know how without putting the module back in.

Rick King

lower the spark gap to 25 or 30. also your fuel presure is way to high at 12 psi. the holley at wot should be given 6 psi max according to the people at holley tech support.. If it is higher the carb must be tunned to handle the higher fuel presure--It is my belief that if you get the fuel presure and feeding issues fixed you will have much mre power, just have your advance fulley tipped in by 3200 rpms.

GB

rk

d1rtyb1rd5252

The fuel pressure is only 12-14psi up to the regulator on the fenderwell. It's 8psi at the gauge going into the carb itself. Holly says anything over 10psi runs the risk of blowing the needle valve.

This is sounding more like a fuel problem for sure. what about the power valve? a 3.5 on an engine that has 14" vaccum at idle doesn't seem right to me(should be 6.5 right?). I put a 5.5 in at it pucked black smoke... would barley run.

Sonix

iTrader: (1)

Put in the 5.5, make sure your PV isn't blown, then swap primary jets to get it to run on the primaries without puking black, you may be running rich.

If you're using manifold vacuum that's ok I guess. There are some problems with it, such as dieseling. Try using 16* base, and use ported vacuum. Maybe someone else can post up how to bypass the MSD and set up your ignition.

d1rtyb1rd5252

Allright first things first, Im gonna set initial timing to 16* and either disconnect the vacuum advance for now or find a port to plug it into. Then swap out the springs in mech advance. I think a lot of the problem lies there as far as getting the correct idle.

With that established I'll put in the 5.5 power valve and swap out the #75 jets to like a #64 and keep the secondaries at #80....however #64 seem low to me for that kind of motor but if it works it works. I have been baffled as to how I can get 14" vacuum at idle with that big cam (I was expecting 9-10) but the xtreme energy advertises more vacuum so whatever.

What is a common setting for the mixture screw on a 4 corner system so I know when Im getting close to the right Powervalve & Jet combo.


Finally do U know which way is which as far as the adjusting screw on the vacuum secondary...my logic tells me turning in should make them open later and out sooner. Our forcast says snow for like 2 days so as soon as the weather cooperates I'm gonna go play hotrod and get this figured out

chilli

iTrader: (2)

Just wanted to throw this into the mix as well, when I did my non cc carb/ dist swap I was having similair problems and for the life of me couldnt figure it out then one day for s*t*'s and giggles I removed the vac line from the carb and hooked it up to a manifold vac port and walah problem solved for some reason with a stock 4 barrel intake and an adapter plate the carb was getting squat for vac on the base ports. Might wanna check what kind of vac your getting off the carb for the dist. Now if your vac readings that you have been talking about are coming from that line then disregard this whole thing.

d1rtyb1rd5252

Yeah untill now I didn't even think putting that 2" spacer would cause this much headache with the vacuum advance, but investigation is definatley in order...Im looking out the window right now and seeing a break in the weather so.......its time to rock

d1rtyb1rd5252

Ok So I did some tinkering today. I got rid of the 3.5 power valve and put in a 5.5. Went from a #75 to a #63 jet and man my eyes feel like there gonna bleed. It wasn't puking black smoke but there was a definate haze. The motor only pulled 11" vacuum at 1000RPM (used to pull 14) and the 4 idle screws were 3/4 a turn out each.

I did however find that the 2 ports at the base of the carb. have different vacuum sources. 1 was manifold(constant) and one was ported(0"). So I plugged the vacuum advance into the ported.

I put a heavy silver and light silver in the mech. advance and set initial timing to 16*.

The timing seemed to jump a little at idle(standard) and evened out around 20* at 2000RPM. HOWEVER past 3000RPM the timing started going all over. The vacuum was steady at 18". I also noticed the timing light went from blinking real fast to about half as fast. Is this normal or is this just a crappy timing light or should I be worred about this distributor.

Anyways the weather wasn't cooperating but I got a small break in the down poor to go putt around the "front stretch" and all it wanted to do was buck around whenever I wanted to give it any goo amount of throttle.

The moto of today is "grrrrrrrrrrrrrrrrrrrrrrrrrrr"

d1rtyb1rd5252

So the roads were relatavely dry today and I pretty much dove in. Turns out that 5.5 power valve was really a 4.5 (oops:-)) but to make a long story short I tryed ever combination from 3.5 to 6.5 and multiple jet combos. I observed that the lower the number powervalve the more the car bucked untill it barley made it out the driveway. So I reversed my course. Stuck in a 6.5 with #63 jets in the pri. and #72 in the sec. BINGO!!!. Car has never run better gobs and gobs of off idle tork (went through a lot of rubber today and even manged to tweak the suspension threw this S-turn at high-high speed) Still some adjustment needed in the secondary circuit but as far as the motor reving out fully and getting out the gate smoothly it's great......car finaly saw the freeway for the first time in it's life. And other than 1 little hic up there was no dieseling all day. I am much much happier