Tuning my 383

[Harlow]

Alright, I'm still having problems with my car and I think its from my tuning. Could someone please tell me what order I should tune the car? After the carb rebuild I think I screwed up tuning it somewhere and now its just way out of whack after messing with it and I need to start from square one. How should I start?

Some specs (if it makes a difference):
383
Holley 750 Vac. Secondary
Eddy Performer Intake
Freshly rebuild Stock distributor
Comp cam (.510 292, thats the cam the previous owner told me he put it)

One thing that I know should not be happening is: After I set the timing with the vac. hose disconnected and plugged off at the carb, when I hook the vacuum hose back up the rpms/vacuum/advance all jump up, I know that the vac. advance should not have any affect at idle in park. I'm pretty sure I've got it connected to the right port (on the primary metering body on the pass. side). Whats the deal with that?


Thanks for all the help guys,
- Scott

[Brightyellow69rtse]

just block off the advance mine runs pisser i havent hooked it up in years per a guy here named neil maybe hell chime in    my 750 float lvls were touchy make sure those are right, i had to adjust mine several times before i got it. its alot of trial and error mines quite a bit different now than it was wheni bought it "already setup for my motor " by a performance company just do one adjustment at a time till you get what you want ........Mike 

[firefighter3931]

One thing that I know should not be happening is: After I set the timing with the vac. hose disconnected and plugged off at the carb, when I hook the vacuum hose back up the rpms/vacuum/advance all jump up, I know that the vac. advance should not have any affect at idle in park. I'm pretty sure I've got it connected to the right port (on the primary metering body on the pass. side). Whats the deal with that?


Thanks for all the help guys,
- Scott

Scott, you have the vac advance hooked up to full time vacuum.....not ported vacuum. That is why the idle speed increases when you connect the hose.  That's a pretty healthy cam....it will want lots of advance at idle. I would leave the vacuum advance off and tune w/o it. Bump the intial timing up to at least 15* at idle and see how it responds. Put a vacuum guage on it and see how much vac it's pulling at idle and report back.


Ron

[Harlow]

should I keep the vacuum gauge hooked up where it is right now (full time vacuum) or should I change it to the manifold vacuum to do the vacuum test?

[firefighter3931]

should I keep the vacuum gauge hooked up where it is right now (full time vacuum) or should I change it to the manifold vacuum to do the vacuum test?

Both locations are fine for the vacuum test....i would use the port on the carb. Adjust the advance to maximum vacuum then put the tining gun on it to see what you've got. When the idle speed increases, which it will, simply readjust your idle speed on the carb. 


Ron

[Harlow]

Alright, heres an update on what the car is doing.

I got it to run and actually took it out on the street. The issue now is that when I punch it to about half throttle I hear the carburetor suck in air but no significant rpm increase and then the engine stumbles. I am also still having issues with rpm drops (850 to below 600 and dies) when I put the car in gear. I really just need someone to give me a full "how to" on tuning and see if I can work this out. I'm starting to get really discouraged about this and my dad needs the car to be able to move when we need the garage space because were moving, so I need to have this solve ASAP.

If you need anymore information just let me know and I'll answer your questions.

- Scott 

[BrianShaughnessy]

Your cam sounds similar to the MP 509 which is known for a fairly rough idle with fairly low vacuum... which I know of personally.  You should do your idle adjustments with the car in drive (wheels chocked,  parking brake on) instead of neutral - which would be the preferred method for a stick car.
Rather than spend your limited funds on a renew kit,  you should probably buy stuff like a vacuum guage and make sure you have a good timing light.   Then you can buy things you need like a correct power valve and reusable bowl and metering plate gaskets (the blue holley ones), secondary springs, carb cleaner, etc. 

[Harlow]

I've got a timing light and vacuum gauge. Yeah its got a rough idle and low vacuum (6-7"Hg). I've been making all adjustments with the car in neutral. So I should be making adjustments with the car in gear?

[Harlow]

I got the car out tonight, I'm think that its missing on atleast 2 (possibly 3) cylinders. What are the things I should check to try and find the problem? I hear a ticking/clicking noise on the drivers side bank, I ran it in the dark and didn't see any arching on either side.

- Scott

[BrianShaughnessy]

I'm gonna guess your exhaust stinks like unburnt fuel and burns your eyes.   You'll probably have to change or clean your plugs several times before you get this tuned up right.   You're probably fouled up now.

Here's the description of your cam from the comp catalog.

HYDRAULIC-Serious street/strip effort.     Hyd. Hyd. 3000 to 6200 21-242-428 292H 292 292 244 244 .501 .501 110°
383 needs 3000-3500+ stall. 440 needs       Single-Bolt
2500-3000. 750 to 800 CFM carb. &
headers 3.91 gear up.

It sure won't like any stock type converter in the trans.
I'm gonna say you're gonna have to back it off to about a 4.0 or a 4.5  power valve to start and see what happens.   
Yes... normal idle tuning for automatics is done in drive with the wheels chocked and e brakes on for best results. 
Ron said you'll probably need to start at about 15 degrees initial timing... maybe even a little more.

[Harlow]

yeah, the exhaust smells real bad. I bought both a 35 and a 45 power valve. I put the 35 in first. I'm going to pull the plugs on friday (got school off) and see how those look. Thanks for the help. I think I'm on the right track tuning this thing. I'm trying to get the idle speed up without having to open up the primaries too much. I advanced the timing to about 22 initial (highest vacuum) and it seemed to run a alot nicer. Thats when it became much clearer that the engine was missing on that drivers bank. I'll also try tuning it in gear on friday.

- Scott

[BrianShaughnessy]

If you're up at 22 initial then you're gonna have to limit your mechanical advance on your distributor because you're probably way over what you want to be running at anything over 2500 - 3000 rpm and you'll detonate like crazy.

You'll probably want to back that off some depending on how the engine cranks when you try to start it when it's hot.

Good luck. 

[Harlow]

I was guessing that was going to be way too high, I just wanted to see what it ran like. I'll try something more like 15*.

[Harlow]

Alright, it turns out my new plug wires had gone bad (cheap Duralasts). I got my money back on those and got a good 8mm set. the engine doesn't miss anymore! It was missing on two, possibly three cylinders. Now it is drivable, but I still have some fine tuning issues. It has an off idle stumble and if I punch it from idle it just stumbles briefly and then dies. Is it possibly too lean? I hear that with a big cam lots of times the throttle blades will be cracked open too far (cause it needs more air) and this can cause an off idle stumble. Anyone have any idea what the problem could be? Are there any other symptoms of having the primary blades open too far? It seems like my exhaust smells really bad, could this be due to the primary blades being opened too far at idle?

[Charger-Bodie]

first off [WITH THE ENGINE OFF] look down the throttle bore and see if the nozzle squirt gas even if so you may need to adjust the acc pump for more or less initial charge 2nd thing to try also not running , adjust the idle mix screws by screwing them both in and then screw thm back out 2.5 turns this should be a good place to start , hook up a vac gauge and fine tune the adj from there

[Harlow]

what do I look for when the nozzle squirts gas, does it just need to have even squirts on both angles?

[Charger-Bodie]

what do I look for when the nozzle squirts gas, does it just need to have even squirts on both angles?

yes thats just to find out if the accelerator pump is infact working

[Harlow]

yeah the accelerator pump is working. I have the idle mix screws out 1 1/4 turns, because thats where I got max vacuum. I'll try it with them out at 2.5 and see how it works

[Charger-Bodie]

yeah the accelerator pump is working. I have the idle mix screws out 1 1/4 turns, because thats where I got max vacuum. I'll try it with them out at 2.5 and see how it works

if thats where you have max vaccuum they will prob end up there 2.5 turns is just a starting point and usually ends up pretty close

[Harlow]

alright. I set my mix screws out to around 2. It seemed to run better. I then set the timing to 12 and did a test run (did a few test runs with different initial timing and 12 seems best). There wasn't anymore off idle stumble, but the engine does not have much power at all. For my set up I think it should be able to break the tires loose (it used to before the carb rebuild) with a good 3/4 throttle stomp. Well now I go from a dead stop to FULL throttle, foot to the floor, and I got them to break loose for maybe a second and then stop. Whats going on? What could cause this? I need some ideas. I've made a lot of progress, the car is now drivable. The next step is to figure out this performance issue. Thanks for all the help.

- Scott

[myk]

How are the plugs, again?  If you haven't already, I would check those out and post what their condition is here on the boards.  Also, how old is the motor and the build on it?  I remember trying to tune up my 'cammed up motor when I first bought the car, only to find that there was zero compression as well as other issues and in need of a rebuild anyway...

[Harlow]

The plugs were blackened, and 3 were wet with fuel because of bad plug wires (that was why it was missing). The build is about 10 years old. I think I just need to make some more tuning adjustments, because before I went through and rebuilt the carb, distributor, etc I could break 'em loose at about half throttle. Could the problem be that  the accelerator pump linkage is not adjusted properly (thats why it was stumbling off idle when I would nail it) so I had to turn the idle mix screws out about 3 turns (which fixed the off idle stumble, but still not much power) so that it would have the extra fuel needed when I would nail it?

- Scott

[Charger-Bodie]

are you sure that the secondaries are opening ? they can sometimes catch up on the base gasket, and sometimes the linkage can bid up too

[BrianShaughnessy]

What was your vacuum reading AFTER you changed the power valve to the 3.5? 

[supserdave]

Is the motor pinging any? With that much timing, I would watch out for that. Black spots on the plugs is a sign of it to.

What is your total timing?