Tuning tips

I'm trying to get my engine running correctly, and I could use some tips on tuning.

It is a 350 SBC with a 600 Holley.

It is running rough and backfiring through both the carb and exhaust.

The valves were adjusted when the motor was ***embled. 1/2 turn past zero lash, with the manifold off so I could see it seat in the lifter.

Ingnition timing is, or was 10 BTDC plus 28 built into the distributor.
The dist has moved so I need to reset that.

I also fouled some plugs so I plan on putting in some AC R45's.

The carb is adjsted at 1 1/2 turns out right now.

When I first set it up it ran like a champ, but after it ran for awhile it started to run rough with the backfiring and stumble.
What order do I go through this to get it right.

 

Sounds like the valve adjustment may be too tight.

A lot of guys spin the pushrod and figure all the play is out when it stops spinning.
Most times they've gone past the zero point.

Re-adjust the valve train.

Check for all play out by getting the pushrod close and moving it up and down while monitoring play.
When all the play is out then do the 1/2 turn - or whatever - tighter bit.

What happens when you spin the pushrod to check play, it will start pushing the lifter cup down and you can still spin the pushrod by hand easily.
Checking for play by moving the pushrod up and down is much more accurate.

Fwiw, it's not necessary or recommended to soak the lifters in oil overnight or to pump the lifters by hand with a pushrod when the lifter is submerged in oil.
Doing so will make initial adjustment difficult.

 

I thought that may be something because it ran smooth at first but maybe the lifters pumped up and caused a problem after that.

What is the proper way to adjust a holley once the motor is running?

 

Any other tuning procedures, or tips?

 

If it's a GM points dizzy, set the dwell at 30 deg with the allen wrench before you set the timing. Any other type of points dizzy...set the points gap...again before you lock down the timing.

If it's HEI then....never mind!

 

I set the air/fuel screws with a tach and adjust the screws for highest rpm at idle for each screw then adjust your idle.

 

Tommy, can't you do a shade tree setting on these by:
Making an initial points setting of .014 - .016.
Warming up the engine.
Open window, insert allen key.
Then crank the allen key one way until the engine stumbles lightly and then turn it the other way till you get a stumble then returning the allen key to the mid-point?

Seems I remember you're supposed to go one way till it stumbles and then turn it so far as per the manual which gives you a very close dwell setting.

I'm a big help.
I remember doing something along these lines, but not exactly how it was done . . . and me with a rebuilt points distributor sitting on the bench for the 31....

I do remember you're supposed to close the window when you're done.

 

if it were my luck, the cam would be wiped out.....

 

I thought of that but this is the second time for tuning the motor.
I ran it before and broke everything in, then it started to stumble and backfire.

I changed some things but ended up pulling the motor to have the car painted, and went through it all again.

When we fired it up again it was right on, but after it runs for a while it goes back.

that's what made me think the plugs were fouling and the valves were too tight after the lifters were pumped up...

 

I'm suprised no one has mentioned it yet, but here you go. To set the valves, pull the valve covers, start the engine, and back the rockers off one by one. Back one up until it clatters, then tighten it until it gets quiet, then 1/2 turn. So on and so forth until they're all done. Sometimes you might have to go back and re-adjust a couple once you've done them all once, but this method has always worked fine for me.
As far as the idle mixture screws, hook up a vacuum gauge, and adjust to the highest vacuum reading.
Adjust the valves, then play with the carb, then re-adjust your timing, then go back to the carb...Repeat as necessary.

 

My initial thoughts would be that the valves are a little tight, but I know absolutely nothing about your mill. I run mine @ 1/4 turn on a real mild cam with good valve springs you can get away with 1/8 but it'll chatter and if you have a mdoerate to extreme cam it will be too loose at 1/8.

After I ran the valves I'd light it off and check for a va***m leak. A can of WD-40 will work spray it around the carb and intake and listen for it to rev up. Shazaam leak.

To adjust your Holley grab a vacuum gauge and hook it up to the vac port the open one not the one that goes to the dizzy. Then start to work back and forth on your idle screws it will start to smooth out and you'll probably have to back the dile speed screw off a bit. keep working back and forth until it makes the most va***m at idle that it can make. its adjusted.

if its an older holley and it has backfired many time or at least one good one you may have popped the power valve. that will also mess with you.

One last thing while you have the rocker cover off check for a bent pushrod. And an SBC should be set @ 12 degrees advance with the vac line unhooked.

Something else you could look at is if its jumped time. Like I said I don't know anything about your mill.
Roll it up on TDC then pull the distributer cap the rotor should either be pointing at the #1 treminal or 180 out. if its on some other spark plug trerminal it has jumped time or the dizzy has really spun.

 

I suppose you could. The manual always called for 28-32 deg so I set them at 30. Of course as you know you are changing the timing when you adjust the dwell/point gap. We always just pulled the coil wire and set it with a dwell meter using the starter motor. It only takes a few seconds and it's much easier than the the old feeler gauge routine laying across the fender with your elbow in the carb. (Chevrolet, Olds and Pontiac) Your Buicks are up front aren't they?


As far as tuning an engine I personally stay pretty close to specs on the points/dwell settings. I set the timing by advancing it until it pings under load and then back off until it will pull a hill without pinging. Not very scientific but it works for me. When we lost the 103 octane gas, the book spec for timing on the older higher compression engines needed to be adjusted for todays fuel. IMHO

 

You can pick up a lot of good tuning information at this web site http://www.nationaltbucketalliance.com/tech_info/techindex.asp

 

What is the proper way to adjust a holley once the motor is running?[/quote]

What model Holley is it. A friend of mine had no end of trouble just like you describe... Is it running really rich, blackening the plugs? After much coercion he changed the power valve and it runs great. You have to drive it with a vacuum gauge hooked up to find which valve you need as your cam has a drastic effect on your vacuum.

Flatman

 

Thanks.

The motor is essentially new.
Holley 600 manual choke.
Delco Dual point dist.
030 over 10:1 compression
Crane cam 480 lift; 280-something duration.

I plan on doing the valves at 1/4 turn past zero
Re verify the static timing. It was at 10 when I installed the dist.

Then once running I can attach a vac guage to dial in the carb.

How would I tell if the power valve is gone?

 

take it out and **** on it, if air goes thru it it's bad.