help tuning sbc 350 timing or carb?

[Grandprixpaul]

Ok heres my problem ,i know i need timing set at 14 per the engine builder but how do i set the timing,keep idle low and get carb set right ? What should i be doing first? Everytime i set timing at 14 it seams to be idling to high,i turn down carb and timing is off again got to the point where the adjustment screw on the carter/edelbrock was all the way out no adjustment left ?

 

[bigtmoney]

Do you have your vacuum canister hooked up on the distributor? Is the hold down at the base of the distributor tight? Do you hear vacuum leaks when the car is running?

 

[richp85elco]

sounds like your tuning with the advance hooked up, you need to set your timing with the vacuum advance disconnected, and the plug where your getting the vacuum from plugged (either from your carb or manifold). Set your timing where you want it, you can set it by ear for highest rpms, or at 14 if thats what you want, then tighten it down so it wont move while the engine is running. Next you need to decide whether your going to be running full manifold vacuum or ported vacuum to you dizzy and plug it back in, i'm assuming you have it on ported from your carb. Now you can begin adjusting your carb, set your idle as low as you can, if you cant get it low enough then you'll have to start adjusting your mixture screws, which can make your idle go up and down. So you will have to keep transitioning from idle screw to mixture screws to get it down to where you want it. Really just depends on what kind of carb your running

 

[anthonychacon80]

i wrote this for someone else having trouble tuning their Qjet



Things you will need.
1. vacuum gauge
2. Tachometer
3. Idle mixture adjustment tool
4. screwdriver

Block your tires! and set parking brake!!

Section 1.
WITH CAR OFF
1. Disconnect and plug the distributer vacuum advance. plug the vacuum gauge into manifold source
2. Turn your idle mixture screws in all the way, but not too TIGHT as you can damage them. Turn them OUT about 3.5-5 turns max. Make sure you turn both out precisely the same number of turns.
With CAR ON
2. Leave the car in PARK, adjust the idle speed screw on side of carb as LOW as it can go without the motor chugging or stalling.
3. Set your initial timing to the specs for your engine. This is the base timing NOT counting the degrees advance of your accretion curve or the vacuum advance.

Your car should run acceptable at this setting. Now you need to fine tune it.


Section 2.

1. Put the car in drive. Have someone with their foot on the brake as well for safety. Your car should NOT be able to move. DO NOT ALLOW ANYONE to press the accelerator, and do NOT open up the throttle with your fingers while your car is in DRIVE.
2. With the car now in DRIVE adjust your idle speed screw again as low as it can do without the car chugging, OR to the RPM on that is on the sticker of your radiator shroud. the car should run smooth and idle nice. Try putting a glass of water on the top of the car and make it so the water is still and no vibration rings. A V8 should run nice and smooth in drive! (depending on the CAM and exhaust resonance you might not be able to get it perfect) If the car can not stay running at the RPM you are aiming for move to next step... THE END GOAL IS TO SET THE RPM AS LOW AS YOU CAN WITH AS LITTLE GAS AS POSSIBLE WHILE STILL HAVING A SMOOTH RUNNING ENGINE
3. with the Idle mixture adjustment screw tool turn out each screw a LITTLE until the car can stay running. Also keep an eye on the vacuum gauge. You should see the gauge rise to a higher and higher number and then STOP and not gain anymore. Once you find where this point happens back it off just a little. Repeat on the other screw. You SHOULD be keeping track of how many turns you turn out each screw and match them as precisely as possible.
4. Check the RPM again. If it has change from the specs on the sticker then turn it up or down again.
5. If you adjusted the speed UP you should be able to turn your idle mix screws DOWN a little bit. Turn them down till you just start to lose some vacuum and then up just a little. Adjust the other side the same always making sure you are just at the max vacuum and correct RPM.

You curb idle speed and mixture is now perfectly set. On a stock 305-350 I think the idle speed in drive is 500-700RPM

note: If your car is not stock (bigger cam?) you might find that you need to readjust your timing a little bit at this point. It is a process of trial and error till you get the car running perfect with as low an RPM and gas as possible. Whatever this timing is you arrive at THIS becomes your BASE/INITIAL timing for the additional step at the end of this...

Step 3.
1. Put the car in park. The RPM should shoot up to about 300-400 RPM (at least on a stock SBC).
2. Plug the vacuum advance back into the correct source. It should be the one that opens up after idle but closed at idle. You do not want it pulling your RPMS up while in park otherwise you are going to have the same problems with the throttle plate opening up and the engine getting too much gas. When the car is in park and low RPM it you should not feel much vacuum from it. If you do check the manual for your carb and find out which port you should be plugging into. ON a stock SBC the vacuum advance is actually plugged into a vacuum delay valve that is in the mess of tubing attached to the manifold water sensor and the air cleaner and NOT directly into the carb.
3. Turn off the car. It should not diesel anymore and your mixtures are set properly for the most vacuum at park and at load (aka in drive).

Last step
1. With the tires blocked and again with the car in DRIVE (and someone on the brake just in case). turn on the AC system. You should use the Tach again to make the RPMS of the engine the same with the AC OFF and ON. If the engine slows down with the AC ON, then put the car in PARK, open up the throttle a little, and turn out the idle solonoid just a enough so that when you let go of the throttle it comes back to rest on the solenoid slightly higher than it did before. Put the car back in DRIVE with the AC on and see if the idle speed is the same in drive as it was drive with the AC off. Keep repeating the process of putting the car in PARK and upping the throttle and screwing the solenoid OUT till you hit the RPM you want. Remember to NOT open the throttle with the car in DRIVE otherwise you are going to run over your blocked tires, over your foot and into the back of your garage or other cars in the driveway! ALso, if your car is revving too high at idle (even though you JUST fixed that) that your parking brake can't keep the car from moving then your rear emergency brake is not going to help much in stopping you! SOOO fix that next!

Additional step
1. Depending on where you set your timing in the first step you MIGHT need to readjust your timing curve and advance stop on your distributer. Unless you are running a stock distributer you need to look up how to do that. Some distributers have a advance stop and little springs that you can change. Some vacuum advance pots you can adjust with a allen wrench, others you can't. In any case you need to start with your Initial Timing you set in the first step and then figure out what you need for TOTAL timing. This is a WHOLE other thread though....

 

[Grandprixpaul]

Thanks guys im getting there , the fast idle cam was set to high and holding the rmp up to high when i set timing ,now its close im idleing inbetween 8-9 hundered rpm getting down there and timing is staying at the 14 from what the builder recomended with med springs in the distributor, going to mess with it later tonight ,i know my rear end isnt helping right now,i have 229 stock ls,hopefully getting this 373 rear from a guy soon, my set up is 366 dyno'd hp ,turbo 350 built with 2200 stall rpm,full power tops at 5500 ,hei distributor,105 amp alt.625 carter performer carb. Full length large tube headers,2 1/2 in exhaust with cherry bomb welded mufflers, still not seeing the power i would think i should be though ,pretty sure im holding correct fuel pressure ,i have good 8.5 plug wires,a.c delco plugs,seams to loose power mid range , going to work on it tonight and see what happens ,thanks for the posts ill try that tuning and see what happens

 

[MPac]

You might see power fiddling around with your timing some. Just because he recommends 14 degrees doesn't mean that's where all the power is. Instead of focusing on base timing look at your total timing on most performance engines they like to sit between 32 to 36 it depends on the application.

When you set your timing your fast idle cam shouldn't be on. That's tell me your engine wasn't warmed up. You want you engine at operating tempture before you do any adjusting. You should swap your carb out for something else along the lines of an edelbrock 650 or a Holley 650. Are you aiming for power or mileage? If power go with a Holley Double Pumper.

You mentioned that your not getting the power you want. Are you sure it's jetted right? Warm your car up then take it out and do a full throttle run for about a half mile then as soon as you let out of it shut it off, pull over and take out a spark plug. Look at the color of your plug it will tell you if your running rich or lean. It would be very wise to invest in an O2 sensor.