Need help with tuning

[dknine]

I need some help I have a 350 with long duration cam, ported 30 over, 600 cfm edelbrook, headers, dual flowmasters and stock distributor. But I bought this truck like this so I don't know the exact specs on the cam or head job they gave it. But my problem is it needs tuning. Can anyone help me in setting the timing and carb adjustments? Do I need a tach to make the adjustments and if so how do I hook one up. I know this is alot to ask but the truck runs like crap it bogs down on the take off and the carb pops like a backfire also when I floor it on the freeway and it gets about 7 miles to the gallons I know this can't be right.  

Edited by: dknine at: 4/23/04 1:50 am

[1quik86]

Timing should be about 34 degrees total. I would plug off the vaccum advance and leave it that way. Vaccum advance is actually a high speed retard. (emissions) If you don't have an after market harmonic damper you can buy a timing tape to stick around the damper. You will need the extra marks. Using a timing light to watch the timing marks rev the motor. The timing should advance because of the wieghts in the distributor. Move the distributor until the timing mark is on about 34. This should provide about the best timing. Occasionally the outer ring on a stock balancer will slip causing the timing to read wrong. This is not real common. I'm not an Edelbrock carb. fan so I'll let someone else get into that. If this combination is not accompanied by some lower gears that could affect the low end. Ported heads will also effect the low end. If you can find out the cam specs and what kind of head work was done that would help. Also the rear end gears. I hope this helps.  

[dknine]

It helps alot thanks I'll try to get some better specs.  

[roundedline]

Quote:Vaccum advance is actually a high speed retard. (emissions)

You lost me with this statement.  How can it advance and be a high speed retard?  There is no advance at full throttle.  Ported vacuum advance did start with the emissions, before that, all motors recieve full manifold vacuum.  Vacuum advance only affects idle and off-idle characteristics, full timing isn't affected.

My suggestion is to drive it without the vacuum advance connected and plugged with whatever gas you plan to put in it.  Take the vehicle to a safe place for checking full throttle response.  1/8th mile track would be my suggestion.  Advance the timing slowly until you hear it pinging.  Back it down some recheck it and lock the distributor down and that is your optimum mechanical advance.  Typically this occurs at 2800-3000rpm, but is depended on the camshaft profile.

Now hook the advance back up and check how the truck runs off idle, idle quality and ease of cranking.  I would check ported and manifold vacuum to see what is the best.  Most performance apps. will want manifold as most big cams have little vaccum anyway.  After you determine what the motor responds to the best, drive the truck and check for pinging.  If there is just a intermitten pinging on light throttle that is ok, but if it keeps pinging you need to change the vacuum unit on the distributor (it is marked the amount of vacuum it will use), or you can get an adjustable unit.

Chris Lucas
www.73-87chevytrucks.com
www.captkaoscustoms.com
Project Su
Jimmy 2WD Project