Turnin20s

iTrader: (12)

Well here goes, S10 with a couple different SBCs. Used to have a '92 TBI motor (with the TBI heads) with a cheap dual plane intake and a 525 cfm Road Demon, stock tank w/siphon tube, electric fuel pump @ 6 PSI, MSD Pro Billet Distributor and 6AL ignition box. With this setup it worked great for 2 years, took it to the track and ran a 14.6 @96 with a horrible 2.6 60 ft (cold day and 275/40/17 street tires).

Now we decided that it needed more power so we swapped a set of hand ported (earlier style) heads with a rebuilt set of valves and heavier valve springs. Same carb, intake, and fuel system. Valve ended up hanging up, ground down the cam, and sent chunks through the bottom end, but the headers would glow on this setup before it let loose.

Now on to the new setup...'96 Vortec motor, Vortec heads, '95 LT1 cam, Summit dual plane intake, Holley 650 cfm w/mechanical secondaries, same fuel setup. Now after the motor runs for 5 or so minutes the headers start to glow red. We have tried adding timing, but then we can't get the idle under 1500 RPMs. We have tried to add fuel at idle with no real change.

Now I'm starting to think that its something in the fuel system that is causing the problem. The gauge on the carb reads 6 PSI at idle, but I'm wondering if it needs to be at 7 psi, or if the siphon tube is sucking air, or the fuel pump can't keep up with the better flowing heads. I'm running out of ideas and would like to drive this thing before the snow comes.

If anyone can help it would be greatly appreciated

toomany

Have you checked for vacuum leaks? Do all the tubes glow? Or just a select few. Are you using the same distributo/ignition system? Is it installed correctly (not 180 out)? What about balancer/timing cover? Have you verified the balancer reads correctly? It's possible the outing ring slipped and is throwing you way off when you try to time it.

Turnin20s

iTrader: (12)

Had one vacuum leak on the carb spacer but got that fixed. All the header tubes glow red, smae ignition as before. Don't think timing is 180 off, it runs too good to be off 180* and pretty much key drops every time you start it whether its warm or cold. The balancer is newer and the marks look good when we had the motor apart, set the timing to zero to set the valves and everything looked right.

Now as far as timing we had it too far retarded, probably 6* advanced or less, but if we go any farther I can't get the idle down. With the timing set ~14* it idles at 1600 RPMs which makes me think there is a vacuum leak because I don't have any more adjustment on the throttle plates to bring it into check.

I'm going to pull the cap and make sure the springs and ramps move freely in the dizzy, I'm going to move the vacuum advance from the carb to the intake to eliminate that. I'm going to grab a vacuum gauge and mess around with it to verify there are no leaks, and may use smoke to find leaks. I might also pull a valve cover and check the valves, but they seem right but they could be a touch on the tight side now that the lifters are all pumped up.

Right now I think its a timing/vacuum issue after researching for a couple hours last night. I have tomorrow off and will check everything out then and maybe get to take it for a drive

Turnin20s

iTrader: (12)

BTW thanks for the reply man, I appreciate it.

If we get everything worked out I'll post back

Brian Tooley Racing

iTrader: (13)

There is only one correct place to put the vacuum advance line for the distributor and that's in the metering plate "spark port" location. At idle that port should have zero vacuum on it. At part throttle it will have vacuum which advances the timing for part throttle timing, and then goes back to no vacuum at WOT. If the spark port has vacuum at an idle it's because the throttle blades are open too far exposing that port to manifold vacuum.

If you hook the distributor to full time vacuum, then it's adding lots of timing at an idle. As soon as you tip into it, the vacuum can drop and decrease timing, the exact opposite of what you want it to do.

Headers glowing red are a result of fuel being in them, either by retarded timing or being too rich. Your base timing should be around 14-16 degrees and you should be able to idle it down below 1000 rpm. Make sure the secondaries are not hanging open also. I've had to turn the small screw in the secondaries to close them down some before.

I hope this helps.

Turnin20s

iTrader: (12)

^^Thanks man, I'll check the secondaries and see if they are slightly open. I'll also check the spark advance on the carb and see if it has vacuum at idle. I also think the ramps in the dizzy may be hanging up and that's causing fits.

Turnin20s

iTrader: (12)

Well I figured it would be something dumb....when I rebuilt the carb I didn't center the blades and they wouldn't close all of the way and thats why when I advanced I couldn't get the idle down.

So we adjusted the blades, and it idled at 500 rpms right away. Bumped the timing to ~16* advanced and it runs nice and cool now. Pulls good vacuum, almost 20#s at idle and idles at about 600 rpms. Everything is good now.


Thanks again for the responses guys