Thread: SBC help Thanks in advance, it has some length to it but the detail is pertinent

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Hello, I am having grief with a little trail truck I have been building and thought I would turn here.

SETUP:
Timing set with light while distributor unplugged and carb plugged. 12 advanced

Floats set to 1/2 " to reduce fludding on trail.

Brake booster runs to back of Edelbrock carb.

Front vacuum goes to valve in valve cover.

Vacuum advance set on passenger side of front port.

Transmission on intake manifold behind carb.

I am jetted for 9000 ft of elevation and have gone trough all of the tuning process given by Edelbrock.

The motor has had the rack run on it, has 45psi oil pressure at idle and stays at 190 F idled up to warm.

Motor:
307 Ci sbc with 305 heads, cam out of a 400ci motor, performer intake manifold and carb, stock bore and compression other than heads change. HEI distributor with new MSD wires and New plugs true dual exhaust running to turbo mufflers.

PROBLEM:
The truck pulls hard when putting it into gear and idles down quite low.
when starting the truck after killing it, the idle is slow until it has been throttled once. At this timing setting the truck sounds kinda like it is under load and the idle has to be brought up.

It was set before with the timing around 22deg advance did not miss and did not act up at least tuning in the garage.

I have also tried tuning it this way and it ran better than the way I have been told to tune it. Idle set at 12 deg advanced, carb run to stronger driver side vacuum port. showing nearly 30 degrees of advanced timing at idle. BUT IT RAN BEST THIS WAY.

One last problem, the drivers side bank seems to be running a little richer fuel wise than the passenger

You may have answered your own question about the advance. Better at 22º than 12º, so why not try it by the seat of the pants and slowly bump it up from 12º and see what's best? Don't forget that when you hit the pedal your vac advance all but disappears.
For your rich/lean fuel try checking to see that you have NO gasket leaks anywhere in the intake system.
Is there a particular reason you used 305 heads? Are the valve sizes the same? Any idea what the chambers measure in c.c's?

I'd guess that you have the distributor a tooth or two off when it was re-installed.

Originally Posted by Dave Severson

I'd guess that you have the distributor a tooth or two off when it was re-installed.

Dave, I don't think that's very likely. Forgive my memory for not being what it once was, but I seem to recall that the HEI gear has an oddball number of teeth on it, something like 13 maybe? That may not be right, but it's a low number. The bottom end turns through two revolutions while the distributor goes around once. So you have 720º of crankshaft rotation for every 360º of distributor rotation. With so few teeth (can someone either correct me on that number or check it...) on the distributor, it turns something like 55º+ for each tooth. If he was out one or two teeth I don't think he could get it to fire unless he twisted the distributor an awful long way from where it's supposed to be...no?

With out going out and counting I don't recall the number of teeth BUT the engine will run being 1 or 2 teeth off in either direction THATS 4 teeth by turning the distributor. With the higher spark from HEI I have run them way off (Not on purpose)

Yes, the distributor can be a tooth off and it will run with the distributor cranked around enough to make it run. Could also be the outer ring on the harmonic balancer has slipped, or maybe the timing chain jumped a tooth, or it's the wrong timing tab???

Everything is guesswork until the OP comes back on and supplies a bit more info.

I chased a tuning problem for months before finally figuring out that my base timing was off - I set it at 10BTDC, then tightened down the hold down and called it good. Problem is the dizzy was very tight in the manifold (both new), and it was not firmly seated so when I tightened it down it pulled down another 3/16" or so and pulled my timing 12 degrees retarded. I was running -2BTDC thinking I was at 10BTDC. Had to lift the distributor, shift one tooth, and re-time - my clearance/adjustment room is veeeeery tight!! Has to be on the right tooth or no room to make it right on the light.

Maybe I`m blowing smoke here, should he use a piston stop, confirm TDC, mark balancer and rotate engine by hand to line up mark where he needs it, reinstall plug, loosen dizzy, use a timming light, turn key on without starting engine, rotate dizzy by hand until light fires then lock down dizzy, he should be right on the mark regardless of what the balancer says if it has slipped. I`ve set up a lot of rebuilds this way to insure its right upon fire up.