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Old 07-24-2011, 05:34 PM
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400 sbc timing issue

im having trouble understanding this whole timing thing any help would be appreciated
i have a 406 sbc with a lunati 60105 hydraulic tappet cam with 546 lift aluminum heads 10 to 1 comp. quick fuel 750 q series carb 350 turbo with 3200 stall when motor was installed i put the slot on my balancer a 12* btdc then put distributor in the engine. which is a brand new accel already set up with a good coil and curve kit installed fully adj. vac advance. motor starts fine runs awsome
my question is do i take a timing light now and set my balancer slot to zero on my timing tab? i'm lost from here and i want to fig. this timing out

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Old 07-24-2011, 06:36 PM
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If nothing else, at least throw a timing light on it to see exactly where it is now for future reference. I would look into trying for more advance like 14-16* initial with your cam. Turning it back to 0* would kill your power and torque across the board.
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Old 07-25-2011, 02:02 PM
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Your engine with that Lunati cam in it will run best when you lock out the mechanical advance curve in the distributor and set the fixed locked timing at 34-36deg BTDC. When the timing is locked out it does not advance with rpm.

The big cammed motor needs that much timing at idle. (34-36deg)

To aid starting when hot with locked timing install a ignition power interrupt switch on the dash, to kill the spark when hot cranking.
Make sure the required GM OEM rear starter brace/bracket is installed.
The two starter bolts are not enough . If yours is missing get one.

Aftermarket timing tabs are rarely accurate. Some are off by a lot.
Verify the timing tab location using a piston stop to find true TDC.
Ya it matters.

Search my old posts. It's all there.
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Old 07-26-2011, 01:37 PM
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you should had put a mark on the balancer at TDC (0 degrees), then use a timing light with a dial to set the timing.

locked out timing with a start retard would be a good solution.

otherwise, set the timing at 25 at idle, and 36 total. should start ok warm with 25 degrees and a big cam.

is your distributor adjustable?
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Old 07-26-2011, 02:59 PM
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yes my distributor has an adjustable vaccum adv.
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Old 07-26-2011, 03:18 PM
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You need an adjustable mechanical advance slot.
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Old 07-26-2011, 03:31 PM
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whats a adjustable mechanical advance slot?
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Old 07-26-2011, 04:59 PM
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It allows you to set the amount the distributor advances.

so if you set the timing at 25 at idle, then you could reduce the amount of mechanical advance to only add 11 more to limit the total to 36 degrees (25 + 11 = 36). The stock advance is typically 20 degrees.

less advance is important with a big cam because it allows more initial advance without advancing too far, which is required for a big cam.

When you use a non-stock cam, it is important to use a non-stock timing curve.
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Old 07-26-2011, 07:20 PM
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i found tdc and my timing tab is correct i had 12 intial then i set it to 24* running at idle made marks on my balancer with precise measurements with a plastic tape i made a mark for a total of 36*. after i set my idle at 24 i then reved the engine to 3000 and it was all in by 2500 rpm. is this ok ?
my carb was really rich once i got my timing set




































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Old 07-26-2011, 08:10 PM
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This cam can use even more than 24deg at idle.
Try it locked out at 36deg BTDC.

Remove the carb. Flip it over and reset BOTH the pri and sec throttle blades/ idle transfer slot exposure at idle (.020"-.030") replace the power valve with a 3.5 or 4.5".

The pri and sec throttles must be open at the right amount at idle for the idle circuit to work correctly. If they are not in the sweet spot at idle it will idle rich. The extra idle timing allows this.

reinstall and fire it up with the locked mech timing @36deg and let it warm up at 2000+rpm. When it warms up set the idle mix screws for best idle quality.

PCV must be hooked up to the base of the carb and functional.

Make sure the OEM GM rear starter bracket/brace is installed. If yours is missing get one.
Take it for a ride and clean it out. its all fouled up now. May need fresh plugs now.

Vacuum advance can be retained but it will need to be set up.
limit and rate.

If its hard to restart with the locked out mech advance, install and use the spark interrupt switch.

Last edited by F-BIRD'88; 07-26-2011 at 08:17 PM.
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Old 07-27-2011, 06:43 AM
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makes sense, as more timing can run a leaner mixture. turn the idle speed and idle mixture down. That cams needs to idle at 1000 rpm.

so you are saying 24 initial and 36 total at 3000 rpm?

try revving it up to 4000 or 5000 rpm. I would guess the timing will go over 40. (not good)
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Old 07-27-2011, 04:16 PM
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I tried revving the engine further and the mark I made for 36deg didn't keep going it stayed where it should
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Old 07-28-2011, 08:00 AM
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that is good!

so how is is running now?
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Old 07-28-2011, 04:58 PM
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it will blow the tires off at 30 mile n hour it runs really well i just need to fine tune my carb n i think i will have thanks for all the help
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Old 07-28-2011, 05:26 PM
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Quote:
Originally Posted by 81malibuman
it will blow the tires off at 30 mile n hour it runs really well i just need to fine tune my carb n i think i will have thanks for all the help
That's fun isn't it
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