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69lemans
Tribal Scout

USA
24 Posts

Posted - 27 May 2017 :  5:40:36 PM  Show Profile  Reply with Quote
Hi Guys, I put a very mild 428 in the lemans a few months ago and I started noticing a miss, and is not very snappy from a start. I am using a Mallory Unlit Distributer and a MSD 6 box, Pontiac performer intake with a 750 Demon,Street Demon carb. (First time I have used this carb on anything still not sure if I like it) I was checking the timing and as I was advancing it the car shut down. I tried to start it and it wouldn't start until I bumped the timing down a touch. Timing was reading right at 0 when I started it as I got closer to 8 it shut down again and now it won't start. I also noticed that it does not seem to hold the timing I set. If I set it at8 or 10 a week later its at 4. The clamp is tight. Any thoughts.

cortcomp
Coyote

USA
5335 Posts

Posted - 27 May 2017 :  7:05:57 PM  Show Profile  Visit cortcomp's Homepage  Reply with Quote
if it's mild, just run a factory HEI, no box or MSD stuff? then you can be sure you're reading the timing exactly right and theres no MSD trickery going on, simpler, and likely no improvement at all on a mostly stock engine.
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69lemans
Tribal Scout

USA
24 Posts

Posted - 27 May 2017 :  10:15:50 PM  Show Profile  Reply with Quote
Thanks, I took all the MSD stuff off and went back to just using the
coil and it fired up. It seems to run well but it stumbles off idle. I haven't tried
Adjusting the timing again to see if it shuts off again. I will mess with it in the morning.
Just happy it runs again.
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Blued and Painted
Chief PONTIAC

USA
3405 Posts

Posted - 28 May 2017 :  12:31:37 AM  Show Profile  Reply with Quote
What plugs and wires?
What is the power source for the distributor? It needs a clean circuit without feed back from other hi amp accessories.
Did it act flooded when it came back to life? Took a few seconds to clear-out.
Is there anything else you can add about the skip?


Bull Nose Formula/ 461/ Q-Jet/
TH400/ 3.08 8.5 / R44TS.
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69lemans
Tribal Scout

USA
24 Posts

Posted - 28 May 2017 :  09:23:39 AM  Show Profile  Reply with Quote
I am using MSD 8mm wires and Autolite plugs. I just re gapped them to .40 a couple of weeks ago because it looked like they were burning cold at .35. when it re fired it was like nothing had happened. when i accelerate hard from a start it stumbles all over it self ,sometimes i get a carb backfire and it stalls. if I am already moving and accelerate hard it goes like a bat out of hell. I adjusted the accelerator pump to come on a little slower and it didn't change anything.FYI, TH400, 3:73 gears.
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69lemans
Tribal Scout

USA
24 Posts

Posted - 28 May 2017 :  09:56:20 AM  Show Profile  Reply with Quote
I might as well give you all the specs. 69 lemans,428 bored.30 over,flat pistons,8X heads,Lunati Voodoo cam with 220/227 at .50 and 267/275 advertised duration,Roller tip rockers, Ram Air exhaust manifolds,Edelbrock pontiac RPM intake, Demon Street Demon 750 Carb,Mallory unilite Distributor with vacuum advance, MSD coil,MSD 8mm wires, TH400,3:73 posi.
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cortcomp
Coyote

USA
5335 Posts

Posted - 28 May 2017 :  2:25:45 PM  Show Profile  Visit cortcomp's Homepage  Reply with Quote
get that timing up to like 13-14 and try it again. Also make sure the accel pump is working by looking down in the carb and trying it (engine off)
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Blued and Painted
Chief PONTIAC

USA
3405 Posts

Posted - 29 May 2017 :  11:10:15 AM  Show Profile  Reply with Quote
Yes, A back fire thru the carb is normally caused by #1 a lean mixture, #2 late timing.
With engine off, visually check for a strong, steady, accelerator pump shot of fuel when operating the throttle linkage, . It should start with the slightest movement of throttle blades.
On a Holley style carb, the pump lever should almost touch the accelerator pump when at base idle adjustment, choke off. Like less than .010 ..
If you cant get a good pump shot, The accelerator check valve in the Pump body may be defective, deformed or missing.


Bull Nose Formula/ 461/ Q-Jet/
TH400/ 3.08 8.5 / R44TS.

Edited by - Blued and Painted on 29 May 2017 11:19:04 AM
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69lemans
Tribal Scout

USA
24 Posts

Posted - 29 May 2017 :  7:59:45 PM  Show Profile  Reply with Quote
Thanks guys, I will check the accel pump and reset the timing . I will let you know the outcome. Thanks again for the input.
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69lemans
Tribal Scout

USA
24 Posts

Posted - 16 Jul 2017 :  12:27:30 PM  Show Profile  Reply with Quote
I haven't had time to let you know what happened with my ignition issues. I removed the MSD box and reset the timing and it runs Awesome. I still don't know if it is a faulty MSD box or if the motor just didn't like it. It runs great so I am going to leave it alone.
Thanks for the help.
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Bill Boyle
Horse Feathers (Charter Member)

USA
4794 Posts

Posted - 16 Jul 2017 :  1:55:50 PM  Show Profile  Visit Bill Boyle's Homepage  Reply with Quote
I've never run an MSD box of any kind, so I'm no expert on them, but problems like Tim (69lemans) experienced are a turn-off for me. Part of my non-use of an MSD box is my ineptitude when it comes to understanding and solving electrical problems. Keeping it simple works best so I prefer the HEI.

"Dedicated to keeping the classic Pontiac engine alive."

----
400 bored +.030, forged TRW pistons, ported 62 heads, Hedman headers, 2.5 SS dual exhaust X Pypes, Comp 276AH10 cam, Scorpion 1.65 RR, 850 Q-jet, stock intake & tuned HEI; original owner.

Edited by - Bill Boyle on 16 Jul 2017 1:57:01 PM
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