Brawlin' Boss

Fellow members, I need some assistance with a 67 Shelby GT500 428 dual quad. It belongs to a customer of mine and we've already done some repairs i.e. carb overhauls, wires, cooling etc.... The car starts and idles perfect. I took it out for a run and what a beast. Everything works perfect, unbelievable torque and acceleration. The problem I am seeing is that around 4500 rpm is starts to sputter and breakdown. Pulls hard up to that point, through you do feel some misfire what feels very much like ignition breakdown randomly at any rpm. We replaced the plugs and ignition wires, I inspected the cap and rotor, they look good. It has a mechanical advance distributor with dual points. That's as far as I get. I know carbs but never messed with point style distributors. What can it be, what do I look for? I am certain it is ignition breakdown just hate to start throwing parts at it. Not my style. If someone can guide me on how to diagnose or what to look for. Thanks for the great help as always.

texastboneking

Sounds like you need to adjust the points

HOSS429

how does it do just to rev it beyond 4500 .. is it a automatic or manual ..an automatic you can do a brake stand and see perhaps what is breaking down . my 69 r code had dual points and would burn up a set bout every month ..

Brawlin' Boss

It's a 4 speed. I haven't tried revving past 4500. I will give it a try. I am currently setting the dwell on the points, (thanks youtube!) Just not to sure for the specs for this motor. Anyone know the dwell setting for these?

mustangray

If I remember the dwell was 30 and 33 deg. I ended up change everything over to a Petronix set up and never had to mess with it again

texastboneking

Make sure the points are still good.

Brawlin' Boss

Points are good, new, looks like someone installed them years ago. They had a lot of corrossion on the point. He doesn't drive it much, I took them off and cleaned them just setting the dwell. I really don't want to change the distributor type, rather my customer doesn't for obvious reasons. This car is a survivor 428 dual quad Shelby 500, not too many in this condition I promise.

Brawlin' Boss

correct me if I'm wrong, set the primary points first then the secondary points? right? What setting on the primary points? I imagine the 30-33 is total dwell, right? Just want to get the procedure right thanks for all your help so far

mustangray

again if I remember this was the old way to do it (but it has been a long time since I've had to do it) to set the points on a dual point dist you would put cardboard or other insulating material between one set of points and set the other set and then do the other one dual point dist were set at 25 1/2 degrees each point to get 30 to 33 degrees finished total.

Brawlin' Boss

Believe it or not, I found the Shelby owners manual in the glove box. It say 22-24 total dwell. What doyou guys think?

mustangray

If it's a stock original car I would go with that and see how she goes

Brawlin' Boss

IT IS!! I set it already, just having lunch and will drive it see how it drives. Let you know

mustangray

Excellent ! let us know how she works out

Brawlin' Boss

She didn't like it one bit. Spits and sputters any time you get on the throttle now. I am going to try bring it up to around 30.

HOSS429

you`re obviously in the right neighborhood .. i dont remember "dwelling " mine .. i set them with a feeler gauge .. or is it the same thing now ..

Brawlin' Boss

Well I read up on that, everywhere I read it says gap is for initial start up. Then dwelling is necessary for correct tuning. I'm getting frustrated. I set it to 32 and it just feels weak now. It sputtered on me once but just felt like a pig, no power.

texastboneking

That's why you get rid of the points system!

Brawlin' Boss

Well I went back and set the gap to .17 on each point. Verified timing to 8 deg. as per owner's manual. I took it out for a drive and drives much better now, but still has a sluggish feeling and really won't go past 4k rpm. I get a random backfire through the carbs every once in a while too! Any advice?

HOSS429

time it a bit higher .. till it pings then back off till it dont .. sometimes you gotta throw the book out .. ( dont blow it up ) if the owner never drives it that hard he will never no it wont go ...