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Classic Mustangs Tech Forum

Technical discussions specific to 1964-1967, 1968-1970, and 1971-1973 Classic Mustang. Discuss all tech related to in-line six cylinder and V8 powered Vintage Mustangs here.

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Unread 02-28-2010   #1 (permalink)
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Default 351w timing help with mutha thumper cam

can anyone help me in getting the timing right with this cam? i have the msd pro billit dist. i dont know where to set initial timing and which springs to use as well for the stop bushing. it is in a 68 mustang w/c4. bored .030 at 9.1 comp. i am also using a smaller carb 600 edel. what jet size shld i go with and needle and spreing? it was surging real bad on my first try out with it. i am now at the #19 setting in the edel chart. i dunno yet if it will help with the surging or not. i was in the #7 spot before. so yeah im lost with the timing and carb thing. i could use real good advice with people who have used this cam and knoledge of these kinda cams...tried and tru stuff plz....thx..
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Unread 02-28-2010   #2 (permalink)
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Best deal is to take a timing light to it and get the timing right that way and then work on the carb. from the stock the carb shouldn't be so bad that it throws the idle to a surg causing it to need different jets. However I have experienced surging from my edelbrock 575 at an idle when the idol fuel passages were clogged. try removing the idle mixture screws spraying 3 good sprays of carb cleaner or starting fluid with a nozzle down the holes, or air duster then put the screws back in all the way and back them out 2 1/2 turns. do all this once u got the timing right with a timing light.(if the problem persists)
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Unread 02-28-2010   #3 (permalink)
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Quote:
Originally Posted by shagadoodle View Post
Best deal is to take a timing light to it and get the timing right that way and then work on the carb. from the stock the carb shouldn't be so bad that it throws the idle to a surg causing it to need different jets. However I have experienced surging from my edelbrock 575 at an idle when the idol fuel passages were clogged. try removing the idle mixture screws spraying 3 good sprays of carb cleaner or starting fluid with a nozzle down the holes, or air duster then put the screws back in all the way and back them out 2 1/2 turns. do all this once u got the timing right with a timing light.(if the problem persists)
ill do that. i did go through the carb not so long ago but i can do it again just incase. but getting the thing timed right is my big issue. i am unsure where it needs to be at. big overlap long duration...
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Unread 02-28-2010   #4 (permalink)
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hi! stock is 6-8 degrees, you can go from 10 to 20 degrees at idle with a bigger cam, I would start with 12-14 degrees BTDC at idle, with your comp ratio 36-40 degrees full mecanical advance and you want full advance around 2500-3000 RPM.
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Unread 02-28-2010   #5 (permalink)
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Quote:
Originally Posted by zr2_wolverine View Post
hi! stock is 6-8 degrees, you can go from 10 to 20 degrees at idle with a bigger cam, I would start with 12-14 degrees BTDC at idle, with your comp ratio 36-40 degrees full mecanical advance and you want full advance around 2500-3000 RPM.
hey thx. when i started @ 6 and set idol to 1000 then shut her down it puked through carb so i adjusted timing till it didnt anymore @ 18. but when i shut her down and start it up she starts great but quickly starts do die like being choked out...i feather the gas till it clears out. any thoughts???? also when i put into gear it wants to choke out as well and die. i do have the recomended 2500 stall but it does seem like it doesnt stall at all. i goes into gear like a factory stall. i did drive it and i dont feel it stall at all???????thx for the help guys
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Unread 03-01-2010   #6 (permalink)
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Does your carb have a line running to the intake for intake vaccum? cleaning the carb didn't help?
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Unread 03-01-2010   #7 (permalink)
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i have a line from car going to vac adv tothe carb and pvc. the other vac port on carb is blocked off. which way should i go with this?
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Unread 03-01-2010   #8 (permalink)
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Hi! with that cam your idle vacuum should be really low, I would only use vac for the pcv valve and block off the distributor advance for now and see how it run. The other port on the carb should be for power brake.
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Unread 03-01-2010   #9 (permalink)
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I haven't tuned Edelbrock carbs before so I can't help you with that but, on most carbs there are two possible places to attach the vac advance on your distributor, one is a full manifold vac and the other is a ported vac which actually increases your vac as you open the throttle, this is only used on some emissions engines. Make sure you have full manifold vac to your distributor, but disconnect and plug it when you're setting your timing.
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Unread 03-01-2010   #10 (permalink)
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That's a huge cam, with an advertised duration of 311*. You'll need a lot of initial timing, like 18-20*.

Set base timing at 18*. Then hook up a vacuum gauge to the manifold port. Adjust timing until you get the best vacuum.

A SBF seems to make best power around 36* total timing, all in by 2,500-3,000 rpm's. So adjust your mechanical advance to get there.

Vacuum advance is a good idea, even for a big cam like that. On light throttle cruise, you'll want the timing to advance anywhere from 4-10*. The engine will run cooler and be more efficient.
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Unread 03-02-2010   #11 (permalink)
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Quote:
Originally Posted by .boB View Post
That's a huge cam, with an advertised duration of 311*. You'll need a lot of initial timing, like 18-20*.

Set base timing at 18*. Then hook up a vacuum gauge to the manifold port. Adjust timing until you get the best vacuum.

A SBF seems to make best power around 36* total timing, all in by 2,500-3,000 rpm's. So adjust your mechanical advance to get there.

Vacuum advance is a good idea, even for a big cam like that. On light throttle cruise, you'll want the timing to advance anywhere from 4-10*. The engine will run cooler and be more efficient.
the duration @ .050 is 235 intake and 249 exhaust. lift is .501 int. and .486 exh. tried 18 but it didnt like it either.....seems i am having carb issues. its the edel 600 #1406. i went through it and cleaned it and it still isnt working properly. no adjustments on the throttle linkage side and the squirter on top isnt squirting as much as the pass side. and after i drive it a while it runs well but then when i shut her down and start it up it loads up and wants to die bad. untill i clear it up and go down the road a lil bit then it seems to run beter. but i have to have idol set @ 1500 to idol in gear.??????? dunno if its the timing thing too or what...??????
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Unread 03-02-2010   #12 (permalink)
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Hi! can you remove the squirter and clean it, How did you did you set your idle mixture, you need to set the idle rpm around 1000 rpm maybe 1200 with your cam, use a vacuum gauge to read manifold vac and adjust all the mixing screw equally to get the max vacuum reading. You probably are going to see your vac around 10 inches. Recheck your fire order and make sure all 8 cylinders are firing.
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Last edited by zr2_wolverine; 03-02-2010 at 06:53 AM. Reason: editing
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Unread 03-02-2010   #13 (permalink)
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Quote:
Originally Posted by zr2_wolverine View Post
Hi! can you remove the squirter and clean it, How did you did you set your idle mixture, you need to set the idle rpm around 1000 rpm maybe 1200 with your cam, use a vacuum gauge to read manifold vac and adjust all the mixing screw equally to get the max vacuum reading. You probably are going to see your vac around 10 inches. Recheck your fire order and make sure all 8 cylinders are firing.
thx for all the help guys! ill check and recheck and do what you guys mentioned. im going to pull out the sqirter and see whats up with it...weird..the carb is a few years old but only about 500 miles drive time on it. maybe somehow a piece of junk got into it. but i did squirt carb cleaner in all orfases real well. but ill look. thx again guys.. ya have been a big help.
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Unread 03-02-2010   #14 (permalink)
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Have you reset the carb back to the stock configuration? The owner's manual for the carb usually has some really good advice about tuning, and has some pointers for huge cams, too. You might also invest in a wideband air-fuel ratio sensor. It should be around i believe 13 at idle and 11-12 on full throttle.
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Unread 03-02-2010   #15 (permalink)
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If you know anyone with a carb that you can borrow, that would be nice to see if your carb is your issue. I've also heard that the edelbrocks can be very difficult to tune with such a hot cam. May be worth trying a holley, but you should to be able to get your car running better with your carb than it is.
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