i have 225 slant 30 over port polish head v8 oversize valves, 4 barrel clifford 650cfm edelbrock, clifford headers, comp custom cam .502 lift 286 duration, mopar peformance electric ignition.
having trouble with ignition timing i have it set with vacuum advance unhooked to 3 degrees not sure total. it idles real rough, i advance timing to 6 degrees and it idles ok but when i should the engine off after 3 seconds i have backfire through carb. my cam is timed in correctly with degree wheel.

Advance it some more, at least 6 to 10 degrees initial. If your breaking it in and just starting to tune, it takes awhile before the engine settles down. After the 20 minute break in, I would run only 10 minutes at a time then let it cool down 3 or 4 hours before restarting. It gives the pistons and rings a chance to conform instead wearing in, especially if you built it tight.. Hopefully you didn't pop the power valve on that back fire.........

An Edelbrock or Carter is a more forgiving carb on break-in.

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Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG

I hope the static compression ratio is at least 10:1 with the cam. Having said that... you're going to want probably 15° initial timing. You will have to reduce the amount of mechanical advance in the distributor to keep the total timing to about 30°. We have discussed distributor recurving a lot around here so a quick search should give you lots of info.

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Joshua

My Guzzi car initial is about 20,,,,30 total,every car and dist is different,I would try 28-30 TOTAL,and see where initial is,Mark

Sounds like a cool buildup. These guys are steering you right.

Where are you located?

Best of luck with your tuning!

Lou

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Home of Slant6-powered fun machines since 1988

how do i change the mechanical advance??

You have to tear down the distributor and shorten the slots in the advance plate to reduce the amount of mechanical advance. To change the advance rate you need to change the springs.

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Joshua

i see everyone says between 12 and 16 btdc for timing. i'm at 4 atdc. and my car starts and idles better when i'm at 8 atdc but everytime i turn off the engine i can hear the carb well not backfire but i can hear ignition of sometime through the carb(like fire starting). i try to go back toward 0 or anything btdc and the car will has trouble starting. do i have the wrong timing mark? there is a small notch on the pulley but then up a little ways there is like a cut out thats like 2 inches long. the car is running ok. low end dawgy but expected with cam. but with timing 8 atdc can smell exhaust isnt right.

maybe i can just sent my total timing and it will be ok. i have also seen guys say no more thatn 36 total timing but then some others are saying 52 total. including initial, mechanical and vacuum

Better check to see that you have TDC correctly marked on the balancer for the timing mark you are using. When you are sure you know where TDC is measure 30 degrees ahead on the balancer and mark it with a dab of white out correction fluid. Disconnect the vacuum advance and run the engine up to 2500RPM or so where it quits advancing. Turn the distributor until it flashes at your 30 degree mark when fully advanced. If it not close enough you may need to adjust the advance plate bolted to the bottom of the distributor or even move the distributor gear.

See how it runs with 30 degrees total. Eventhough it seems to smooth out a rough running engine, over advancing under high load conditions with hurt your engine. You didn't say it you have a manual or automatic transmission but with that cam the engine will never run very smoothly under 1800RPM. If you can't drive it to keep the revs higher you probably won't like it, on the other hand that cam makes great power up in the 4000-5500 range. Keep an eye on your oil pump drive gear as that particular cam has a bad reputation for eating them up.

I have run a similar set up and I have seem some pretty spactacular fireballs when starting it up cold for the first time in the spring. After the first time it usually is not a problem. If you get the total timing right and it still backfires consider other causes. I have a manual trans and I have never bothered to recurve my distributor because it really doesn't operate much between idle and full advance. With an automatic transmission and a tight converter this is much more of an issue. Good luck. Let us know how it runs when you get it sorted out.

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If you didn't drive it there, it's not a street car.

I agree 100% with the last post,Mark

The 52 to 55 degrees total is for a street car trying to get max mileage, not a race car. I was at 55 degrees total and getting ready to make a few runs at the track and found it was way over timed causing the engine to flutter or cut out but it didn't ping. So with some careful tuning of the vacuum advance, (running it 3 turns out) so it won't kick in right off idle and under load or WOT plus a heavier secondary spring I got it to stay put right at 30 degrees from 2000 rpm on up at WOT. It makes good power now down the track and no more fluttering from over timing. 10 degrees initial timing seems just perfect for my particular recurve which provides 20 degrees mechanical with 20 degrees from the vacuum advance and it will still get 23+ mpg in town and 25+ mpg town and freeway combined.

I was running 16 degrees initial and 2 turns out on the advance and a lighter secondary spring was too much timing too soon. It was very punchy but not right for WOT driving.

You will have to do some experimenting to get the balance right for your motor and rpm range. You can't use the same set up as mine for your engine build. You may end up with 15 degrees initial and 15 degrees mechanical on your engine.

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Aggressive Ted

http://cid-32f1e50ddb40a03c.photos.live ... %20Swinger


74 Swinger, 9.5 comp 254/.435 lift cam, 904, ram air, electric fans, 2.5" HP2 & FM70 ex, 1920 Holley#56jet, 2.76 8 3/4 Sure-Grip, 26" tires, 25+MPG

You will want to keep the total to around 27-30, no more. Trying to get enough initial that it will be drivable without filling the slots will be impossible. Tearing apart a distributor to fill the slots sounds hard, but it really isn't.

Until you get a handle on your timing you're pissing into the wind.

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Official Cookie and Mater Tormentor.

thanks for all the help guys. got my good mac digital timing light out today and timed it right up easy as cake. i set to 14 btdc at idle vacuum unplugged and then its about 42 total advance. seems to idle good and drive good. still good peformance and cruising seems better too.

if anybody is close i'm going to the syracuse nationals carshow next week end july 18th and going to dyno her.

42° is way too much. At least now you know how much you need to take out!

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Joshua