I'm working on tuning my 318 with a whiplash cam. It has .519 lift and about 230 duration. I have the timing initially at 12deg. It runs and idles fine but as soon as I bring it up to 3000 rpm it stumbles all over. This is with the vacuum advance connected. Without it it's fine. It's a summit dist, stock replacement with a summit ignition box. I've tried moving it around but with the vacuum hooked up it always starts missing at higher rpms. Runs good disconnected though. But I know not running it will sacrifice mileage and performance. Any thoughts suggestions?

Not near enough initial IMO. Crank it up to ~18-20* and limit mechanical in the distributor.

Disconnect/plug the vacuum adv until you get it sorted out.

Remember as a kid working in a gas station and a customer's 55 Chevy with almost identical problem.

I discovered pulling vacumn hose all was well. Pulled distributor cap, wire going from coil to points was broken inside. Advance plate would move far enough with anything above 1500 rpm,,,pulling wire apart. Repaired wire all was well.

I however agree more with more initial advance requirement,,,but lack of should not create a misfire slobbering all over itself.

(1) rotor phasing (2) too much timing. with the can plugged in see what your timing is at at 3K (where it is acting up). Unplug the can & set it at 3K & crank the dist till the timing is back to where it was with the can plugged in so the RPM is the same & the timing is the same just that it ain't coming from the can. If it's OK now then it's rotor phasing. Only the can alters rotor phasing & since you need the can for street use there's several ways to reclock the rotor & the NAPA rotor may reduce the gap distance back to where it wont misfire. To rephase. easiest is to cut another rectangular notch in the top of the dist shaft where the rotor notch locates (carefull measureing required/measure twice (at least)/cut once. It's strong enough there to handle one more notch. NAPA offers a rotor (MO3000) for $8 & change out the door with a .060" longer metal blade that reduces the radial gap from rotor tip to cap terminal(s) & helps with circumferential phasing issues as it is the total gap that once it gets wider than the spark can jump then it misfires

I had it all the way up to 30 initial. Same outcome. Unplug the advance all the problems go away.

Without a doubt rotor phasing. Another possibility is the other system the can alters which is pickup gap tho usually that change ain't enough to effect a misfire. It's handy to have a hand held vac pump available for dist work as you can see (& measure) the pickup gap change with more vac applied to the can on your bench. To check phasing cut a 1/2" hole in the top flat of a dist cap 2/3 of the way between the center cap terminal and the #1 cap terminal then shine a timing light straight down in the hole while idling & it will freeze the rotor like a strobe light will do to bodies on a dance floor & see how far around the circumference the tip clocking is from dead center on the cap #1 terminal. You can also make a mark on the top metal perimeter of the dist rim at the center of a cap bulge then take off the cap & see how far the rotor is from pointing dead on to it (rotor retracted & not into the springs & they likely will be retracted if free) & the can will shift rotor phasing CCW from that position on a SB and CW on a Big block. You have that circumferential distance and the radial distance from a too short of rotor blade. If you like math you can get the degrees of the can from the number on its arm and the diameter of the dist housing & C=Pi x dia & divide 360 into the circumference to figure the distance around the arc 1 degree is then multiply that number times the # of degrees the can will shift the rotor around the arc. EDIT the X factor is at what distance does the required voltage exceed the available voltage (that's when it startts to miss) & each ign system is different & required voltage is the greatest at WOT & that's when you want the pickup gap to be close to .008 and rotor phasing to be in the good range

It may sound crazy but I've seen this more than once so here goes. Make sure the wires from the distributor pick-up are connected correctly to the ignition box. If they are reversed (there is a pos and negative) the car will run when you adjust the distributor position but throws the rotor phasing way off. In your case the extra vac can timing will push it too far.

This is all really good info. I'm gonna dig into it this weekend. Thanks guys

So I tried using a different port (manifold) and still the same results. There is something that is weird. When I press on the brakes my idle goes up. I tried it all over from 5 to 30 degrees. Is the mechanical advance enough? Do I really need the vacuum advance connected?

Just leave the can unplugged. Too much b.s. for little gain, imo. Never ran one in any hot rod I've owned.

Not yet. I did a little reading on the mopar performance instructions. I'm gonna start with the set screw all the way in on the vacuum pod (disconnected for now) starting at 5 degrees. Crank it up to 2000 rpm and see whats goin on with my mechanical advance first. It feels good otherwise. Pulls really hard. I'm definitely sold on the whiplash cam. Made my little 318 come alive.

I'd take off the cap & see what cap terminal the rotor blade is closest to then put the cap on & make a mark on the dist metal top rim in line with that particular cap bulge then take off the cap & with a 1&1/4" socket/breaker bar turn the crank slightly till the reluctor tooth is dead even with the magnet & at that point see how far the rotor blade is off from being dead on with the mark you made. The bold text is what I neglected to add to check phasing in my prior post. This ain't quite as accurate as the timing light method but it is very close & will tell you something significant regarding phasing in 5 minutes. Holler how it turns out for you

What's the reluctor tooth?

You might bump the crank CW till the tooth Boogie showed JUST moves past dead center on the magnet (& I'm talking a c hair past dead center) as it fires when the tooth just moves past being lined up dead on centered with the magnet. Im also thinking the NAPA 8 dollar Echlin MO3000 rotor may fix this WO you havein to mess with phasing but first see where it is. EDIT check the gap also (.008" with brass feeler gauge)

Im gonna get that rotor. This is becoming an issue. What causes rotor phasing?

318 whiplash cam open headers: http://youtu.be/7RW-M3mHr7Q

Don't mind the mess

I would check the tooth/magnet gap first. Speaking of the gap not RP you set it at .008" at rest (eng off/no vac) & the can increases it but not to the point where it will misfire but if the gap is too much greater than .008 to start with at rest then when the can kicks in it will increase it past it's "limit" where it will then miss with the can activated. The can changes reluctor gap and RP. A stackup of tolerances in the wrong direction from poor machining can shift it (RP) past it's (functioning) limit.