I put an msd ignition 6AL with the billet dist. in my 77 F250 with a 460. Now it hesitates when I hit the gas from a stop. It is timed at 13 degrees. It has a 225/235 cam in it with a Holley 750 carb. I am stumped. I worked on it all afternoon and could not figure it out.

Any help would be very much appreciated.

Ryan

 

Check for vacume leaks before you do anything else. If the dist is timed right and the rest of the electronics are new, I'd suspect the carb. MSD's 6al only needs 12v in, 2 trigger wires and 2 coil leads. Double check voltages and connections and they should be fine.

 

The billet distributor with no vacuum advance unit?

 

yup. it's the one without the vacuum advance. i was thinking maybe the accelerator pump went bad again. it went bad due to the reformulated gas once before. after sitting all winter, maybe that is the problem. i know it doesn't have vacuum leaks. I already checked that out.

What confuses me, is it is just off the start. After it get's rolling, hold on.

 

well I can tell you without reading any further eric is about to tell you that the entire problem no matter what it is will be cured when you buy a new dist with vac advance, then if you still have the problem you will find out that it was being hidden by the dist without vac advance.
sounds like you have a problem with your accelerator pump circuit, not enough too much, or not working at all.

 

And Monsterbaby will tell you a distributor without vacuum advance works perfectly on the street and that vacuum advance is not necessary. Of course all of the newer EFI engine engineers would love to hear how this is done, it would sure simplify engine controls... Maybe Monsterbaby has a new career as an automotive engineer!

A mech advance only distributor is only good for high RPM racing applications. You can get them to run on the street but the vehicle will run like crap compared to how it would with a good distributor.

 

I don't need anybody to stand in for me... the problem lies in the distributor, you NEED vacuum advance for these motors.

 

I don't know if this has anything to do with it, but I hit my accelerator pump by hand today, and the engine bogged down, don't know if that is good or bad.

I DID have a slight hesitation with the duraspark, but now that I have the MSD, it much worse.

Also, if I hit the gas hard right away, there is no hesitation. There is only hesitation when I hit the gas gradually, like when I'm behind one of those import things.

I have no clue if that makes sense, but those are the symptoms.

 

WOT -wide open throttle is what that distributor is made for. It does not work well with part throttle operation. Send it back and get the part #8350 or 8477 or similar unit with vacuum advance that will work with your box if you absolutely have to spend the $$$ on MSD parts.

The MSD 6AL ignition also does not contain the start timing retard circuit which is often needed with the 460 for easier starting. The MSD system is not nearly as good as the stock OEM DS-II system with the OEM type Motorcraft ignition module. MSD is more expensive to begin with and much harder and higher $$ to troubleshoot and repair.

 

I've had better luck with the Multi Spark Capacitive Discharge units, namely Crane FireBall Hi-6s than just the factory boxes. The MSD unit doesn't eliminate the factory box, it just supplements it.

 

He has a 6AL unit that replaces the DS box.

The OEM DS-II has several advantages over the other aftermarket units for normal use. It has the timing retard function for easier starts especially with a hot engine and big cubes or high compression. Lower starter amperage means less wear and heat in the starter and cooler cables with less voltage drop. The DS-II is also optimized for performance below about 5K and gives a few more ponies on the low end than the aftermarket units that are generally optimized for high RPM operation. The OEM modules are easy to test at just about any parts store for free. You have to buy another aftermarket unit for shotgun testing on those systems. The DS system is much cheaper than the aftermarket units, even buying a brand new Motorcraft module!

 

Hmm maybe all the auto makers fired all the smart engineers then, cause I can't think of a single car built in the past 20 yrs that used vacuum advance. And if vac advance was so wonderful then having a set way of working it would in fact be the way to go, but none of them agreed on how it should work, ford used ported vac, GM ran manifold vac (actually retarded timing at full throttle) and one even had the vac locked out until the mechanical side advanced a certian point right around 2000rpms, wait a minute that means they were running pure mechanical advance off idle, man those suckers must have been horrible about stumbling off stop signs
As to high rpm race, well actually not so much, if your stall is 3500 rpm then whats the point of having a advance at all, and in fact most of the racers I know, me included don't run any advance my timing is locked out at 32 degrees, and I can and have done it to prove the point stomped the throttle off idle with 32degrees of advance right at that point, and no stumble at all, in fact it revs so fast you can't get your foot out of it before it hits the shift light if your free reving it. ooops so much for the theory of to much to fast causing a stumble off idle. Now why doesn't mine stumble? gee maybe cause the carb is dialed in properly.
Also the 6al box is not a high rpm box for racing only, it's actually a street box and is basically all done at 6000 rpm (goes to single spark around 4500 rpm)
another cute little fact that seems to be overlooked in this discussion, a stock or any vac advance dist is 85% mechanical, the vac only makes a few degrees of difference plus or minus which won't cause drivability problems unless something else is wrong, then it's just covering up the real problem. you put a advance curve on a mech only dist to run right up the middle of what the vac/mech will do and you won't see any difference as the total difference at any given moment will not exceed 2 degrees, and most timing marks on stock dampeners are actually off by more than that.
Last night I searched my memory to figure out how many mechanical advance dist I have run on the street, currently I have had 12 of my own, not one ever stumbled off idle unless I had a vac leak or a mis adjusted or bad carb. My dad runs a mallory on his pickup, mechanical only (I actually don't like the mallory but that has to do with the stupid photo cells that go out all the time) he has had it on that truck for 15 yrs, and he did in fact have a stumble off idle, had a local guy talk him into putting a vac/mech advance dist on it, and golly still had a stumble although not quite as bad. The guy then tells him well you also have a bad carb, so dad took the truck home and bought a new carb stumble went away totally so out of curiosity put the mallory back in and gosh no stumble gee maybe the carb was the problem, oh no couldn't have been he just got lucky with the new one I guess.
I ran one in a 454 GMC 1 ton I used for towing my stock trailer had it 6 yrs pulled a 28ft gooseneck trailer with up to 18,000lbs of cows at a time, got 11mpg loaded and 13 empty with 4.56 gears and a 4spd. and once again no off idle stumble EVER, guess I was just lucky.

 

Monstababy give it up, you are way off with your "calculations". You forget that the new cars DO use manifold vacuum, throttle position, and mass flow etc to figure in a correction for load and mixture into the timing tables which is exactly what a vacuum advance does so EVERY car built in the last 20 years still has the equivalent of vacuum advance built into the timing tables. Just because you are clueless about engine controls and engine operation does not mean that anyone fired any engineers.

And I will still say that even if you do get a mech advance only distributor to "run" on the street it will run like crap compared to a proper setup with a vacuum unit. They just don't run right without a vacuum unit for part throttle period. Timing has to have the load input into the equation. There is a world of difference in getting something to "work" vs getting something to work right. Hell even MSD makes a distinction between street and race distributors, guess what, the street distributors have vacuum advance units!

The MSD 6AL "advertised" specifications:
OPERATING SPECIFICATIONS
Operating Voltage: +10-18 VDC Negative Ground
Current Requirements: 5 Amps-5,000 RPM
10 Amps-10,000 RPM
RPM Range: 15,000 RPM with 14.4 Volts
Spark Duration: 20° Crankshaft Rotation
Energy Output Max: 105-115 mJ Per Spark
Weight and Size: 3 lbs, 8"Lx4"Wx2.25"H
Voltage Output Max: Primary: 460-480 Volts
Secondary: 45,000 Volts (Blaster Coil)
http://www.msdignition.com/ignition_6_6420.htm

 

Eric I know what MSD site lists as the specs for the 6al but it's mostly hype that is a street only box, doesn't work well over about 11:1 compression and has virtually no advantage over a stock ignition above about 4500 other than a more stable spark, it looses the multiple spark discharge that they are named for, and they just aren't hot enough to fire a 13:1 comp engine running 112 octane fuel or other race fuels, it will fire but you will lose a LOT of HP.

As to not having a clue, well thats funny ASE master auto tech, second highest graduating score from WTI, only student offered a job as an instructor before graduating, CCT journeyman in diagnostics, electronic, and drivability as well as trans and a couple others. i may be a dumb ole truck driver but wasn't always one. I also know that every drivability problem that you ascribe to a mechanical advance dist usually isn't, I have seen to many put on a vac dist and find out the problem still exist just like it did before. wonder of wonders.
the vacuum advance is for economy not drivability issues as you ascribe to them, yes you CAN get a vac dist to get better fuel economy in variable driving formats than you can a mechanical but they DO NOT CURE THE DRIVEABILITY ISSUES, well unless you have the mechanical locked out. Do you know what the limp home mode timing is? it's a rpm only based timing curve, and guess what most people don't even realize it has gone into that mode as far as the way the car drives, Ford is real good at it. if the computor is in open loop it does not use vac as a source to figure the timing, it uses rpms just like a mechanical advance dist uses and guess what no off idle stumble, also as to the off idle issues you keep subscribing to mech advance dist, they DONT advance the timing until around 1400 rpm thus they aren't affecting off idle at all. and rarely does a vac advance even begin to advance until around there also with the exception of GM and some chrysler vehicle. also most of the early electronic timing controls did NOT use vacuum in figuring timing they used a knock sensor the timing computer would advance until detonation was detected (so slight as to not be noticable by the human ear, or cause any engine damage) then slightly retard and begin advancing again, several times a second. always going for max timing when it could unless the tps was in idle position.

edit for a clarification, you don't see me telling people to go out and buy a mechanical advance dist, but I do tell them if thats what they got it can work just fine thank you very much. instead of telling people to go out and spend another hundred or more on parts that aren't going to cure the problem.

 

I'm wondering if that Holley carb accelerator rod is indexed correctly ?

Perhaps taking a stroll though the holley site might help ?