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View Full Version : Still having problems with my 7531 please help


Quarter Flash
04-21-2008, 08:52 AM
Very hard to start, backfires and flames out of carb when trying to start, When it runs it runs very poorly and still backfires and shoots flames. Wont run under 2500 rpm. I have checked my programming ten times, although not at all familiar with the 7531. The engine was professionally built and the builder says he indexed the cam. I have MSD Super Conductor wires with copper coil wire. I did cut them to fit better and did not hook the copper coil wire to the end terminal. I guess I didn't remember if they were hooked before I cut them. The only other thing I can think of is I did run the primary distributer wires in the same loom as the radiator fan, trans cooler fan and the fiber optic line. I will take the plug wires back apart tonight and attach the coil wire to the end terminals and see if that helps. Please any suggestions.

Bob

Eric David Bru
04-21-2008, 10:23 AM
Are you running a crank trigger?

If so, did you phase the rotor?

Keep your main trigger wire separate from other wires.

EDB

Eric David Bru
04-27-2008, 10:39 PM
Bob,

Did you get this sorted out?

EDB

msdtech21
05-05-2008, 12:00 AM
The only other thing I can think of is I did run the primary distributer wires in the same loom as the radiator fan, trans cooler fan and the fiber optic line.
Bob

Try fixing that first. Better yet, shield the wires with a PN 8862 harness. Thats probably the problem right there. Those wires can act like an antenna and start picking up electrical interference. That in turn will make the box do some crazy stuff.

Thanks,
MSDTECH21

540elcamino
05-14-2008, 03:18 PM
I was playing around with stuff a few days ago and I can replicate every symptom you have by running 25 degrees start retard and having my phasing way out of whack. Why MDS builds in more that 20 degrees start retard is a mystery to me. 45 degrees between cap towers so anything over 22.5 is going to hit the wrong plug if its phased properly.
:confused1:

msdtech21
05-14-2008, 03:48 PM
:confused1: The start retard is adjustable in the data editor. By default it is set at 10* in the 7531 and can be adjusted accordingly.

654

Thanks,
MSDTECH21

540elcamino
05-15-2008, 01:21 PM
Yes I know, I just dont understand why MSD allows adjustment to 25 degrees when a properly phased system can not function correctly with that much retard. 22.6 will jump to the incorrect plug. It should be changed to 20 degrees max.
:thumbup1:

msdtech21
05-15-2008, 03:05 PM
Rather than typing up a book, let me show you 20* of retard on the rotor phasing.

http://msdpromag.com/mpeg/procap.MPG

The popular misconception is to line up the trailing edge of the rotor to the center of the terminal or the the trailing edge of the terminal. Thats when you run into problem.

Thanks,
MSDTECH21

540elcamino
05-16-2008, 12:22 AM
Now show 23 degrees and make my point for me. Its simple math whats the problem?
Is 20 degrees less than 22.5? Damn Pete whats the problem here? Its common sense.

msdtech21
05-16-2008, 09:36 AM
Jim,

Theres a gentleman here thats worked with Pro-Mod teams (both blown and nitrous cars), for over 20 years, and he would like you to call him. 915-857-5200 ext. 2396. He will be more than happy to answer your questions.

Thanks,
MSDTECH21

mpwr2004a
11-05-2011, 10:03 AM
I'm having the same issue with backfire thru carb, one time it acts like timing to far advance and buck the starter, the hit the switch again and spins forever then fires up.

I have a dodge 440 with a mopar perf distributor, no crank trigger, I put the heaviest springs in it because I cant lock out the dist. and put it all back together because of the reluctor plate. its a magnetic pickup distributor.

msdtech21
11-07-2011, 10:29 AM
I'm having the same issue with backfire thru carb, one time it acts like timing to far advance and buck the starter, the hit the switch again and spins forever then fires up.

I have a dodge 440 with a mopar perf distributor, no crank trigger, I put the heaviest springs in it because I cant lock out the dist. and put it all back together because of the reluctor plate. its a magnetic pickup distributor.

Which box are you running?

mpwr2004a
11-07-2011, 10:58 AM
im running the 7531 box. and running a red blaster coil not the 8251 or 8261. in the wiring book it says that the coil I have is good to go.

msdtech21
11-08-2011, 08:56 AM
Is it backfiring only during cranking? How much start retard is programmed into the box? What is the total timing set at? Have you checked the rotor phasing?

mpwr2004a
11-08-2011, 01:37 PM
it is backfiring when reving and under load, not sure what the cranking retard is at, total is set at 35*, it pops thru the carb like late timing. I phased the rotor but the dist isnt locked out. this is a used box, and had Eric set all back to factory shipping specs when he tested it for me at the Nationals here at Royal Purple Raceway. this box came out of one Frankie Taylors blower motor cars. I have a locked out Mallory Unilte dist. can it be hooked up to this box.

scot9055
11-11-2011, 03:39 PM
Double check your firing order program. Is this a new cam? If so you could have a cam with a funky new timing order.

Connect to box
click view
tree
spark SEQ
now check your firing order

My engine will back fire thru the carbs a little if its lean on the start. I always pump the gas twice to the floor and about 20 seconds later start the engine with the throttle cracked just a little and she fires right up.

mpwr2004a
11-15-2011, 01:37 PM
I'm new to this box so do I turn the power on and then connect my Laptop or connect the laptop. or does it matter.

scot9055
11-15-2011, 09:21 PM
I connect mine to computer then turn ignition on.