I own a 72 BB which I have equiped with a Pertronix Ingnitor replacing the points and condenser. Added at the same time was the high out put Flame Thrower coil.

Now the problem I run into. Please note I have never owned a BB 4 speed prior to this one so I can't fall back on knowledge previously learned. If and when I choose to really really grab a gear and haul a** the engine seems to begin breaking up (as in misfiring or some durn thing) I'm not sure what to look at first. This "break up" occures way before red line but only during hard acceleration.

Vehicle is original with a rebuilt 454 in the late 90's. She was bored .0030 over and a mild cam was installed. Carb is an original Carter.

I'm not a mechanic just a learning parts changer so I'm not real sure where to start looking. I am wondering is timing might not be a consideration.

Any offered advise would be grealy appreciated. Oh and as an after thought as far as just normal driving and acceleration goes, she runs fine and idles well.

 

Dist gear????

 

I've been trying to find and fix a high RPM break-up on one of my Vettes also. Mine is a smallblock but regardless some of the areas to look into are:

if you still have points in your distributor make sure they are the hi-performance 32oz points and a good quality condenser. These points are good for 6500 RPM without break-up.

make sure your distributor cap and rotor are good. make sure the contacts inside the cap and on the rotor is clean and free from dirt and oil and no cracks on either.

Make sure the black ground wire connected to the breaker plate on the distributor and going to the coil is good and has a good connection on the breaker plate. This wire tends to get ignored and a bad connection or an old wire could go bad inside but still look OK from a quick visual check.

Make sure your coil is still good. If it is going bad it can cause high rpm issues or even cause the car to die when it gets to a high operating temp.

Check your ignition wires carefully. If they are old, dried out, and/or showing cracks in the wire or plug connections change them out.

How old are your spark plugs and are they gapped correctly?

As far as timing goes, make sure total timing is set for 36º total timing with the vac advance can disconnected and plugged than reconnect the vac advance can. Make sure vacuum advance is connected to a full manifold vacuum source (won't make a difference on your missing but car will run better).
also, related to the timing, assuming you still have points in there, check dwell to make sure it's set at 30 and as you rev the motor that it stays steady. if it flucuates or varies a lot as you rev the motor up your distributor mainshaft needs shimming.

This should at least be a starting point for you........... good luck!

EDIT: opps, sorry, I missed that part where you replaced the points & condenser with a pertronix unit and a new coil. Forget the above suggestions that involve points, condenser and coil, and dwell

As Hugie mentioned, it's easy to mis-wire the ignition when swapping in a pertronix unit and their coil. see the diagram for the correct wiring on this:

 

I did a big block 427 in a 74 and it can only be a few simple things. First - you cannot use the resister wire from the stock ingnition for the positive wire on the HEI. The resistor wire knocks down the voltage and the HEI runs out of juice Second- You may have a weak valve spring (it happens) If you rev it up slow and steady with no load you barly can tell BUT put a load on and watch the flames NOW this is ASSUMING all your ignition parts are in proper working order- Cap, Rotor, Wires, Plugs, Module, Distrubutor, Ect... Hope This Helps Hugie

 

OK let me see if I can narrow it down some based on the input supplied. Cap is less then a year old, wires are new, plugs are new, Wiring used on the Pertronix is simply hot to hot on coil and ground to negitive on coil. Car runs beautifully at normal speeds and works awesomely through normal acceleration. She also idles just fine.

I have not checked the timing as yet but, correct me if I'm off base, the 454 ought to pull very solidely to well near red line on full, all out acceleration.

 

I'm chasing the same problem on my 73 BB, exact same symptoms except mine tends to be intermittant, eg yesterday it ran fine. I don't have the pertronix unit in my 73 but the Mallory conversion, and I'm starting to think it may be the issue. Getting ready to change it over to the crane unit like I have in the 69. By the way your original carb is a quadrajet not a carter, not that it really would be a factor in this situation. If you still have your stock points laying around bolt them back in and see what happens.


Pat Kunz

 

I have a BB454+ and fought this for months. I went the ignition route and that is the obvious. Then Lars got me going on the other leg of the triangle --- air, flame and fuel. Check the hoses on the fuel pump and make sure the "S" hoses are not kinked or collapsed from age along with the pump. Run a check on the fuel o/p with a hose, can and volumn. Next check the fuel pickup in the tank and the damn sock. If covered in crud you will literally run out of fuel on a BB at high RPM's. Last check the fuel filter and float level. If you can borrow another carb or get an adaptor and put on a holley or edelbrock and see if you run out of fuel. These can be tough.

 

if you have a holley you might try setting the float level alittle higher
I set mine at the bottom of the hole and had the same problem
raised it up to where it was running out the hole good and no more problem

 

Try a simple test with a voltmeter and check your voltage at the coil + terminal to make sure you have the proper voltage at idle and higher RPM. If the voltage drops as the RPM's increase that could be the problem.

 

A weak spring will do this or a bad lobe on cam

 

And not saying that this is really important, and I don't know which years, but Rochester couldn't keep up with demand, so Carter did build some Q-Jets for Rochester under contract.

Not knowing the specifics, it could be original.

 

My 75 does the same thing do a search on the Pertronix Ign. there were some issues in the past I called them they gave me some stock numbers to look at on the module mine only does it when I'm on it hard I've not looked at mine yet.,But I'm gonna put the dynamod module back in as soon as I have time

 

Breaks up? If this means detonation... You could have a lean condition that is presenting itself when you really get into it. It could be a distributor/electronics problem. When did you last replace the plug wires? Did this occur after you put the petronix in? Was it occurring prior? We need more information...... Dave

 

You are correct mine is a Carter built Q jet

 

Hey Dave, wires are less then 2 weeks old and are original type grounded BB wires. The plugs are also 2 weeks old. And yes, if memory serves me correct it has occurred both before and after Pertronix.

Ken

 

Timing must be set properly!!!!