Hi Folks,
Need some guidance here. I have a 66 Vert. 327/300 original.
I have replaced the rotor with an electronic unit and the car runs very well except under hard acceleration. If I accelerate gradually, the engine performs smoothly and with expected power and response. If I am too aggressive in the throttle, the engine stumbles and sputters until I back off. Timing? Carburetor rebuild? Any suggestions, as where to start would be very much appreciated!
Thanks once again.
Mark

 

I had similar isuses and tured out to be the float adjustment on the secondaries were off. Did this start after you changed the rotor?

 

The old phrase "Too little, too lean or too late" applies to stumbles on acceleration. Either your accelerator pumps are squirting too little gas; your carb is set too lean (could be floats too low, as suggested above) or your timing is too late.

 

Forgot. If you have vacuum secondaries, check that the spring is not way too light.

 

You could also check to see if your vacuum diaphragm for the secondaries is intact.

 

Thanks for the tips...I will investigate all and report back!
Not sure if this was the case before I changes to the electronic ign.
How do I check to see if the seconday diaphram is operating correctly?

 

Besides all that was mentioned already, I've seen old fuel pumps act the same way. Try your gas filters also.

 

If it just started, then I would look at the dist, as that is the last thing you changed.

Accelerator pump shot should **** out gas from the slightest movement of the throttle lever.

If the bog is instant when you nail the pedal, I do not suspect float level, as it takes a second to run the gas out of the bowl. But check them anyway.

Check you timing specs in the shop manual. Check all three variables of the dist timing functions. Initial, vacuum and mechanical.

Mark

 

If it is breaking up immediately, and the entire time you have your foot in the throttle, it sounds like ignition. I doubt it has anything to do with your secondaries on the carb, or the float levels, or the fuel pump, or filter. They would cause problems only after a few seconds of acceleration, but not immediately. An accelerator pump failure would cause only an immediate, momenntary hesitation on acceleration. If you are getting any popping or backfiring out of the exhaust, it is an ignition problem. Wrong timing will not cause the ignition to break up. It will make the car ping, or accelerate slowly, but smoothly, and maybe backfire once or twice through the carb.

What kind of electronic system did you put in the distributor? On many systems the air gap between the pickup coil and the trigger is critical. You can also check the ignition by hooking up an electric tachometer, like one on a dwell meter. Then when you accelerate, the tach will not work smoothly, or will jump around, if you have a problem on the primary side of the ignition. A bad coil will usually backfire out of the exhaust. If the primary side is OK as per the tach test, and it is popping, try another coil.

Point ignition systems will break up badly under mid to hard acceleration if the condenser goes bad. Poorly set points will break up, but not a severly as a bad condenser. Rich

 

I used the PERTRONIX IGNITOR II w/ flamethrower coil.
Mark

 

If the car accelerated correctly before the ignition upgrade and did not afterwards I would pose that it is the ignition upgrade. You need to recheck the installation...the Pertronix setup with the right coil can push 45,000 volts through the ignition so if you have any weak components they will show up (e.g. spark plug wires, etc.). That is where I would start looking.

 

Did you bypass the ballast resistor on the fire wall? If you mean a dead spot or hesitation when you first apply gas, its a good bet that you have a lean condition, or a bad, or maladjusted accelerator pump.

 

Where did you connect the red wire that feeds the module for power? What's feeding the (+) terminal on the coil?

 

I believe that the car has had this issue for quite a while and before I upgraded the ign. I am generally pretty easy on it and with reasonable acceleration pressure, the car pull along nicely. I will check on the red wire and no, I did not bypass the resistor on the firewall. The car starts and idles properly, has a clean gas filter (added, as the 66 did not have an inline filter). There is no backfiring, ever, and the only time this happens is if I mash the gas pedal whether from a standing start or while I am already moving......OYE!

Thanks again for ALL the advice and suggestions!!!!
Mark

 

Yes, it DOES have a filter - there's a bronze filter inside the Holley fuel inlet fitting; if it's clogged, it will cause exactly the symptoms you describe.

 

That's RIGHT, there is that small filter in there and I don't think I have ever replaced it!!!...I will pull that filter tonight and take a look.
Sometimes it's the little stuff. Thanks for that tip!
Mark

 

How did you pick the Ignitor 11 and why the flamethrower 40,00o volt vs flamethrower 11 45,000 volt? What about keeping stock appearance too...are you using 7mm stock look or upgrade to 8mm? I'm in the process of doing this myself and want to make sure I'm getting the right stuff and also concerned about "stock" appearance. Great forum...I love this place.

 

I bought the package complete from one of the standard Vette suppliers that recommended the combination. I actually bought it in the chrome body as I am not concerned about the stock appearance and was looking for something a bit more dressy.

 

Note the orientation of the bronze filter when you pull it out...it only goes in correctly ONE way but will fit EITHER way!

 

Not to hijack this thread but the Pertronix web site gives information on selecting the right coil for the Pertronix ignition: http://www.pertronix.com/prod/ig/flame/coils/chart.aspx

Only go with the Ignitor II or III as the I is susceptible to damage if the ignition is left in the ON position too long as well as being less sophisticated in controlling dwell... I run the stock reproduction plug wires with gap set to 0.035 on the plugs..