I have a 72 914 that is popping through the carbs and missfiring over 3000 rpm. The engine is a 1.7 w/ 96 mm pistons and a mild skatt cam. I am running Dellorto 36's w/ 60 mm idles. I am using a 009 w/ points, blue coil, bursch exhaust. The car had run great for about 5000 miles after engine rebuild and then symptoms arose. Last week I changed plugs, plug wires, cap, rotor, points, (did not change condensor), adjusted valves, & pulled and examined idle jets. When the car idles is sounds smooth, it revs nice, and even drives o.k. at low rpm. At about 3000 is starts to missfire (sounds like it is gargalling). If you accelerate hard it makes power but does not sound or feel right. I understand that perhaps the 009 is not the best distributer for this application but the car ran terrific for a year prior. Any ideas?

I don't know the dellorto carbs as well as the IDFs.

So it worked great before, and now its not working as well? Is the popping coming from the exhaust or the carbs?

if you have replaced all the electircal stuff, and the car is timed for your dizzy, this is what I would look for.

1) Have you checked your valves? bad valves will effect how the engine pumps air, and that effects the carb jetting requirements. it may not be carb related at all.

2) Check balance between carbs. Even if you are balanced at idle, you may not be balanced as you move to WOT. Put your synchro on and measure flow at 3K and 5K (or a few hundred RPM below your redline to see where you are at WOT), just to be sure that you are still balanced. unbalance between the carbs will cause a lean condition on one bank, and the result is popping.

3) you could be over jetted. 3K for me is usually around town cruising with either just a touch of gas, or coasting. Withe the butterflys closed, if you are over jetted at the idle circuit you could cause a rich condition and be dumping unburned gas into the exhaust, which causes popping. A rich condition can also cause misfiring as the plugs start to get fouled, especially at low engine speeds (idle to 3K.) If you have not recently changed jets, though, if this was the case I'd suspect #1 first - as you were running well before.

4) different gas formulas. Have you changed gas stations? Has your gas station started putting ethanol into the gas? Alcohol has different burn characteristics then Gas does, and some producers put more in then others. The ethanol can make the gas turn sour MUCH faster then old gas used to sour. I have noticed in my lawnmower fuel, it starts to yellow within weeks these days. In prior years, my 5 gallon jerry can would stay fresh all summer, and if there was any left over I'd be able to use it in the snow blower too. That is not the case any more.

5) when was the last time the carbs were rebuilt? They may simply be at the end of their duty cycle, especially if you are using gas with a lot of ethanol in it. Carbs go gum up, and rubber gaskets fail and start to leak. Un-metered air will make them impossible to balance.

its a start. others will have more options for you. I jsut don't know Dell well enough to guess more, and some of my ideas my be crap as I am coming from Weber IDF world.

Zach