Calling the Commander Brain Trust

Challenger has been dead in its slip since its launch on April 20. It starts great, idles great and cruises up to 1300 just fine. At 1300rpm and up she bogs and stalls. If we get her past the 1300-1900rpm dead zone (defined as major missing and rough running) she cruises along great at 2100-3400 RPM. At WOT she’s running the best ever. But because of the rough running and potential stall situation in a RPM range, she’s not very reliable.

Her 427’s feature new Splitfire ignition wires, Pertronix ignition, valve adjustments, rebuilt Carter AFB carbs, timing checked, compression all between 160-185, intake manifold vacuum at 21 and rock steady.

To diagnose the engines, a mechanic was called in from another marina and he used an array of infared pyometers, ultrasound digital stethoscope, vacuum gages and timing lights on each engine for diagnostics at the dock and out on the lake. When he asked me to force the throttles past 1300rpm when we were out on the lake, the starboard engine stalled. Back at the dock, he disassembled the carbs a second time. He cleaned the PCV valves and pipe. He confirmed the proper voltage range at the coil for the Pertonix modules. He picked up a vacuum leak under each carb (with his headphones and soundprobe) and we later replaced the 1973 gaskets above and under the plates. He checked ignition advance, voltage at each plug and checked each of the 16 plugs and confirmed that they’re running clean. Exhaust is clean, everything sounds ok and no leaks anywhere. These engines had been running rich for several years with loads of black soot blowing out the exhaust, so at least THAT has improved. He removed the carbs again and checked the float adjustment, checked for any debris and declared everything perfect. Fuel delivery for WOT as well as idle seem fine and the fuel pumps were replaced about six years ago. We even gave her a good hot run at 3300 rpm for an hour. Anway, six hours of visiting mechanic time and 500 dollars later, we still can’t get past 1300 rpm when throttling up. His suggestion is to try a different set of Carter AFB’s and see what happens.

So, relying on my own marina again, the starboard carb is on the marina owners workbench this July holiday weekend and I’m wondering what we may be missing in the troubleshooting loop. These carbs have been off and on several times now. He had some trouble with the rebuild kits over the winter. When launching the boat, it wouldn’t start and he needed to re-order and replace the accelerator pumps in the carbs. He’s suspicious of the metering rods, as we’re getting this ‘bog’ from cruise rpm through acceleration. He doesn't have much confidence in the rebuild kit supplier as he found one part 1/4' shorter than it should be. He is NOT a fan of the Edelbrock 1409 and won’t order them, so that’s not an option. He has dealt with many of them in his experiences and asked that I not consider them as an upgrade, though I know forum members have had good experiences with them.

Last fall he adjusted the valves and installed the Pertonix ignition and re-built the carbs over the winter. Since all this, we’re dead above 1300rpm. Two expert mechanics are stumped on this one and clearly, I am NO mechanic! It would be great if we can get this boat running before we get much further into the summer.

Any suggestions from the Commander brain trust?

Bill M
1973 ChrisCraft Commander 41