Reply to "Engine back-fire"

This reply is from Jack DeRyke. I will be posting responses from him temporarily. Thank you. Dave Adler

"Maybe, but the combination of parts you list will never allow tractor-like engine loads at 700 rpms. In fact, most carbureted 351Cs won't allow such low idle speeds- most idle at 1000or above. A few other things- engines built after mid-72 had 4 degrees retarded cam timing via the crank chain sprocket; most cam-chain kits allow multiple positions of the cam timing such as -4, straight-up & + 4 degrees. You might look at the cam you have & its timing position, maybe with a dial indicator. Also, stock Cleveland cam chains are really only good for maybe 20,000 miles before they're hopelessly worn & stretched. If you haven't yet, I'd suggest a new true-roller-chain & sprockets. Another undefined thing is, the fender tag initial timing of 16 degrees was for a low compression engine. Changing to a closed chamber head increases compression to 10:1 which is a bunch on todays gas. Too lg a carb (or a double-pumper thats not set up specifically for your egine) will also do this almost regardless of how you adjust things. If it really bothers you after checking the above, I'd buy an hour of dyno time & try various ignition & carb secondary tip-in settings; many Pantera owners find they make more power with less ignition timing.

Second question: I had replaced the A/C compressor with a rotary unit. The system was running R-12. My hoses (original) are now shot and need to be replaced. R-12 is no longer available in Canada (where I live). What can I expect if I replace the system with the new R-234 (I think that is what its called) or should I try to replace the hoses and try to get and stick to R-12?

Replacing R-12 with R-134a, your system will leak faster with the same flair-fitting brand-new hoses & cool less unless you change the separator can, the expansion valve under the dash and all the lines & fittings to barrier hose & o-ring style fittings specifically designed for R-134a. Changing compressor lube is also necessary; once all thats done, I'd think your A/C will work about as before for the area you live in. All the vendors offer a DIY kit of this stuff and most will do the installation."Jack DeRyke - PI Boss Wrench