Check vacuum advance plate(same as what points are mounted to) and wiring to points. Under load it moves because of vacuum and could cause such a problem. Check ignition timing(and point gap--this will change timing if off a lot) to make certain not retarded(do not have 100 percent confidence on timing mark on dampner or crank pulley. Sometimes they are wrong because of shifting of pulley or dampner on crank snout. Any water in gas? Any vacuum leaks in intake manifold or carb mounting or vacuum hose disconnected somewhere. Check running engine out with a vacuum gauge. Sounds a lot like accelerator pump problem, but as you changed carbs, probably not. Make sure that coil is wired correctly, negative wire goes to distributor. Also is coil good? Check distributor cap for cracks, and rotor contact. Is spark plug firing sequence correct? No burned or damaged intake valve? Check all wiring to ballast resistor and from there to coil and from there to distributor for faulty wiring or loose connection. Roger Schaaf 300 B Calyfornua ----- Original Message ----- From: Doug Warrener To: Chrysler300@xxxxxxxxxxxxxxx Sent: Thursday, August 03, 2006 9:18 AM Subject: [Chrysler300] 300H Acceleration Problem Greetings from cool (only 95 degrees) Northern California. I need help correcting a recent acceleration problem with my newer H. At low rpm and under load, the engine looses power and then backfires thru the carbs when I "floor" the accelerator petal. This does not occur with the transmission in neutral - the engine revs up with no problem. I have changed carbs and still have the same problem. This is a recent occurrence - car did respond aggressively with no hesitation. All comments are greatly appreciated. Doug Warrener [Non-text portions of this message have been removed] I choose Polesoft Lockspam to fight spam, and you? http://www.polesoft.com/refer.html [Non-text portions of this message have been removed] To send a message to this group, send an email to: Chrysler300@xxxxxxxxxxxxxxx For list server instructions, go to http://www.chrysler300club.com/yahoolist/inst.htm For archives go to http://www.forwardlook.net/300-archive/ Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/Chrysler300/ <*> To unsubscribe from this group, send an email to: Chrysler300-unsubscribe@xxxxxxxxxxxxxxx <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/