mopar woes,running rough

[RedRocket]

This motor's not in my boat but I got good advice here before so please help! Was running sweet and suddenly started running like crap. Backfiring out exhaust and through the carb. At idle it almost sounds normal except for the odd erratic knock or clack noise that sounds high in the engine and the motor shakes when it knocks. I thought the timing chain jumped so I changed it, it had 1" of slop, but it didn't fix the condition. Compression test all 140-150psi. I took great care to line up the timing marks. specs: 360, 9.5 comp, kb pistons (not my choice) hyd. mopar cam, ported stock heads, edel. intake, holley carb, low miles on motor, msd pro billet and 6AL, 8.8 mm wires..All i can think of is spark might be jumping, but it shouldn't. I think a broken internal part would be a steady banging noise. what gives? please help!

[19cobaltcd]

Not sure but just a suggestion. Pull the valve covers and roll the engine over, watch the rockers and see if you have a cam lobe or two going away. It happened to me and the motor would pop and backfire, then when enough got worn away the lifters and pushrods really made a racket. Just a thought.

[RedRocket]

One thing I already did was check for play in the rockers with the valves closed and they were all good, I forgot to mention that.

[Moneypitt]

The closed side of the lobe,/heel, doesn't wear out, its the open part of the lobes that go away..................Watch the rocker action to verify they're all working the same lift/duration................MP

[RedRocket]

thanks, I should've realized that! duh, I'll measure the lift on each one so I know for sure.weird part is how quick it happend. Is something wrong with my lifters if they push down very easy when they are not pressured up?

[RedRocket]

OK I checked the cam lift and all appears to be fine. All rockers have the same amount of travel. I didn't have the most accurate way to measure quickly but at least accurate to a 1/32".

[Unforgiven]

MSD??? Check the cap, then check the box....we've had more problems with the BOX 6al..

[Moneypitt]

The unusual noise in the upper end would lead me away from the ignition. The extremely loose t/chain and now the idea that the lifters colapse easily points back at the valve train. Okay, the only conection to the top end noise and the ignition would be in the area of the dist. gear, which also drives the oil pump, which pumps the lifters..........Anyone had the plug wires off lately??

[RedRocket]

woohoo! the spark was jumping! I took one plug wire off at a time while running and when I got to #7 the noise was gone. Took the cap off and there is a carbon trail going from #5 to #7. There is a very slight oil film, maybe that caused it. seal must be gone on distr.? I'm glad it happened the way it did or I wouldn't have changed the sloppy chain. Thanks for all input! This is way better than all those tech lines that you wait for days and usually don't get an answer. I don't have to rip the cuda apart,I'm happy,someones getting beer bought for them!