rcarney

I have a 241 Liberator with remanufactured 460 c.i. this spring, new edlebrock 750 carb and intake, and 5500 rpm Comp Cam. Engine idles rough but will smooth out with RPM - this is an engine miss not the cam. Starts popping w/ occasional back fire above 4000 rpm under open throttle. Will occassional run up to 4900 rpm but eventually starts popping. Two plugs were black so replaced all and still mssing at idle. Pull wire off of No. 6 cylinder and no difference at idle. Plug has spark. All cylinders compression test at 150 psi or above. Do I have a valve problem?

Thanks, Rick

BY U BOY

Could Be As Easy As A Bent Push Rod. That Is Where I Would Start. NEVER MIND JUST REREAD THE PART ABOUT COMPRESSION AT 150 IN ALL.

SB

iTrader: (1)

Broken valvespring ?
Worn cam lobe(s) ?


Pull valve covers and check.

Oh, don't overlook ignition issues : ie:wires, cap, rotor, proper wire routing, vacuum leaks, etc,etc,etc

rcarney

Thanks. Hopefully its just a couple of bad springs, however, I suspect its probably a couple of bad cam lobes. I am thinking the cam was not broke in properly due to some initial startup problems and cooling issues that took a lot of engine starting and stopping without any significant run time.

merlyn1965

A 460? Probably OMC? If I were you, I'd disconnect the ESA (electronic shift assist) box (black box behind the carb). This was the problem on mine, which had the same symptoms and I blew my engine because of it. It is ment to help shifting but is prone to failure and when it does, it cut the spark to a few cylinders, thus backfiring. In order to correct this you'll have to disconnect both connections leading to it and voila. I've rigged my own
shift assist by using the toggle swith already there by wiring the ground side of my coil through them switches and it works like a charm. The best thing about this test, it'll take you about a minute to disconnect the ESA and if it isn't the problem... well then you may have to take yhe wrench.
Hope it'll help.
Josh

rcarney

No OMC here. I replaced the OMC drive with a Volvo SX drive and all I can say is "its really smooth. kind of like butter shifting with my pinky" Thanks for the thought though. I know how the OMC drive ignition crap can cause issues.

merlyn1965

OK, did you change your rocker with adjustable one? If you did, I'd check the valve adjustment on your 2 cylinder with the bad plugs. When checking the compression there's not enough oil pressure to prevent the lifters from collapsing a little but under power there is so maybe a valve is staying open enough to do it. If your rockers are non-adjustable, check the gap (0.030") between rocker tip and valve stem. When changing cam on the 460 one has to adjust this with longer or shorter push-rod.
My $0.02
Josh

rcarney

Thanks Josh. I have the stock non adjustable rockers. The remanufactured long block came with a little more aggressive cam than stock and of course, I took it up another notch after receiving it. I did not change anything that came with the originaI cam and set up. which may be, as suttle as I believe the cam diff. is, may be enough to cause a problem. I plan on pulling the covers this weekend to take a look and take some measurements.

Rick