ill running 455 help!!!!

i have owned two jet boats a 76 cheetha with 455 olds and most recently purchased a beautiful 82 sleekcraft rebel also with a 455 olds. however been having timing problems, major backfiring throught the carb. the boat has a single point distributor and nobody seems to know what the point gap is or what the timing is set at. when i bought the boat points were at 19 timing was at 10 and the plugs were at 35. got on google and was told points are to be set at 16 timing at 4 and plugs at 30, seem no matter what settings i have the boat at i just cant seem to get the boat to run right. also once the engine gets some heat in it it becomes hard to start if anyone can shed some light on my problem please chim in im desparate.

 

Many of the 455 in pax cars has plastic in the timing chain.

When 75,000 miles is on the motor it needs to be swopped out , or Very erratic timing results.

FF

 

The timing chain can be worn or stretched. Also, it may have jumped teeth. To set the points use a dwell meter. The gap is OK only for initial setup.

 

Gonzo is right about the dwell 28to 32 degrees on this .Also do a compression check to check your inlet valves are closing. Could be running lean ,check fuel pump ,filter, and carb jets.

 

A jumped timing chain will give you a low compression too. It is a good test to start with. If compression isn't good, nothing else will help.

 

A jumped chain which I have never experienced would cause a retarded valve timing, meaning power less and over heat.

Spitting back or back fire could be a weak mixture,-- jets blocked or even a cracked distributor cap or rotor arm.

Difficult to diagnose over the internet you gonna have to check everything out.

 

A loose chain combined with backfiring can jump a chain.

 

thank you all for your input, carb is an old Q jet and it had a hole in the top of the float, apparently the previous owner had put something down the carb and holed the float, got a replacement carb, will install and see what happens, p.s. i am aware of the timing chain issues with the 455. again thank you for your input