Expert: Ben Deutschman - 7/3/2006

Question

   Hi,

   My name is jason and i have been pulling my hair out oveer my 455 olds driven jet boat. i am running a tunnel ram with an 800 cfm edelbrock performer (brand new). I also run an older mallory mech advance distributor with the ignitor two magnetic pickup instead of the old points. here is the problem. cold the engine starts with minimal problems, maybe a bit of backfire through the carb. it runs like a champ for a while, but after shutting it off, the backfire through the carb is outrageous often ending up in fire from the carb. at this point it usually won't start again for a while. im pretty sure the timing is off, but with my motor mods i have no clue where the timing should be. my friend says my coil is weak but it is new. just a stock coil, but a new one. any advice you may have may keep me from having to sink this thing in lake shasta. thank you


Answer
I'd go with pulling number one Spark Plug, and crank the engine over until you get the Piston to Top Dead Center. To be sure you have TDC, also pull the 'Valvecover', so you can watch the Rockers. When both Rockers are at rest (no tension on the Pushrods), and the number one Piston is all the way at the top if its travel, you have Top Dead Center. Then pull the Distributor Cap, and check to see if the Rotor is aimed at number one Cylinder on the Cap. If it isn't, you'll have to pull the Distributor, and drop it back in so that the Rotor is pointed to the number one Terminal on the Cap. After you're certain the initial timing is correct, you can adjust it from there, using a Timing Light.

The only other possibility I can think of, is a Valve that's just starting to go bad, and only starts causing a problem once its heated up. A compression test might reveal that problem.