Motorcycle Repair: top end gaskets, gasket material, exhaust leaks

Question
i have a a 1976 cb550k. i recently replaced the top end gaskets. i am curious about the 6 rubber disks covering some of the head bolts.i thought they were there to keep junk out,so i never put them back in.they were not in the gasket set i bought,and my clymer manual made no mention of them at all.when i got the bike together oil appeared all over the cooling fins,this is the most i have ever seen it leak. took it all apart again and made my own gaskets out of gasket material. seems to work but am still getting oil from around the exaust collars on 2 and 3 cylinders.not nearly as bad as before.should i buy the honda gaskets at 6 bucks each,or should i use more sealant? also i am getting an exaust backfire, what could this be?

Answer
Carl, as you have found, the sealing rubbers are important to keep oil inside. Unfortunately aftermarket gasket kits and manuals don't always cover all the repair aspects. I went online at the http://www.powersportspro.com/partsfish/login and checked their suggested price, which seems like $4 each, so your dealership isn't giving you any break on the parts, apparently.
Gasket material probably isn't the best substance for replacing the seals, as they generally have a raised lip around the edges to help seal them more completely. Using something like 3BOND sealer, rather than gooping a bunch of silicone seal into the space. Silicone seal tends to squeeze out, blob up and sometimes work its way down into the oil system causing big problems..

The CB350-400F models used special sealing washers under some of the outboard studs that kept oil from dribbling down. If your bike has those they need to be in good condition and placed where appropriate.

Exhaust leaks at the flanges, pipe and muffler joints can often cause backfires in the mufflers. I will assume that you have good pistons/rings, valve sealing and that the compression is even all the way across.

Other causes for backfiring in an individual cylinder are intake manifold tract leaks... Check O-rings at the manifold to cylinder head connections, check the rubber manifolds themselves. All carbs should be cleaned properly, float levels set correctly and idle mixture screws should all have an effect when making adjustments. If not the cause of the problem needs investigating.. plugged idle jet, incorrect float level, etc.

If course, the ignition timing must be accurately set, clean points, good condensers and spark advancer functioning properly.
Bill Silver