Vintage Dirt Bike Q & A

Just purchased my first vintage bike. It ran the day i bought it has not run since. Previous owner had a new top end by honda dealer in July of 04. Compression is 110 clymer manual says normal is 120 to 150,but, 100 will run. Have good spark and fuel. Tested for both. Have not been able to test compression on lower end to see if crank seals are leaking.Is there an easy way to do that? Manual says you need special test equipment. Any ideas would be greatly appreciated? Next step is a honda dealer and I would rather try and fix myself.

You can try to build your own leak-down tester. If you have access to a lathe this is pretty easy. If not then you can still build something if you use your imagination with what's laying around.

Get something to plug up the exhaust port. I use an expanding plug from the plumbing section of the hardware store. Then you have to make a plug that will fit into the intake manifold. This needs to have a hole drilled through it and fitted with a low pressure 0-15psi gauge available through Granger and a one way air valve of some sort. You can get something like this in the plumbing section as well. Look for what the plumbers use to pressure test pipes before final inspection. Looks like a tire valve. Or what I use now is the squeeze bulb pump off of one of my old blood pressure cuffs that I retired off my trauma bag. You can get this separately from a medical supply house.

OK, assuming you can build this pump the pressure up to 9psi and see if the pressure drops. There will usually be a little bit of drop over time but if you are getting more than 1psi drop per minute you have a leak that needs fixing.

Put a small about of dish soap and water into a spray bottle and squirt this on the areas where gaskets are used and check for bubbles. If you get pressure drop and no large bubbling around cylinder and manifold gaskets check for bubbles out of the gearcase vent. This would indicate leakage in either the main seals or the crankcase leaking into the tranny.

Now if you can rig something together w/o the gauge you can just check for bubbling as above. To give an example last year the day before Chehallis I was at my buddies fathers house up near Portland. He was having troubles starting and running his old Husky. Being several hundred miles away from my test equipment I still rigged up something using a handball found in the shed to plug the exhaust and various pieces of innertube, duct tabe, bicycle pump, and whatnot to test his bike. His leak was so bad you could hear it coming out of the vent tube. Needless to say the Husky didn't make it to the race the next day.

Another idea before you do all this though is to check the timing on the bike. You can have great spark and fuel flow and compression but if the timing is to far out of whack the puppy won't fire.

HTH,

Loren