Vintage Dirt Bike Q & A

I bought this bike about a month ago and have noticed black gas oil mixture fuel driping from the exhaust expansion pipe where it meets the engine. This also comes out the scilencer and the engine has generated a slight "pinging" sound from inside. Since this is my first dirt bike I cant recognize the loss of power if there is any but when I kick the engine over it does not take much effort. This is an 81' and has only had one ring change on it. My questions are; Is it time to rebuild the engine? How long could it last like this without a rebuild(estimate)? What do I need to replace: only the ring or t the whole piston? What size ring or how to determine this? Sorry if this seems to be alot of questions but if you can answer any of them I appreciate the help.
-Subzero

The black stuff (Drool) is a standard 2 stroke thing with Honda CR's. My 250 was doing it, as was my 125 back in the day. Usually means that your running a bit rich and the seal at the cylinder isn't doing its job anymore. Pinging sound is much more troubling, usually means that your running the wrong fuel (regular 87 pump gas???). The bike was designed to run premium fuel/race gas, greater than 91 octane.

You also are desribing a lack of compression. This would be why it is so easy to kick over. As for what to replace, your best bet is to do piston/ring/wrist pin & bearing. You will need to have the cylinder looked at prior to buying these parts so you get the right size ordered, you may also need cylinder work done. I went through the Nik-a-sil coating on my 250, and have to re-do everything now.

Pinging can really do a number on this bike. You could find a busted piston (ring land area) or broken ring. Both with cause the bike not to run properly, or just blow-up the entire top end (worst case).

How long will a rebuild last? Depends on you. If you ride really hard, not as long as trail riding. The bigger bikes call for rings every 15 hours of run time.

One last thought, what ratio of oil/gas are you running? Honda says 20:1, but the modern oils are 50:1. That will help with some of the smoking & drool. You won't foul out plugs as often either. Let us know what you find.

Jim

Yes Im running 87 with 20:1 oil ratio. Its valvoline multi purpose 2 stroke oil. Should I drain the tank and start running 93 octane? Thanks for the reply.

When you say "blow up the entire top end" what do you mean? Im going to try 93 gas and see what happens. Thanks