Vintage Dirt Bike Q & A

Let me start with an apology, as this is not an Elsinore based question, but is is a motorcycle question. This is about my son's bike and y'all are the only people I really trust the advice from.

He has a Suzuki RM60 that did not want to start on Sunday. I thought perhaps he got water in his gas because of the way it would run when it finally started. The last time it died I tried to kick it over again and it back fired. Not a loud pop but more of a poof or puff. It has not started since. I drained the tank, put in brand new freshly mixed fuel, cleaned the carb and checked the spark. They are all fine. I did have very fouled plug, it was totally black and wet. I cleaned it off and it is sparking fine. I have been told that the funny backfire could mean that the crank seal on the left side is bad resulting in a less than airtight seal. I want to do a compression test. If the compression test is bad how do I know if it is the crank seal or if I need rebuild the top end. I put my finger over the plug hole and I cannot hold back the pressure but I also cannot get my finger over the hole very well. I am at kind of a loss here. thanks guys

replace the plug. Cleaning it won't work unless you glass bead with 60 or less abrasive.

So even if the plug is showing a spark it may not be working? That could be good news.

If the bike starts, but runs bad with white smoke I would suspect that you have a leak in the primary drive oil seal. It is the tranny oil being sucked in that makes the smoke.

If it runs and idles fast with the throttle closed the oil seal on the other side is letting air in under the ignition rotor.

If it it backfires you might want to pull the rotor off and check the woodruff key has not sheared, but that is a "big" bike complaint normally. Is there any reason that the ignition timing could have changed?

If the plug is wet, you are either getting too much fuel - double-check that the float valve is closing OK etc. - or the plug is fouling while the engine is turning over without a spark. If you can see a spark, and are using a new plug, the ignition should be OK, but you might want to have it checked by a dealer.

I believe a compression test will only show the quality of your top-end seal i.e. the peak pressure that the pistion, rings, and top-end gasket can create when all the ports are closed. A leak-down test down by a dealer will check there are no leaks between the carb, head, base, exhaust, crank etc...

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Michael Stiles
1979 Honda CR250R Elsinore | 2006 Husqvarna SM510R | 2007 Service Honda CR500R-AF

It won't start at all. I have not put a new plug in it yet. I cleaned and reused the fouled one. The last time it started it would not idle and even holding the throttle a little it would still die eventually. I did notice that the chain had a dark oil on it that is not usually there and I could not find where it came from. When it back fired it was not a pop it was more of a cough. I thought maybe if the seal had gone then there would be a puddle of gear oil under the bike.

The oil seal is internal to the engine and allows transmission oil into the crankcase. You would not see it under the bike, just coming - as smoke - out the exhaust. I suggest you have an ignition problem that might even be cured by a new plug.

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Michael Stiles
1979 Honda CR250R Elsinore | 2006 Husqvarna SM510R | 2007 Service Honda CR500R-AF