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'74 Can-Am 125 T'NT question

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Just picked this bike up. It needs lots of work and will cost me a small fortune :thumbsup:

My first (of many) question is why does it appear that this engine runs two spark plugs? There was only one plug in when I got it but there is a second hole right there. I only see one ignition coil mounted to the CDI with one plug wire. Am I missing a coil/wire or is this a missing decompression valve?

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A friend of mine has started racing a very similar bike in some vintage racing, and having ridden with him a bit, I'll pass on what he has mentioned.

The two different plug holes is for two different heat range plugs, so for tight trails, you may want to run a hotter plug, for wide open, you may want to run a colder plug. Just switch the wire from one plug to the other and done. Don't really see anyone bother with it though as one plug usually fouls and becomes useless anyway.

Another thing to modify when you get the bike is to add something to the base of the back of the seat to keep it up in the air. What happens on those bikes is if you come down hard sitting on the seat, it will crush the air filter and essentially seal the entire intake. The end result is the crank seals getting ruined.

I've also heard a lot of complaints about the Bing carb that comes on the bike. Carb is alright, but getting any parts for it is very difficult. And they also leak. According to the guy my buddy knows, they are called "Bing" because that is the sound they make when they hit the trash can. You can replace with a Mikuni carb, although you need a new intake boot, and a certain year Chevy S10 CV boot fits perfectly, can't remember the year though.

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Lots of great info, thanks man. I think I'll find a short bolt and a crush gasket to simply plug the second hole. I'll also pay close attention to the seat/air box relationship.

Thanks

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A friend of mine has started racing a very similar bike in some vintage racing, and having ridden with him a bit, I'll pass on what he has mentioned.

The two different plug holes is for two different heat range plugs, so for tight trails, you may want to run a hotter plug, for wide open, you may want to run a colder plug. Just switch the wire from one plug to the other and done. Don't really see anyone bother with it though as one plug usually fouls and becomes useless anyway.

Another thing to modify when you get the bike is to add something to the base of the back of the seat to keep it up in the air. What happens on those bikes is if you come down hard sitting on the seat, it will crush the air filter and essentially seal the entire intake. The end result is the crank seals getting ruined.

I've also heard a lot of complaints about the Bing carb that comes on the bike. Carb is alright, but getting any parts for it is very difficult. And they also leak. According to the guy my buddy knows, they are called "Bing" because that is the sound they make when they hit the trash can. You can replace with a Mikuni carb, although you need a new intake boot, and a certain year Chevy S10 CV boot fits perfectly, can't remember the year though.

Switching the spark plug wire between the two different heat range plugs will have no effect on performance. The heat range alters the combustion chamber temp and has nothing to do with spark like many people seam to think. The second hole is most likely for a decomp device. The short bolt sounds like a good idea to me.

Edited by 79yamdt
I was mean

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Switching the spark plug wire between the two different heat range plugs will have no effect on performance. The heat range alters the combustion chamber temp and has nothing to do with spark like many people seam to think. The second hole is most likely for a decomp device. The short bolt sounds like a good idea to me.

Yes the the second hole was for a compression release valve usely you only see then on 125cc way 400+cc cly head that way girl get it started but it was main use as backup spark plug for racing becuases in good old days 2 stroke oil was hard on spark plug and fouled out a lot so no it not the different heat range plugs.

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It is just a spot for a spare plug. If you were to fowl the main, you can just switch the plug onto the spare.

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