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Discussion Starter · #1 ·
I picked up the bike a while back but haven't had much time to work on it.
I've cleaned the carb and currently got the tank off to clean up the rust (bike has been say in a garage for a good number of years). I haven't tuned the carb yet.
When I run the bike is blowing a lot of white smoke it the exhaust at idle, fill the double garage pretty quickly amount.

Being that this is the first bike I've worked on, and never really worked on cars, I don't know if this due to not set the carb up correctly, or something else I may have messed with.
I've done some research and the valve stem seals sound like they could be the issue but I haven't found a guide on how to verify if this is the issue.
Can anyone confirm that they are the likely culprit and if so, how I could go about checking this?

Cheers.
 

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Firs off it is preferable to run the bike outside. It doesn't take much exhaust to fill a 2 car garage.

The bike has been sitting for an extended period of time. It may be as simple as burning off moisture that has collected in the exhaust. There could be some type of storage lubricant in the cylinders. The rings may be stuck which can sometimes be addressed without disassembly. The valve guides are not a particularly likely culprit.

You have the bike running, ride it around the block a few times, If it doesn't create visibility problems in the neighborhood, do it again. A few warm up/cool down cycles may lead to improvement. If the rings are stuck and that doesn't free them up there are some other tricks we can try.

There really is hardly any "tuning" to the carb. Once it is properly cleaned and assembled with the float level correct , the cables and choke linkage adjusted, you adjust the idle mixture. That's pretty much it. If it were a carb related problem the smoke should be black.
 

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Sure it's white, not grey or blue? Normally, white smoke is caused by moisture in the oil or in the exhaust. Change oil get it running and ride it far enough to get the exhaust pipes hot enough to drive out the condensation. It won't get hot enough just sitting there idling, excessive idling will just impair oil circulation and causes other problems. Oil smoke from valve guides or rings will cause blue smoke, not white. Black smoke is a sign of over-richness from carburetor issues.
 
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Good points Mike, I should have started with the oil change.
 

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Discussion Starter · #5 ·
Thanks guys, sorry for the slow response, been pretty busy lately. Will take a look at the bike this week for sure and report back.
 

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Discussion Starter · #6 ·
Also, regarding the colour of the smoke, how blue is blue smoke? This stuff looked pretty white to me but I don't have a reference, is it white with a blue tint or if it is blue it's definitely blue?
 

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I will concur with others here, white exhaust is water for sure. Maintain that motor well because Gen1 CMX250 parts seem to be hard to come buy.

Like Mike said, get it hot and burn it out if that is in fact the issue. Side note though, like most air cooled bikes letting it sit and idle for too long can damage that old engine. They were not that great at cooling, in fact a lot of the Gen1's had overheating problems from people not shutting off the engine at long stop lights.
 
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