Weird smoke coming out.

Ok, so when i start up my bike it's alright. within about 5 or 6 minutes of idling there is smoke coming out from my exhaust, not blue but a dark smoke indeed. there is a small crack in the muffler clamp underneath where the two sides are connected by that pipe, but that's a side-note to add to the problem. i was told it could be running rich, but i'm wondering why it would be smoking after 5 or 6 minutes? i'm thinking a possible gasket or seal somewhere is old and needs replacing. any ideas?

thanks.

What kind of bike is it?

my apologies for not posting that. it's a 1981 kz 750

Could it be burning oil? Have you monitired the oil level in the oil window?

i recently changed the oil and filter, and noticed the oil level was pretty consistent before that as well. it doesn't smell, look or feel like it's oil being burnt.

cperrotta wrote:

i recently changed the oil and filter, and noticed the oil level was pretty consistent before that as well. it doesn't smell, look or feel like it's oil being burnt.

What can happen on those bikes is if the oil level had been over filled at some point, excess oil can get forced into the airbox and saturate the air filter. It would make it run rich as a result.

i blew out the air filter the same day i changed the oil, it was clean as a whistle. the gasket underneath the filter though was soaked in gas.

cperrotta wrote:

i blew out the air filter the same day i changed the oil, it was clean as a whistle. the gasket underneath the filter though was soaked in gas.

Does this mean that there's fuel collecting in bottom of airbox?

Good Luck!

looks to be the case. the fuel hoses are ok though.

when is the last time you changed the air filter?
believe it or not i have seen a dirty air filter cause what i call too much vacuum and pull fuel out of the bowls.
(sucks too hard? :blink: )

as far as i know it's the same air filter. now could there to be much vacuum with the filter cap not secured down properly, or am i thinking in reverse here? seems like it would try to suck more air w/o a proper seal.

The danger is possibility of leaking float valves allowing excess fuel to rise into the carb throat and migrate into the crankcase whereby the oil becomes contaminated with raw fuel.

Would sniff-test oil and examine its physical condition.

If oil is fuel-contaminated, would change oil and filter, and not again run the engine until the issue is resolved.

Good Luck!