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Hello,
I have owned a 1988 MC19 for about six months. I would rate my mechanical skills as beginner and I am having trouble finding an answer to my problem. I have visited this site many times but this this is my first posting. I am really hoping to get some advice from more experience riders. BTW the bike has 27,000+ kilometers on the clock.

Here is my sob story. When I first purchased the bike last year I took it to a shop for a tuneup. They replaced all the fluids, spark plugs, and rebuilt the carbs (new jets, float valves, mixture screws, and gaskets). The bike ran pretty well right after that, but with winter nearing I did not get to ride it much. So I filled up the tank, put fuel stabilizer and connected to a battery tender. I would start the bike every couple of weeks and let it run for a few minutes.
A few weeks ago I warmed up the bike as usual. The following day I decided to take it for a spin but the bike wouldn't start. After a few cranks it backfired through the exhaust. I tried the next day and got the same results, so I decided to check out the carbs. After I took the air box off I found a good amount of what I think is gas mixed with oil coming from the top of the air horns. I am including a picture for further reference. Several days later there is still a little bit of oily residue left, that's why I am thinking that this was a gas/oil mix. The gas inside the tank and in the carburetors was clean, and there is no varnish inside the carbs either. What could be causing this problem?

Thanks in advance for your feedback
 

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First port of call would be to check your spark plugs.

Starting the bike up and idling doesn't burn shit off your plugs and can cause them to foul up, it's better to let the bike sit.
 

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Hello,
I have owned a 1988 MC19 for about six months. I would rate my mechanical skills as beginner and I am having trouble finding an answer to my problem. I have visited this site many times but this this is my first posting. I am really hoping to get some advice from more experience riders. BTW the bike has 27,000+ kilometers on the clock.

Here is my sob story. When I first purchased the bike last year I took it to a shop for a tuneup. They replaced all the fluids, spark plugs, and rebuilt the carbs (new jets, float valves, mixture screws, and gaskets). The bike ran pretty well right after that, but with winter nearing I did not get to ride it much. So I filled up the tank, put fuel stabilizer and connected to a battery tender. I would start the bike every couple of weeks and let it run for a few minutes.
A few weeks ago I warmed up the bike as usual. The following day I decided to take it for a spin but the bike wouldn't start. After a few cranks it backfired through the exhaust. I tried the next day and got the same results, so I decided to check out the carbs. After I took the air box off I found a good amount of what I think is gas mixed with oil coming from the top of the air horns. I am including a picture for further reference. Several days later there is still a little bit of oily residue left, that's why I am thinking that this was a gas/oil mix. The gas inside the tank and in the carburetors was clean, and there is no varnish inside the carbs either. What could be causing this problem?

Thanks in advance for your feedback
This is actually interesting and the answer may be surprising. I have an MC19 that I just rebuilt (new pistons and valves job done), and despite the rebuild I was burning oil still! Now interestingly I found that when I accidentally put too much oil in, it burnt oil like crazy, but when I drained the oil to the correct amount, it barely burnt any oil. I did some research and found a Scotty Kilmer video explaining about how cars burn the gas in the top head into the cylinder rather than vent it into the atmosphere. Well it turns out that’s also what happens with the MC19 (and MC22)! The oil on top of the carby is due to oil gushing out of the gas vent (Located on the right side of the head with a hose connected to the air box) and into the air box where the oil is then sucked into the carby and into the piston chamber! That is most likely your trouble and can be the main reason these bikes burn oil! Your engine is most likely fine, all you have to do is put something like a sponge in front of the little pocket in the air box where the gas comes out of to stop the oil gushing out. Also, check your oil level is on that half mark

Hope that helps out! 😁
 
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