Was given a 1997 Bayou 220 for free that had sat in the back of a barn for almost 9 years. Owner had parked it because his kids got too big for it, and they have other bigger bikes, said when it was parked it ran fine. He gave it to me as a trade from some networking I did in his home. First steps: *Marvels Mystery Oil bath down the cylinder to free up the piston rings (I let sit for 24hrs) *New battery as old one was shot from not having a charge for 8 years. I took my multimeter to the entire wiring harness and cleaned EVERY contact possible, as not even the headlights were working. After a few hours, everything electrical is now working. Headlights, green dash light, red reverse light (goes on and off with changing from reverse to neutral), and starter spinning strong (after a conversation with my mallet). *Drained old oil (no glitter!) 2qts fresh oil with new filter. *CDI was shot-- had zero spark and using a multimeter up the wiring harness everything was good up to the CDI—replaced with new one along with new plug wire and new plug now have excellent spark The original carb was a total loss. I'm assuming it was parked full of fuel with the fuel switch on. It looked like they found it buried in the sand and put it on, it was so eaten and corroded my thumb went through it trying to get it apart—so new carb. I did also inspect the intake and none of what was in the carb made it into the engine, thankfully. After oil bath, compression was still low—threw some brake cleaner down the intake and noticed smoke escaping from the head gasket—took the head off and saw the original head gasket was completely shot. Replaced that, and now compression is up to 90 from 50. I'm assuming, it'll need to go through a few heat cycles for the compression to really build back up (had the same issue with my 2000 Kodiak 400 from siting for 5yrs after a few heat cycles went to 180) While the head was off, I did a leak test on the valves and liquid stayed, so no signs of gaps in the valves sealing. Also took a look at the piston and wall and both are in excellent shape, very clean conditions. At this point, the bike should fire off or at least pop… but now that compression is back it's sucking air in though both the carb AND the exhaust pipe. Putting my hand on the pipe (no muffler) I can feel it sucking air in, doing the same with the back of the carb, I can feel it sucking air there as well. It isn't pushing air out anywhere. I've checked timing and it's correct. The TDC mark on the flywheel is lined up with the spot on inspection hole. The mark on the timing gear in the head is lined up with the mark on the casting there as well, so timing is spot on. I don't believe it has a leak from the exhaust valve due to the leak test I did. I also don't believe a valve is sticking, I can see them both moving just fine when looking through the inspection holes. In the past, I've had a bike have intake from exhaust and exhaust going out carb, but that was the timing being off, which doesn't seem to be the issue here. Any advice on this would a big help as I'm stumped on what could be causing double air intake. Chances are it might be something simple that I'm not even thinking of. At this point, I'm about to order a box of hair from Amazon Prime from all the head scratching going on.

You should check it first.. Look for small bubbles in the top of the radiator or the overflow bottle. There could be wear on the waterpump shaft causing water in the oil, or corrosion somewhere near a gasket or O ring, corrosion in a frost plug in the engine somewhere, a crack somewhere. Most of those won't make bubbles in the coolant.

A blown head gasket can cause it...

I also run Mobile 1 in all my vehicles have for 20 plus years and like it very much. In my ATV I have stuck with mineral oil , only because mine are older and that's what was recommended for them at the time of production, not sure if that's right or not, but that's what I do. I do stick with the manufacturers oil, only for peace of mind, because I feel like it is formulated right for their engines. Im sure there are probably better oils out there but yamalube has one of the best rating iv read, but I don't always believe everything I read, especially on the internet. One more thing I might add I did change one of my older vehicles to synthetic, a 99 V8, that had been using mineral oil since new and I noticed that it seemed to burn more oil than before, and synthetic to me seems thinner than the the same weight in mineral oil, so I switched it to high mileage synthetic and it even burned more oil, just my experience.