250-500cc Problems with WR300

Hello Everyone,
I have a WR300 which started running terribly all of a sudden last run. It started loosing power, dying then picking up a bit then dying again. it would finally stall and be very difficult to start. I ended up pushing it home because I could not re-start it. It may have even backfired, but I cant remember for sure. Mainly just running bad, loosing power and when it finally did start it did not want to idle, like the idle speed was too low but the engine speed also changed on its own a bit.
I thought it may have been crap in the carby so I cleaned it out and removed the tank and tipped the fuel into another container with a filter to make sure the fuel was clean.
I am used to playing with outboard motors, but I'm new to bikes. ive had this about 6 months and only used it about 10 times or so. I have not done any maintenance on it because I don't really know what I'm doing. It's my second bike (upgraded from a super reliable KDX200). Any help on what to do from here would be greatly appreciated. I am pretty new to bikes, but I am also rather mechanically minded. I did do a compression test (150 PSI).
What sorts of things should I do first?

what year is WR and how many hours on it total?

first impression was carb.. but if carb is good and compression is good (btw, 150 is on the low side) check ignition and timing..

Air leak?

The symptoms you have described indicate a lean condition. To add to what the other posters have suggested:

- air leak is a good suggestion, especially if this came on suddenly. The boots on either side of the carb should be good and snug. Assuming they are try spraying around the boots, carb top, reed block, head, cylinder base and spark plug with WD40 or carb cleaner with the motor running and listen for changes in motor speed

- check fuel is flowing freely from the tank to the float bowl of the carb. I like to remove the float bowl then, leaving the fuel line from the tank to the carb connected and the fuel tap in the 'on' position, push the floats up using your fingers. Fuel should flow freely from the inlet valve. This is of course messy so do it somewhere outdoors.

- check the fuel level in the float bowl. Not sure what carb you have but a search of this site or the web generally should confirm the correct level. A lower than recommended level can cause a lean condition. If the level is too low, bend the tang on the float assembly to achieve correct fuel level.

- was it particularly cold on the day you were riding? If so you may have been lean on your carb settings due simply to the ambient temps. Try going richer eg by moving the clip on the needle one position lower.

What did the spark plug look like? That should give you something to help narrow down what's happening. Seems like the compression is OK. I'd check the reeds to see if they are starting to get frayed or broken.

Change plug, if its rich it will be black brown my bike did the not start thing every 4hrs cus the jetting was so far outta whack.
If new plug doesn't remedy check stator plate that may have wondered but i highly doubt it.
My moneys on too rich jetting

Thanks everyone. The bike is a 2009 with about 6000 Km on it. Can't get to re start. Will keep trying. It did seem to be blowing a lot of smoke

I just noticed cracking on the rubber piece that the carb connects to. Not the air box side, the reed valve side. What is thar rubber piece called?

intake boot

The reference is : 8000H0586 , cost 19€ here in Spain

my wr250 does the no start thing every 4th ride, always just put in a new plug. Plug looks like it is to rich but haven't checked compression. Also pipe is bent back in front to where it is touching hoses, may be that?

Thank you for rhat. Do you think I would be able to go over the "intake boot" with silicone until I get a new one? I will need to order one and have it posted because there are now no husky dealers anywhere near me. The one around the corner has now become a yamaha dealer. Are there any gaskets or anything else I would need to order.

ive used silicone before or gasket maker, just let it cure properly first

yeh I got that stuff but the red version(hi temp). used it to plug a crack in my pipe & still holding!

I've also used black silicone for patching the old boot, I actually still use it having the new one already, Will use the new one when I get the Lectron

Thanks again everyone. Will try it next week. Been flat out at work. Could be a long wait on the part as there is none in the country. Will seal it up and replace it later. I appreciate the help guys.