I think that filter could be getting oil saturated from the blow back which is normal on piston port engines and it can throw off your mixture enough to have you going nuts to tune it since the blowback sends the fuel and air mix out the carb inlet then it gets sucked back in on the next intake stroke making the mixture extra rich momentarily, then on the next down stroke it sends some of that charge out the inlet where the filter can catch part of it again. You should notice the engine behaves better without the filter if the foam in the filter is holding the blowback then it's getting sucked in on the next intake stroke.
You may need to make some kind of a runner tube between the filter and the carb inlet to put more distance between the 2 to help prevent the filter from getting too wet with the fuel and oil since it can throw out a good tune or make tuning very difficult if not impossible... maybe try a larger cotton gauze screen type filter like the K&N or its clones. And if you ride in a very clean and dust free environment you can get a cheap K&N clone filter and carefully burn the cotton gauze out so it's just a screen, this will stop bigger debris but not the small dust particles so it can't trap the fuel and oil mix during blowback. This will make tuning easier but you definitely can't ride in a dusty environment. Another solution would be to use an oversized K&N type filter and use a longer intake duct to prevent filter saturation.
That foam filter you got most likely works great on a reed valve engine where blowback isn't a problem but may be what's keeping you from dialing your engine in since these are piston port type. The easiest way to prevent saturation from blowback is to use the biggest filter you can fit on the bike, even if you need to fabricate an adapter or longer wider intake duct. Luckily pvc piping is cheap and plentiful for this, and it can be painted to hide what it really is.
One of my bikes uses an oversized K&N clone filter with a pw80 inlet duct clamped to the carb so the filter is larger but also about 8" away from the carb inlet.
You can also use an oversized K&N clone with the cotton gauze burned out so it's just the pleated screen then stretch a nylon stocking over it which will still give more than enough surface area, very little restriction, but much safer if in a dusty area. I use this method on my Harley but I use an Outerwears rain sock over the filter to keep dust and water from getting in... it's truly the next best thing to running no filter at all but it protects better than a freshly oiled k&n...
You may need to make some kind of a runner tube between the filter and the carb inlet to put more distance between the 2 to help prevent the filter from getting too wet with the fuel and oil since it can throw out a good tune or make tuning very difficult if not impossible... maybe try a larger cotton gauze screen type filter like the K&N or its clones. And if you ride in a very clean and dust free environment you can get a cheap K&N clone filter and carefully burn the cotton gauze out so it's just a screen, this will stop bigger debris but not the small dust particles so it can't trap the fuel and oil mix during blowback. This will make tuning easier but you definitely can't ride in a dusty environment. Another solution would be to use an oversized K&N type filter and use a longer intake duct to prevent filter saturation.
That foam filter you got most likely works great on a reed valve engine where blowback isn't a problem but may be what's keeping you from dialing your engine in since these are piston port type. The easiest way to prevent saturation from blowback is to use the biggest filter you can fit on the bike, even if you need to fabricate an adapter or longer wider intake duct. Luckily pvc piping is cheap and plentiful for this, and it can be painted to hide what it really is.
One of my bikes uses an oversized K&N clone filter with a pw80 inlet duct clamped to the carb so the filter is larger but also about 8" away from the carb inlet.
You can also use an oversized K&N clone with the cotton gauze burned out so it's just the pleated screen then stretch a nylon stocking over it which will still give more than enough surface area, very little restriction, but much safer if in a dusty area. I use this method on my Harley but I use an Outerwears rain sock over the filter to keep dust and water from getting in... it's truly the next best thing to running no filter at all but it protects better than a freshly oiled k&n...
