I have a question about the Air Suction System. (This is what some of you call the Smog system)
I was doing work on my KLX and was about to remove all of the hoses for this system and plug the hose at the front of the engine, the small tube at the front of the carb and the tube at the top front of the air filter housing.
When I started looking at these hoses it looks to me like this system is there to evacuate any gases that may build up inside the engine (blow-by, etc) and draw them into the air filter housing which are then pulled into the engine and burnt.
I've seen in some threads that some of you are plugging the front hose (or using a block off plate), and then putting a small filter on the rear engine breather hose.
I'm thinking that if you plug the front hose on the engine and remove the Air Suction system then the engine will not have a looped system to evacuate gases from the engine.
Is this how the air suction system works or am I off base? The shop manual shows the system and tells you how to test it, but it doesn't say what it's there for!
Thanks for anyones input on this.

 

My understanding is that this system allows fresh air to be passed through a reed valve type system into the exhaust tract to make a kind of second burn of any unburnt fuel or other emission products after cylinder combustion. This is supposed to "clean up" what comes out the exhaust. I may be simplifying it too much. I think Kawasaki had this design since about 1979 or so. It actually doesn't affect performance as it occurs after the combustion process and apparently doesn't affect exhaust evacuation. I think most of us remove it to simplify the hoses and piping, and to prevent the occasional backfire that this setup can cause in some instances.

 

Thanks TNC. Sounds like it does a different job than I thought and can be removed without any adverse effects.

 

Yep you are more or less on to it.

The amount and nature of the anti smog stuff can vary from market to market but you do need some sort of crankcase ventilation.

The common thing to do on the these bikes is to open it up so air can flow more freely and this is supposed to allow the crank to spin up more quickly. (mine had a rubber restrictor wedged in the hose).
But I doubt it makes much difference to be honest.

The anti smog stuff that really matters is the stuff to do with jetting and air flow.
The biggest gains are made when the bikes restrictive airbox/exhaust set up is modded and the carb jetted correctly.

 

Thanks for your input Neil. For the crankcase venting the factory hose runs from the back of the engine to the air box. Is this sufficient to vent the crankcase or is something else required.

 

canklx, some say the opening for the crankcase vent hose from the engine to the airbox is too small. The airbox entry hole is indeed quite small. Some say this is keep oil from flowing into the airbox when the bike is taking a dirt nap or such. I had my airbox off doing some other work when I got the bike, and I opened up the hole more appropriate to the size of the plastic part of the stub in which it resides. It may or may not be an issue of allowing more crankcase pressure to flow into the airbox, but I'm sure it can't hurt if the hole is larger.

 

I've been wondering what people were talking about with drilling out the air box vent. It make sense to make the hole bigger. I don't think having oil run into the air box would be too much of a concern for the most part.
Thanks very much for the info!

 

It makes sense but..........

Stick the bike on the dyno before and after doing this mod, and only this mod. 2/10ths of SFA will be the result.

 

Yeah, I wouldn't think the mod would add anything to performance. I'd consider it only to help with the venting of the crankcase.