To start:::
Vent Hoses: My 400 EXC had been fairly trouble free so I had not dwelled on this, recently spent a day on an 03 EXC RFS and we where slopping in mud. The engine had tried to die once in a stream crossing and I had read several posts about vent hoses and was thinking about them. I had also noted the ones on my ’01 ended about the swing arm pivot, on this 03 they hung at least three inches below the bottom of the chassis. I had one glove that was totally gorped with mud so when we rode into a wide shallow river, not even up to the pegs, I said “good opportunity to wash that glove”, I stopped, idling in neutral and bent down to rise the glove. The engine died, would not restart, I had to push out of the stream, then waited for the bowl to refill and use the choke to start it. Obviously what is happening is not water getting into the carb, rather gas can not get in without pushing displaced air out and the pressure difference is not adequate to push the water aside. This is a bit like putting your finger on a soda straw, then pulling the straw out of the soda only in reverse.
Later at home I ran a test, started the bike and let it idle on the stand, I took a cup of water and held it under the bike dipping all of 4 the vent hoses into the water, in a few seconds the engine died. Then I bought on of those $19 aftermarket kits that is supposed to fix this, they talk about another problem that I may have experienced and did not know it? That is where you are going fast in bumps and gas bounces into the tube, can not run in out as pressure/vacuum is balancing in the carb and causes the floats to flood?? Not sure I am buying this theory? Anyway they believe the cure is to vent “up” rather than “down”.
Looked at the stock setup of two “T”s and four vent hoses (plus on drain hose) and determined somebody at Kehein is nuts? (In their defense the reason Kehein likes these tubes hanging down is it reduces the risk of drooling gas on a upside down bike causing a fire.)
I looked at the $19 kit which includes an mini air box & filter to put in the air box, thought is was overkill and if the hoses are just run up I have a concern that if the bike lays on its side the vent hoses could spill gas on a bike tipped more than 90 degrees. After soaking up the info that was in the kit (and believing some) I tossed it. Of the five hoses one is a bowl drain (from the bottom of the carb) which we can ignore, four are vents, come from the upper part of the carb. If I may number these vents;
#1: Comes from the side of a “T” on the left side of the carb and goes down.
#2: Comes from the top of a “T” on the left side of the carb and goes up, over & down the right..
#3: Comes from the side of a “T” on the right side of the carb and goes down.
#4: Comes from the top of a “T” on the right side of the carb and goes up, over & down the left.
Also on the float bowl screws there are two tabs to retain downward hoses.
Dave’s Way;
#1: Is left alone.
#2: Is run over the top but shortened and run into the right side “T” thus negating #4.
#3: Is run up into the air box and with a small piece of tubing spliced on the hose you have left over from #4 and go to the bottom of the air box. My preference is to pinch it with the air filter to secure it there!
Then I tossed the right side tab, Hose #1 can run thru the left one.
Now if the bike is in water the bowl will still be vented via the top hose, and if the bike is upside down and you ran the hose to the bottom of the air box it should not let gas run out. If you let it end at the top of the air box gas can run out, get on the exhaust as you stand the bike up creating some risk of fire.
