07 450 exc Carb and CC Breather

Just putting my scent on a recently purchased ride with a bit too many miles on it.  I'm doing a baseline tear down to verify condition of things, bike ran very lean off the bottom of throttle.  I expected to find a # 40 pilot jet, however, there was a # 48 in the hole.  JD Red at 4th position, main at 165, mixture screw at 1 1/2 turns out.  The float bowl was nice and clean but when I opened up the carb top, I was appalled at the nasty condition of the carb. 


It appears that the crankcase (CC) breather is putting oily nastiness on the inside of the upper carburator.  I can't think of any reasonable benefit to recover CC gasses to the pristine temple of fuel/air metering.  I'm not seeking jetting answers to my lean condition with a #48 pilot jet until I've THOROUGHLY cleaned the carb, but I have read about the possibility of the CC breather contributing to the leanness.  Any similar experience here?   I welcome your advise.


Also, I noticed different part numbers for air filters.  What is the difference between a 2 stroke and 4 stroke air filter (seriously)?

Edited by Icechopper

The 2007 450 exc was the street legal from the factory. Previous versions required post-production modifications to make them street legal (or at least plate-able). The CCV into the intake system is a way to reduce emissions. I recently looked at my 2006 450 exc's CCV and it is vented direct to atmosphere. I have never had an abnormal oil usage issue and my intake (carb included) is as clean as can be. The reason i checked mine was because a riding buddy's 2010 450 xc-w had an oil usage issue. With the amount of oil being used, some blue smoke would have been prevalent is it was rings or guides, but never. Also, his transmission oil level never increased, so it wasn't that issue which occured with early versions of the XC4 engine. His CCV was routed into the airbox. A reroute cured the issue.


Even my truck came from the factory with the CCV into the air intake tract. The effect of sucking oil out of the engine is even more pronounced with a turbo that boosts to 35psi; it'll suck air from wherever it can. I rerouted the CCV and have never had oil in my intercooler and intake manifold since. And there is no oil leaking out of the new CCV tube.


While I wouldn't think the foam is any different between the 4T and 2T filters, there might be enough difference is shape to not seal adequately when used in the other's application.

Okay, here's the follow-up on the bike.  I found the intake valves tight.  I backed off the adjustments two sixths of a full turn to get the the adjusters to zero, then another sixth out to measure .005 clearance.  Both intakes were exactly the same.  Exhausts were both at .005. 


Once the valves were set, it was time for the carb.  I had a serious lean condition off of the bottom and obvious on decelleration.  I found the main at 165, JD red needle at 4th clip, a #48 pilot jet and the mixture control screw (MCS) at 1 1/2 turns out.  Once I cleaned the oily crap out of the top side of the carb, I made a decision NOT to reconnect the CC breather.  A local shop said it was common practice to plug the carb and reroute the breather hose to the rear of the bike. 


I understand that the breather only inhales and exhales with the movement of the piston but I was not comfortable leaving the end of the breather down so low on the bike.  So,for the end of the breather hose I opted to cut the threads off of the carb hose barb and shove the brass barb up the end of the breather hose about 6 inches.  I then cut pieces of an old air filter into a 6 inch strip and shoved it up the breather hose to the brass barb.  The breather was routed up from the front of the engine, under the fuel tank and cut (angled) just above the carburator.  The breather will allow air to move freely through the filter material but keep out gross contaminants.


Now with a pristine carb, I began the jetting process.  First thing I found was no washer or o-ring on the MCS.  That condition prevented the venturi action of the airflow from allowing the fuel to be drawn into the throat of the carb, thus, a very lean off-idle condition.  I replaced the 165 main with a 172, dropped the red needle clip to 5th position (raised the needle to enrichen), verified the accellerator pump (AP) was working, replaced the pilot jet with a #45 and replaced the MCS with a Scotts unit and new o-ring, washer and spring (11/2 turns).  With shop running the bike, I settelled with the MCS out 2 turns.


My engine didn't like the #45 pilot jet.  Although I am at sea level and 80' F during the process, I was surprised that I still had a lean condition.  I tried a #48, then settled with a #50!  I test rode the bike today up a nice log twisty 2500' paved road.  The bike pulled hard and smooth throughout the different throttle positions.  I noticed a slight buildup of unburned fuel on downhills that would pop with the kill button pushed, but that went away by bringing the MCS another 1/2 of a turn in.  The bike starts easily, idles very smooth although I haven't yet started the bike on a crisp/cold morning.  I do notice a stumble if I dump the throttle to wide open from closed position, but I didn't notice this to be an issue on this street run.


I read a lot of post here regarding jetting and AP issues, thank you for sharing your experiences.  I wanted to share this information with those who may find their bikes are not conforming to what other's say they should.  I have jetted in quite a few bikes through the years and this one is now set up very well, albeit outside the norm.




It is odd that your engine prefers a #50 pilot jet!  Has all of the DOT stuff been removed or deactivated?  


A highly recommended mod for RFS engines is to add a one way check valve to the crankcase hose. They provide a beneficial slight negative pressure to the crankcase plus they inhibit any dirt or water from entering the engine.  ThumperRacing has a nice one way valve plus they are also available from other sources.  

Yes, all of the smog was off when I purchased to bike.  I'm going to open up the silencer / spark arrester to see if the insides wern't gutted.  I can't fiqure out the #50 pilot jet.  No vacuum leaks in the carb top or boot... I was really methodical when looking for unmetered air sources.  I'm anxious to ride the bike at some altitude next to see how it works.  I'll consider the check valve.  Thanks.

Edited by Icechopper

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