FCR Carb Dirt

[KXcam22]

I was changing my needle setting and was shocked to see that the under side of the top cover on my FCR carb was poluted with dirt after 20hrs from new.  Is this normal?  I can't tell where it came from and the cover oring was clean.  Any ideas. Cam.

[don46]

I've had the carb off my 07 and never noticed and foreign debris in the slide area. thinking about it there are only a couple of entry points to get to the top of the slide, either the cap gasket or the shaft coming from the throttle cam. neither seems likely, oh yeah I forgot the throttle position sensor.

[kaw rider]

throttle cable

[KXcam22]

The dirt/grease is right in the center of the cap but clean around the perimeter.  It is made of carbon blowback residue and a small bit of dirt that is stuck to it.  The carb slide sounds gritty.  On TT someone claimed it was dirt getting siphoned up the overflow hoses by the engine vacuum and that you can buy a filter kit.  This is quite possible as inside the carb top there appears to be an inner vent that is aimed at the underside of the cap.  I will investigate further to determine the exact cause and post. I was not happy to see it.  The throttle cable is also possible - they do not have any kind of sealing boot over them, just cable end into an adjuster.  Thanks. Cam.

[KXcam22]

I'm stumped. Throttle cam is a sealed unit so no dirt through the throttle cables.  All other possible entry points look clean. Hmmm. Cam.

[hughes]

http://7602racing.com/catalog_Yamaha.php

It's time for these

http://www.brpmoto.com/product_info.php?cPath=45_287_699&products_id=1914

[maddoggy]

at first i was thinking that there was no way that dirty air would be flowing through the vent tubes. i was thinking that the intake air would be following the path of least resistance theory which would mean that 100% of intake air would flow through the airbox. then i got to thinking about a time my atv wouldn't run right at higher rpm's. i found that some of the vent tubes were plugged up on the carb. after i replaced the vent tubes the issue went away. i've assumed that the issue was that the carb wasn't venting properly,  but now i am wondering if it was not allowing the suction that the carb was wanting. i have my doubts but one never knows. those filters that hughes suggested may be a good idea. they certainly can't hurt.

[KXcam22]

Hughes,
 I've been all through the carb and the vent lines is where it is comming from.  Those filters are the answer.  I built my own but they are a bit too large, not as nice ans comact as those.  I think that the big 4-strokes can make so much vacuum on decleration that they pull dirt up through the vent hoses.  I have seen other pictures of people with vent systems so it seem fairly common. Cam.

[hughes]

I have found dirt in my vent lines on my YZ250. The engine is down for complete rebuild at this time. Those filters will be installed before first start up of new engine.

[KXcam22]

Here is a easy solution using fuel filters. Cam.

[BDI]

Thats one hell of an idea It will be interesting to see how much crap accumilates in the filters and which ones get dirty first.

[hughes]

Here is a easy solution using fuel filters. Cam.

You think those will stop the very fine/dust particles?? Maybe after a few rides back flush the filters and see what you catch on a white paper towel. Those fuel filters are alot cheaper.

[KXcam22]

Those fuel filters are rated at 75 microns.  As far as I can tell engine vacuum leaks into the chamber over the slide which then draws air up the vent hoses that vent that chamber.  Cam.

[DoldGuy]

Cam,
During the old Moto Days we would route the vent tubes to the airbox and slice the ends of the hoses at a 45 degree angle to help prevent them from clogging. Just my 2 pennies if it helps.

[KXcam22]

Doldguy,
  I have read that on the modern 4-strokes you can't do that since the negative pressure waves in the airbox causes it to draw air from the vent lines. No proof though.   The more I research the more instances I find of people doing this and some attributing their previous early life valve failures to it.  Funny, I recall the film canister carb vent filter from the old days and I see it being resurected as a home made vent filter system.  My goal is to build one for no-cost- tossing around a few ideas. Then I will post. Cam.