anyone have a guess? sand in the carb.

6 replies to this topic
  • CRF100biker

Posted December 31, 2011 - 05:25 AM


ok, my yz400f has been running a bit poor when you nail the gas from nil to WOT. as part of my winter tear down i decided to investigate. everything in the carb checked out as perfect except for this..

Posted Image

that's not cool! how'd this happen? there are no leaks anywhere. i clean my filter after every ride. i believe i'm currently using bel ray (maybe maxima, i can't remember right now and don't feel like walking downstairs) filter oil, but it doesn't feel as tacky as the twin air stuff i used to use. the twin air stuff could actually be substituted for glue in a pinch. i cleaned everything up and the diaphragm and all associated rubber appears to be ok. i know for a fact no sand is getting into my tank while fueling. the diaphragm is intact and isn't rotten yet. this is also the only place i could find sand in the carb. everything else was immaculately clean inside as i took it apart. anyone seen anything like this before? i want to know if there's anything i should be fixing before i put the carb back together.

  • GreenHornet450

Posted December 31, 2011 - 05:44 AM


It's either fuel, the air element or the seals to the AP need replacement. I would replace the AP Diaphram and Orings. Even check the AP Rod. Dump your fuel and clean the tank and I GUARANTEE that's CRAPS in the engine.

  • CRF100biker

Posted December 31, 2011 - 06:19 AM


where would i expect to see it in the engine? my guess would be around the plug and valves, correct?

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  • RasmusDK

Posted December 31, 2011 - 07:58 AM


Thats normal on the old carbs. that sand comes in along the sides of the rod. The parts you are showing is not in contact with the fuel :bonk:

  • GreenHornet450

Posted December 31, 2011 - 01:25 PM


The plug would give and indication. Sand gets into EVERYTHING over time. If it's just isolated to the AP then your lucky, but since your doing a winter tear down take a further look. It sure as hell can't hurt.....DEFINITELY DO AN AP OVERHAUL...

  • 2grimjim

Posted January 01, 2012 - 09:22 AM


That's from water getting on top of the AP diaphram. This is a common problem on bikes equipped with the FCR carb with the plastic cover over the belcrank/cable assembly. Later FCR carbs have a metal cover with a rubber seal to keep water out.

The trick for reducing the likelyhood of this happening again is to put a small amount of waterproof grease on the AP shaft when it's assembled.

  • CRF100biker

Posted January 01, 2012 - 02:25 PM


thanks all for the help! :bonk:

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