Weird Problem/Need Help -
Exhaust & Fuel Delivery Tips on how to get the most out of your bike

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post #1 of 3 (permalink) Old 12-28-2016, 11:26 PM Thread Starter
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Weird Problem/Need Help

2012 CBR600RR After a crash and rebuild the bike cuts out above 7500 RPM but get this, it only does it when the fuel tank is completely full. After the gauge goes down two or three bars the problem goes away completely! When it is happening it's like its on the rev limiter. I'll be on the highway going 65 70 mph (which is around 6500 RPM with my gearing) and then when I wick it on it goes fine up to 7500 RPM and then its like it running on 2 or 3 cylinders or something. It still will slowly pick up speed as its bogging but its really not right.

Here's what I've done so far. Checked and re checked the fuel hoses for obstruction. Replaced the fuel pump/ float assembly. Checked the tank and made sure the vent hoses are clear and un-kinked.

Again, most importantly the problem goes completely away after the fuel tank empties out a little. This exact problem is repeatable every time I fill up the tank. Even after tearing it all apart and changing stuff and checking stuff it happens in the exact same way every time.


2012 CBR 600RR with improvements
erobison is offline  
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post #2 of 3 (permalink) Old 12-29-2016, 12:33 AM
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ok,think of it this way?

Tank full, and prob starts right away.

if you have an unvented tank, full of liquid, and remove liquid from it, a severe flow problem develops immediately........(can't pull vacuum on liquids)

As fuel is used(how does this happen without collapsing tank?-points to partially functioning one way air valve INTO tank) problem goes "collapsed fuel tank" OTF

Please (re) recheck air vents/one way vents in/out of tank very carefully?

(suspect partially blocked tank suction air vent?)

Also try this: with tank brimmed full, make bike stutter as described above, and pull over right away.

SAFELY open gas cap, and see if vacuum is present?

Maybe try this in garage is smarter?
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post #3 of 3 (permalink) Old 01-04-2017, 11:02 AM
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I 2nd Tary's diagnosis. Happened to me on my Magna. Cruising along at 5/6k spit sputter and if I held it, stall. Around town, no problem. Turned out a spider made a nasty little nest in the vent tube. I just replaces the tube when I noticed spider eggs... Them spiders move in quick!
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