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Discussion Starter #1 (Edited)
Hello again all :)

Now that I have the steering head back together and the suspension sorted I finally got out for a shakedown ride. I should throw some photos up on that thread. First 20 miles were slow and easy just to be sure everything was OK and bed the new pads, then it was out for a romp in the woods, as it were.

Bike is a 1994 CR that isn't much of a CR any more. FCR's (came used with the bike, with unknown jetting), K&N Filter with open top airbox, Termi slip-ons, 904cc hi-comp pistons, fresh CA Cycleworks coils/plugs/wires, fresh Kokusan igniters.

Starts great, runs as expected up to 5000 RPM. Once over 5500 RPM it starts to hesitate and by about 6000 RPM there's sputtering and popping in the exhaust and it feels like a fuel cut rev limiter on a fuel injected car. Same response at 1/2 throttle, 3/4 throttle and WOT.

Being independent of throttle position, my brain jumps to fuel feed/delivery. Considering that everything else on this bike has been in "basket case" status, I'm assuming the worst here as well - needing a new pump, filter, lines, etc.

Am I going down the right path or is there something else I could/should consider?

Thanks!

-Brad
 

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Discussion Starter #2
Went for another spin this morning to top up with some 92 Octane Ethanol Free gas. On the way there the problem was non-existent, so chalk this up as intermittent.

Could it be that yesterday the temperature was around 100 F, and this morning it was about 65 F?
 

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Carbed Ducs are sensitive to jetting so maybe the mixture is rich on the top and it ran better with the higher oxygen content in cooler air? Also, is the restricted in the return line ? If not, you may have low fuel pressure. I don't know what fcr's require.
 

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Average Weird Guy.
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Starts great, runs as expected up to 5000 RPM. Once over 5500 RPM it starts to hesitate and by about 6000 RPM there's sputtering and popping in the exhaust and it feels like a fuel cut rev limiter on a fuel injected car. Same response at 1/2 throttle, 3/4 throttle and WOT.
My '95 had a running issue that was exactly like this Brad. Sometimes the bike would run perfectly fine at high RPM's and other times it would simply spit,sputter,pop,and lose power.

The cause turned out to be there was so much rust floating around at the back of my fuel tank that it would occasionally clog the pick-up fuel filter screen.
The pick-up filter screen sits right at the very bottom of the fuel tank and looks like a little tea bag that's attached to the back end of the fuel pump.
With all the gas and rust that was sloshing around at the rear of my fuel tank it's not surprising that the problem was intermittent.
 

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Premium Member
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Discussion Starter #6
Thanks guys! I appreciate the ideas - I'll have to pull out the mirror and look around in the tank. When I picked the bike up a few years ago it looked pretty clean and shiny and untreated, but I didn't do a mirror inspection to really look back into the corners. I've been fortunate not to have kinked the lines so far, but I will double check that as well.
 

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I am having the same problem with my 2001 750 Sport. I just did the cam belts and pluges yesterday. This morning on the way to work i reved it up from 6K to 7K and it sputtered and pop all the way there. I guess i should give my fuel system an overhaul. (filter + screen "teabag")
 
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