07 Dragon 700 Backfiring, running rough

[seth25]

07 Dragon 700. 2900 miles. Compression tests good. TPS was a little off, set it to specs. New plugs, fresh fuel.

Starts and idles fine. From around 4-7k rpm sled backfires and runs rough. Clears up from around 7-8k rpm.

Any ideas?


Thanks

 

[bboll]

clean exhaust valves, sometimes they stick.
pull clutch and check for broken primary spring.

 

[gtwitch]

Had a similar issue on my 97 Dragon 700 early last season and after a lot of digging , I found a plastic rivet tail stuck under a reed in the reed valve body, took it out and issue went away. No damage! The rivet tail came from when the dealer put on the SLP powder vents in behind the windshield and one of the tails went through the air box and lodged under a reed leaf 4 years later. Go figure!?!!

gtwitch in wyoming

 

[seth25]

Thanks for the replies. Power valves and reeds both good.

Any other ideas?

 

[MORSNO]

From the factory these engines were lean in the midrange and rich on the top, that is why so many of us installed PC III or PC V's. We were able to richen up the middle and get rid of the "bobbling". Also, have you replaced your fuel filter recently?

 

[seth25]

I have not replaced the fuel filter. Mid range problem is not simply a tuning problem. There is a malfunction somewhere.

Thanks

 

[reecerrider]

07 Dragon 700. 2900 miles. Compression tests good. TPS was a little off, set it to specs. New plugs, fresh fuel.

Starts and idles fine. From around 4-7k rpm sled backfires and runs rough. Clears up from around 7-8k rpm.

Any ideas?


Thanks

Had same problem with mine. It was the throttle body adaptor - essentially a rubber boot between the throttle body and block. The bottom had separated. Easy to check - remove the airbox and reach down under the throttle body and see if the rubber pulls away. Also will see gas/oil in the bottom of the engine compartment. Might as well replace the reeds and the fuel filter while you're in there