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Advice sought for sudden Hi RPM revving 36mm DellOrtos

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guzzimike:
 This morning,  My CX100 engine would not back off from 3 -4KRPM when shifting from 1st to second gear.

The last time I rode the bike, just before Christmas, all was OK, as normal as could be and has been for a long time.

Now, I starts and Idles just fine, and my Pre Ride Static Check showed No unusual issues. By Static Check I mean the bike is on Centerstand, engine Off, Key is OFF. I do a visual for spots of oil or fuel under bike, check tires and look for anything amiss. Next I back bike out of garage and onto driveway by the house. Baclk on centerstand, I flip Key to position two and check all electrical components - EXCEPT Starter. I flip Fuel petcocks from OFF, Past ON and onto RES., then Back to ON. I verify positive fuel flow into Banjo Filter through see-through fuel lines . I blip the Tomaselli throttle 2  3 times to verify smooth cable operation, Ditto for clutch. Verify bike is in NEUTRAL, flip Choke, and fire up engine.

So far A-OK. I pull clutch, flick it in First and ride off down the street. When I reach around 3500 RPM, I attempt Up-Shift into second as I always do, but THIS time the RPM does not fall Off as normal. Instead, Chopping the throttle has No Effect on RPM. I upshift into 2nd, and thinking that this may be one of those "quirks" I go for Third Gear, hoping for a normal upshift. NOPE.  RPM acts up and won't respond to my throttle chopping input.

The only way to bring RPM under control is to Apply Brakes while in Gear; to the point of almost Stalling. Downshifting gets dicey.  Looks like we won't be riding much today.

I return home, shut engine off and place bike on center-stand. I check the Throttle, its Cables and the throttle return springs at each Carburator. All looks OK, nothing binds anywhere, all parts look normal., no Broken springs...Nothing.  Just to be sure, I take apart the Tomaselli throttle at the clip=on and ibnspect function. All looks good. I spray a small amount of  Silicone Lubricant on the rotating assembly and also down into the cable sheaths, just to play it "safe", but all action was smooth and showed no binding anywhere prior to the Silicone Lube.

And again, in static Mode ( on center-stand, engine Off, gearbox in NEUTRAL )  everything checks out OK.

I twist throttle half way and release; then Full twist to its stop; and release, and both times the Throttle  Chops down with authority. I verify at each Carburator that the Throttle Springs Reset the throttle to its full Backstop; as usual.  These Carbs are 36mm DellOrtos with functional Accelerator pumps.

I try another test ride, and the issue re occurs exactly as before.  

Again, I park the bike and go over the Hand throttle, cables and carburetors as slowly and thoroughly as I know how to do. Nothing looks amiss, and all  moveable parts that I can think of to check looks to be operating perfectly well..in the driveway.

BUT as soon as I place the engine Under Loads, Up-shifting on the road, it turns to shyt.


So at this point, I can't think of what else to check. FWIW, 3 Gallons of Fuel was added recently, ( Chevron Premium, as usual.) Bike lives sheltered in a Garage, which is attached to my house. Garage roll-up door is always locked  down so no-one has access to it other than yours truly.

That's the existing situation, and I am stumped as to the causation for this sudden, recurring High RPM issue.  

Any advice or suggestions would be appreciated greatly


TIA





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Old Jock:
Hi Mike

I'll let the Gurus comment.

This happened to me with the Sfida and I never found the cause it just sort of stopped itself.

I disassembled the carbs and put them back together also checking the enrichers were free, ensured slide operation got the slides were lifting uniformly and balanced the carbs with vacuum gauges then redid the timing. The thing was although some of it was out a little there was no smoking gun.

I was really down that I found nothing then when I went for a test run lo and behold it had gone

I'm sorry that its not of much use but just to let you know you're not the only one to have experienced this weird phenomenon.

If it happened to me again I wold make sure that as well as checking out the carbs I would verify the timing. But what do I know?

John

Vasco DG:
Obvious things would be jammed cables or, (If your bike has them?) the bell crank on the LH carb hanging up on the choke cable. One long shot would be the front of the slide has broken off. It's rare but obviously when it happens it creates a lean condition and high idle. I know you look after your bike Mike but when were the carbs last looked at seriously?

Pete

Charles in Lake Charles:
How about centrifugal advance sticking?

Chuck in Indiana:
Vacuum leak?

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