[Ducati] NDC- possible carb issues with CCM? Help please

[Rich Roberts]

Hmmmmm, these sorts of things can be so many causes, but my focus would be the carb, how is breather on bowl routed? how does fuel get from tank to bowl? Vacuum style petcock? Pump? Is all of that in order? When you pull carbs what do you do? I ask because I have a DRZ400SM and the slow jet has a real tendency to clog, also the original location of vaccum for petcock was sorry routing and it would pinch and you would lose vacuum to petcock erratically which will eventually cut off fuel flow. I ended up rerouting entirely and after running kehein CRs and Yosh ti pipe sold all and went back and rejetted the stock carb with much success. Do not forget slow jets have a huge imact on jetting that is often overlooked as jets somewhat overlap. a poorly chosen slow jet can cause top end issues. I saw this on a NSR 250 years ago, mains, needles nothing would correct the fact it just would not pull in high gear, it would fall flat on its face, upsized the slow jet
 and miraculous recovery. Also some of these small jets are esp sensitive to the minutest of crap. I cleaned the original slow jet on the DRZ a number of times, each time it would be fine for awhile and then....same symptom. starting problematic needing excessive choke, throttle response sucks etc etc. So the point, look at carbs closely, clean them out well. granted pilot air screw can have a profound effect esp if slow jet is right size. if not the air screw will just be crap to crap or little to no effect. get it close and you will see the effect in and out. Also sometimes you have a couople of jet options, depends on how many turns of the air screw you make, esp if sizes in 2.5 increments like you find on some small jets. 


----- Original Message ----
From: Garth Williams <garthfw at gmail.com>
To: Ducati List <Ducati at ducati.net>
Sent: Monday, October 1, 2007 9:40:17 AM
Subject: [Ducati] NDC- possible carb issues with CCM? Help please


Good morning listers,

I've been having issues with my CCM supermoto lately and am asking for the
advice of the list.  This CCM uses a 604cc Rotax motor with a single
dell'orto carb (at least I think that's what it is).  In trying to diagnose
and solve other problems, I've replaced the coil, wire and plug.  I've also
had the carb out several times.  The issue now is this:  in lower gears, the
motor runs fine.  However, when you go full throttle (or near it) in higher
gears, where you have a long time in the gear, the engine "bucks" like it's
either starved for fuel or spark.

On Sunday, I fiddled with the air-fuel screw, going both in and out in 1/2
turn increments.  There was no real change in the condition.  I've also
swapped the old coil back in place to no avail.

I'm thinking there's not enough fuel in the float bowl and it's starving.
Any other hypotheses?


Thanks,


Garth
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