Triumphrat

mlc · 05-22-2007

i know that doesnt mean much - - but if i could lay out some observations / symptoms, i sure would appreciate any advise you guys could offer.

Bike: 06 Bonnie 790, Staintune Reverse Cones, jetting unknown (got the dealer to fit cans and they assure me they fit the jets that Staintune recommend - but they now cant tell me what the exact ones are)

Recent Service (10thou klm): Bike was running lean. Mechanic put a shim under the stock needle

Observation: Bike pulled harder from low to mid range (from richer mix I guess), easier to start, + sat on 120-140km/hr much easier (less throttle twist), purred along.

Recent Observations: last 1000km (in about a week and a half) including some vigorous twisty action on weekend - Popping worse than before. Still starts easier than before service, but vibes in bars worse. Increase in heat from engine (marginal) BUT the biggest thing ive noticed is that acceleration and sitting on any speed above 80km/hr or so is requiring significantly more throttle action/work. Seems to need to be worked harder to achieve same accel as just after the service. The only different thing was that i put a tank of 95RON petrol/gas instead of the dealer recommended 98RON about 2 tanks ago + it recieved a bit of a flogging in the twisties on the weekend.

When running at speed/revs, taking throtle off altogether = engine braking/fork dive.

Questions
1. Is this just a sign that things are lean again
2. Was the shim a good idea just to fix mixture ratio
3. Should i just adjust mixture.
4. Would the mixture go 'out' that quick/easy

sorry for length of post, but any comments or advice would be greatly appreciated guys. bike still a blast though - love the bonnie in an almost unnatural way!!!

badrufus · 05-22-2007

Whenever I hear someone talk about problems occurring without a change having been made in the bike, the first thing I think of is carburetor synchronization. That is something that can change over time, and if the carbs are no longer synchronized, you will often notice more buzzing and rougher running. So I would suggest having the carbs synchronized (balanced) or doing it yourself.
As far as the shim, it doesn't make sense as a cure for lean running, but then I'm not at all sure what your mechanic really meant when he said it was running lean. You usually shim because you have a flat spot somewhere in the rev range, often around 4000 rpm. If the mechanic told you the bike was running lean, did he mean at idle, off-idle, mid throttle, full throttle? Did he even test it on an engine gas analyzer? Usually, if a bike is referred to as running lean, you think of upping the main jets as a first step. I think it would be helpful to read Jenks Tuning Guide
Jenks Guide
which you can download in pdf by clicking on "link" and then print out.
The increase in popping and the increase in engine heat point toward a lean condition. The drop-off in acceleration is harder to interpret. If you read Jenks Guide, you'll see that interpretation depends on whether a symptom occurs when the bike is cold or fully warmed up. The problem is that you can be lean at one point (like wide open throttle) and rich at another (like mid-throttle) which is why it's important to understand how the whole carburetion system works and why it's important to get a bike dynoed and sniffed throughout the rev range.
In any case, the bike is out of tune and needs some attention. I think if you read the Jenks Guide you will be able to better diagnose and describe what's happening. You may end up needing to find someone with more tuning expertise than this mechanic.