Gaffer,
In addition to what Vince said:
- If you are currently running rich and you put on a freer flowing exhaust, you might luck out and not need further tuning. I would definitely try that first.
- Once the exhaust is on, should there be performance issues: Make sure the bike is thoroughly warm, then ride it enough to understand consistently what issue is happening - and when it happens.
- Personally, I would not worry about exhaust sounds (popping, burbling, etc) when you close throttle at higher RPMs. These can be expected and not always eliminated completely. Regardless, that can be the last issue to address.
- I have not changed the jet in my Electra X (I swapped in an Amal instead) but have done so on many other bikes. I expect that you will access the main jet by removing the carb and turning it over. Remove the float bowl. The main jet is typically the center-most jet. Upon unscrewing it you should see the end of the needle where the jet was. (Which will confirm that you removed the main jet).
- The needle is accessed from the top of the carb. Remove the cover and you should find a diaphragm that raises and lowers the slide that houses the needle. The needle is held at the right height in the slide by a clip. A spring usually holds the needle/clip in position.
- I'll try to get out to the shop and confirm that my 2006 Electra X carb is like this. UPDATE: SEE NEXT ENTRY FOR DETAILED STEPS.
- Only begin tuning the carb on a thoroughly warm engine. This is important.
- While you're checking the main jet, remember that it controls at and near wide-full-open throttle. It is at that open throttle position that you'll want to pay attention to performance. Too rich and it might noticeably stumble. Too lean and it might backfire. Plug condition should confirm performance indicators - especially overly rich being black, sooty, and or gas fouled.
- While you're checking the needle position, remember that this affects off-idle and up (until you are in the upper throttle range where the needle is no longer causing any blockage and you are effectively running on the main jet). It is a transitional control where both the height and the taper of the needle come into play. Visualize the needle as it goes in and out of the the tube effectively blocking it and freeing it, respectively. If the needle is too high, too much gas will get through and it will run too rich. If it's too low, not enough gas will get through and it will run too lean. Both can cause the bike to feel like it stumbles. However there are ways to distinguish. Again, the general rule for lean is white spark plug and backfiring. Too rich: black plug, white smoke. ALso: Lean conditions improve as bike gets up to temperature; rich conditions worsen as bike is ridden. One way to understand which is occurring is to exaggerate symptom: If you have an issue and you're not sure what's happening: raise the needle again: does that make it even worse? If so, the needle might have been OK in its original position - or you might need to raise it 1/2 position.
- When you don't have much experience, sometimes it seems like you really can't tell what's wrong - just that it's not running right. This is is why you concentrate on one change at a time and one throttle position at a time. Don't panic if what you feel isn't immediately recognizable (as lean or rich) by the symptoms. Keep test running the bike to reproduce the symptoms until you get a good feel for what they are and when they occur. Do this before trying to correct them (so that you'll definitely know that you resolved the issue). Again, sometimes the best way to make sure you understand the symptom is by exaggerating the problem. As with the clip example, you can also use this technique with the main jet. Buy two or three larger jets. If a larger jet produces a *specific* symptom you don't quite understand, put in yet a larger one and see if it exaggerates that *specific* symptom.
- As they are precision devices, there are times when you actually have to raise or lower the needle by 1/2 increments using an ultra thin washer under the clip.
- Every time I have my diaphragm out, I take the opportunity to soak it 24 hours in vinyl dressing. If you choose to do this, make sure you wipe it off real good before reinstalling so that excess dressing doesn't affect the running (in the short term).
Matt