Here are the symptoms:
left cylinder has difficulty at idle,
bike will not find a consistent idle (sometimes at lights it will sit as high as 3000)
will not run well on anything but 'prime' for more than a few blocks (I'm assuming the floats are not filling)
occasional backfires on downshifts.
I have done the carb clean X2, then adjusted the float levels to factory specs (I live at a high altitude, and did not make that adjustment as I will be heading to the coast soon. Is this something to look into?).
All the lines to the fuel filter have been cleaned as well as the petcock.
Spark plugs have been replaced and checked with the visual spark check.
Compression tested with the crude 'thumb over hole method' Both cylinders seemed the same qualitatively.
Did the vacuum check using a propane torch and found nothing so I am assuming there is no vacuum leak (double checked the lines to the petcock).
I have also used seafoam to help clean into the engine past the carbs.
This seems to be pointing to a clogged pilot jet in the left carb, but I can't see how after two cleanings it could still be clogged. Before I go in for a third time, is there something else to check? A mechanic told be that sometimes the spark plug can fire differently under load vs. at idle in particular situations, but I can't see how that would be the case here...
Additionally, is there any problems with running the bike on prime as long as I switch it to another setting when parked?
Thanks for all the help from the community troubleshooting the previous problems,
It is OK to run on prime as long as you remember to turn it to on or reserve when the engine is not running. It sounds lean--have you turned the carb adjustments screws out (richer)? Mine runs at 3.5. Check for vacuum leaks in the little tube that goes from the carb to the petcock and any other vacuum tubes. Also, when was the last time you adjusted the valves?
I'll try fiddling with the mix adjustment. I have not moved that around yet as I wanted to get the floats set beforehand. I did quite a thorough vacuum check on the line from carb to petcock using propane. I did not find anything, but the bikes idle does not like to sit perfectly flat anyways so the test was lacking a control.
The last owner did the valves, so that would be about 1000k ago. Judging from the amount of overtorqued and nearly stripped bolts on the bike, though, I'm not sure how well they were adjusted.
Just a tip: when cleaning idle jets, make sure you hold it up to a light and you can see the light through the tiny jet. I like to use thin wire (like from a wire brush wheel) to push through the jet and clear out any latent debris/build-up that your compressed air or carb cleaner didn't already remove.
Cheers.
Fuel intake valves are very important. they are the responsible for keeping a contant fuel level inside the carb.
If the fuel level in the carb is not propperly regulated, it will change from rich to lean and you will not be able to know what's happening.
The best is to change them if they are older than 12 years. if not available, you can assemble them in a drill and use a 2000 grade sand paper to try to remove the degraded rubber. Not a good solution but helps until you can ebay for a couple of new needles.
It is looking like we are going into the carbs for a third round.
I got the bike back from a once over at the shop (I am heading out for a long trip and wanted an experienced set of eyes to take a look at some other stuff) and they are quite confident it is a pilot jet issue, maybe a weak coil, but probably the pilot jet. So, round three will commence in the next couple days. The guys sent me off with some complimentary better carb cleaner than what I was using (they swear by the suzuki brand) and said the overnight soak is actually quite important even if they look clean.
Will update.
Another interesting tear apart of the carbs... I did rip them apart and did the whole cleaning again with a couple differences - different carb cleaner, finer wire (e string from guitar) and I moved the reassembly of the carbs inside to minimize dust. This seemed to clean them up very well. However, during the cleaning I dropped the rubber pilot jet cap onto the floor of the garage as I was taking it apart. I live close to a good bike shop so I figured it would be easier to swing by there and spend five bucks than tear through my poorly lit garage looking for a tiny rubber part.
Now it gets interesting. They had no idea what part I was talking about. They pulled up their diagrams and the carbs did not have this piece, they went to grab the repair manual and that as well did not have the piece on the diagram. Given the history of the bike (I had been by a few times and they know the previous owner did some odd additions to the bike, most correct, some incorrect) they told me all my issues were probably from a cap that should never have been there. So I started the bike up without them, it ran perfectly and I thought I had a win. Take it for a spin and the engine floods as soon as it goes past half throttle. The caps are necessary... And, the garage got swept out to the other rubber one is way gone. Anyways, if you go onto partsfish their carb diagram has this rubber stopper on it, so I followed the trouble shooting and yes, THE BLACK CAPS ON THE PILOT JETS ARE NECESSARY.
Measure three times, cut once, that is the lesson here.