Thank you for the reply.
I thoughly cleaned the carbs years ago, and have done so again. The carb to motor boots went on fine but have always been rock hard and the air box to carb boots have always been nice and soft but were a major hassle to install then and even more difficult now. Is it likely they have all shrunk? I am thinking of ordering all new boots and starting fresh. Thoughts?
Thank you.
If it's only idling on choke, you're running lean, aka not enough fuel and too much air. You can verify this by pulling your plugs. Put new plugs in, run the bike at idle for 2-3 min (try not to use choke, use idle adjust screw or throttle to keep it alive if possible). Pull plugs, see if the engine is running lean or rich.
1. It's possible you have a vacuum leak at the intake boots. While the bike is running, spray a fine mist of carb cleaner at the boots. If the engine sound changes, you have a leak.
2. My first thought is that 40 slows are too rich with simply 4:1 and K&N filter in airbox. I run 40s in my PD41As and I have very open 4:1 and K&N Pods, bike idles like a sewing machine and low end performance is solid.
However, only idling with choke on suggests that you are too lean which doesn't make sense with 40 slows on, to me. The stock sizing is 35, I would guess #38 would be a better choice if you're not running pods.
3. Where did you get these #40 jets? If they are from anywhere other than jetsrus, they are 99% certainly not sized correctly. The margin for error on aftermarket brass from 4into1, CB750supply etc is simply too large. Jetsrus sell OEM main jets and OEM equivalent slow jets for these carburetors and having recently spent time tuning my CB750F2, I can confidently say the difference is dramatic. I had 4into1 #120 mains and my high end was garbage. Switched to OEM #120s and it is perfect, plugs are beautiful.
4. Have you thoroughly cleaned your slow jets/ passages, and how did you clean them? If you put a brush in there, you may have ballsed up the brass. Have you pulled them out and inspected all the wee holes on the ends? Use a high E guitar string to clean them out. Varnish, particulates, etc, may be starving fuel.
5. Have you verified your bowl fuel level with the clear tube method? Not all floats are the same, so the measuring device can only be relied upon to get you in the neighborhood. My current floats prefer to sit around 14mm rather than 14.5mm, my previous floats preferred closer to 15.5mm. When I changed the floats recently (two of them kept jetting stuck) I used my old 15.5mm measurement and the bike wouldn't start, the fuel level was too low.
7. Take a picture of your fuel hose routing and post it here. You may have fuel starvation issues because (in my opinion) the fuel intake for the PD4X carbs is in a weird spot, making it tough to go straight to the petcock without going "down" after the carb front plate. If you have the fuel line looping up, over, down, and back up around the carbs you may be causing fuel starvation issues.
8. Do you have an inline fuel filter installed? If so, and the fuel in the filter is clear without any particulates, throw it away. A lot of them will cause fuel starvation issues.
9. How clean is your tank? Do you have any fine rust debris in your bowls? If you do, that can absolutely make the bike run poorly.
10. Are you using
non-ethanol gas? Regular gas has a tendency to quickly build up these white deposits, looks a bit like limescale, which can clog things and make your bike miserable.
