Hi all. I need help with right cylinder missing on idle. I have an 83 with bs34 all stock.The carbs are clean (3 times) and 3 pilot holes are spraying fine with aerosol carb cleaner, same for mix screw and choke plunger. Float is dead on at 22mm, pilot jet you can see through clearly, rubber plugs on, new float valves and synced . I have switched the coil wires , plugs , and mix screws with no difference, so i took both carb banks out and, fit the left bank on the right cylinder , it purrs. When on choke..both work fine, both spark plugs after idle are almost black with mix screw set at 3 turns out. After half hour drive .. both plugs are light gray with a medium brown at the tip of the porcelan. I have sprayed for air leaks with no difference and i like to do the dead cylinder test on the bad one, but it'll die when set at 1200rpm after 5 or 10 seconds. Sorry for the long post.. but by saying what i've done, it'll maybe point you at something i missed. If anyone can help..it's much appreciated. ps.. cam chain tension done, valve clearance done.
-
Enjoy XS650.com? Consider making a donation to help support the site.
XS650.com receives a small share of sales from some links on this page, but direct donations have a much greater impact on keeping this site going.
carbs, how do i test the pilot circuit?
- Thread starter dimitri
- Start date
-
- Tags
- carburetors
Your post isn't at all too long, it's just long enough to let readers know that you've tracked the problem down to the right side carburetor without second-guessing or taking anything for granted. Well done!
I know you've set float height; now I'd suggest that you set up the carbs on the bench, level them carefully, rig a fuel source, and inspect with a sight tube on the float bowl drain valve. If memory serves (correct me if I'm wrong here ) the 83 tank had a single petcock feeding the left carb, with the right fed by a crossover from the left. If that's the case, ensure that the right carb is getting enough fuel; lower the sight tube into a jar with the valve open and check flow.
If the right carb passes those tests, the next thing to check is the right side float bowl gasket; is it intact, and do the holes line up without blocking passages that need to be open? If that's good, check the right side pilot jet and pilot air jet; either of those could be defective. Swap them with the left carb and see if the grief changes sides, and be sure the PAJ passage is clean. Also have a look at the needle and needle jet; there are strong interactions between those components and the pilot circuit. Make sure the right side needle is correctly installed. If there's any evidence of wear or damage, replace; aggressive cleaning often hogs out NJ's and renders them useless.
If there's no joy from any of the above, I'd suspect the carb body itself.
I know you've set float height; now I'd suggest that you set up the carbs on the bench, level them carefully, rig a fuel source, and inspect with a sight tube on the float bowl drain valve. If memory serves (correct me if I'm wrong here ) the 83 tank had a single petcock feeding the left carb, with the right fed by a crossover from the left. If that's the case, ensure that the right carb is getting enough fuel; lower the sight tube into a jar with the valve open and check flow.
If the right carb passes those tests, the next thing to check is the right side float bowl gasket; is it intact, and do the holes line up without blocking passages that need to be open? If that's good, check the right side pilot jet and pilot air jet; either of those could be defective. Swap them with the left carb and see if the grief changes sides, and be sure the PAJ passage is clean. Also have a look at the needle and needle jet; there are strong interactions between those components and the pilot circuit. Make sure the right side needle is correctly installed. If there's any evidence of wear or damage, replace; aggressive cleaning often hogs out NJ's and renders them useless.
If there's no joy from any of the above, I'd suspect the carb body itself.
Bravo, excellent post! (both youse guys) Has a vacuum gauge or manometer synch been done? Compression test results?
Thank you gentleman for your advice. It's been raining here for 5 days and no chance of doing any fiddling yet. I've been thinking though ...wile synchronizing , i'm able to make each cylinder work right ,but one at a time and this is done by turning the synch screw a half turn each way. When both vacuum gauges are reading the same.. the right cylinder is weak and misses every other puff. Will let you know after i check the things you advised. Compression was 180 and 185 but i don't trust the gauge as per that high. thanks again gents.
That adds another dimension to your troubleshooting; the problem could be in your instruments, not in your carburetors. What kind of gauge are you using, and are the lines well sealed?
