Super rich on LH side

The sort on my 72 rebuild continues. On its maiden trip seem to be having some carb issue. Stumbling on acceleration, popping back ect. Pull plug lead off lh side and rh ran fine on its own, was able to adjust mixture and idle.
Pulled off rh side and lh side would barely run. Again stumbling on opening the throttle, popping, turning mixture screw had no effect. When I had the bad sides lead off I stuck it on a spare plug and layed it on the head. Was getting a good blue spark. So I'm going to assume at this point the ignition system is okay. I had also strobed and rechecked the timing prior to going on the ride. Pulled the plugs after fiddling with the carbs and the offending lh side was extremely sooted while the rh side looked nice and clean with a little tan color.
The carbs are 32mm ones and both are jetted the same with 106 needle jets and clips in the middle position. They both have the new stayup floats. Where is the best place to start looking to solve what appears to be some extreme richness on the lh side, float level?

1. Pilot jet clog
2. Float level
3. ignition still mis timed on one side assuming points or maybe condensor shot.
4. Air leaks in misfiring intake paths
5. Needle fell out of clip.
5. Slide missing a piece cracked off inhaled and spit out leaving valve lip bend for nil compression sealing at low rpm
6. Water is bowl bottom
7. Weak plug that bad out the box or bad after misfiring.
8....? tell us what else really causing it to add to list.

Thanks Hobot. I'm making a checklist of things to look at tomorrow, starting with a new plug. Ignition is a Pazon with wasted spark so timing should be the same on both cylinders.

hobot said:

1. Pilot jet clog
2. Float level
3. ignition still mis timed on one side assuming points or maybe condensor shot.
4. Air leaks in misfiring intake paths
5. Needle fell out of clip.
5. Slide missing a piece cracked off inhaled and spit out leaving valve lip bend for nil compression sealing at low rpm
6. Water is bowl bottom
7. Weak plug that bad out the box or bad after misfiring.
8....? tell us what else really causing it to add to list.

Click to expand...

Possibly choke slide disconnected, so slide is blocking air flow, richening the mixture on just that side.

Easiest stuff to do is with the carb on the bike.
1)Put a vacuum gauge on the manifold spigots. Vacuum should be same for both carbs. If not, in the general ballpark, check for vacuum leaks, either a cracked manifold, loose manifold, or bad gasket, manifold-to-head or manifold-to-carb.
2) double-check valve clearances.
3)You can pull out the idle mixture screw and clear the passage with a fine wire (like a single strand of a clutch or throttle wire), or a #78 drill bit.
4)If that doesn't work, take the fuel bowl off and check the float level. If the older nylon float, you have to tap the inlet seat in or out . If the new float with metal tangs, bend to get right height. While the bowl is off, check that the main jet is screwed in to the main body nice and tight.
5) if that doesn't work, pull the top off the carb and check that the needle is still attached to the clip, and that its in the same groove. Its possible to have the needle hit the edge of the main jet and actually get bumped up to the bottom groove, which will make the carb run richer. More common is to knock the needle off the clip, and it either drops into the main, sealing it off, or hangs up on the side, giving full main jet all the time.
6) while you got the top off, check that throttle cable and choke cable are working properly. Remember, slackening the choke cable engages it. Pulling the cable pulls the choke off.
7) while you've got the top off, check the slide. See if there's a chunk missing (unlikely, but possible). Slide should move up and down in the body without hanging up, but not so loose that it rattles. Worn slide will let too much air in, and the idle screw will have no effect on running.

When I started my '73 back up a couple weeks ago, I couldn't get the right side to adjust. Careful inspection showed the cable was hanging up ever so slightly, so the sheath was seating in the cable junction. I re-routed the cable and bingo! bike settled right down.
I use a carb stick like this:
to balance the carbs. I use it get optimize idle, then to adjust the throttle. Carbs are synched when vacuum moves in unison on each carb as you move the throttle. I got that carb stick 30 years ago to balance the four carbs on my old Yamaha.

I sure go through mood swing extremes with my Commandos, hope your's swings high once she's purring on both sides. Stealing time to fix not riding is a downer. Its possible there a pilot jet mismatch as I tried some with thumb screws but the tapper was blunter or something and couldn't get idle settled so gave up on em. I've gotten a small handful of crappy tuned Commandos going w/o any instruments though not against them just not needed for vast majority to run about prefect. I"ve greased worn slides to see if that allowed idle and it did, so had to get Anodized one/2 cut out richer. I'm putting off my own Trixie reassembly so glad to be active on a commando project from rocking chair.

If it's a Pazon try swapping plug leads and plugs to opposite side and see if trouble moves with it.

HTH,

Jeff

Thanks again for all the suggestions guys. And the winner is: clip came off the needle. Which also happened to be the first thing I checked (not usually how it happens for me). Engine sounds pretty healthy now. Was able to set mixture and idle on both sides. Now to put some miles on.

Whew, a relief to have the other shoe drop. It helps to know others had will power to take something apart again to get going, when its comes my turn, again.

Good news! Glad you didn't have to pull the carb off.