Popping/stalling

My usually placid and well running Commando began acting up on the way home on a ride yesterday.

We rode about 80 miles, some of it over extremely rough, "jolt your teeth out" cobblestone streets accompanied by potholes. As we were riding back, it began stalling whenever the clutch was pulled in unless I gave it throttle. I thought maybe the vibration had caused the idle screws to back out. Also noted that there was suddenly some popping in the exhaust. Figured that was probably a loose exh pipe - which has happened before. Made it home with no issues but in the garage I could not get the bike to idle - adjusting the idle stop screws either had no effect or suddenly ran the "idle" to 15-1800 RPM. I discovered one exhaust pipe was loose but even after tightening, the popping continued. With the idle screws quite advanced, the idle would alternately surge quite high and fall, accompanied by popping, eventually stalling.

I checked the carbs themselves and they were perfectly OK, there were no vacuum leaks and the the balance tube was OK. The slides were free in their bores and were moving properly up/down - no sticking or anything.

We had to leave town (San Miguel de Allende) this morning and drive back to Mexico City so I didn't have time for further troubleshooting but I am going to come back to the bike this coming Sat and see if I can isolate the problem. Seems ignition related to me at the moment but we'll see. All elec grounds (I have added ground wires everywhere!) seem OK and a cursory glance didn't reveal any broken/disconnected wires around the coils, etc that may have come loose due to the vibration. Batt voltage (Shorai) is fine. All ignition connections under the point cover (Trispark) are OK.

It'll be interesting to see what the problem is...

Interested to hear what you discover. My 850 started doing very similar things at the rally. I'm guessing it's electrical but it could be anything. My new Ducati project is keeping me busy at the moment so it might be a while until I can look at the "Not-run".

A guy on one of the group rides sputtered to a stop in the middle of nowhere with similar issues. His turned out simply to be a loose connection at the coil. He was able to tighten it up and continue on. I hope ours turn out to be that simple!

Change out the spark plugs to start with and inspect the old ones for color irregularitys.. If you can wait until late January it's D.F. then Puerto for Puerto Blues Festival and I'll give you a hand in person. You could enjoy the best Bus system in the world until then and get fatter too. Maybe a carb slide fractured. Maybe the fuse shifted. Maybe a needle jet unscrewed from vibrations over those lovely old cobblestone roads. Maybe a stray Mex. dog leaked on then into the points cover.

Maybe time related after the beating something may have moved .If you follow a methodical system of checks your problem will appear.
Craig

"Maybe time related after the beating "

Yes...me and the Commando both took a pretty good beating; my wife was on her 2012 BMW F650GS and both she and her bike were pretty much unfazed. I suppose there is something to be said for modern suspensions!

She has offered to buy me a new Triumph Tiger 800 for an anniversary present as a better bike for the type of riding we do (without a doubt) but so far I have continued to turn down the offer. By God, I'm a COMMANDO RIDER!

Maybe a needle jet unscrewed from vibrations over those lovely old cobblestone roads

Click to expand...

yes, this sounds more carb related than electrical, other to definitely pull the plugs and look em over good

I would focus on the carbs for now by taking the tops off and pulling out the slides to verify that the needles are still in the same notch clip, one of these could have shaken out, and also check each carb for both pilot and needle jet still in place

do the slides both life at the same time, pull the carbs off the air cleaner and watch the back of them

the throttle cables going into the carbs, could one have pulled off being seating into the top of the carb?

Mi Chihuahua Mexicana no meha ofreseedo eso. You are a lucky man ,take that Tiger by the tail.

Thanks

That was the one bit of troubleshooting I had time to do - pulled the tops off the carbs and the slides out. All OK. needles were properly clipped and I even removed the slides from the cables and dropped them into the carbs to check for any stickiness - both slides dropped with a pleasing "thwack" when they bottomed. Both were opening together, so it seems that the upper "half" of the carbs was fine. I'll start on the lower half of each when I go back up there this weekend.

"You are a lucky man ,take that Tiger by the tail."

We'll see about that Tiger...I have to say that it just doesn't do anything for me - none of the dual sports do - though it would be a much better choice for our riding here. I'm the only person in our "group" of riders (maybe 10 people) that doesn't ride a fairly current dual sport.

I hear ya about those dual sport bikes, too much shit hangin off of them. This would be cool in the rough stuff...

Do you suppose the shaking up may have dislodged some sediment that is now clogging the pilot orifice

This might sound a little stupid...but maybe some old crud broke loose in the gas tank plugging the fuel flow. The fact that you couldn't get the carbs to change with adjustment leads me to think something simple happened. Could be electrical but the description sounds like a surging problem and that leads to dirt somewhere in the fuel system. If you increased idle setting then the surge makes sense as fuel comes through the system. I would do a flow check on the petcocks and hope you have a fuel filter in the system...maybe change that once you verify flow out of tank.

Thanks guys,

Good suggestion re checking for gunk that may have been dislodged. I agree that since it began AFTER much shaking/pounding, there is a good chance it's related to that.

I don't have an aftermarket filter in the fuel system, just the oem fine screen that is part of each petcock and the small oem fine screen that mounts at the base of each carb.

Check all of those screens. You may have to clean the carbs too...screens don't stop everything. Get an inline filter when your done

Seems to be fixed...

As was suggested, it appears it was a bit of gunk in the idle mixture jets though the gas/carbs looked totally clean and all filter screens were clear. Carbs looked like new internally, all settings were correct, no air leaks, loose jets, etc. I thought about mechanically cleaning out the idle mixture jets at that point. They looked clean but I wanted to do one thing at a time to really try to isolate the problem. So I put it all back together...still wouldn't idle. I then ran a piece of .016 guitar string through the mixture passages and started the bike...other than out of adjustment, it ran fine. After a bit of adjustment, idle is now perfectly normal. So apparently there was something in there obstructing the idle mixture jet. I can't imagine what it could have been since there was NO dirt/gunk anywhere in the carbs/fuel system but obviously something got in there. It certainly withstood 60PSI of air pressure and yet, when I inserted the guitar string I felt nothing at all - no roughness or the feel that something was being "removed."

As has often been stated - no substitute for mechanical cleaning of the idle mixture jet, regardless of how clean it looks!

I had problems with silt from a tank that had sat empty for years clogging my Amal idle circuits. Installed a set of Pingel filters and never took the carbs apart again.