Rough running under no load?

Hi all --

What would cause my 850 Commando to run rough when riding under no load?
In other words, it idles nice and smooth, pulls very strongly when you twist the throddle, but when you are cruising along a flat road with the engine "floating" or not being loaded, it is very rough. Can't tell yet if it's misfiring cylinders or fuel issues or what.
Before I start looking at everything, any suggestions on what it could be will be much appreciated.

Thanks -- Scott

scott12180 said:

Hi all --

What would cause my 850 Commando to run rough when riding under no load?
In other words, it idles nice and smooth, pulls very strongly when you twist the throddle, but when you are cruising along a flat road with the engine "floating" or not being loaded, it is very rough. Can't tell yet if it's misfiring cylinders or fuel issues or what.
Before I start looking at everything, any suggestions on what it could be will be much appreciated.

Thanks -- Scott

Click to expand...

Has it always done this or did it use to not do this?

Sounds like it's a bit rich.

Fullauto said:

Sounds like it's a bit rich.

Click to expand...

That makes some sense. If it is too rich the motor isn't going to really realize it while it is accelerating but only after getting to speed. Check the plugs and see what they look like. You can drop the needle lower by one notch (Amal carbs?) and see if that helps.

Russ

We really need more information ubout your set up.
Could be condensers, HT lead, loose needle, needle jet worn, air leak etc.
Is ign. timing correct first, carbs set as manual?

G'day scot121180,
Do you know how to do a plug chop.?
If you do I'd go and do one.
If not, ride your bike somewhere safe, at the speed, or revs, that is giving trouble,... Say 3000 revs for example.
Third or fourth gear.
Ride it at that speed for a short time ( say a minute minimum ) at a constant rate, don't change the throttle position, then
pull the clutch in and hit the kill switch as quickly as you can, and coast to a stop. Don't let the clutch out till you have stopped.
NOW YOU WILL NEED THE PLUG SPANNER THAT YOU FORGOT TO TAKE WITH YOU.
Remove the plugs and have a good look at the colour on the electrodes. Ideally you want greyish brown.
If the plugs are leaning towards being White, you are too lean, If they are looking dark brown to black (sootty) then you are too rich, at those revs.
Try again at slightly lower revs, then again at slightly higher revs, to sort your Carbies out.
Some would say to only use new plugs, but if you haven't got any I'd go and try it out anyway.
AC.

Hi all --

Thanks for the suggestions on rough running. I haven't done anything yet as it's been so bloody hot.

But to answer a couple questions,

It ran fine last year, but this trouble has been around this year with my first start-up.
You ought to know that I had a crash with the bike last year --- hit a deer. Broke my shoulder, ruined my summer. . . but the bike suffered minimal damage. Replaced a turn signal and other minor stuff, then this summer it fired right up. No apparent damage.

But this rough running. . . Could be bad gas? But I'd expect that at idle or other speeds. I do have fresh gas in the tank. The spark plug check technique is a really good idea. I'll do that.

Not sure how the carbs would get out of whack and now be too rich. . . But I can check that, too.
I also thought maybe the points were closed up a bit. Again, why would any of this happen all of a sudden.

I'll report back what I find, and thanks for any other suggestions on where to look.

--Scott

Stuff like this can be so hard to guess at. Basically you need to do the plug check and see if the carbs are running rich. You might as well check the points and the timing. Assuming you have points. Make sure the air cleaner isn't full of nesting mice or dust or whatever else might have gotten in there. You need air, fuel and fire in appropriate ammounts and at correct timing. That is the circle you work until you find it. While you are at it you might as well clean the friggen kill switch. Just in case.

You need new needles and needle jets.

batrider said:

You need new needles and needle jets.

Click to expand...

Or fresh gas, start with the simple things.

New gas.
Clean carbs.
Then look for more expensive things.

It runs good everywhere else. Just my own experience over 39 years but if it has not had needle jets in 5000 miles it needs them. The description of the problem fits perfectly. Normally I would agree to do the simple things first but this is it I tell ya.

Good advice swoosh, batrider you are probably right.
Scott as per batriders suggestion, these Amal carbs do wear easily.
If your bike becomes mysteriously rich through out the mid range, it can be a worn Needle jet.
If your bike becomes mysteriously lean at idle and low revs, then you may have worn slides.
These two issues are the main reasons for poor running Commandos.