Idles rough when warm

My bike starts, idles, and runs well, but just lately it has started to idle rough occasionally when fully warmed up. The first time I thought I had gotten some bad gas, but this is the second tank. When it started today I tried to add some enrichment and it immediately shut off. It started right up, but I could tell that it was skipping starting from a stop, but ran well otherwise. The plugs look good and have less than 1000 miles on them. I think I will replace the plugs anyway, but what else could it possibly be. The carbs were cleaned several months ago and I have an inline filter as well as the mesh caps on the float seats.

 

And when was the last time you checked your valve clearances? Been more than 5K miles? Starts/runs fine cold, issues when warm is often a classic symptom of needing a valve adjustment.

Otherwise, it might be time to replace that inline fuel filter; and despite the mileage and how they look, pop in a new set of plugs.

Also check and be sure you don't have a resistor core working loose in one of your plug caps. I've had sudden-onset stumbly running brought on by that.

 

Valves were checked about 1000 miles ago, but I can re-check them. I'll check the wires, hadn't thought of that. I'm also going to replace the plugs. the inline filter is relatively new also, probably less than 1000 miles.

 

If the valves were in spec 1K ago, they still are. Don't fret that.

Check the plug caps for sure. Look inside where the spark plug tip goes; there are screwdriver slots on either side of the hole. Ensure the resistor cores are snug in the caps.

And definitely fit some new plugs. The fuel filter should be OK unless it stopped a really big hunk o'crud.

One other thing: how are the little rubber caps on the vacuum ports?

 

I'll check the plug caps, hadn't thought of that either. The vacuum caps are probably original but seem to fit snugly. I'll check my spare set of carbs and if those aren't any better, maybe I'll order a set form Chacal. I might make some out of vacuum hose just to see if that's the problem.

When I first got the bike I had an intake gasket leak and that caused some rough idle, so I guess bad vacuum plug would do the same thing. Lots to do in the morning.

 

You can get those little rubber caps at most auto parts stores too; or at least something similar enough to function temporarily.

Pull yours off and see if they're still soft and pliable. Quite often they LOOK fine but are in fact as hard as rocks and no longer do any sealing.

 

I'll put those on the list. Believe it or not, I had to order spark plugs. No one had them in stock.

 

While I am waiting for my plugs to come in, I'm checking everything else. the plug caps for 2 & 3 are Denso caps and have the screwdriver slots, and both were slightly loose. the caps on 1&4 were not Denso, but were the same, and do not have the screwdriver slots, however one was loose on the wire and I twisted it back on and it's firm. It appears that a po installed new caps and perhaps trimmed the plug cables because there isn't much play in 1 & 4. I hope I don't have to do this, but what is a fix if a plug wire is too short?

 

Len sells replacement wires and a double screw to splice the wires into the old ones.