irregular idle

Mine idles better than it ever did with the sure fire, even when I first got it. I was always fighting it to keep it running at idle. It's a relief to be able to take your hand off the throttle once in a while. But yeah, it's not perfect.

Dave
69S

OK, Here's my mates idea, if an engine is rebuild ie a bit tight, rebored or it's an older engine with something tight ..valve ,bush etc...the amount of tick-over fuel as to be increased to overcome this...when cold, but as the oil heats [ thin']s the engine as less resisttance..so the engine speeds up. Yes it's basic stuff, just an idea that's all. :?:

The commando premier carbs come with #17 pilot jets. They are removable. Normally they idle well with the #17 jets. Sometimes they idle on the weak side, depending on exhaust and air filter upgrades/changes. I send them #19 pilot jets and usually it fixes the issue, if it is carb related. The jets are not stamped the jet size. They have grooves. 2 grooves are #17 and 3 grooves #19.. 19 is richer. Hope this helps.

Thanks for the info. I've about ruled out that it is a carb problem as it had the exact same symptoms with the Premiers as it had with the rebuilt original carbs. Strangest behaviour I have ever had on a bike. Start it up and its idling around 1000 rpm, ride for 5 minutes and it starts idling around 1500, keep riding for another 20 minutes and get it really warmed up and idle is back to 1000 rpm. Every ride is exactly like this regardless of weather or any other conditions. On all my other bikes they idle a little slow when cold then increase when warmed up good. Never had one go up and then back down. I have basically just learned to live with it. Causes no real harm except to my ego for not being able to correct it.

Try moving to Dobbin(j.k.)Cheers from another Magnolia,Tx new Norton nut.

Sure sounds like spark timing unstable to me, d/t mechanical wear or bad battery or charger connections.

I do ride through Dobbin every so often, does that count. Battery and 3 phase charging system are new, checked the voltage output and it was good. Seems to be related to engine operating temperature, but not air temp. Timing chain stretch?
What's puzzling is how it repeats the exact same pattern every ride.

hobot said:

Sure sounds like spark timing unstable to me, d/t mechanical wear or bad battery or charger connections.

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I had a terribly unreliable idle until rebuilding the AAU, as the springs were loose, allowing the timing to jump all over the place at idle. Mine would idle around 2000 once warmed up when rolling to a stop, but I found I could get the AAU to "reset" by dragging the engine down with the clutch to around 900 rpm, which would then hold a steady idle. However, the moment the throttle was blipped, it would race back up to 2000.
However, after looking at the the Pazon website, they say it eliminates the AAU, making my post totally useless. I got nuthin!

Like I said it doesn't really bother me that much. I tend to set my idles a bit high on my old Brit bikes anyway, generally around 1100 rpm. My idea may be a bit crackpot but seems like it might not be a bad idea to have the oil pump spinning a bit faster circulating just a bit more oil. Also, I occasionally blip the throttle just a bit when sitting at a long red light. This started after I got my BSA Thunderbolt and the oil pressure light would routinely come on when stopped at a light.
Unnerved me at first, but a search of the BSA forums confirmed it was routine behavior and nothing to worry about. Even JB Nicholson mentions it in his book Modern Motorcycle Mechanics. Setting the idle up a little helped and blipping the throttle makes the light go out, so I started doing on all the bikes. Maybe, its a good thing Commandos don't have oil lights. But then again my Bonneville has one and it never comes on, something to be said for plunger pumps.

Yep Sir Nater that's exactly the routine I go through when another AAU gets faulty in one or more of its several ways of wearing out. AAU's not being made anymore it by far the main reason electronic found a market. The least time spend under cam break in surfing ~2000 rpm the better as long as don't over heat burning that much fuel sitting still. I don't sit long so 900 is my level of low oil pumping and charging - unless some tuning issue arises then bump up till solved.

The next time you adjust the carburetors, just make sure that the engine is nice and hot, a 10 mile run should do it.

Have you checked camshaft timing chain? Perhaps too tight when cold...perhaps worn chain sprockets.

There are lots of various factors that can cause this.

I recently had a go at my GPZ305 engine with a Colourtune kit, but like Dracula, I only get it out of the box at night, it is much clearer to use.
I finally diagnosed a low speed misfire the would not have shown up in daylight, all the fault was a suppresser cap.