I didn't know they made a Burgman 400 in 1993! Wow!
On my 2003 Burgman 400 I use regular unleaded. I believe some folks have mentioned that some of the additives in certain higher octane gas (like detergants and the like) can cause problems but I thought that was mainly with lubrication. I can;t answer your question but have you checked your spark plug for tolerance and wires for connectivity?

 

I do not think it would be anything to do with valve clearances.

Of course your Burgman is very very very old and it could be cobwebs in the air-filter. (Joke! :lol But you did say 1993.

I think it is more likely to be a sensor fault affecting the fuel injection but you may need a competent dealer to diagnose. If it is a regular problem (rather than intermittent) it should be easy for them to pin it down.

Good luck.

 

If it were a car I'd suspect a vacuum leak, but I'm not learned enough on motorcycle engines yet to know if they even use vacuum.

 

I meant 2003 (what do I expect when I get my husband to write the message for me!)

His work on the scooter is much better than his writing, honest! :lol:

Selias- regarding your suggestion - the spark plug is new, and gapped properly, and the connection is fine-

Overall, the fluctuation doesn't seem to affect the scooter's performance, and the variations don't occur when it's being ridden- only at idle-

For further explanation: Once I stop (like at a light), the idle will settle in at one idle speed and stay there (within 1-200 rpm). The next time I stop, it'll settle in at a different RPM and stay there, etc.

 

You got me! Sorry
I'd check the hoses though to see if they are all connected/none missing (like Wyldman suggested).
It does sound like some issue that should/could be resolved though.

 

I would check the throttle cable and linkage to make sure that they are returning to there proper position each time. It maybe sticking just enough to cause the variance in idle position that you are witnessing. Also make sure that the rubber grip itself is not rubbing at the end. This may also contribute to your erratic idle.

 

Could it be the auto choke on the EFI system not realizing when the engine is warm, or just plain sticking? The sensor fault not sensing when the engine is warm could be as simple as a loose sensor connection.

When you come to a stop, try holding the brakes and revving the throttle on and then back off. If it goes up and stays up then I'd suspect your throttle cable is sticking and causing it.

Lubricate your throttle cable just to be safe. Also - there is no reason to use anything more than regular unleaded in your bike. The higher octane "super" gas only benefits engines with high comression. Your bike was designed to run on regular unleaded, and will not run better on anything else...

If your valves are out of tolerance I'd say to adjust them, especially when you are experiencing a problem. I don't suspect them - but they aren't helping...

The 800-1000 idle is the one that makes it hard... Was your idle maybe set that low, and your throttle cable is sticking making it idle higher? Check and lube your throttle cable, check your air filter and the airbox to efi connections, check your spark plug and cap, check your idle adjustment screw, check for loose wires to the efi, stop using supreme, adjust your valves...

Does it do it more/less on full tank of gas than on a near empty? Does it rev higher at the beginning of the ride, and lower after it's hot? Somewhere there is a pattern...

 

doobalies wrote (snipped)

I meant 2003 (what do I expect when I get my husband to write the message for me!)

Well now in all fairness the "9" is real close to the "0" :lol:

 

Thanks for all of the excellent suggestions- I think we'll check the throttle cables first, then progress to the rest of the suggestions (and my husband WILL make sure the valve clearances are within the proper range!! :evil: )

Will report back with any findings...

 

Idle Speed Setting On Engine

Changed oil & tweeked idle speed up a little from 1150rpm, which just seemed too slow & rough. Now idles at about 1350rpm when warm. ALSO, noticed that this adjustment changed two other items:

1/ It "enabled" a fast idle when the engine is cold on startup. Before there was just the single slower idle speed, and the engine ran rough til it warmed up. Now on start-up the engine will idle at about 1700rpm, and this will decrease to 1350 as the engine warms up.

2/ The engine doesnt make an odd "slicing" noise when I shut it off.

Ya' think the dealer didnt adjust the idle speed when he set the scoot up??? I do.

 

I noticed your address is California so I would suggest you check your oxygen sensor which sits close to the exhaust flange. I know with some fuel injected models and leaky exhaust or faulty oxygen sensor can effect the idle. First check that your exhaust manifold is not leaking exhaust. Then step towards the oxygen sensor.