2004 Burgman 400 K4 Running Lean

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mightbesane
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2004 Burgman 400 K4 Running Lean

Post by mightbesane »

My Burger's running fine. Getting good gas mileage, not burning oil, starts first punch, decent tire wear. But I just replaced the plug after 6,500 miles and it showed lean - not drastic but enough that I'd like to adjust the mixture. Can it be done?
Without deviation from the norm, progress is not possible. ~Frank ZappaImage

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Data
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Re: 2004 Burgman 400 K4 Running Lean

Post by Data »

Hello mightbesane, only just seen this post. I would reckon that you have solved it by now but just in case you have not, is the bike running the correct spark plug? If not that might be the reason it is showing as too lean. It could be a hotter running plug than the engine needs. So, if you haven't already done so, just check that first. Secondly, check that there are no air leaks in the airbox and intake pipes to the engine. I think the fuel cap on your model is air vented, so make sure that is fully clear too. If it's not fully clear, it will make the bike run lean just before conking out. Are you using a fuel system cleaner in the petrol? Some do, and use it all the time. Not needed all the time but if you are and it's overdosed, it will make the bike run lean. Lastly, going from memory only here, you can I believe adjust the carb mixture with a screw on the side of the carb. You need to be sure which one it is as there maybe two. One of them affects the mixture upto one third throttle opening. If you don't have a manual on this is may be worth getting one as it will tell you how to set it up properly. You may find having altered the carb mixture it doesn't make much difference. If that's the case the carb may need an overhaul as it is worn and air is leaking past the throttle body butterfly. That will make it run lean.

You may already know this stuff or have done it, sorted it or whatever, but post back if you can so we know how you got on. Cheers bud. ;)
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mightbesane
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Current Ride: Burgman 400 K4
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Re: 2004 Burgman 400 K4 Running Lean

Post by mightbesane »

Thanks for the reply. The plug is an NGK in the medium range, so it should be OK. I don't over use fuel system cleaner - one dose at each oil change should be about right. As for the rest, I'll check the fuel cap - didn't think of that. And I do have a service manual but I didn't see an adjustment at first pass. I'll take another look. Finally, I'm reasonably certain it's not an air leak. I had a bum intake on my old CH250 so I know what that's like. But next time that I strip the plastics I'll spray some brake cleaner around. As I said, it's not a fatal looking plug, just a bit lean, and since I commute six days a week in all weather, I'm reluctant to strip her down until I need to. I sure do hope it's not the carb itself, but after 20,000 miles - most by a guy who didn't seem to be too careful about maintenance - I can't rule it out.
Without deviation from the norm, progress is not possible. ~Frank ZappaImage

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