I just installed the pro-meg system from White bros on my 400ex. A lot of people talk about jetting but W.B say that that it's not nessisary .Has anyone tried alternative jetting.The motor revs heaps stronger and harder with the new pipe.I also tried taking the air box lid off but the seemed to flatten out up top.Any experience would be appreciated.

 

oz_400ex,
Well, I'm not quite sure what you mean by alternative jetting, but if your engine is not making power at the top end after removing the airbox lid it's almost certainly starving for fuel. You have drastically increased the air flow mix without a corresponding increase in fuel flow. In other words you have to rejet to a fatter mix.Evidently you're not having a problem in other parts of the band since you don't mention any, so you are just lean on your main jetting.If you have no plans to do any other upgrades, such as a filter, just go to a size fatter main jet. If you plan to run an open air box, I'd go up two sizes on the main and test ride. Two sizes fatter without a filter upgrade may be a tad rich, but will even out when you improve the filter system and in any case a slightly rich condition won't damage your engine like running lean can do.
You could also do a plug read after testing at full throttle, but my experience with reading 4 stroke plugs hasn't been very definitive...not like 2 strokes where oil is a factor.A 4 stroke plug will often read brown & normal even if slightly lean.

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[This message has been edited by hot_shoe_cv (edited 11-28-1999).]

 

I have a E-series (Stock discs) pipe and K&N filter and I added a power up kit (mistake) on a 99 400EX. I am at 160 main jet from a stock 148. I've had a 155, 160, 165 and 170 in and we came up with this by a timing about 100 yds rolling 1st gear start and the 160 times were the best eventhough the power up kit suggested a 170 for the 1000 ft above see level. I still have some work to do on 1/2 throttle circuit, but that's where I am at.
Another trick to see if you are rich or lean is to duct tape around the air filter covering about a third of it. If it is gets worse, your too rich. If it is better your too lean.
Adams44

 

Thanks for the input so far.The bike was definately leaning out with the air box lid off.I'll have to get a k & n filter and go up on the main jet. Adams44 whats in a power up kit.