400E main jet

02' 400E. It came with a Yoshi exhaust, airbox lid gone and rode perfectly. I've since put the stock muffler back on and drilled out the tip as detailed here on the site. I checked the main jet an it is the stock 142. The bike runs perfectly still, all be it a bit less grunt. I pulled the plug and it's a tich rich looking, tanned insulator but black side walls. The fuel milage isn't the best, 160km per 10L all in dirt throttling it most of the time :rolleyes:   reading thru the shop manual I see that some of the E models came with a main jet of 165 and some, like mine, came with a 142. Anyone know why? since the plug already looks a tich rich is there a point to me trying a 165? I haven't pulled the carb out yet to see if a kit of some kind has been put in that'll be my next step. Appreciate any input. 


27828216139_393336f168_b.jpg2018-01-09_06-13-26 by Rob Ert, on Flickr

24737678977_c3b5fbd6d8_b.jpg2018-01-09_06-13-10 by Rob Ert, on Flickr


getting things tidied up and ready to install 

The color of a well used sparkplug really doesn't tell you much about the mixture, especially the main (unless you ride at 3/4 throttle or higher all of the time). Plug readings should be done with a new plug and only (try) to use the portion of the throttle that translates to the circuit in the carb you are trying to tune. This was real easy with 2 strokes where the plug was easily reachable. It's damn-near impossible on a 4 stroke.

Different regions get different jets due mostly to EPA regulations, secondly due to regional conditions. My guess is bikes sold in a high altitude location like Colorado get a lean jet.

Jetting is changes/adjusted to maximize throttle response. Don't chase jets for fuel mileage or power.

I agree on the plug chop difficulty on these bike, no thanks. That’s a good point about jetting for throttle response but I don’t think dealers picked main jets based on their altitude. Thanks for the info. 

On 12/1/2018 at 5:32 PM, bbccdd said:

02' 400E. some of the E models came with a main jet of 165 and some, like mine, came with a 142. Anyone know why?


165 for bikes without airbox lid,  142 for those with airbox lid.

The Suzuki factory sent out a bike without an airbox lid?


yes, for example in italy

2 hours ago, 30x26 said:

yes, for example in italy

Last I checked Colorado isn't in Italy. In the United States vehicle manufacturers have to appease the EPA before the customers. 

Edited by Gary in NJ

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