I have found that many users install KLX250S cylinders 300, 330, or 351cc. With slight modifications to the carburetor get acceptable performance.

My question is if someone has installed a KLX250 a 300cc EFI with good results? OEM injection is not enough to fuel supply? Can anyone tell me some experience in this regard? Or is it absolutely necessary to equip a Power Commander, Two Brothers, etc?
Thanks in advance!

 

I would bet the injector would have enough flow for the 300 jug, but you would most likely need the power commander to tune the fuel delivery.

I have no experience what so ever in the mod you are talking about but since the increased fuel requirements from the 250 to the 300 (carb wise) are not that drastic i think the stock injector would have enough headroom to keep up.

 

On the 250/300 jetting comparison, I already had all the mods to my 250 before I installed an OEM 300 jug and piston. Power increase was noticeable, but even a surprise to me was the fact that jetting remained exactly the same...and I swapped bigger jets in just to find out. It comes down to what I think is referred to as volumetric efficiency. At least for the 300 swap, the head, valves, aftermarket exhaust, and airbox mods all still suit the 300 displacement increase to the degree that power increases with the previous fuel requirements of the 250. Because of this I'd think the 250 FI would/should fill the requirements of the 300. However, one problem is that for the most part we're talking about comparing modded 250's to bone stock 250's and the compliance of the FI system, so I think a fuel mapping tweak might be required via a Power Commander or such.

 

I found the same thing, no jetting change from 250 to 330. I had a problem when I fit a KLX300 muffler though. I got it off eBay with no baffle, and the lower backpressure screwed up the jetting in the low RPMs. I made a very quite (and some would say 'restrictive') baffle because I hate loud bikes, and voila! The jetting came right back in line.

So are you all talking about something available, adaptable?

I initially didn't care for FI as I had an R1150GS that I could never entirely get rid of surge on. My wife's 2007 BMW F650GS, however, is an FI success. That sucket starts and runs flawlessly and gets insane fuel economy. Lowest per-tank mileage we've gotten is 68, and the highest per-tank mileage was 86 in the Colorado mountains. Now that's with the bike geared up 2 teeth on back and one on the front so it doesn't scream feel like a small bike at freeway speeds.

If high quality EFI kits were available I'd buy them! With a machine shop and TIG welder, adapting an O2 sensor is easy enough. My KLX400SR would get the mod first. Geared up 39/16, it flies down the highway at 85mph easily, but it becomes a total fuel hog as the carb is WFO at speed. The KLR650 is not so bad in that regard, but more consistent fuel delivery would be a plus. My KLX300 was a royal pain in the *** to jet precisely for altitude last year. I changed jets a bunch of times and still could not get it to meter well on the bottom from 10,000 to 12,500 ft. An easily programmable FI would be a Godsend.