KX250F feedback

mxbigd17
Posts
403
Joined
9/1/2010
Location
Johnstown, OH US
4/25/2017 5:18pm
Ok, anyone and everyone please chime in if you've had experience with building up a 250F please. I'm torn on what to do so I need some feedback about your experiences...good and bad.

I talked to Tom Morgan about modding my 2015 KX250F. You guys know.....port/polish some kind of head work, hot cams, HC piston.......OR everything mentioned above except running a 270cc kit.

I ride a lot of practice days and race occasionally, usually the age classes +25/30/40. I'm a decent rider, went from 250t to 450f bikes but this is my first 250f bike and I really like it because it handles a lot better than a 450 and I don't get wore out in 6 laps of riding it. I'm an average size guy 5'11, 185 lbs so the 250f isn't horrible by any means. But on a full gate in the age classes, guys usually have 450's which makes getting a start tough but not impossible. A little more power wouldn't hurt and I'm not interested in going back to a 2t.

What have you guys done to your bikes, was it worth it or not? Who was the engine builder, was the bike reliable or did it require way to much maintenance above and beyond normal maintenance. Was the HP gains really noticeable and worth the price tag? Just needing some feedback....
And by the way....why is Porting/Polishing so damn expensive!
|
Yamaknockers
Posts
108
Joined
4/25/2017
Location
Floral Park, NY US
4/25/2017 5:30pm
Try going up a tooth on the rear sprocket. Porting and polishing the sprocket will only help on a 125, so don't waste your money. Make sure to properly torque the sprocket bolts and use a good quality chain lube BEFORE you set the sag to compensate for the larger sprocket.
zziptie
Posts
9
Joined
1/3/2014
Location
indiana, PA US
4/25/2017 6:45pm
270cc kit is definitely worth it if you're going to keep the bike. I've seen them win in open classes full gate. 270 kit, full pipe, remapped efi, hot cam great mods = fun bike
JWACK
Posts
2479
Joined
8/7/2009
Location
NM US
4/25/2017 6:49pm
I would just buy a 350.
nytsmaC
Posts
5959
Joined
8/10/2009
Location
Frig Off CA
4/25/2017 6:53pm
Get a 300 like I didCool



The Shop

ianhendry46
Posts
395
Joined
8/18/2011
Location
Murfreesboro, TN US
4/25/2017 7:06pm
Don't listen to yamaknocker, port and polish does help. It cost so much now because of the technology and development that these engine builders use and do.
You want to do two things, make power and be reliable. And then you need to ask yourself two questions: How Much are you willing to spend off the bat? And : How willing are you to keep up with the shortened maintenance intervals?
As someone who prefers a 250f to a 450, I had this same problem, along with working for a few pro guys that need all the power they can get.
A good port and polish, along with a good set of cams(hot cams stage 2 work well), a properly set up valve train matched with a good high compression piston, a pipe and last but definitely not least, a remap of your stock ecu to match your mods and choice of fuel or if you can afford a vortex or GET ecu. These combined mods will make enough HP out of a 250f to do what you need to do.
pCp 252
Posts
670
Joined
1/1/2008
Location
Hampden, MA US
Fantasy
2497th
4/25/2017 7:22pm
I currently have a mostly stock 2015 KX250F & 2014 KX250F that's been highly modified . Had 4 of these machines since 2009. Also owned YZ250's and have ridden many of the late model bikes. 5'11, 150lbs, LL Amateur MX class.

Without getting super detailed my 2014 KX250F has an engine package that I would imagine you'd see in many privateer SX/MX 250F's. CNC ported head, CrN coated Del West valves, copper beryllium valve seats & guides, DC cams, Hi compression piston, Crankworks crank with billet rod & ISF/REM treated crank halves, transmission ISF/REM treated, Hinson clutch, PC exhaust, VP T4 fuel, and custom ECU tune from Tokyo Mods. The bill for this motor package was about the same price as a leftover 450 !
Once you start adding HP with porting/cams/piston, you'll need things like the Hinson clutch, hi performance valve springs, coated Ti valves, copper seats, a stronger transmission and crank rod & more to keep it all together and running for longer than 20 hours.

This motor has a complete tear down service interval every 25 hours for inspection and replacement of all wear parts. Mostly because I do not want this motor to get damaged (blow up) at all costs. At the bare minimum this is about $500. For this reason, I will probably only put 25 hours on this bike this season. My point is that unless your racing program allows for this budget, I would not recommend going full blown race motor.

The things that I did to my 2015 just make more sense for most people including myself and are the best bang for your buck. These ¼ liter bikes are pushing the envelope about as far as they can go stock. These motors spend a lot of time between 10k up to 13.5k rpm. That's a lot of revolutions!

2015 setup
- Remove the mesh air screen just past the air filter.
- VP T-4 or your choice of performance fuel
- Exhaust
- ECU remap (Custom tuned map for all the modifications)

Is porting worth it? Lots of mods work in conjunction with each other. If you've changed your exhaust flow and introduced more air into the engine, then the porting will be more effective at boosting HP than without intake/exhaust mods. It depends on your budget. The seat of the pants dyno tells me you will only feel a minor difference in porting if the rest of the bike is stock.

The difference between my 2015 and 2014 is fairly significant, depending upon who you ask. It's certainly no where near the power of a KTM 350 as some have articulated it. I wouldn't even say it matches the power of a 270 kit either. It just feels like a very healthy stock bike, it has a similar power curve to the stock curve, with just a few more HP throughout.

I can say the KX250F much prefers the stock 50t rear sprocket compared to the 51. Even on trails, I prefer the 50.

What's your budget? I could lead you in the right direction with experience. You just want to allocate enough $$ for rebuild time because the valves & seats & many other components do not last forever.

Post a reply to: KX250F feedback

The Latest