Best upgrades for 250es/sx engine

[Homeless Dave]

I’m at a point where I’m going to be inside the engine of my big red, it needs a cam chain and it smokes. I’m doing valve seals, cam chain, fresh cylinder on stock bore, and have a new piston kit I go from eBay. not sure on the compression ratio, but I’m guessing around 11:1? What camshaft do you guys recommend? I have an aftermarket exhaust on it already. Carb will be moved up to a 300ex carb or possibly jet out the original.
I’m wanting more low end power from it, I have 27” Kenda rampages on it. I love how they perform, but wish it had more power to get ‘em turning (they are HEAVY). I’m not looking for top speed or anything, just more grunt to go up a hill or through some mud.





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[shortline10]

I would see if WEB or fourstroketec sells a performance camshaft .

[Homeless Dave]

I’ve looked at the catalog for WEB and mega cycle, I’m looking to see if anyone has any experience with some of the cams. I’ve bought cams from both before, but never built a big red engine that wasn’t stock.


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[ATC King]

If it's in need of a rebuild, it'll have more power when done anyway.

Higher compression will be the easiest and least expensive power upgrade, beyond that you're starting to go down the cost versus improvement rabbit hole. It will cost you over time, due to needing to run higher octane fuel.

Looking a Web camshaft site, you'd be in about $400 just for the cam and rockers. That's the basic cam they sell. The next one up also needs a bunch of other work done..$$.


Put it back stock except for a bump in compression, which you should at least measure the static. Spend the money to have a O2 sensor bung welded into the head pipe and use a wide band sensor with gauge to really dial in the carb, no guessing. Money saved and maximized at the same time.

Tune, tune, tune.

It would be very beneficial to install a programmable ignition. Not being able to adjust the timing on an engine build is just leaving a lot of meat on the table, and pretty much a waste of money for other parts that need the ignition adjusted to maximize their potential. Also, with increased compression, the timing may actually need to be retarded a bit, and two programmable maps could help increase low end power or maximize top end, on the fly, or be a safety mode in case of high temps and detonation. A good programmable ignition will probably cost less than a cam and be worth more in tuning ability.

Skip any 'racing' ignition. If it isn't programmable, it isn't for racing, at least not since programmable CDIs have been available the past, 20(?) years.


I thinks there's several good videos about the impact of proper tuning, what parts are worth it and what aren't, and just how deep one can go into the rabbit hole if trying to build something into something it wasn't.


I think these two are a good example of just how important tuning is compared to throwing money at parts or copy+pasting internet results from one engine to another and expecting them to respond the same. Two new engines, in the same two vehicles, built on the same day, may need slightly different tunes when performance is the main goal.

Hellcat channel, Mr Nasty 100hp banshee YouTube videos:

2022 xr650l stock vs piped lid removed and tuned
Honda 650l 2400 miles review tuned on dyno ,no Dave's mods


For a good idea what is really needed, the tools, skills, and experience, to sure enough do a proper build and just how real the money gets, real quick, I like the Kaplan America XR650L build. That's a lot of cost and labor for a 50% power gain. They didn't address some of the other issues needed for longevity on an engine build like that, but they probably don't know about them being they work on so many other motorcycles, all with their individual issues. Those would've been some of the Honda Baja and Dakar race bike modifications, custom stuff, not then and not now available to the general public. Those engines do a have a racing history, but they're not race engines as available, except for maybe hare scrambles with a certain, well known rider.

Not that it's not worth it to some people, but it'd be much simpler and could be less expensive to just buy something higher performance to start with.


KAPLAN AMERICA YouTube videos:

BASELINE DYNO FOR OUR XR650 PERFORMANCE BUILD!
OUR BUILT XR650 HITS THE DYNO!
TESTING THE XR'S ONLY XR650 PIPE



If you've watched those videos, the point I'm trying to make is a well tuned stock engine can be just as fun, or more, than dropping a wad of stripper toilet paper into it. Keep it simple, keep it reliable, keep having a good time for longer with more jingle in your pocket.

If you know of any 250ES dyno run videos with mild to wild builds, I'd like to see them. It'd be really interesting to know just how much another 5-10(?) HP really costs and if they're even enjoyable to ride. I've driven and rode some pretty terrible engine builds. Ones with a parts book thrown at them and were so poorly done, the stock engine was more enjoyable. Total waste of money and a less reliable to boot.

[Homeless Dave]

Isn’t that xr650 exhaust video the one they show the XRs only made less power or no difference? I’ve seen it , but was a while ago.
I’ve built performance engines before, but those were meant to be run balls to the wall all the time. those engine generally got into the point of poor idle and poor low end, basically set up for WOT and not much else. But that was back in my racing days as teenager. I’m just wanting some more grunt, but still have decent reliability. As I have found out before, as performance goes up, reliability goes down. I’m shooting for a decent middle ground. I think I might go with the mild cam from WEB or leave it stock. I’m already gonna have a fresh engine with some upgrades. I just hope it’s noticeable while trying to turn those heavy 27s.
As for programmable cdi, that’s something I didn’t think of! Do you know of anyone that sells them for the 250? Mine has the round 85 cdi plug.


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[ATC King]

Yeah, the last XR650L video from Kaplan was about the XR's Only header. They were already using the XR's Only muffler, which I think is a reverse cone megaphone, and if it's like the FMF Megamax (which I have), a reverse cone works great on those bikes.

They didn't show any real gains with the header except at something like 7,000 RPM, which is race bike type operation. Even then, the power gain was minimal. Overall, not a good header for anything but actual desert racing and that 600 RFVC platform won't win races anymore compared to newer bikes. Something to consider is just how built that engine was and still done better with the stock header. I've run a whole slew of exhaust on my XR650L and am going back to the stock header with a FMF Megamax, which is what I had before I put the '88-'90 OEM twin stainless headers on with a stainless Supertrapp. I've probably gone through a couple grand just swapping exhausts over the years on one bike. The stock exhaust, muffler and header, with the baffle removed sounds great and probably runs good enough for stock engines. The stock muffler isn't very heavy either. No need to dump a lot of money there on that bike.

Myself, on the four stroke utility Honda ATCs, I prefer good running stock engine. A larger carb and/or larger exhaust moves the power curve higher and takes away from the fun of trail riding them.Even a stock engine can be fine tuned for more power, which is where I like to spend my effort.

I think a 250ES with a stock cam and higher compression is ideal. Porting the head and a mild polish (cleaning up casting lines) wouldn't hurt. If you'd like a bit more flow with the stock cam, the intake valve could be back cut, but I don't know the longevity of multi-angle grinds and back cut valves on a 250ES. More frequent valve adjustments would indicate the valves are wearing faster.

As for a programmable CDI, it's not needed on stock engine but some of the potential features are nice. A dual ignition map, rev limiter, tach output, and other functions can be beneficial. On a built engine, a programmable ignition is a must and relatively inexpensive anymore.

I don't think you'll find any plug-&-play ignitions for the 250ES. Unless someone does a group buy for them, you're going to have to wire in a universal unit. That's not a big deal, there's only a handful of wires to deal with and the 250ES runs on a 12V DC system, so there's more choices.

There's a multitude of programmable\adjustable single cylinder CDIs out there.

One that I've got on a bike is from the Czech Republic. It was less than $200 and programmable with a laptop. They have proven to be very reliable ignitions.

https://www.ignitech.cz/en/

They have a few single cylinder models to choose from. If you wanted to go that route, I could help you choose one.

Someone on here tried the MSD CDI and I don't think they ever got it to run right or weren't happy with it. The MSD CDI is also much more expensive. There's several programmable CDIs out there but Igni Tech seems to be a solid choice and dependable.

[shortline10]

I have had experience with the midrange cams from web in the trx300fw basically the same engine as the big red and can tell you it did make a difference in bottom end grunt .
I would say your piston , web cam , trx300fw OEM carburetor , jetting should be real close and a little bit better breathing exhaust should give you the results you’re looking for .

[Homeless Dave]

I saw that WEB offers a cam for a 300 that is a high lift short duration, so you think that cam would work well for what I’m trying to do?


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[big specht]

I have had experience with the midrange cams from web in the trx300fw basically the same engine as the big red and can tell you it did make a difference in bottom end grunt .
I would say your piston , web cam , trx300fw OEM carburetor , jetting should be real close and a little bit better breathing exhaust should give you the results you’re looking for .

I second that. And 10.25/50 compression piston would have to make a difference. And there is a guy on bookface that selling SS muffler and head pipe combos for not a bad price and are top notch quality