24.3HP modified XR250R

[twr7cx]

The bike was run on the dyno late last week in order to setup the new Mikuni Flatslide carby. The result was 24.3HP:

 

 

 

2000 Honda XR250R modifications:

XRs Only Mikuni Flatslide Carburettor 34mm Kit

Uni Filter Dirt Bike Air Filter with High Flow Cage

XRs Only Piston Kit – 78mm / 10.5:1 / 284cc (Ceramic Coated JE Pistons piston)

Ferrea one-piece stainless steel valves

Kibble White Titanium Valve Springs

Cometic Top End Gasket Kit

Rick’s Motorsport Electrics 15-603 Hot Shot Series High Performance CDI Box (ignitor)

XRs Only Crankcase Ventilation Kit (K&N filter)

XRs Only Competition Exhaust Header

FMF Powercore 4 exhaust pipe with spark arrestor removed due to a blockage

 

The standard camshaft is still installed and I intend to retain due to it's low down torque profile.

 

 

You can see that it is still running too rich even with the smallest jet installed (peak HP didn't change with any of the jets installed). The carby specification sheet from XRsOnly specifies a K&N airfilter, not a UniFilter, it's been suggested that the K&N may flow better so I have ordered one to try.

 

From what I have read standard HP is around 19, so it's almost a 25% increase achieved.

Edited September 21, 2013 by twr7cx

[Baja trail Rider]

your smart to use stock cam,but dont ever use a KN air cleaner on a dirt bike.Stay with the UNI the KN is ok on the street.

[twr7cx]

your smart to use stock cam,but dont ever use a KN air cleaner on a dirt bike.Stay with the UNI the KN is ok on the street.

Do the K&N's just not filter enough for the dirt?

 

Included with the filter that I purchased is a K&N Precleaner, it's like a stocking that fits over the K&N airfilter to add an extra layer. I wonder if combined there is enough filtration?

[Baja trail Rider]

With the KN precleaner it flows less then the UNI.Yes The KN in the dirt is real bad,fine dirt goes past it.No one will run KN in Baja.Unless they want to suck dirt in the motor,also nice when the carb slide sticks wide open.I had to ride a bike with the KN with the kill switch,for 400 miles.BTR

[n2omike]

Not bad for a stock cam!  An aftermarket cam will allow more rpm, which is what unlocks more horsepower... as long as the airflow path can keep up.  If you were going after dyno numbers, a bigger cam would make a huge difference, as you have the airflow path to properly support it.  I'd be tempted to at least try a small cam.  ?

 

Good Luck!

[Baja trail Rider]

Aftermarket cam in the 96-04 Xr250 does very litttle,as it has a hot cam stock..Very short life span in this motor with aftermarket cam.We do have a custom grind cam.Made by Web cam.Dont know if it makes more power,its for making the motor live,at hi rpm.BTR

[Tasos Meli]

 

The bike was run on the dyno late last week in order to setup the new Mikuni Flatslide carby. The result was 24.3HP:

 

 

 

2000 Honda XR250R modifications:

XRs Only Mikuni Flatslide Carburettor 34mm Kit

Uni Filter Dirt Bike Air Filter with High Flow Cage

XRs Only Piston Kit – 78mm / 10.5:1 / 284cc (Ceramic Coated JE Pistons piston)

Ferrea one-piece stainless steel valves

Kibble White Titanium Valve Springs

Cometic Top End Gasket Kit

Rick’s Motorsport Electrics 15-603 Hot Shot Series High Performance CDI Box (ignitor)

XRs Only Crankcase Ventilation Kit (K&N filter)

XRs Only Competition Exhaust Header

FMF Powercore 4 exhaust pipe with spark arrestor removed due to a blockage

 

The standard camshaft is still installed and I intend to retain due to it's low down torque profile.

 

 

You can see that it is still running too rich even with the smallest jet installed (peak HP didn't change with any of the jets installed). The carby specification sheet from XRsOnly specifies a K&N airfilter, not a UniFilter, it's been suggested that the K&N may flow better so I have ordered one to try.

 

From what I have read standard HP is around 19, so it's almost a 25% increase achieved.

 

 

Have you ever ride a stock XR400R? If you have tell us if the difference between a stock XR400 and your 284cc is big or not.

[twr7cx]

Not bad for a stock cam!  An aftermarket cam will allow more rpm, which is what unlocks more horsepower... as long as the airflow path can keep up.  If you were going after dyno numbers, a bigger cam would make a huge difference, as you have the airflow path to properly support it.  I'd be tempted to at least try a small cam.   ?

 

Good Luck!

 

 

I did have a Hot Cams for it (purchased cheap second hand on eBay USA) but elected not to fit in the end (much advice received on here about the effects). I like to use the bikes low down torquey grunt and shifting the power band to the higher revs would be detrimental to that. It's not about the dyno numbers, the dyno was just used for tuning purposes and I thought some may be interested to see the results.

 

Have you ever ride a stock XR400R? If you have tell us if the difference between a stock XR400 and your 284cc is big or not.

 

No, sadly I haven't ridden any other XR's.

Edited July 28, 2014 by twr7cx

[Silverado 996]

Have you ever ride a stock XR400R? If you have tell us if the difference between a stock XR400 and your 284cc is big or not.

 

 

The bike was run on the dyno late last week in order to setup the new Mikuni Flatslide carby. The result was 24.3HP:

 

 

 

2000 Honda XR250R modifications:

XRs Only Mikuni Flatslide Carburettor 34mm Kit

Uni Filter Dirt Bike Air Filter with High Flow Cage

XRs Only Piston Kit – 78mm / 10.5:1 / 284cc (Ceramic Coated JE Pistons piston)

Ferrea one-piece stainless steel valves

Kibble White Titanium Valve Springs

Cometic Top End Gasket Kit

Rick’s Motorsport Electrics 15-603 Hot Shot Series High Performance CDI Box (ignitor)

XRs Only Crankcase Ventilation Kit (K&N filter)

XRs Only Competition Exhaust Header

FMF Powercore 4 exhaust pipe with spark arrestor removed due to a blockage

 

The standard camshaft is still installed and I intend to retain due to it's low down torque profile.

 

 

You can see that it is still running too rich even with the smallest jet installed (peak HP didn't change with any of the jets installed). The carby specification sheet from XRsOnly specifies a K&N airfilter, not a UniFilter, it's been suggested that the K&N may flow better so I have ordered one to try.

 

From what I have read standard HP is around 19, so it's almost a 25% increase achieved.

 

Hell yeah, I like those numbers... 25%, not bad at all. 2 thumbs up for UNI filter.

[4strokeridertt]

No K&N filter for dirt riding. Remember it's not all about horsepower it is a also about ridability. Sometimes you have to go slow to go fast.

[Silverado 996]

Nicely put 4stroker.

[twr7cx]

No K&N filter for dirt riding. Remember it's not all about horsepower it is a also about ridability. Sometimes you have to go slow to go fast.

 

Whys that? Does the K&N not provide enough filtration for dirt riding?

Hell yeah, I like those numbers... 25%, not bad at all. 2 thumbs up for UNI filter.

 

I got it wrong, the filter was a Twin Air brand rather than Uni.

[4strokeridertt]

Whys that? Does the K&N not provide enough filtration for dirt riding?

 

I got it wrong, the filter was a Twin Air brand rather than Uni.

K&N will not filter down fine enough. You would get dirt past the air filter. Now if it was just about power and you had a dyno to play with.

 

Twin Air or UNI does not matter much, they both do a great job when prepared correctly.

[roj0000]

What jetting did you end up using with the XRs Only Mikuni Flatslide Carburettor 34mm Kit?  Does anyone else have any jetting specs for that carb?

[roj0000]

would you say the  (Rick’s Motorsport Electrics 15-603 Hot Shot Series High Performance CDI Box (ignitor)) is worth the money??

[adnohguy]

Plus 1 for the Twin Air filter.

[twr7cx]

What jetting did you end up using with the XRs Only Mikuni Flatslide Carburettor 34mm Kit?  Does anyone else have any jetting specs for that carb?

 

I may have the details written down. I'll have to have a look.

 

 

would you say the  (Rick’s Motorsport Electrics 15-603 Hot Shot Series High Performance CDI Box (ignitor)) is worth the money??

 

No idea. I was having spark issues and replaced the box as part of resolving this. Did some other work at the same time and hadn't ridden it for a while so can't comment on any difference.

[twr7cx]

What jetting did you end up using with the XRs Only Mikuni Flatslide Carburettor 34mm Kit?  Does anyone else have any jetting specs for that carb?

 

You can see the jetting settings for the runs on the bottom of the dyno sheet. On my last run on the dyno, the settings were: 190 main, 35 pilot, needle 1 clip leaner. It was still a tad rich on this setting and it was suspected that this was due to restriction from the foam air filter.

 

The carby spec sheet states the following:

 

 

...

• ...
• 45 Pilot Jet (optional jetting)
• 35 Pilot Jet (optional jetting)
• 190 Main Jet (optional jetting)
• 200 Main Jet (optional jetting)

Your carburettor is now fitted with a 195 Main Jet, a 40 Pilot Jet, a 2.0 Air Jet, a 6DH3 Needle (clip in 2nd from top groove) and a 0-2 Needle Jet (Nozzle). This is an "average" jetting package which will allow you to establish a baseline for fine tuning.

...

 

...

For high altitude (6000'-8000') and high humidity, we reccomend these settings:

• 0-2 Nozzle
• 6DH3 Needle
• 190 Main Jet
• 35 Pilot Jet

For low altitude riding (under 1000'), we recommend these settings:

• 0-2 Nozzle
• 6DH3 Needle (clip in position #4)
• 200 Main Jet
• 45 Pilot Jet

There are two combinations of needle/nozzle to use. Generally we only recomend using the richer specs. when used in conjunction with a XR's Only Exhaust System.

Lean

• 0-2 Nozzle
• 6DH2 Needle

Rich

• the specs are unreadable on the paper, but it may say:
• 0-2 Nozzle
• 6DH3 Needle

Edited August 2, 2014 by twr7cx

[twr7cx]

K&N will not filter down fine enough. You would get dirt past the air filter.

 

Just noticed that the XR 280 - 34mm Carburettor Kit spec sheet recommends the use of a K&N air filter with it:

 

 

Thank you for purchasing our new 34mm Carb Kit for the XR280. This Mikuni TM34 Flatslide Carb will give you a noticeable increase in power throughout the entire RPM range. In addition to the Carb Kit, we recommend that you install a K&N replacement air filter. Remove the baffle in your stock muffler, or better yet, replace the stock muffler with a low-restriction aftermarket unit such as a XR's Only, Cobra or Supertrapp system.

For external modifications you should:

1. Remove air inlet baffle from the top of the airbox.
2. Replace exhaust system, use a K&N Filter and re-jet stock carb.
3. Replace stock carb with this 34mm TM Mikuni Flatslide Kit.

 

From what I understand XR's Only have been rather involved in the offroad racing of Honda XR's over the years...

[VortecCPI]

Just noticed that the XR 280 - 34mm Carburettor Kit spec sheet recommends the use of a K&N air filter with it:

 

 

From what I understand XR's Only have been rather involved in the offroad racing of Honda XR's over the years...

 

Back in the 80s and 90s Al Baker built the best bikes on the planet.  We had two of his 1984 XR265s and they were insanely-great bikes.  The suspension was awesome and the engines were incredible.  They claimed the all-out twin-carb engines were making 30+ RWHP.  The old big-bore, short-stroke XR265s (84-85 only) revved to infinity and were a lot like riding a 2T.  They required a lot of clutch work and were scary fast.  We surprised the heck out of every KDX rider we came across.

 

Contrary to popular belief the engines were extremely reliable and east to start, cold or hot.  Al recommended oil changes and valve adjustments every 200 miles or after every hard race.  We did the same and my bike is still in use to this very day.  We used Mobil 1 15W-50 automobile oil and had no clutch issues except a tiny shudder when the engines were a million degrees.

 

We were so impressed we flew to his place to check it out and meet everyone.  I met the guys that built my engine and suspension and they gave us a nice tour of the place.  Al had bikes ready to go right on the showroom floor.  You could take them right out and hit the trails across the airstrip.  It was awesome.

Al was instrumental in the development of the RFVC engine series.  Al won uncountable events and his XR600s were insane beasts.  He had them making almost 70 crank HP back then.  Al was an inventor and an innovator.

After his death from his small plane accident things changed a lot there.  It's not what it used to be.