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XR 250 carburetor in CRF 230f

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Hey just wanted to know how this goes and what has to be done in order to get the best power out of the bike. My Crf 230f is bone stock but plan to get a aftermarket exhaust and air filter. Not bothering about rebore or anything to expensive, i will have a new bike before i need that to happen. I just want to know if i need different needles, fuel line etc.

 

Any other mods to give more power would be much appreciated.  :thumbsup:

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The fuel inlet nipple will be very close or even hit the frame.  I pulled mine and epoxied a bent piece of tubing in its place.  You will need to port-match the intake manifold to the carb.

Mike Coe has jetting recommendations for this carb here in TT.  I believe I used a 45 pilot and 132 main with the CRF230 needle.

Edited by VortecCPI
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This is a great mod best power increase for your money! I tried the above jetting but was not perfect for my bike. I am running a 48 pilot ( 45 would be OK too!) But I found the xr needle on third clip with a 128 main to be spot on. I have an aftermarket pipe but this probably doesn't change the jetting needs too much. You'll be stoked with the results. Mine is crisp everywhere and climbs hills a gear taller than the stock carb and flogs a stock uncorked bike!

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ok thanks what else will i need to do the mod to make the carb compatible?

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As VortecCPI pointed out you need to open up the intake manifold to suit the larger throat/bore of the xr carb. This will make sense when you look at these parts. I didn't need an elbow on the fuel line as the bend although a bit tight was OK but you will need a longer line. The bike needs to be uncorked of course for the jetting recommendations. Other than that its a bolt in. Good luck!

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This is a great mod best power increase for your money! I tried the above jetting but was not perfect for my bike. I am running a 48 pilot ( 45 would be OK too!) But I found the xr needle on third clip with a 128 main to be spot on. I have an aftermarket pipe but this probably doesn't change the jetting needs too much. You'll be stoked with the results. Mine is crisp everywhere and climbs hills a gear taller than the stock carb and flogs a stock uncorked bike!

 

That is very interesting.  I tried the XR250 carb on my stock CRF230 and lost a gear on many sections of our two-mile enduro test track.  I lost so much off-idle and low-mid my track times increased significantly.  I had to shift way later and hold gears way longer.  I found myself constantly down-shifting because the bike wouldn't pull third gear coming out of slow sections and/or tight turns.  On long, straight stretches the bike felt faster with the XR250 carb but I did not confirm this on the dirt dragstrip.  The bike felt a lot more like the XR250 we have - Less bottom and more mid.  It felt like it had more power but I wasn't willing to sacrifice track time.

Edited by VortecCPI

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IMO

It's not the best carb for a stock engine. Especially if you do not match the intake manifold to the intake port and the carb itself.

If you don't do at least the matching then it's a complete waste of time and $.

But Used with: Matching port and carb, 89a Cam, higher compression (Wiesco), a ProCom ignition then it would be a whole new bike that would be very impressive.

Add a BBR or Wossner big bore kit, cylinder head porting, oversize header pipe, and proper jetting would be another complete step up again.

Add a Millers Vintage Cycle 250cc Arias 12.5 bore kit, a Terry Miller "Mega 1.5 cam kit" some 100 octane Race fuel, then your 30HP at the rear wheel bike will need suspension upgrades so badly that it will only be rideable on the street until you upgrade your suspension also.

I'm just saying....

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IMO

It's not the best carb for a stock engine. Especially if you do not match the intake manifold to the intake port and the carb itself.

If you don't do at least the matching then it's a complete waste of time and $.

 

I agree.  It feels like a stock LG-4 305 Chevy with a 750 CFM Holley.  Mike Coe also said gains would be minimal, if any, on a dyno.

Like I said above, though, the bike felt faster but the track lap times were slower.  My ability to power slide around turns at slow engine speeds was completely killed.  This is why I have been considering boring my stock carb to 27mm or 28mm.  I think that might be a good compromise for a stock engine.

Edited by VortecCPI

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As I said I tried the Mike Coe jetting and found at 3/4 throttle it was so rich it had a fluffy weak spot and wot was too rich also. After heaps of trial and error I found that the 230 needle just didn't feel spot on so in despair I put the original xr250 needle back in and like magic the tune was perfect. Second clip was too lean with a little pinging under load but third clip seems perfect. 132 main was too rich still so put in 128 and now runs flawlessly. This carb seems more difficult to jet properly than the stock one I would say but when its right its a big improvement even on a stock engine. From what I've read no one or very few people left the stock needle in it to try maybe this is why there has been a mixed reaction to this mod.

Edited by Landerz

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hey im not real sure if i will still bother about the xr 250 carb should i just jet it up with a 120 and 45 jets i am 300 meters above sea level and it is extremely hot reaching 50 degrees Celsius and 20 during winter.

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is that really true about the 30 horsepower if i did the bike up that well. I mean a 250 is pushing not much more then that!

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That jetting will be fine.

Edited by Landerz

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is that really true about the 30 horsepower if i did the bike up that well. I mean a 250 is pushing not much more then that!

 

Mike Coe got 27.5 RWHP out of his CRF230.  His CRF150 (250+) conversions have made 30 RWHP.

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As I said I tried the Mike Coe jetting and found at 3/4 throttle it was so rich it had a fluffy weak spot and wot was too rich also. After heaps of trial and error I found that the 230 needle just didn't feel spot on so in despair I put the original xr250 needle back in and like magic the tune was perfect. Second clip was too lean with a little pinging under load but third clip seems perfect. 132 main was too rich still so put in 128 and now runs flawlessly. This carb seems more difficult to jet properly than the stock one I would say but when its right its a big improvement even on a stock engine. From what I've read no one or very few people left the stock needle in it to try maybe this is why there has been a mixed reaction to this mod.

 

I dind't have any problem with high throttle positions.  The carb worked well in high-mid and WOT ranges.  At higher engine speeds the XR250 carb worked very well.  The problem was low engine speeds.  The stock carb will take WOT from a slow pace in third gear.  No hitches or stumbles.  The XR250 carb wouldn't, just like almost  every other bike I've ridden.  For most riders on most tracks this might be okay but it wasn't acceptable to us.

 

I'd guess most people would care less about the slight hesitation due to the bigger carb.  For tight technical tracks, however, it is a deal breaker.  Like I mentioned above, it made my CRF230 feel a lot like our XR250.  More shifting and more gear holding.  Again, though, I'd bet most people could and would easily live with it.

I suggest anybody who has access to an XR250 carb try it out and let the timer tell you if it works or not.

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I dind't have any problem with high throttle positions.  The carb worked well in high-mid and WOT ranges.  At higher engine speeds the XR250 carb worked very well.  The problem was low engine speeds.  The stock carb will take WOT from a slow pace in third gear.  No hitches or stumbles.  The XR250 carb wouldn't, just like almost  every other bike I've ridden.  For most riders on most tracks this might be okay but it wasn't acceptable to us.

 

I'd guess most people would care less about the slight hesitation due to the bigger carb.  For tight technical tracks, however, it is a deal breaker.  Like I mentioned above, it made my CRF230 feel a lot like our XR250.  More shifting and more gear holding.  Again, though, I'd bet most people could and would easily live with it.

I suggest anybody who has access to an XR250 carb try it out and let the timer tell you if it works or not.

 

It is always a good idea like Landerz did to try the original needle. It's possible the jetting was off. A slightly larger carb jetted real well shouldn't necessarily have a bog. Not that I believe an XR250 carb works well. Never did well on my XR250-300 especially compared to a bored 32 mm Mikuni flat slide. In those carbs the answer was using the stock needle out of a early XR250 with a P-08 bleed type needle jet. A proper needle in a carb can make or break a great running bike.

 

I never found a great needle for my 28mm Mikuni flat slide on my XR80 bike with a XR200 motor. Mikuni needles are usually not suited real well for a four stroke motor.

 

Hopefully someone will give the little 28mm PWK carb a shot. Full throttle at zero RPM's and zip no hesitation. An amazing performing carb one of my favorites at atomizing fuel into the motor. The only problem is no one has a manifold that bolts the spigot carb up directly. It's possible the spigot mount in crossplayers PWK carb post may mount one to the head.

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I never found a great needle for my 28mm Mikuni flat slide on my XR80 bike with a XR200 motor. Mikuni needles are usually not suited real well for a four stroke motor.

 

Hopefully someone will give the little 28mm PWK carb a shot. Full throttle at zero RPM's and zip no hesitation. An amazing performing carb one of my favorites at atomizing fuel into the motor. The only problem is no one has a manifold that bolts the spigot carb up directly. It's possible the spigot mount in crossplayers PWK carb post may mount one to the head.

 

I have traded emails with Frank Nye about using his 28mm on a stock CRF230.  He thinks it is a very good idea.  Not cheap, though.

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I have traded emails with Frank Nye about using his 28mm on a stock CRF230.  He thinks it is a very good idea.  Not cheap, though.

 

I'm not sure what needle he is using because they don't run that great and I tried everything I could find.

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