Our "new" 2004 CR250

mx-4-2
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mx-4-2
Edited Date/Time 5/1/2014 9:03am
We just picked up a low hour '04 CR250. Plan to race it in the 2 stroke B/C class. Bike has very little time on it. The owner bought it new and was too much for his son (first motorcycle). Will have Factory Connection mod the suspension. I also have jets coming to dial in the carb as well as radiator braces, tires and other spares.

Any issues with running 100LL av gas with the Honda HP2 oil? We use av gas in our 4 strokes and I really have no past experience with 2 stroke MX bikes as we started after they were already phasing out. Any other engine adjustments or mods we should be thinking about? I scanned some past posts and sounds like the engine performs well mid to upper rpms but has soft low end. Any specific pipe that helps? My son is moving up to the B class and has advanced to the point he should be able to push the bike hard.





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Cmiller493
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Cmiller493 12/28/2013 8:32pm
12/28/2013 8:32pm
Get an Airstryker Carb, MX Bonz airbox seal kit, 05 base gasket and an FMF shorty with factory fatty. Good to go!
Socket946
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Socket946 12/28/2013 9:07pm
12/28/2013 9:07pm
Also get foot pegs, the oem ones were horrible. Consider the works connection clutch perch and lever, it helps to get a lot more clutch feel, something a 2 stroke needs!
Socket946
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Socket946 12/28/2013 9:10pm
12/28/2013 9:10pm
Also, almost forgot! http://www.crfstuff.com/productimages.html and scroll down to the article on the front brake....your kid will not like the front brake going from a '10 250F to that bike.






New link-type front brake master cylinder linkage and Bronze
Lever Pivot bushing improves front braking power by 15 percent!

In 2007 Honda made some major improvements to the front brake lever and master cylinder designs on the CRF 250R and 450R that greatly improved brake performance & feel. Basically the mating surfaces between the lever and master cylinder were upgraded to ball & socket link designs that greatly reduced friction. The pivot surface of the lever also got a bronze bushing upgrade. The result is a silky smooth feel at the lever that doesn’t fade away or require constant servicing. The previous style wasn’t bad when it was new, but quickly deteriorates to a notchy / stepped feel that makes it difficult to modulate the brakes. This upgrade is an excellent way to improve the brakes on your 2006 or older CRF R model and all CRF X models.

We have installed this upgrade on several older CRF's and the results are excellent.







You'll need one each of the following parts from your favorite HONDA dealer for this upgrade.
#3 MASTER CYLINDER SUB-ASSY.45510-MEN-J01 $126.89
#12 BOLT, HANDLE LEVER 90114-MEN-J01 $3.32
#13 COVER, R. HANDLE LEVER 53176-MEN-J01 $6.58
#20 SPRING, BRAKE LEVER 53174-KN5-006 $2.40
#23 ROD, PUSH 45525-MEN-J01 $6.26
#24 LEVER, R. HANDLEBAR 53171-MEN-J01 $21.71
(please note, these are HONDA retail prices Jan 2009)
mx-4-2
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mx-4-2 12/29/2013 4:05am
12/29/2013 4:05am
Thanks guys. Very helpful.

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CamP
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CamP 12/29/2013 8:50am
12/29/2013 8:50am Edited Date/Time 12/29/2013 8:52am
I run 100LL in all my 2-strokes. It works great.

The best carb for the 04-07 CR250 is a '00-up YZ250 carb. It can be rewired to keep the TPS functional. Replace the powerjet jet with a stainless steel set screw. Install and 178 main, 48 pilot, and CEJ needle with the clip in the 4th position during the winter, and 3rd position in the summer.

Install a 05-07 base gasket. It's .010" thinner than the 02-04 base gasket. For even more low end snap for the 02-04 CR, mill .020" off the base of the cylinder and deepen the head's squish band .020".
crashnburn11 12/29/2013 10:05am
12/29/2013 10:05am
The thing you have to watch with 100ll is the minimum specific gravity the oil will mix at. 100ll has a sg of .68 to .74 at 60 F. Most synthetic oils (hp2 included) work with this no problem. Castor 927 does not mix well with 100ll. If you have a clear gas can you can definitely see the oil separate from the fuel.
Socket946
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Socket946 12/30/2013 3:28pm
12/30/2013 3:28pm
crashnburn11 wrote:
The thing you have to watch with 100ll is the minimum specific gravity the oil will mix at. 100ll has a sg of .68 to .74...
The thing you have to watch with 100ll is the minimum specific gravity the oil will mix at. 100ll has a sg of .68 to .74 at 60 F. Most synthetic oils (hp2 included) work with this no problem. Castor 927 does not mix well with 100ll. If you have a clear gas can you can definitely see the oil separate from the fuel.
I don't want to cause an issue in this thread, but I never understood castor 927. The Super M is a superior product in all ways.
mx-4-2
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mx-4-2 12/30/2013 6:05pm
12/30/2013 6:05pm Edited Date/Time 12/30/2013 6:08pm
CamP wrote:
I run 100LL in all my 2-strokes. It works great. The best carb for the 04-07 CR250 is a '00-up YZ250 carb. It can be rewired...
I run 100LL in all my 2-strokes. It works great.

The best carb for the 04-07 CR250 is a '00-up YZ250 carb. It can be rewired to keep the TPS functional. Replace the powerjet jet with a stainless steel set screw. Install and 178 main, 48 pilot, and CEJ needle with the clip in the 4th position during the winter, and 3rd position in the summer.

Install a 05-07 base gasket. It's .010" thinner than the 02-04 base gasket. For even more low end snap for the 02-04 CR, mill .020" off the base of the cylinder and deepen the head's squish band .020".
Camp - couple of clarifying questions - on base gasket, I am understanding this as gasket under cylinder and not the cylinder head gasket. Both part numbers for base and head gasket have changed from '04 to '07 so I want to be sure. Also, on the milling the .020" off the base of the cylinder and corresponding amount to regain clearance in the cylinder head, does this need to be .030" in the head if I use the thinner '07 gasket?

These changes look to lower the ports in the cylinder hence increasing displacement. Am I understanding this correctly? What is the result? I would guess better low end torque with no detriment on top end performance but pls confirm.

Also - which piston mfg have you found works the best? Vertex uses casting with added silicon content vs Weisco forged pistons which I am more familiar with.

Thanks.
CamP
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CamP 12/30/2013 6:21pm
12/30/2013 6:21pm Edited Date/Time 12/30/2013 6:22pm
The base gasket is at the bottom of the cylinder. The thinner gasket drops the cylinder, which increases the compression ratio and retards the port timing. It doesn't change the displacement. The stock 02-04 squish band clearance is typically .060". The ideal clearance is .050", so running the .010" thick 05-07 base gasket also corrects that clearance. The result will be a better running bike.

If you would like a bigger low/midrange boost, milling an additional .020" off the cylinder base and head squish band is a good mod. Doing this will increase the cranking pressure to the point that good fuel will be required. Straight 100LL has enough octane to keep it out of detonation as you increase the compression with these mods.

I always run OEM pistons and gaskets.
Darryl916
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Darryl916 4/30/2014 9:49am
4/30/2014 9:49am
crashnburn11 wrote:
The thing you have to watch with 100ll is the minimum specific gravity the oil will mix at. 100ll has a sg of .68 to .74...
The thing you have to watch with 100ll is the minimum specific gravity the oil will mix at. 100ll has a sg of .68 to .74 at 60 F. Most synthetic oils (hp2 included) work with this no problem. Castor 927 does not mix well with 100ll. If you have a clear gas can you can definitely see the oil separate from the fuel.
Socket946 wrote:
I don't want to cause an issue in this thread, but I never understood castor 927. The Super M is a superior product in all ways.
This is good to know. I have been running 100LL and Castor 927 in my 07 CR250 at 40:1. Makes me thing I'm at risk of messing something up....

I run 100LL because it's better than pump gas but more easy for me to get and cheaper than VP or Sunoco

I run Castor 927 because of word of mouth (before the internet). I always heard it was the best. It also smells yummy!
FGR01
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FGR01 5/1/2014 9:03am
5/1/2014 9:03am
Darryl916 wrote:
This is good to know. I have been running 100LL and Castor 927 in my 07 CR250 at 40:1. Makes me thing I'm at risk of...
This is good to know. I have been running 100LL and Castor 927 in my 07 CR250 at 40:1. Makes me thing I'm at risk of messing something up....

I run 100LL because it's better than pump gas but more easy for me to get and cheaper than VP or Sunoco

I run Castor 927 because of word of mouth (before the internet). I always heard it was the best. It also smells yummy!
Castor 927 and Super-M are both excellent products that work great. You are not at risk of damaging your engine from 927.

However, you are at risk of major silencer packing spooge and carbon buildup. You'll know it when your exhaust sound gets nice and crackly and obnoxious. For this reason I use Super-M.

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