'99 CR250: Taming the Hit

[Faded]

I'm currently helping a new riding buddy that just picked up the sport by purchasing a fairly used 1999 CR250. He has ridden it a couple times and says that he's intimidated by the abrupt midrange hit. It has a few minor flaws that we'll be attending to and at the same time we'd like to do what we can to increase bottom-to-mid power and try to smooth the hit/delivery as much as possible to make him feel more comfortable. It seems that the normal modifications used to reduce hit also contribute to more top-end power, i.e. retard ignition timing, double base gaskets to alter port timing and reduced compression, etc. I'm looking for opinions on how bottom-end boosting modifications will affect the hit, i.e. shorten silencer, raise compression/reduce squish (by milling the head), dual stage fiberglass reeds, etc. and if there is some combination of the above ideas (or any others) that might work to help add to the bottom end while smoothing things out for him. Since he just bought the bike big money mods aren't really an option.

We'll be going through the top end to make sure it's fresh and that the power valve is clean and working properly. Also we'll be replacing the crank seals (left side leaks). The bike is stock except for an FMF Fatty pipe. Any help or ideas are appreciated, thanks.

 

[marcusgunby]

Might want to try a std pipe as the fatty might be making the hit worse.

 

[Faded]

Might want to try a std pipe as the fatty might be making the hit worse.

Marcus,

Thanks. I did think of that as well, we're starting to gather parts and we've made a note to look for one.

 

[dirt bike dave]

I bought my '99 CR from an AA enduro rider/A Cross Country rider and it was dialed in for very smooth power delivery. It's a great bike with a sweet, friendly motor that also rips. My mods are listed in "The Garage" tab.

Porting and pipe are stock. When I bought the bike, it came with a spare FMF pipe, but I never bothered to put it on as it ran so good and smooth with the stock pipe. I was told the stock pipe was better for offroad. Sold the FMF pipe.

An aftermarket spark arrestor (mine is an FMF Turbine Core) may smooth the power over the stock MX silencer.

A flywheel weight is a great addition. My bike has an e-line lighting system, which adds approx. 12 ounces of flywheel weight.

A Delta V-Force reed cage w/carbon fiber reeds helps. Mine has the original V-force 6 petal, non adjustable reeds. the V-Force 2 is a different design - not sure if it works as well or better than the original V-Force.

Also, mine has a 'powerjet' carb from a '97 CR250, so my jetting specs are not going to be useful. But I am sure you can get the stock carb to work fine.

According to Eric Gorr's book, the '99 cylinder is preferred by many riders due to its superior low end power.

 

[JTT]

My old '99 had great bottom end. It pulled right off idle, but didn't rev great, if anything it was too much bottom (read: abrupt). Totally stock. I found that running a little rich on the pilot helped take the edge off the abrupt power at the very bottom. The pipe is likely your problem.

 

[Faded]

Thank you for the replies. I'll see if we can't locate a stock pipe, play with jetting, see about a flywheel weight and go from there. Thanks again for the feeback and ideas.

 

[kenrkoch]

You might also try a reed spacer. I got mine from moose racing. This moved the power lower in the powerband. It was too much, too low on my CR500 so I had it machined down until it was half as thick. Perfect

 

[darringer]

I have run the fatty and now have the gnarly pipe on my 99. The gnarly does help the bottom pull more. I had read that the stock pipe was very good, but am looking to buy one (hopefully cheap) to try out against the gnarly. I have a 12oz. flywheel weight that has helped a great deal with smoothing out the powerband. This bike has a very strong pull right off the bottom, but smooth. I have pro series reeds also. I also tried a powervalve spacer, which is currently still on the bike. It gave the bike a little more bottom. For hillclimbing, it pulls like a tractor, and is very hard to stall. I currently run a 45 pilot, stock needle, and 175 main, which is quite a bit leaner than stock, but I am at sea level. As mentioned above, the bike doesn't have much overrev. It really likes to be short-shifted. Once used to the bike, I love the powerband. Whenever I ride my friend's '02, I am constantly missing all of my lowend.

 

[dirt bike dave]

FWIW, Truespode just listed some Honda parts for sale in the classifieds. He's got a '99 CR250 pipe for $35 + shipping.

 

[MikeT]

Here is THE CHEAPEST mod you can do that will lessen the hit. Go and buy a new steel front sprocket from Rocky Mountain for $7.99 with an extra tooth on it and that should do the trick. You couls also get a new steel rear for $14.99 with 2 or 3 less teeth on it and that will lessen the hit even more. Then as he gets more confidence you can go back to the stock gearing.

What do you think of that?

 

[dirt bike dave]

MikeT - changing to a bigger front/smaller rear sprocket is cheap and would certainly reduce the hit.

However, on a CR250R, first gear is already pretty tall for tight technical trails. I use either 13/49 (stock on a '97) or 13/50 (stock for the '99). Even with some mods to increase bottom end/smooth the power, I've had to slip the clutch pretty good getting out of some tight places.

BTW, you can feel a difference with just one tooth change on the rear. The advantage over going 13/49 instead of 13/50 is you can hold 1st or 2nd gear just a little longer and avoid a gear change on a nasty trail when you least want to upshift.

 

[Faded]

Thank you everyone for the additional ideas. The gearing idea is a good though, and something we actually used to his advantage. Our Honda parts order finally came and I just finished the bike Saturday. I hadn't ever ridden it before and was just going off his comments on the bike. To make a long story short the PV actuator rod in the cylinder was pinched the last time "they" did a top end rendering the PV assembly unmovable and stuck in the 3/4's open position. After a minute of riding it prior to tear down I knew something was very wrong. :ohmy:

The previous owner of this bike must have been a real piece of work. Not only did he mess up the PV, but the PV actuator rod in the case was set in the full open postion making it impossible for it to open when the revs came up. Also, he used a chisel/screw driver to pry the cylinder off the cases, causing an air leak and requiring 0.010" to be machined off the base of the cylinder (should help low end). Amazingly enough the cases weren't damaged. The left side crank seal was also shot. I am suprised this thing even ran as good as it did (which is terrible) considering the circumstances.

With everything repaired it runs very strong off the bottom and is smoothed compared to what is was. It falls off hard on the top, but the main jet is definately too big for our elevation (175). I checked my notes on my '98 and I was running a 165 or 168. I'll step down to a 170 first, but will probably settle on the 168. The pilot is a bit rich (42), but helps my buddy out as he's still trying to adjust to the new found bottom end power. :)

The gearing is 13/49 now, I thought that would help as confirmed by DBD. The old broken reeds were tossed in favor of Boyesen power reeds (dual stage fiber glass). The FMF pipe seems to be working just fine so we'll keep it for now. I still need to dial in the jetting, especially on top.

Thanks again for all the suggestions and replies, I appreciate everyone's opinion.

Take care,
Andrew

 

[dirt bike dave]

FWIW, on my '99 with the '97 powerjet carb, my jetting is 165 main, 55 pilot, 5.0 slide, R1370M needle in middle position, air screw 1 1/8 out. This runs great at 3,000'- 5,000' elevation. My bike is very sensitive to airscrew position.

On a negelected bike like that, make sure the spark arrestor/silencer is properly packed. Another thing to watch for is the lower shock mount bearings - they seem to wear out faster than the rest of the linkage. The tabs on the seat where it mounts to the frame also tend to crack/break, so keep an eye on those.

 

[Faded]

DBD,

Thanks for the extra tips. Didn't check the seat tabs, but the rear suspension looked good. Yes, it was a beat/abused/neglected bike, and unfortunately it was purchased without really looking it over. The silencer will get repacked when I change main jets later this week. The carb is almost there and I'm guessing we'll end up close to a 40 pilot, 1.5-1.75 out A/S, Stock R1370DKA Needle, 2nd clip, and 168 main for 4700+ft combined with the dry 70+F heat.

Thanks,
Andrew