1991 CR250 peaky powerband?

[quino]

Just got my first bike, have questions
Just got my first real dirt bike, a 1991 CR250

Here is a pic: http://www.coserv.net/~quino/bike/CR250.jpg

I used to ride when I was a kid, but have not ridden 2 strokes in about 15 years.

It starts and idles good, but I have a question about the power band.

It seems awful peaky. It has a FMF gold series pipe, and a FMF silencer. Those are the only mods I am aware of. It sure seems like this bike only likes it full throttle. It "bogs" before you get to the power band, to the point that it sounds like it is choking... and then it takes off like a rocket, only for a split second, then you must upshift and get back on it, or it will start to bog again on the upper range of the rpms/power band.

I know this is the nature of the 2 stroke... but damn this thing seems peaky.... and really runs rough if you are not getting on it.

Is this more of a function of the pipe? Would the factory pipe give a broader power range?

I just want to kick around a bit.... and ride trails mostly... and I think this might become an annoyance.... what do you guys think?

 

[ochster]

IMHO..very nice bikes, and yours look's great!

The HPP exhaust valves were verry prone to carbon sticking, and require a fair amount of cleaning/maintenance. It is important when doing this to keep the alignment of the "rack" operating the valves, timed correct. You also need to make sure it is connected to the actuator in the lower case. A manual will be needed to make sense of this, and Eric Gorr of Forward Motion covers this precedure thoroughly on his web site. With this done, this bike being in good mechanical shape, (crank bearings/seals, piston and rings, carburetion), is a great midrange machine. The majority of these I have seen, have the HPP valves and rack messed up.

 

[evenslower]

I would be inclined to go power valve fishing first as well. Eric has some really good articles on p.v. maintenance on your motor. While you're there you might also want to check out his article on jetting. Your bogging could be carby related but what do I know. Eric is the expert.

Great looking 91 by the way.

 

[mx547]

Originally posted by ochster


You also need to make sure it is connected to the actuator in the lower case.

that happened to me once. sometimes it's kinda hard to get it aligned when you're putting the cylinder back on. the bike ran like a 125 on steroids. the good thing is, if this is the case, it likely means that a top end job has been done on it.

 

[quino]

Ok guys....

I took off the HPP left side cover, started and warmed the bike to operating temperature.....

It appears the exhaust HPP power valves are working properly to me.... from what I have read on the www.ericgorr.com site.

When the bike is idling, it looks like this:

And when I open the throttle wide open, it fully extends like this:

When it goes back to idle, it retacts to the original position.

From what I have read, this is correct... yes?

So... it sounds like this is not my problem.... ??? correct?

To be very clear, my bike does not act like it is going to die or anything, it just doesn't have a lot of bottom end power, and runs very rough until it hits the power band.... then takes off like a damn rocket.

From my reading last night, it seems the first area to look at on the 91 CR's is the HPP valves... after that, consider a new boysen reed valve (dual stage or something like that) and having the flywheel weightened.

Does this sound like a good plan of attack?

I dont know too much about the carbs.... but I will be reading. What should I look for... as in, what if someone has monkeyed with the jet sizes, and settings? What are the factory jet sizes? I would think that I would want to set everything back to factory and go from there... no?

Thanks!!!

 

[zilla]

Sonds to me like maybe the carb is the culprit. There was another thread here a few days ago with similar symtoms.. Do you have to fan the throttle to get the bike to pick up? If so then your pilot jet is laquered up.. If you haven't already done it, take the carb off and thoroughly clean it.. Pay special attention to all the little orifices and the pilot jet. I use CRC Lectra Motive to clean my carbs.. Secondly, I'd look for an air leak. Thirdly, how old is the fuel in this bike? If it has been sitting for a while, then dump the fuel and get some fresh stuff in there..

zilla

 

[ochster]

zilla is correct...a thorough carb clean, and blowing out with compressed air or a pressurized cleaner is in order. Remove the jets and blow them out, the pilot ( long skinny one) is usually the one crudded up. Considering the age, it would be good to replace the float needle ($5), and the reeds like you mentioned.

Make sure the ignition area is clean and free of dirt/corrosion. The plastic covers allowed of moisture into these, and it creates havoc when allowed to corrode things up. While your in there check for oil residue leaking from the left side crank seal.

Stock jetting is a 55 pilot, 175 main, 1369 needle w clip in the middle, air screw 2 turns out. It was common for most to run a 172 main with clip in the fourth position from the top. Most guy's are running 40:1 with a clean burning oil like MobilMX2T, or HP2.

Make sure the air cleaner is cleaned, and properly oiled. And it would probaly help to repack the muffler packing, if it is black and oily. This should get you close!

 

[Saratoga]

Quino: You already posted this question in the What bike do I get category. You titled it- I just got my first bike, have some questions. What gives?

 

[quino]

I posted it there but then saw this forum and posted it here because it probably belongs here more.

I tried to delete it, but I cannot. Sorry if I offended you... I know... I am a newbie here.. making the typical discussion board newbie mistakes.

Thanks for all the help so far guys! I feel better knowing the power valves are working.

I am going to clean the carb, throw in a new dual-stage reed (cheap) and then put some fresh premix in it and see how it goes.

Thanks again!

 

[Durt Cycler]

Same thing is happening to my cousin's '84 RM125. The bike revs fine but when you rev it real high and let the cluthc out in first instead of wheeling or doin' a holeshot it just bogs down and you just go off going 5mph. 1st gear rides like crap and you got to hold the throttle wide open for it to pick up or if you work the clutch over and over it will speed it up more untill you hit the powerband in 1st gear then the bike freakin flys. I don't think the jetting is the problem cause it is very close to stock 42.5 pilot (45 stock) I put a 260 main jet in it (270 stock). I noticed he has the reed stopper peice still on the reeds and they are Boyesen Power Reeds and I thought if you install the dual stage reeds you need to take off the reed plate thing? Could this be the problem?