2001 CR250 carb/jetting problems

[ryancr500]

I recently purchased a 2001 CR250 which is virtually BRAND NEW.
The owner said he has not adjusted or touched the jetting.

The only situation where I feel there is a carb/jetting problem is at FULL Throttle. It almost seems like the plug is fouled (which I changed and the problem was not fixed). It will not rev out cleanly when at full throttle. I am mixing Maxima 927 at 40:1 ratio. I don't think it is a fuel/oil issue.

Does anyone have any suggestions?
What should the stock jetting be?
What would cause the motor to not 'clean' out when at full throttle

I need help since I am going biking this weekend and would like the bike to perform at it's best!

Any help would be greatly appreciated

Ryan

[stormbringer]

Did you try cleaning the carb? It might just be clogged from old varnish gas. Also while the carb is off check the reeds. If you have the owners manual it tells you how to check if they are in spec, the reed petals can also break, it will be almoast obvious if one has broke.

[ryancr500]

I haven't cleaned the carb.

I give it a thorough cleaning

Any other ideas.... just in case?

Ryan

[stormbringer]

Try using this as a guide it helped me jet my overbore yz125.
[Only registered and activated users can see links. ]

[MotoMan]

First thing to do as was mentioned is take the carb apart and give it a through cleaning. Use compressed air and blow thru the jets and passageways.

If that doesn't work, off the top of my head I would say the main jet may be a bit rich. However I am betting on the good cleaning curing most of your issues.

[bikepilot]

If the cleaning doesn't fix it (don't forget to set the float level) look for other problems, even with the stock jetting my 01 ran strong on the top, just loaded up with slower riding and was a bit blubery down low, but had no issues cleaning out and running really strong on top. You might want to check that the exhaust valve is opening - you can remove the plug on the left (clutch) side of the cylinder and watch it move - it should move all the way to "H" when you rev the bike up.

good luck

[MotoMan]

Originally Posted by bikepilot

If the cleaning doesn't fix it (don't forget to set the float level) look for other problems, even with the stock jetting my 01 ran strong on the top, just loaded up with slower riding and was a bit blubery down low, but had no issues cleaning out and running really strong on top. You might want to check that the exhaust valve is opening - you can remove the plug on the left (clutch) side of the cylinder and watch it move - it should move all the way to "H" when you rev the bike up.

good luck

Good thought on the power valve....Ive been away from 2 strokes too long lol.

[ossagp1]

possible problems may be an obstruction in the air passage or exhaust. I am betting on the main jet being too large and or the float too high. We tried the mikuni off of a 2001 on our 2000 before going back to the Kehien. We used main jets from 330-350 at sea level-500 feet, and temps in the 50-70 degree range.

[bikepilot]

Did it even run with the 350 main jet? My 01 feels a bit lean with a 410 in it!

[Dirtgood1]

The 2001 was notorious for jetting problems. For some reason that year honda swithched to a mikuni. The best fix for the problem is to replace the carb with a keihin from a 2000 model, then jet as you normaly would. If you do a search on here you will find that most people that have and an 01 have done this. Unfortunately not matter how much you tinker with the stock carb, you will never get it just right. I had and 01 that had an 2000 carb on it and the difference from my buddies 01 with the stock carb was night and day.

[ryancr500]

I'll probably switch to the 2000 carb, but I would like to try to figure out the current problem.

I'm not great at jetting, but aren't different jets operating at different RPM levels. Which jet would affect the higher RPM's more?

The bike runs perfectly at Idle, mid range. seems to Load up and it's unable to clear it out even at full throttle. I'll clean the carb to eliminate that as a problem.

[KKXR400R]

I wouldn't bother changing the carb. I think just hammering out your jetting will solve this problem. My bike runs perfect, nice sparkplug color and shoots out of corners like a bat out of hell...shooting the '01 jetting nightmare' stigma down. If you don't have a manual I would suggest getting one ASAP. Sounds like your Float level is out or your main jet may be too large. Checking both will be benificial. Your main jet is what effects the higher RPMs the most. If you have time, take your carb out and check EVERYTHING with a fine tooth comb. I found that if the float level is out even by a little it makes the bike run funny. I do agree with ya though...jetting sucks, but it is a reality in the dirtbike world and your gonna have to face the music. Stay with your premix numbers. Changing these will only complicate things and frustrate you. If you do need anything from the manual please let me know and I would gladly help. Good luck

[bikepilot]

Originally Posted by ryancr500

I'll probably switch to the 2000 carb, but I would like to try to figure out the current problem.
I'm not great at jetting, but aren't different jets operating at different RPM levels. Which jet would affect the higher RPM's more?
The bike runs perfectly at Idle, mid range. seems to Load up and it's unable to clear it out even at full throttle. I'll clean the carb to eliminate that as a problem.

Yeah, get that fixed first. I'll admited the Mikuni is a bit funky to jet, but we are talking very small issues, not major running problems like not clearing out on top. You've got issues other than slightly off jetting.

good luck


Oh, btw the Eric Gorr book says the coils on these things are prone to failure and can cause all sorts of weird running issues. If you verify that the carb is clean, floats are at the right level, no blockages and the pv is moving you might want to look into that.

[ryancr500]

Thanks for all your help.

I'll let you know if I get the problem solved after this weekend!

Ryan

[ossagp1]

Bikepilot!! Thanks. Those were notes for a 2002 . We did run with a 400 and a 390 in the 2000 CR 250though. If yours is lean with a 410 you may have a fuel problem, or air leaks. Our temps are usually on the cool side, and we run that lean no problems with 20-1 oil. Didnt like any combination in the Mikuni as well as with the Keihin that came on the 2000. The 2002 liked it WAY better than anything we could do with the Mikuni. FYI on our 2000 the 2001 cylinder with the 2000 carburetor was a little better than the 2000 cylinder with the 2000 carburetor. Nothing I could measure with tells me there is any difference in the cylinders though. Just FYI stuff.

We have had the 2000 since late 2000 with no electrical problems whatsoever. Haven't read Gorr's book, but did he actually say "notorious"?

[ossagp1]

Ryan, you asked a question about jets and which ones affect an RPM range. They DONT affect an RPM range. They affect throttle openings. In the end that should translate into RPM of course, but you have to understand the difference to really be able to get the most from a particular carburetor. Before you go chasing anything electrical, check the float for correct height, check the exhaust valve to see that it is opening all the way, and it goes without saying make sure the aircleaner is still clean and that there are no other obstructions or reed issues.

A bad crank seal on the transmission side makes some bikes act really rich, but usually it translates into fouled plugs at the lower rpms too, really thick exhaust smoke in some cases too, none of which you mention.

[mtk]

Originally Posted by ossagp1

Didnt like any combination in the Mikuni as well as with the Keihin that came on the 2000. The 2002 liked it WAY better than anything we could do with the Mikuni.

That mimicks my experience with my 2002 and the stock Mikuni. I even bought the Honda Optional Parts Kit for the carburetor, which consisted of a dozen different needles and an assortment of main and pilot jets, and I even bought an S-8 nozzle in an effort to try and get it tuned. In the end I sat the Mikuni on the shelf, put on the PWK from my 2000 and never looked back.

[bikepilot]

Originally Posted by ossagp1

Bikepilot!! Thanks. Those were notes for a 2002 . We did run with a 400 and a 390 in the 2000 CR 250though. If yours is lean with a 410 you may have a fuel problem, or air leaks. Our temps are usually on the cool side, and we run that lean no problems with 20-1 oil. Didnt like any combination in the Mikuni as well as with the Keihin that came on the 2000. The 2002 liked it WAY better than anything we could do with the Mikuni. FYI on our 2000 the 2001 cylinder with the 2000 carburetor was a little better than the 2000 cylinder with the 2000 carburetor. Nothing I could measure with tells me there is any difference in the cylinders though. Just FYI stuff.
We have had the 2000 since late 2000 with no electrical problems whatsoever. Haven't read Gorr's book, but did he actually say "notorious"?

Thanks for the info!
That makes sense. I'm quite sure my 01 doesn't have any weird issues affecting jetting. The previous owner bought it new and I've been around the bike since the day he bought it (we are good friends). The stock main is a 430 I think. I've also compared jetting with other 01 owners and we all seem to end up pretty close for a given tempature/altitude - in fact I'm a bit on the lean side, but I mostly use the bike for technical off road riding. For MX I raise the needle a notch.

I read somewhere that the 01 has slightly larger or higher ports than the 00 and I think different ignition mapping. Whatever the case, I'm quite impressed with how it runs. It does have a FMF fatty pipe and turbine core II silencer/spark arrestor (<93db!).

I'd like to try a carb from an 00 sometime, but with my current jetting its quite tollerable. I am at sea-level which may have something to do with the larger jets.

[ossagp1]

Pretty close to sea level here. The 2001 did come kind of rich on the bottom. The idle jet and the needle also affect top end. Ours was left with a 40 low speed jet so that we could start it easily on cold mornings. The jet needle was stock and usually run one clip up from the middle, and with the smaller mains. If you dropped to a 30 or so on the low speed, you may still need the larger main. Response was better with the larger jet, but it will blubber if you go slow too long.

The keihin just seems more responsive and remains so in altitude changes which we sometimes do, but seldom are we over 2500 feet.

That last cylinder breather was the best Honda ever made, I think. I have the two cylinders in question in the garage right now, I should go measure again, but even on the degree wheel I couldnt find anything other than the usual one port being a little more advanced than the other from side to side on the same cylinder.

Bring it back now in the 2002 and newer frame and I think it would be in the same league as the new YZ is.

[bikepilot]

There's more than one third gen CR250 chassie with a 01 motor out running around. I'm told the swap is pretty easy

Yeah, I do have a smaller pilot - a 32.5 and I also have a S-7 nozzel. It never loads up, but I think it does feel a little more responsive with richer jetting, but then I run into troubles when I lead a beginer trail ride or otherwise end up riding really slow for a long time. Sooner or later I'll order a carb for a 2000 CR250. Still, I'm really nit-picking it runs quite well and has more response/power than I need.


Perhaps the cylinder differences are in transfer port flow or something hard to measure like that? I've never compared the two so I really don't know.

have fun