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Not much top end on CR125

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I have a CR125 2004 and it has a good bottom end excellent mid range but the top just seems to level off at about 8,000 - 9,000RPMs and goes a bit flat.

Eg. The bike pulls okay starting about 3,500RPM and then kicks in hard but smooth at about 6,500RPMs or so and then keeps pulling hard till about 9,000RPMs then seems to go flat. I thought these bikes made most of their power at 11,000RPM?

I rode a 2005 YZ125 and it had absolutely no bottom, decent mid and excellent top end with a heap of over rev.

What I would like to know is, what could I do to try and get a better top where you can actually rev the bike out a bit more but not losing any bottom or mid?

I have to shift gears all the time on my CR because it seems to run out of power in that gear. I really enjoy the bike and after riding the YZ I liked it even more for the awesome mid range but I was a bit jealous of the top end :bonk:

The owner of the YZ thought my CR was quite powerful (the Keihin carb helps a lot) but noticed the same thing with it not having much top. Most fast 125 riders always seem to be ringing them out but on my bike it just doesn't seem that way works...

So in conclusion is it possible to gain top end power while still having a very good mid range but a decent bottom.

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add the 05 intake boot, drill the airbox and then adjust the power valve cables.

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I have heard of doing this, putting three 1/2 inch holes in either side of the airbox and putting on the '05-'07 airboot but does it really need more air? And do you get more dust and such in the airbox because of of it?

And what do you mean by adjust the power valve cables, as far as I am aware they are adjusted to the specs in the manual...

Thanks for the input.

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Also will that cause much of a loss in bottom or mid, I could lose a bit of bottom but I do like the midrange the way it is.

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yes they need more air. If your worried about dirt in the filter, that is why they are washable. You should clean and reoil the filter every ride.

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Is your main jet too lean?

No, I don't think so, James Dean set up the carb for my altitude and tempature so it should be pretty spot on.

yes they need more air. If your worried about dirt in the filter, that is why they are washable. You should clean and reoil the filter every ride.

I replace my air filter after every ride in summer with a cleaned one (I have 4) which has been treated with No Toil filter oil, it always seems pretty dirty after a tank of gas in dusty conditions with the air box in the stock state. Just wondering if it would be worse still with the holes in it, I have heard of a plug or something you can put in the holes you drill which have a small filter?

They seem to have about the same air gaps for sucking in air as the YZ125 I noticed but if this does help a lot I'll try it out if I can find a '05-'07 airboot as well.

Thanks

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I'm usually hesitant when it comes to drilling airboxes and stuff since it is not reversible. For a little more air flow, check out the Cycra Powerflow rear fender. It should allow for a little extra air flow.

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adjust the power valve cables.

Bump for this... I've also got an '04 and I've heard this mentioned a couple times, but no one has elaborated. Are you adjusting to stock or to have it come on earlier? And how do you do this?

And I also just got done drilling 7 little 1/2 inch holes in each side of the airbox and backing it with a mesh. Doesn't effect the strength of it at all, and worst case scenario, it's a $50 part to replace. Soon to come is the '05 airboot.

Also, correct me if I'm wrong, but you would see NO difference in the amount of dust on the filter. This mod doesn't change how much air passes through the filter (RPM and jetting would) or how clean the air is; it just changes how hard the bike has to 'pull' for the air.

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Okay cool, and did you find it made much difference to power or the noise of the bike? I have heard the bikes get noisier sometimes with drilled airboxes.

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I believe 8,000-9,000 rpm is pretty much topped out on these

without moving ports and adjusting crankcase volume.

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Just got the bike back together and did a couple pulls up and down the driveway. The bike may be a hair louder, but more than that it sounds and feels snappier. Basically it feels like the bike revs cleaner and more freely than it did before. Overall, I'm pretty impressed. It's not night and day, but it's pretty noticeable. It feels like the difference between a clean and very dirty air filter. I hope the '05 airboot helps just as much.

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I believe 8,000-9,000 rpm is pretty much topped out on these

without moving ports and adjusting crankcase volume.

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That's just a guess of where the RPM's are at but it sounds about that anyway.

I have noticed in my riding though that going up steep hills and on straightaways that I seem to wind the throttle to about 3/4 and then hold it there and to me that is "full throttle" this might be some of the reason why it feels like it "levels off" because it is leveling off because I am not completely wide open on the throttle.

Just got the bike back together and did a couple pulls up and down the driveway. The bike may be a hair louder, but more than that it sounds and feels snappier. Basically it feels like the bike revs cleaner and more freely than it did before. Overall, I'm pretty impressed. It's not night and day, but it's pretty noticeable. It feels like the difference between a clean and very dirty air filter. I hope the '05 airboot helps just as much.

Thanks for the info and the picture helps a lot, I will probably try this soon, how is the mesh held in?

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Been off the bike for a while but just did a rebuild and was thinking about the airflow topic again, does anyone recommend the Uni Air Box Vents? I was thinking about these but after doing a fair bit of reading some people say drilling the airbox is completely unnecessary and some say it's pretty much the first thing you should do on a pre '05 CR125.

Still undecided, anyone got any solid evidence on what to do here?

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Been off the bike for a while but just did a rebuild and was thinking about the airflow topic again, does anyone recommend the Uni Air Box Vents? I was thinking about these but after doing a fair bit of reading some people say drilling the airbox is completely unnecessary and some say it's pretty much the first thing you should do on a pre '05 CR125.

Still undecided, anyone got any solid evidence on what to do here?

I definitely recommend drilling the holes in the box, once done its something you wont reverse. The CR airbox is somewhat restrictive so all your doing is let it breath better.

If you're paranoid about it letting in extra dirt/water in, put some fly sreen mesh over the holes and some thin foam over that (which I have done) and have noticed a gain not something to rave on about but a gain is a gain on these CR 125s of ours.

Edited by noysy1

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