the quest for bottom end

[CR69r]

here is what i have wasted my money on so far in an effort to gain bottom end in my 2003 CR250:

pc pipe with shorty silencer
vforce 2
port job with decked head - race gas 50/50
yes i changed sprokets too - 13/50

the port job was really the only thing that added any bottom end worth mentioning. but unfortunately, it still falls short of a stock KX or RM.

i want to spend a bit more money on solving the problem before i throw in the towel and just go and buy a KX. I also don't want to spend money on an area that i already have - for example i'm not going to buy an FMF pipe.

i'm thinking of trying either a different throttle slide or a vortex ignition. how significant will either of these effect the powerband?
anyone tried these?

 

[DEX]

The Vortex ignition could help aswell as changing the timing I believe.
Also depending on how much you want to spend you can bump up the head mods and run it at a higher compression with pure race fuel.

 

[gonzo843]

Have you tried just putting carbon fiber reeds in? I had bad luck with the VForce.

 

[Crash 142]

I had bad luck with V-force on that bike, too. I went back to the stock reed cage with Boyesen superstock reeds (same performance as stock). The biked jetted much cleaner after that. I can't remember if I gained bottom end, but I think it helped a little everywhere.

I tried a PowerNow on that bike and didn't like it, but if I remember correctly, it did add bottom, but took away from top. Maybe with the stock reed cage and the Power Now you can get what you want.

The final cure I went with was a 2004 RM 250. Better bottom but more importantly much better throttle response. I think it was MXA that said the CR 'hangs at an RPM,' and that's true. The Suzuki is responsive everwhere.

 

[CR Swade]

I've got a Keihin PWK on the way, I've heard good things from people, hope its true. If it just cures the vague, cranky jetting and hard starting I'll be happy.

 

[steve125]

CR69 who did the porting??? The kind of bottom youre looking for is not in a pipe or reeds. Most of the problem is poor cylinder design.

 

[colin mitchell]

Re; Cr Bottom End

The UK bikes are just the same...I'm about to fit a flywheel weight [light] to give more traction and knock the edge off the "hit" also go tall on the gearing at 14/51. I'll let you know...

 

[Steve47]

Dude, first of all you own a CR250, don't try to find bottom end power as there is none! Neved had, never will. You can put all the money in the world in that thing and you won't get close to the bottom end of the KX/YZ. I rode a Reynard mods CR250 and it was fast as **** but still no bottom end.

Now if bottom end power is what you like, you might want to reconsider your bike choice.

 

[mtk]

Why don't you ask Eric Gorr how to get bottom-end power? If anyone can do it, he can.

 

[Lissa]

I had a '00 CR250 and I did get to ride a '02 CR250. My '00 had more grunt down low. Even with the mods I did it was still a little pale down stairs in comparision to a KX/RM/YZ though. Have you tried going up a tooth or two larger on the rear sprocket to put the hit a little lower in each gear? I usually need to go one-two larger on the rear on every bike I've owned to put the meat where it's needed, especially the CR. Try gear ratios before dumping more money into the motor.

 

[bedell99]

Truthfully at this point I would save your money. You have the same basic mods I did and I'm happy with my bike. I did find that running a good moto-specific race gas helped a lot with throttle response.(C-12/MR2) Other than that I think your maxed out.

Erik

 

[pace]

I agree with Erik..

I noticed a significant improvement in the bottom-mid transition after application of the PC Platinum and Shorty, but little or not discernible gain in low end. If you can't get the power delivery you want from that and the port job, you may be on the wrong bike. I've ridden several pre-04 KXs and personally hated the monster bottom end and premature sign-off, so to each their own.

-pace

 

[placelast]

I'm the least experienced to speak on this although I may remember reading in Eric's book the transfers' height need to be lowered. Since you've already milled the head, then that may be not an option anymore.

Eric did thus on a spare cylinder of my 250's - removed material from the base of the cylinder (as opposed to milling the head/upping the compression anymore than it was). The results were: essentially the same power response, but -everything happened at slightly lower RPM; and a little flatter throughout, yet these results were in the right direction with a little more net responsive off the bottom, or as some call it: chug.

So, sorry to say, the approach should have been a little different by leaving the head alone and milling the base of the cylinder. Maybe you can find someone willing to trade parts, and start over?

Give Eric a call and see if he can sort it out for you - otherwise look for a trade.