loss of power at high revs

[TJsBlaster]

I'm doing a top end in my son's stock blaster and had a question for some of you with Blaster experience. This is the only Blaster I've rode so I have nothing to compare it to (other than his KX85 which might not be fair). Here is the concern...when you roll through the throttle, it really seems to run great in a sweet spot (power band I suppose) but then sort of dogs out on the top end and you have to shift to keep it in this very narrow sweet spot. Any suggestion of what I should be thinking of doing to broaden the sweet spot while I'm into the top end? I was planning on a clean bore and hone job, replace the piston with Wiseco, V Force 3 reeds, and maybe replace the Mikuni stock carb with a Keihin (not the cheaper one) I think its a PWR?
Anything you guys could contribute would help. Is this normal for a stock Blaster? Would mild porting help? Should I go up in the carb size if I'm buying a new one anyway in case I add a pipe later?
Thanks in advance for any help!

 

[mr_3_0_5]

porting wakes em up...
pwk is the carb you want....ive seen people with mild mods run the 30mm.. id go bigger myself..
slap an exhaust.. i think your power curve will be alot better after these mods

 

[coreyownz]

get a good port job like a 30mm carb vforce 3's and a pipe get a right bend though like a factory seven from projectblaster.com dynoport also from site lrd and theirs a couple other good ones

 

[hickskateboarder]

yeah, if your gettin a different carb, get a bigger one. you'll probably feel a slight increase even on a stock blaster.

any aftermarket exhaust will wake it up. if your not planning on going big (porting, big bore, stroker) you'll probably be happy with an fmf, but if your thinkin of porting or something i'd get something else.

you could get a shearer from kennedy_power now, then if you want to wait a little longer to get porting you can, the porting and shearer pipe from kennedy really wakes the thing up. you won't believe it.

reeds are also a good mod. v-force are said to be the best, i have boysen 2 stage and am happy with them. for now anyway.

 

[TJsBlaster]

Thanks guys! A quick follow-on question:
Okay, sounds like you all agree - If I'm going to buy a new carb go bigger. So how big should I go if I only plan to do the mods I mentioned and get the pipe later? I want to use the same carb now as well as later when I do the pipe (just re-jet I guess?). I also need suggestions of who I should send the cylinder to for bore and hone with a mild port job to "wake it up" a bit. I want to keep the thing reliable - it's my son's machine. The power is a little on the lame side now. I'm riding a 700 raptor and he would like to have a little more "get up and go" like Dad.
So who can I send the cylinder to for quality work? What size carb for now and for future new pipe?
Thanks again for all the help!!!

 

[mr_3_0_5]

if it were mine id check into flotec, kennedy or wildcard..
my bike was done by CT. very costly tho.

my guess on the carb is 34 to 36mm

 

[2smoker85]

i have a 34mm, v force3, lrd exhaust, 1/2: spacer, and trust me it will be plenty "get up and go" for your son,mine has not been ported yet, so you want to go with a 34mm, if you plan on doing extensive porting or boring then go with a 36mm.

 

[quam]

firstly, don't bother w/ the bore and hone unless you think your rings are compromised. do a compression check to be sure. if you have good compression then boring the cylinder is a futile effort to find power. even if you bore the stock sleeve to it's max ( i believe it's like .080" over or something ) you wouldn't even feel the difference in power...which would be like an extra 10cc. so you'd go from like a 194cc cylinder to a 204cc cylinder. not worth the $200 you'd spend on a new piston, a bore and hone and all the shipping.
the pipe is the number 1 best way to modify your powerband. a 2stroke pipe is completely different than a 4stroke's. the wrong pipe will completely destroy your engine's power band. the right pipe can add 10hp.....sounds to me like you're looking for more of a trail type powerband, i'd HIGHLY recommend the shearer pipe like hick said. it's a LARGE increase in power over the stock pipe (and a even a very large increase in power over the factory 7 pipe i had on before the shearer). the power band is much wider, comes on a LOT stronger in the bottom and tops long. that is, it doesn't reach the peak then just drop off real quick. it's power from bottom all the way to the top and has great over rev.
the port and polish is also a huge mod that yields a LOT of power. you can talk to flotek, wildcard or kennedy_power about it. i always recommend kennedy_power, angus is easily the most engine smart dude i've ever come across and he has a couple dynomometers at his shop so he can fine tune his port and head designs.

 

[nd jat]

I had a blaster that was like that, in that the band was short and dropped off like it had a small sweet spot as you put it. Id atleast do a plug chop on the full throttle. it kinda sounds like it might be lean at the top of the throttle range. does it surge after you hit the power band?