04 xc 450r motor ?

[fultz416ex]

I have a 04 450r with mild head work, hotcam stage 2 cam, 13.1 wiseco piston, and a full fmf system. My question is when it revs out it doesn't hit the rev box like it should. It doesn't bounce off the box quick. It hits the box and revs outs real slow, like it hesitates slow instead of bouncing fast on the box. It runs real strong down low. Wish you could hear it. Any ideas what it could be? CDI box is stock. I am running a 200 main jet, so it is getting plenty of fuel on top. I went all the way up to a 210 main and it ran the same. Help!

[DnB_racing]

who did the head work? it could be that the combnation of pipe port and cam and air filter arnt working together,

[fultz416ex]

A local guy who works at a dealership. Where should I start?

[DnB_racing]

Originally posted by fultz416ex
A local guy who works at a dealership. Where should I start? find out what type of porting was done, if your intake was opened up and not enough exhaust its more of a bottom end port, and might not work well with high compression piston and a stage 2 hc
if he just went in and cleaned it up sometimes more damage can be done then good,one way to check is by putting air lid on and see if it makes it worse or better..

just checking have you done a plug chop to see if your jetted properly, what happens at a 190 main?

or your valves might need replacing, if your intakes are leaking by it will definitely affect how it revs. do a leak down test, to check your valves and rings and gaskets, you could have a head gasket leaking, many things can cause loss of top end, including fuel, filter,rings, weak spark, bad wire,...
you have to try and narrow down what was done and when it started to be able to narrow down possible solutions

[fultz416ex]

Valves are all new, piston and rings are new also. I will try a 190 and see where my jetting is with that. Also I will find out what was done with the head. Thanks.

[airmobile101]

I'll take a stab at it. If jetting is spot on, then I would start questioning that exhaust your running. With the current mods you have, that pipe is hurting more than helping. You need a better flowing exhaust IMO.

[fultz416ex]

Headwork was for all around power gain. I have a new coil I will put on and install a new spark plug. What is wrong with the exhaust?

[DnB_racing]

Originally posted by fultz416ex
Headwork was for all around power gain. I have a new coil I will put on and install a new spark plug. What is wrong with the exhaust? if porting is for all around power, then its was ported for power,and you might loose top end,
was the porting done by someone that understood what you have in your quad, and did you tell him what you wanted?power and top end are completely different,

also as airmobile has said your pipe is more of a low to mid range type of pipe, but your cam is a mid to upper range,it sounds like your port was done for more torque then high rev, between your power porting and pipe I think your getting chocked up and loosing top end.. If it were me I would trow a stage 1 cam and take advantage of the power gain from your XC porting,and I would get a better flowing exhaust

but that's just an idea since I dont have all the details, and the quad actually in front of me.... it could be something entirely different,
every modification that you do will help one area but compromise another, you cant have a drag racing xc machine, when you add in one area you take away from another

but if its not your jetting or fuel or spark,
then it must be a flow issue!

[airmobile101]

Heres the deal with pipes....... FMF, HMF, Big Gun, etc................ are all great pipes with a stock to lightly mild engine, but after you start tossing on high compression, stroker, porting, etc. The above exhaust start loosing on the top end compared to a Dasa, Rossier, LTE, Terry Design Concept, etc......... Its mainly the header and mid pipe that needs to be changed out.

I personally know this because I ran a Big Gun EVO and a HMF Competition series exhaust on my 07's before I put the HC pistons in. After I put the HC piston in, those pipes would fall flat on their faces on the top end. Couldn't even get it to hit the rev limiter in 4th. Then I tossed on a Rossier and WOW!!!!!!!!!!!! What a difference. Revs out and everything. Now, thats just my experience, and Im not trying to tell you thats the problem, but its worth checking into.

[fultz416ex]

Thanks for all the reply's. Guess I will start looking for a pipe. The wife will be happy now! LOL. Going to try a few little things before I do that.

[250RXCrider]

I have very similar set up with hmf exhaust and I am running a 180 main. I would try dropping your main jet to something smaller.

[fultz416ex]

I think jetting was the problem. I dropped the main to a 185 and took the screen out of the air filter. It revs better and hits the box like it should. Haven't ridden it yet, but it sounds better.

[250RXCrider]

Originally posted by fultz416ex
I think jetting was the problem. I dropped the main to a 185 and took the screen out of the air filter. It revs better and hits the box like it should. Haven't ridden it yet, but it sounds better.

I forgot to include I run the HRC air box lid on my set up. Good luck