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Discussion Starter #1
Moving from 400ex into 450r. The one I'm looking at has 11:1 piston w/mild port on head. Stock carb has been rejetted but sounds like everything else is stock. Is this a noticeable difference in performance? Also is there a big difference in performance between the 04/05 and 06+? Thanks
 

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04 had a 10.5:1 compression piston - 05 and up had a 12:1 compression piston, so if it had the compression ratio lowered, it will rev a bit higher, but suffer just a tad on the low end grunt - you won't feel the difference, but it would show up on a dyno run.

Carb was rejetted for what? Altitude? Air box modification?

Difference in performance between the 400 and the 450 is huge, but the biggest difference in performance for the 450 was between 05 and 06 - 04 and 05 were the same - 06 through 09 were the same - more changes to the chassis than the engine - most of the changes in the chassis was BNG (Bold New Graphics). Biggest changes from 05 to 06 was decreasing the size of the carb from 42 to 40 for better throttle response and bumping up the compression. The hot ticket is an 06 or newer 450; better throttle response, more low end grunt and better handling.
 

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Discussion Starter #3
Rejetted for the new piston, port and open air box I believe. So there is a noticeable difference in the 05 to 06 and up?
 

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A change in piston, porting or camshaft does not require jetting changes - running an open air box will affect jetting - changing carbs will affect jetting - changing the exhaust will affect jetting in the mid to high end only. If you have been riding an 04/05 for awhile and get on an 06 or newer you will feel the change in power, but will be more impressed with the better handling.
 

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Discussion Starter #5
How bad are the transmission issues that plagued the 06+ ? I read a lot about them
 

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Most transmission issues are caused by the operator not knowing how to shift properly.

Everybody thinks they know how to shift and 90% are wrong when quizzed about how to shift properly.

The transmission in almost all motorcycles and quads is a 'constant mesh' design. 5 speeds = 10 gears - 2 gears engaged perpetually - 1/2 of the gears are splined to the input or output shaft and their mates freewheel on the opposing shaft. A gear is selected by mating a splined gear on one shaft to a freewheeling gear on the same shaft - this effectively locks the freewheeling gear to the shaft the splined gear rides on and transmits power to the splined gear that is meshed with the freewheeling gear which causes the output shaft to turn.

Shifting is not this sequence: disengage clutch, operate shift lever and engage clutch - this can damage the engagement dogs on the gear attempting to mate with the freewheeling gear.

Proper shift technique is: disengage clutch, operate and hold the shift lever, engage clutch and then let the shift lever return to the ready position.

It takes a little practice, but in a short time it becomes routine.

I have raced a CRF250X since it's inception - I have an early production model (production sequence 000126) - the early production reportedly suffered from transmission problems - I know how to shift and the majority of shifts are made without the use of the clutch - I raced every weekend for 8 months each year since March of 2004 and while the engine has been rebuilt as a matter of routine maintenance two to three times a year, the engine has never been out of the frame and the clutch cover has never been off - zero problems with the clutch or transmission to date and the early models had transmissions issues (sarcasm). I believe the owners had shifting issues - not the vehicle having transmission issues. But I have a bad attitude - I can live with it.
 

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Discussion Starter #7
Wow. Good stuff!

Explain this a bit if you would :


Shifting is not this sequence: disengage clutch, operate shift lever and engage clutch - this can damage the engagement dogs on the gear attempting to mate with the freewheeling gear.

Proper shift technique is: disengage clutch, operate and hold the shift lever, engage clutch and then let the shift lever return to the ready position.


So you are saying to properly shift I squeeze clutch, lift foot, shift and hold it then release clutch and drop foot off shifter?
 

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Yep - either lift or push down, hold, let off clutch lever then let off shifter - that is the sequence. Will not eliminate transmission issues under hard use, but it will certainly decrease the likelihood of operator caused damage
 
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