wr 450 09 power loss

hi i am having a problem with my wr 450 2009. The big starts fine and runs great at low speed. Once i hit mid range it starts to bog down really bad. Just kind of has power surges. Bike was working great but i had to replace cyclinder and rings also adjusted exhaust valves to spec. I had factory jetting and tried going to 48 pilot and 168 main bike won't start so went back to 42 pilot and it starts fine, went for ride and power loss happened. went back to factory jetting and put restrictions back on still a little better but still has a bog

Can anyone help

hi i am having a problem with my wr 450 2009. The big starts fine and runs great at low speed. Once i hit mid range it starts to bog down really bad. Just kind of has power surges. Bike was working great but i had to replace cyclinder and rings also adjusted exhaust valves to spec. I had factory jetting and tried going to 48 pilot and 168 main bike won't start so went back to 42 pilot and it starts fine, went for ride and power loss happened. went back to factory jetting and put restrictions back on still a little better but still has a bog

Can anyone help

Not sure I understand what you repaired and why; Cylinder and rings, but no piston, wristpin, etc?

You have to describe your problem by throttle position and by rpm: like this:

" 1/4 throttle is fine in any rpm, but at 1/2 throttle the power goes away as the rpms rise..."

Then we can give advice without guessing.

I collapsed the rings and rebuild with new rings piston and cylinder.

Took it out for test ride and bike started good can rev it up to full trottle in neutral. @ 1/4" Still runs good. But @ 1/2 Trottle and up the bike starts to spit and sputter and won't increase in speed. This happens in 1 st and 2 nd gear didn't get any higher in gears.

I had a 168 main jet and went back to a 162 main

If you 'put the restrictions back on and it ran a little better' you had a rich lean condition. Reducing intake and exhaust will richen it up a bit.

Sounds like you have a major obstruction in the carb, a loose needle, or a vapor lock (gas cap not venting).

Is it possible you put the slide plate in upside down? The hole goes on the bottom....

checked the carb today everything was in right and changed caps made no difference, took the air filter out and it seemed to bog down more. have any more ideas. Also cleaned all jets and blew out all holes in carb.

Are you getting fuel into the carb??

yes can open the drain in bottom of carb and it flows free.

just wondering can it be a problem with the rings. Went i rebuild the engine i done a leak down test and at top dead center air was coming up around the timing chain. It wouldn't hold pressure at all. Took it of top dead center slightly and held the crank and it pressure up.

just wondering can it be a problem with the rings. Went i rebuild the engine i done a leak down test and at top dead center air was coming up around the timing chain. It wouldn't hold pressure at all. Took it of top dead center slightly and held the crank and it pressure up.

Are you serious? You felt compelled not to mention that your top end won't hold pressure, but you still wondered why it ran poorly??

:thumbsup::bonk::ride::bonk:

Sounds to me like a timing issue. I'd recheck that before messing with jetting more. You didn't try to do a "YZ timing" by advancing the exhaust a tooth did you? Think that only works on the older 450's. Might be wrong on that but search to be sure.

Tdc should have both valves closed fully and therefore hold pressure. No pressure at TDC means rings or open valves, neither are right.

Mike

i replaced the cyclinder piston and put 4 sets of new rings in it trying to get a leak test to hold. Everytime it is the same went by manual and everything sees good until i do a leak down test. Dots are lined up with cycinder head at top dead center. Valves don't leak on leak test it is just coming up around timing chain. Guess the rings are no good. It will hold a leak down test if i take it slightly off top dead center.

i replaced the cyclinder piston and put 4 sets of new rings in it trying to get a leak test to hold. Everytime it is the same went by manual and everything sees good until i do a leak down test. Dots are lined up with cycinder head at top dead center. Valves don't leak on leak test it is just coming up around timing chain. Guess the rings are no good. It will hold a leak down test if i take it slightly off top dead center.

Sounds like you did not mic the cylinder and piston to see if they are a match.

on the very top of the new cyclinder (yamaha OEM) and the old one (original off the bike new) there is a slighty bevel out can feel it slightly but no difference on calibers Can also see a difference in machining there on both. It is where the rings would sit @ TBC. Just wondering being on both cyclinders right from yamaha is it suppoase to be this way for some reason.

the bike has 60 psi compression test, i know auto decompression, and starts fine idles fine, in netural can be reved to the max. would leaking rings cause top end power surges and sputtering. Also when you do a leak down test should you ride the bike first or run it or can it be done once you put a new cyclinder piston and rings on

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