'88 xr 600 runs funny.

[birdhouse]

hello all-

i had to replace the engine in my xr 600 becuase a theif blew up the old one. it starts fine, idles fine, and even runs totally fine until the engine gets warm. at this point when you hammer down on the throttle there is a loss of power and the exhaust gets louder and deeper. back off the throttle and it runs normal.

detail- the bike has been uncorked and has a uni filter. i've been running midgrade gas. honda oil. NGK DPR9EA 9. a roost boost was also on the bike when i got it and have never scrwed with it. skyway cobra exhaust. jetting 170 and 68. my home is at sea level. i yanked the plug yesterday and it was pretty white (lean) this surprised me. i thought there might be too rich and this was bogging down the power, but apparently not. does anyone have any idea on what is going on here?

thanks for any help!

birdhouse

[birdhouse]

EDIT- pilot jet is 62 NOT 68.

thanks

[HeadTrauma]

First of all, take the Roost Boost off and sell it for a few bucks.

Second, try a smaller main jet like 162, 165, or 168. My bike has a 170 main with all of its mods.

The white plug is a little worrisome. Are you absolutely sure the carb and jets are clean? Is most of your riding done below 1/2 throttle? If so, then perhaps try a 65 pilot. Also, what groove is the needle on?

[birdhouse]

head trauma-

thanks for the info. are those roost boosts actually supposed to do anything? seems kinda hokey. i'll yank it for sure.

i need to yank the carb and check, but re-jetted it 4 month ago, and always run clean gas so i guess it would be clean but will check.

i ride almost all on the street. so every time the light turns green it it way past half throttle through 3rd gear. but then yes less than half while riding along.

funny how the plug is white yet i have a 170 in the main! i don't understand this! been super busy with work and gonna be out of town all weekend so i won't get to it til next week sometime.

thanks again!

birdhouse