new to the site 82 Seca 400. intro and questions

Sub Zero

staying orginal
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Orlando FL
alright im brand spankin new to this forum. after a little bit of lurking it seemed like the best place for me to introduce my XS400RJ. i picked it up about a month ago for 300$ to fix up and replace my current commuter bike (XR650L). so far im pretty happy about it. not too fast but im lovin the constant 50 - 53mpg.

When I bought this bike it had a rusted out tank with a hole in it about as big as a clenched fist. I had intended on repairing it myself with fiberglass but after a little bit of poking and scraping and cleaning up the rusted tank its just totally shot and any attempt i would make to fix it would very likely be unsuccessful. So I had a spare XL600R tank in my shed full of spare parts and crap and luckily enough it fits just fine. looks like crap but it does the job and at least i can ride it.

after doing a complete carb clean via simple green the bike is running good. but heres my problem: bike wont go any faster then 85mph. gps verified. Before i had bought the bike I did a little research on it to see the mileage they get and how much balls they got and was happy to hear from many different people and websites that the bikes top speed is between 100 - 107mph. I think the problem is a lean condition at very high rpms. ive done a plug chop and they look alright. maybe a little white but otherwise mostly tan. but im not sure if that could cause me to lose about 15 - 20 mph out of my top speed on a 400?? the sprocket sizes are stock. any suggestions on jetting?? (hope nobody on here is too picky about bad grammar) :)

oh and since all threads are useless without pics.....


stock airbox? check your filter and the snorkel to the airbox. look for obstructions. otherwise clean your main jet and shim your needles with a washer...
stock airbox? check your filter and the snorkel to the airbox. look for obstructions. otherwise clean your main jet and shim your needles with a washer...

yes stock airbox. filter is OEM and brand new. I think the airbox snorkel might be removed?? not exactly sure but it dosent look very restrictive to the airbox. Shimming my needle would affect me in the midrange, but not up top which is where im not getting much power. never hurts to try though. the only thing thats stopping me from taking the carbs out again is how difficult they were to get back on after i had cleaned them. they were basically taped on from the PO and the intake boots did not match up with the air horn at all and they were bent all out of shape and did not want to go back on without a fight.

I think the fact that my mufflers are not stock might have something to do with my lean condition. they are just el cheapo universal ones from a JC witney catalog. Im gonna try to locate some original ones and replace the round speedo and tachomter gauges with the square stock ones. maybe in the future find myself an FJ600 front headlight fairing to fit on my XS.
original ones are welded onto the stock headpipes. good luck with that. If you replace the gauges, I want the round speedo...PM me.
When I go over 40 MPH my engine seems to be screaming and I don't want to push it any farther though it has the power. With a red line of 10K, what is the RPM in 6th gear on a level surface at 55 MPH? Original tach shot, going to add aftermarket. TIA, Phil