250-500cc 360 Power Issues

had the 93 360 for over 10 years and now suddenly it has a flat spot off idle
sat for a while
changed nothing, starts fine, has a flat spot as you come on the pipe then goes like a bat out of hell
pulled the carb all seems fine pulled the pipe looked up the port all seems well
looked at the reeds they look good and seating
checked the compression and it's about 90, not sure of the gauge and have no way of checking it
seems if it was that low it should not even start much less pull that hard on top
plug color is right on, am i overlooking something???
if its lack of compression would it run that well everywhere else??

the most noticable thing when my 360 was down on compression was that it didn't want to start when hot. Other than that it ran the same with a little less power.

Did your problem happen all of the sudden? or did it start slowly and get worse? Have you checked your power valve lately? it could cause a bog if it's not anle to move smoothly

thanks, your @#*#, i mean uranys, it starts 1st kick hot, typical 2-3 cold
it sat for about 6-8 months, then i took it a 3 day ride, it never ran crisp but we were at 8000-8500 and its jetted for 5000
i noticed by the 1st hour it was starting to run less than perfect but rideable, by the end of the trip it was sour, i pulled the plug and it was dirty
jetted for 5000 and riding up to 8500 i'm sure it was a bit rich, well i put in a fresh plug, it really did not do the trick, when it's cold it is WAY flat
as in we rode for an hour took a 5 minute break and before it got hot it ran really flat
back to the question i think it started pretty much at once, i cleaned everything to be sure, new plug and will reassemble and try it, what's to lose besides time
i did pull the pipe and power valve cover, yes it moves freely

heres my 2 cents, i have a mac good quality compression testing kit i bought when i was a tech. it seems to read pretty accurate and ive tested a good 30 autos and maybe a dozen bikes with it. ima pretty good kicker, my 360 tested at 150 when purchased. i tore the motor down to fix and inspect things, measure cylinder etc. installed new wossner at got 160 psi upon assembly. i tested again after about 40 hours and now with a good film of castor everywhere and got 165. i have a ton of squish as i have it set per book. im sure i could probably take a whole 1mm out of my squish and it would not hurt anything and would probably have even more psi.
90 psi sounds awful man.
if it really does only have 90 psi its likely your throttle response has eroded quite abit and the top end revs but doesnt pull like it will with full compression. does the powervalve pull the front end up when youre hammering it in 4th?

not sure what's going on, must have cleared out a bugger when i pulled something apart, my guess a dirty passage at a jet, like the pilot
I put it back together as i won't have time to work on it till later as in the fall, out of curiosity i started it and took it for a spin,
runs great

Low compression means higher top end power, flat spot hust off idle could be rich, has the mix ratio changed or the oil changed sae rating?
10 years and this is the first issue?!? Ace cash that cheque now whip top end off replace rings if the thimg was rich that shouldnt be damaging to piston or bore lean states are the ones that destroy in seconds.
Bizzare that it was fine then all its got is a flat spot, you dent the pipe on the last ride?

found something disturbing while it was apart
that is the end of the pipe wearing through

weird! have to maybe grind the stinger down a tad and weld er up.

going to do a re-ring?

probably re-ring it in the fall or over the winter
that putting the house back together thing gets in the way

took the bike riding, it ran fine, but not as crisp on the bottom as it used to be so i will plan to replace the rings
down side, took a digger on the ride trashed my left thumb, actually re-trashed it 1st time was on a snowmobile and a tree well at about 8000'

thats the spirit..thats too bad about the thumb. bad thing to hurt. im planning to put my wxc throught its paces tomorrow, have a ride planned with a friend. its an event with lots of quads and sxs machines, with only a handful of bikes. we plan on crashing it and hes bringing his kdx 200.

Sounds like one to film justintendo

i really do need a go pro badly. its on the list with many other things, of course.

Cant fault my replay xd, half the price of go pro, but software on the pros is very good.
Plus loads of secondhand units on ebay.

You weld up that pipe 2premo? Any better?

Ouch! No reason you cant weld one handed.. May take a while tho and getting exhaust off will hurt.

will hurt, theres an understatement can't even pick my nose with that

Who the hell picks their nose with the left hand anyway?

it's much more polite, ever see someone pick with their right hand
then want to shake yours

Ha suppose but im covered in grease most of the time very few people try and shake my hand