XR680R What Jet fuel to install?

BuRP wrote:Здравствуйте Lawyer,

Got your bike doctored? Last I heard it was in intensive case, and was wondering if you found it a good nurse


Edit: OK, I only now see it's you who's asking - post a picture of that nurse please LOL.
Your best bet is "too large" and work down from that. I've read about someone having a 200 mounted, and this sounds awfully big - but he said he's happy. Best is to dyno the bike (with very good cooling hmm?), otherwise do some plugchops when WO.
Mind though, with htat big kit I'd rather have 'too big' than too small, but I hunch you alread know that

lawyer999RUSSIAN wrote:What Jet fuel to install?


Engine configuration:

680cc cylinder: nicasil plated
Falicon rod Xr's only
102.4mm Wiseco piston - 11.5/1 copression
Hotcams stage 1
K&N air filter
Full Exhaust FMF: Power Bomb, Power core 4
STANDART Keihin 78aBofV

temperature 85`F (30`C)
ALT 656ft (200m) (218yd)

Main fuel Jet 185-190 ?

BuRP wrote:A 'jet' with a 2mm hole is hardly a measuring device anymore - I wonder if you not should change to a Mikuni TM40? Plenty of needles & needle-jets available for it too, and the jet-size would be (my guesstimate) around 180.

AURORA wrote:
Did you have the crankshaft balanced? -Yes
Do you have the HRC cam timing chain and tensioner? It is installed but I do not understand why you need it?!
1 to 3mm over sized valves? -no
I am surprised that your not running a stage 2 cam with proper valve reliefs to take advantage of the compression. I do not understand you

You will probably have to switch to a larger bore carburetor TM40, FCR41(a pain to install...must grind on engine and reshape fuel tank to fit) or a bored out to 40mm X 42mm venturiEledlbrock quicksilver pumper carb -I know

You need a pumper carb for a street bike! -I know

Stock carb, the 185 or 190 is what I would recommend.

You need to install the 190 or larger (better to be rich than lean). Install a new sparkplug. Start bike (avoid idling) complete a full throttle high speed run in the last gear. With engine at high speed, engage the kill switch while pulling in the clutch lever. Hold in both kill switch and clutch lever until you com to a stop. Remove the sparkplug. Inspect where the insulator touches the shell of the sparkplug. To perform the inspection you will need either a sparkplug inspection flashlight, this is a fancy flashlight with a magnifying lens, or carefully cut the threads and part of the metal base off of the sparkplug. I know this technique, I set up on it. at 200 I have a white sparkplug.

Review this post:

http://www.xr650rforum.com/t1359-reading-your-sparkplug?highlight=Sparkplug+reading

What you and all of us want to see (please post pictures) is the carbon ring around the ground/base of the sparkplug insulator.