xs850-no start

[kustommusic]

I can relate to toolmans problems! Here's mine, I bought this xs850 after it's been sitting a little more than 1 year. Cleaned the tank,replaced all fuel -vac. lines,cleaned the carbs up(great info here on the forum!). Iv'e got spark,there is fuel in the carbs,checked both spark timing and camshaft timing. New battery, etc. The thing will not even fire once! even sprayed carb. cleaner into the carbs.while cranking.
I havent checked compression with a gauge yet but by holding a finger over the spark plug hole it seems the no1 cyl. is weak. A local Yamaha mechanic tells me low(more than 20%) compression in one cyl. will prevent this thing from starting. Has anyone experienced this? Steve Kustommusic

[srq68]

I have a 850 too, experienced some problems but not as much as yours.
Two things I can think of to check: make sure there is a good contact on the ground cable from battery to frame, a bad contact will let the starter crank but starve the juice to the ignition system. The other is to check the compression between the cyls with a gage. Your mechanic is right.
Good luck

[kustommusic]

Thanks srg68! In looking at things I found the intake valve was stuck in the open position. I think that during its time setting that was where the engine stopped. With a little tear down I was able to loosen the valve up enough to close when it's supposed to. I still dont have a working comp. guage, but, it still seems like that cyl. is not as strong as the rest. One other thing, while cranking the engine my helper held his hands over all three carbs. and the thing fired up! But only for a few seconds(2or3). I will definetly check the batt cables but I'm wondering about the carbs. again. Steve

[ratbyk]

Won't Start

Definitely sounds like a lack of fuel. Get an squirt oil can, fill it with gas and give a couple of shots into each carb. Put the oil can AWAY! from the bike and try and start again. If it fires you know that you have no fuel flow. Possible petcocks, kinked fuel line, plugged fuel filter. Needles and seat stuck in the closed position, plugged petcock screen in tank, no gas in tank.
Remember to remove the oil can with gas. If the bike backfires out the carbs you will have a flaming oil can.
Ken/Sooke
78E Ratbyk
82 FT500 "lilRat"

[kustommusic]

Here's an update, I decided to tear down the top end. The rings looked good but the cylinders showed some rust. The valves all leaked when I poured fluid into the combustion chambers. So everything went to the machiene shop. I have ordered parts from Bike Bandit and am now waiting. Hope this works!