Help! I think I broke something.

Srawl

Srawl

XS650 Enthusiast
Messages
39
Reaction score
44
Points
18
Location
Austin, TX
So I was taking a leisurely evening cruise and everything was going great, at about the 40 mile mark I lost a lot power and my top speed dropped about 40mph...

I also noticed there was a lot of smoke coming out of the left exhaust pipe.

I limp it home and find oil is leaking out of the air filters and there is oil at the end of the left exhaust.

What did I do?
 
Possibly holed/cracked a piston. Sounds like a compression check is your first order of business....
 
Last edited:
That's a strong possibility, Jim, but maybe failed fuel control if OP is lucky--elevated oil level due to gas contamination (wrote that suggestion in the duplicate thread that OP should have deleted).
 
grizld1 said:
That's a strong possibility, Jim, but maybe failed fuel control if OP is lucky--elevated oil level due to gas contamination (wrote that suggestion in the duplicate thread that OP should have deleted).
Click to expand...

From grizld1:

Offhand, this is the first possibility that occurs to me: float valve or other fuel control fails in carb, fuel flows into crankcase, crankcase oil level rises, misting out the breather lines increases, breather mist fouls air filters. (Note to amateur theorists: don't embarrass yourselves by explaining that there's no pathway to the crankcase for fuel; too many of us have seen it too often).

I’ll check it out. I had no idea I duplicated, but I also don’t know how to delete threads.
 
Hi Srawl,
the first thing I'd do is a compression test because it's an odds-on bet your bike has holed a piston.
 
Hi Swarl. To edit your posts click on the three horizontal bars in the lower left corner. Just make sure you are working with the short thread duplicate. Not the long one
 
Well... did the compression test... right side is still good at about 155. Left is a whopping 0... so what does that mean to you all?

What caused it?

And where do I go from here?

As an FYI I took pics of the spark plugs. The left is very shiny and oily. The right has thick carbon build up.

E3EFCA49-2D8C-4485-902D-E3E33C92BAB4.jpeg Left

7E36F72C-BF18-4C19-AB6E-2058DD4D328C.jpeg Right
 
Srawl said:
How did I do that and how do I not do it again?
Click to expand...
Well... first we gotta find out if that's what happened. If compression is zero, there's nothing you can do with the engine installed. You're gonna have to pull the head apart.
If it is as some of us suspect... you had some detonation and blew a hole in the piston. The fuel air mixture in the cylinder is supposed to burn at an even rate... called a flame front. If I remember my physics correctly... at about a hundred feet per second for gasoline. If cylinder temp (in the combustion chamber) gets too high, that fuel air mixture flashes off all at once. It "detonates". Instead of a steady pressure buildup as the piston goes down on the power stroke, all that pressure hits just before TDC. It's more than the poor piston can handle.
It's usually caused by a combination of low octane gas and ignition timing too far advanced.... mix into that blasts at high power..... bang.
Edit: Too lean a mixture also contributes to detonation. But looking at your plugs... I don't think that was a factor.
 
Last edited:
Ouch! I was hoping for the best case, but as Jim and Fred figured, you drew the short straw. It's almost always the right piston that gets ventilated because the right cylinder runs a little hotter; this is only the second time after many postmortems that I've seen the left piston holed. But with OE breaker point ignition either points set can be set too far advanced. Be sure to check the timing governor (AKA "automatic timing unit," AKA "ATU"). If timing won't dial in at the retard mark without going too far advanced in the advanced mode, you've found at least one source of the grief. A quick search will tell you more and give you some fixes.
 
Superjet said:
Not nice at all...something to work on winter.
Click to expand...
Not everyone parks their bikes in winter and hangs out in igloos( got crusty old uranium mines to glow in here) Ride almost year round here... the trusty 68 Honda Cub a very good winter sled if I stay at base of mountains and avoid deep snow. Out here winter time good for riding because tourists are gone too!
 
Srawl said:
I’m in Texas, winter is the riding season...
Click to expand...
ahh you have even milder winters than moab...you have the winter jackalopes out there eh? Them and armadillos have me nervous about going to Texas...I hear those 2 critters wreak havoc on everyday life.
 
Last edited:
Moabite said:
In all seriousness though maybe buy a motor and install, then fix old motor?
Click to expand...

I was thinking about this option considering you can usually find engines for sale for close to the price I think this will end up being. My only issue with that is with my luck I’ll get another “project” engine...
 

Similar threads

C
New bike, The works
2
Replies
27
Views
2K
5twins
5twins
zrx1100
Filter/intake flow testing (with results)
Replies
9
Views
521
Kevin Werner
Kevin Werner
toglhot
74 TX650 build update.
Replies
5
Views
564
jpdevol
jpdevol
ForestHasAnXS650Too
New-Old XS650 Special journey - My initial problems
2
Replies
22
Views
521
jetmechmarty
jetmechmarty
fenbrancis
One Cylinder Just a Touch Too Rich
2 3
Replies
40
Views
2K
dps650rider
D
Back
Top