flames out the exhaust...valve clearances and other questions

[BigD_83]

I'm following/participating in a thread on ADVrider where a fella is having running issues on his DR350SEx.


He claims the usual:

Nothing touched since running well, just started running poorly one day (stumbling/bogging with throttle)

Backfiring through carb and into airbox

Valves checked and clearances fine; asked repeatedly, stands by his valve check, no reason to doubt him on this.

A bunch of other things have come up, but the latest in the saga is flames shooting out his tailpipe. To me, this still screams valve problems.


My question to this forum:

Can valve clearances check out okay, but the valves still hang open?

[Agemax]

the only possible way i can think of a valve hanging open is the stem is slightly bent, but i cant see it really...may be wrong!

[BigD_83]

I thought the same thing (bent valve).

There was a moment in the discussion where I thought he may have hydrolocked (could one do that without realizing what was happening (?), possibly bending a valve), but I would have thought more damage would occur.

[Agemax]

I thought the same thing (bent valve).

There was a moment in the discussion where I thought he may have hydrolocked (could one do that without realizing what was happening (?), possibly bending a valve), but I would have thought more damage would occur.

a hydraulic lock up = BIG BANG, lots of damage.....you have no choice but to realize it

[Nessism]

Most likely the bike is misfiring so the unburn fuel is collecting in the exhaust and igniting.

[BigD_83]

a hydraulic lock up = BIG BANG, lots of damage.....you have no choice but to realize it

Thanks for the confirmation on that...

[BigD_83]

Most likely the bike is misfiring so the unburn fuel is collecting in the exhaust and igniting.

Thanks, Nessism.

He's been pointed down that road as well, but has yet to find his answer.

The question in my OP about the valve was the one question to which I didn't have an answer, and I've been thinking the whole time that the valves are involved in the problem. It could just be misfiring/mistimed firing as well (exhaust valves hanging open)

I'll come back with what he determines to be the root cause of his problems, if/when he finds the solution.

[TheCafeKid]

I've read on here, but only seen once, where valves with heavy carbon deposits can be checked and deemed to have good clearances but then a couple of turns of the motor, when checked again they're not the same, or are out of spec.
I wouldn't say that this is likely, but one of the things I HAVE learned in the handful of years tinkering on these bikes is that the phrase "That SHOULDN'T be the cause" or something similar to that are never to be uttered in my shop. Hahaha. Once, after fighting with a cockhandedly modified GS750 my ex-roomie had attempted to get running, I nearly beat him over the head with whatever tool was handy because he kept saying those words instead of actually checking to see if the Chevy ignition coils he had Jerry-rigged to the bike were actually the cause of his ignition problems. "They SHOULDN'T be the problem.."
They were.

Basically, I would kindly suggest to him that if he has exhausted all of the normal explanations to the root of his issue, double checking them all again, one at a time, would actually be a good idea.
I do agree with Ed that mis-timing/misfiring and the subsequent ignition of built up vapor in the pipes is one of the more likely causes of the flame throwing pipes. But I would also be concerned about what is causing the sudden misfiring if the bike was running properly so recently and he'd done nothing to change that.

Besides the fuel and ignition systems themselves, I would suggest looking at the charging system and components related. Perhaps the battery isn't supplying the coils with adequate voltage to fire every time which could possibly cause that?
Did he happen to mess up his cam timing while adjusting the valves?
Etc etc.

[Steve]

The valves might have perfect clearances to the cam, ... but is the cam timed properly to the crank?

It's not entirely inconceivable that the cam chain has skipped a tooth or two.

.

[Big T]

More likely cam timing than valve clearances - the valve has to be open during ignition for flames to shoot out

How's the compresssion?

[850 Combat]

I have experienced hydraulic lock once on a GS850G, my first one. A bad petcock allowed a cylinder to fill with gas and it locked on the electric starter. I hit the starter a couple more times and it finally rolled on through. It blew gas out of the pipe. I kept that gike for several more years, and thousands of more miles. Always detected or thought I detected a little vibration after that, and wondered if it ever so slightly twisted the crank or bent a rod.

[mrbill5491]

I have experienced hydraulic lock once on a GS850G, my first one. A bad petcock allowed a cylinder to fill with gas and it locked on the electric starter. I hit the starter a couple more times and it finally rolled on through. It blew gas out of the pipe. I kept that gike for several more years, and thousands of more miles. Always detected or thought I detected a little vibration after that, and wondered if it ever so slightly twisted the crank or bent a rod.

Anytime you get a hydraulic lock, pull the plugs out and spin the motor to clear it. You'll avoid any damage to the engine.

[BigD_83]

...and the mystery deepens,or unfolds, depending on one's perspective.

The owner pulled the head, and found a HEAVILY carbon encrusted piston and valves which I'm taking to be a sign of low compression. (Post #14481 in the thread below)



I haven't seen pictures of the bore yet, but I'm anticipating broken/displaced rings, and perhaps some scoring. It's been an instructive thread. Here's the link for anyone interested in checking it out:

http://advrider.com/forums/showthread.php?p=20372281#post20372281

RuggedExposure's issues start on post #14037 (ADVrider has some mega-threads that wander around, with multiple topics within the thread. I wish it was more streamlined like here)