Possible Engine Problem

[Toecutter]

When I'm slowly spooling up from idle to about 1750 RPM, I hear what sounds like an intermittent 'clunk' (very mechanical sounding, like a timing chain missing a tooth) at the same time the engine stumbles, like a miss. This is easily duplicated when in neutral, but I've had it happen when pulling away from a stop. It vibrates through the whole bike. Today it happened while I was synching the T-bodies and I noticed the #4 (right hand) mercury bottomed out at the same time. Any ideas before I run it in for possible warrantee work (I hope)?

 

[SkooterG]

No idea whatsoever. But it sure doesn't sound very good.

Good luck!

 

[CISCO]

Intermittent how? Is the clunk sequential? Like a rotational clunk clunk... or a does it do it once and quit? And your saying the #4 carb loses vaccum and the slide drops?

 

[Toecutter]

The best way to describe it is it sounds like the rotational mass is hitting something solid, like a wall. It's only once in a while, like maybe once per accelleration cycle, but not every time I spool it up.

 

[Warchild]

No good... this is no good.

Take it in. Serious.

 

[nusman68]

Geez, makes me wonder if the crank is split/rotated on the one journal (are these cranks press-fitted like most bikes used to be?) But then it would have the noise all the time....let's hope its something 'stupidly simple'. :dntknw:

 

[zorkler]

i agree with warman dont ride it bring it in a.s.ap.

 

[radman]

A misfire in 4. The clunk would be the engine misbalance baring it's teeth when it happens. Very little flywheel effect on these engines, so a misfire makes it's presence known in a big way. At least thats what it sounds like to me, since it's not every rotation, and the vacumn drop in the cyl.

 

[markjenn]

Rad's got it. The "clunk" is not causing the misfire, the misfire is causing the "clunk". It's probably some little intermittent electrical glitch, maybe even a bad spark plug. It doubt it is serious. I'd do a resync, check all your vaccuum hoses, maybe replace the plugs. I bet that solves it.

- Mark

 

[twowheelnut]

Huh! I forgot all about this clunk. Mine was doing that, too. Every now and again at idle or very low rpm's. No rhyme nor reason, just clunk and then back to normal. Now looking back on it, I've not heard/felt the clunk since the plug change & TBS. Me thinks our esteemed colleagues above may have your answer...

 

[Toecutter]

Rad's got it.  The "clunk" is not causing the misfire, the misfire is causing the "clunk". It's probably some little intermittent electrical glitch, maybe even a bad spark plug.  It doubt it is serious.  I'd do a resync, check all your vaccuum hoses, maybe replace the plugs.  I bet that solves it.

intermittent electrical glitch - AKA Demonic posession? Might as well be with my luck at those. I had the problem with the old plugs in and changed them yesterday. It's probably somewhere else, but why the vacuum dump on misfire? I'll hook up the carb sync tool and do some more testing.

 

[radman]

May not be a vacumn dump-but a lean pop through the intake, which would appear as a vac drop. Or a late fire. Might not hurt to do a compression test. You might have a sticky exhaust valve there buddy, which could be a tick precursor.

 

[Ramblin Man]

I'm in the sticking valve camp. Loss of vacuum and a clunk? Thats a valve guys. Get the to the dealer ASAP.

 

[Ramblin Man]

And just out of curiosity, what grade of gas and what kind of oil are your running?

 

[SkooterG]

And just out of curiosity, what grade of gas and what kind of oil are your running?

Baaaad! Very baaaaad!

Just don't get started on the possibly defective knuter valves!

 

[Skippy]

The best way to describe it is it sounds like the rotational mass is hitting something solid, like a wall. It's only once in a while, like maybe once per accelleration cycle, but not every time I spool it up.

If you have recently changed the oil, and overfilled slightly, it may also be hydraulicing.

Too much oil under the piston on the down stroke would feel like it hit something solid.

Skippy

 

[FJReady]

Mine did a similar sounding clunk, usually when warming up. I felt it was a misfire or 'coughing' fuel related thing. Only noticed it one in a while, not every cold start. Problem went away when I changed plugs at 8,000 miles so I figured I had a bad plug or some related symptom. Hope it wasn't(isn't) anything more serious.

 

[radman]

Too much oil under the piston on the down stroke would feel like it hit something solid.
Skippy

A hydraulic lock isn't intermittent. It stops the motor now , often with major damage to internal components.

 

[CISCO]

And your saying the #4 carb loses vaccum and the slide drops?

HAHA I just read back to this post. Ive been working on carb problems all day, I meant Throttle body

Cutter, the question is.....does it do it often enought to duplicate for your dealer service dept? Something for them to chase?

I think these guys are down the right path.