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Something gave way...

sam000lee

sam000lee

Forum Mentor
Okay heres the story.

Bike was sluggish after I took it out this spring. Started up easily, nice idle. There was extremely slow acceleration and I was maxing out the throttle and the rpms were only slowly creeping up.

I pulled the carbs, cleaned them - although not meticulously, put new intake boots on since the old ones were junk.

Starts up again nicely, idles nicely. Same slow response when I took it out. A mile or two in, however, the bike starts to backfire like crazy. There's a trail of smoke behind me coming out of the right exhaust and I notice that a patch job on the muffler has blown off, also.

I turn and head home and suddenly the bike is alive again! Theres about twice as much power and the acceleration is totally revived and feels just as good as ever!

However, the right cylinder is still backfiring and while I'm looking at it, playing with the throttle and scratching my head wondering what happened the idle goes nuts fluctuating and the engine dies. I can start the bike up but the idle is all over the place and it dies quickly.
The right muffler is way louder and it sounds like something is loose or not right in there.

Did something in the carb that I didn't clean suddenly free up? Did something in the exhaust blow? Anybody know whats going on?

Its a 1981 gs450L.
 
Yes... a chunk of the gunk thats clogging the carbs internal passages came loose and shifted. Your carbs need redipped again I am afraid.
 
The one side is probably louder from the patch blowing off. The backfiring is most likely the cylinder FINALLY getting just enough fuel to fire and then not and then again....repeat ..repeat...repeat.
 
Okay that sounds a lot less sinister than what was imagining!
I'm still a little worried about the right exhaust - even between backfiring which only really happens when you revs it up it sounds way gnarlier than the left side. Both are usually pretty quite and it half sounds like a harley or something loud. Could something in the muffler have shifted (maybe causing that patch to pop off)?
 
I suppose a baffle could have broke off the end of the solid part of the pipe. Have to take the cans off and shake them to see if theres something rattling inside.
 
My bet is you have dirty carbs but the main reason you had trouble is the right side exhaust was plugged, probably with broken baffles. Now that the patch blew off your engine can breath again. Happened to a fellow riding a Honda once, his performance slowly degraded until the bike would not run. His right exhaust was plugged and not passing any gasses. So you need fuel, air, spark and a way for the burnt gasses to get out of the engine for it to run.

V
 
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Just cleaned out my carbs again and spent about 2 hours getting a good seal around the airbox boots. Again, it starts and idles easily and I can ride it around for about 15 minutes before it bogs down and the engine dies (had to walk it about a mile home!).
I patched up the exhaust a couple of weeks ago, after the poor response problem was already in full effect - so I'm not sure if the patch blowing off is related to whatever is going on. The right exhaust is still sounding strange so I think gustovh may be right about that being the issue.

I didn't know that the exhaust could be taken apart like that - how do you take the cans out?
Thanks for all your help!
 
Have you removed the petcock to inspect the screen? Is it plugged up with debris? Fuel tank cap venting?
 
Not yet, although fuel deprivation did come to mind and I experimented with switching the petcock to prime while this is happening with no luck. I have an inline fuel filter and I can see that there is plenty of fuel in it when the bike sputters and then dies.
 
gustovh said:
My bet is you have dirty carbs but the main reason you had trouble is the right side exhaust was plugged, probably with broken baffles. Now that the patch blew off your engine can breath again. Happened to a fellow riding a Honda once, his performance slowly degraded until the bike would not run. His right exhaust was plugged and not passing any gasses. So you need fuel, air, spark and a way for the burnt gasses to get out of the engine for it to run.

V
Click to expand...

+1, it's sounding like a clogged exhaust problem. Something came out, maybe it blew part of a mouse house out or something. There's probably a lot more of it in there.
 
It was the fuel line! The routing of the fuel line was pretty whacky and the fuel filter wasn't low enough under the tank. Some re-routing and I'm on the road for the first time since last august!
 
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