'83 XT550 Acting Funny

No, it's not telling jokes and juggling.

I recently put a used Supertrapp exhaust on my '83 XT550 to replace an exhaust that I got stuck with after going to a local shop in a pinch when the Supertrapp that was on the bike when I bought it fell off on the freeway. The exhaust the local shop kludged together was a piece of junk and was basically an open pipe. It didn't muffle anything and back pressure was non-existent.

All things considered, I am very happy with the recently aquired exhaust, as far as sound attenuation goes, but I am missing quite a bit of top end. This muffler only has three discs in it, and has really put a damper on the airflow through the engine.

The "acting funny" came in when I took the bike out for its first longish (30mi) ride after installing the new exhaust. Everything was going well until about 15 miles into the ride. As I slowed down to 25 mph, while passing through a local park, the bike started to chug and sputter a bit. As soon as I was got back on the throttle leaving the park, it smoothed out. As I started the homeward freeway run, I noticed that the bike would surge, and seem to have tons of power, then it would calm back down to it's docile 65 mph, post new exhaust, top speed.

Here's my theory: The restrictive new exhaust has brought me to an overly rich carburetion mixture. If I'm not totally crazy, then adding some discs to the Supertrapp and opening things up should fix things. Am I off base in this thinking?

Edited by rocky-in-cali

what size disc? 3"--4" ? if 3" at least 12 disc--4" 6-8 disc--start with the high # of disc and then start removing them------they are not quiet.

how do you get a supertrapp to fit a 550

anytime an exhauts is modified - as in increasing flow the mixture becomes leaner because exhaust gasses are escaping quickly and new frsh charge of air and fuel is being pulled in by the intake, there is little to no left over exhaust in the fresh charge, mostly 02 (oxygen and the same amount of fuel as was used for the former exhaust) Check dynojet for a kit, and or start going up one on your main and pilot also lower your needle one notch.

Someone on here must have the gouge for jetting and aftermarket exhaust on your bike.

But that is why she is acting funny, it can breathe very well, but is lacking fuel

How does the spark plug look?

and tell your bike to quit acting funny - it's no comedian. ;-) it is a THUMPER. :-)

Hi Rocky:

I agree with you that your bike is running rich. Sluggish acceleration and top end is typical of a too-rich mixture, and the sudden acceleration under high revs and high load is caused by an occasional reduction of fuel level in the float bowl when the engine is working hard. This reduction in fuel supply momentarily leans the mixture causing the bike to "lean surge". This effect is typical with a rich running bike that is using more fuel than required at open throttle.

As you know, there's lots of fixes including changing to a smaller main jet, improving the intake air-flow, or reducing the silencer back pressure. Lowering the needle position might help too.

shot in the dark....


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