'81 gs650 exhaust question

[rahlberg]

Does anyone know if the exhaust pipes are tuned to the '81 GS650 engines? Does it provide a set amount of backpressure on the engine? I as ask this because I'd like to replace and re-route mine but am worried that if I don't get the length and diameters exactly the same, the engine may not run correctly.

Any thoughts?

Thanks everyone!

Russ

[TheCafeKid]

Yes, and Yes. Messing with them will cause need for tuning of carbs. UNLESS you pick up a aftermarket kit, such as a Vance and Hines pipe, specifically designed for you bike. Usually they are set up to rock, tho some will require minimal tuning. What did you have in mind?

[rahlberg]

I picked up a used 650 and the pipes are pretty rusted over. Rather than throwing down $$ for a whole new set, I was looking into hacking off the mounting plates and welding up a new set.

How exact are they tuned? If I stayed to the same diameter and length (and used the muffler which for the most part isn't rusted), would I be in good shape?

[Dave8338]

I picked up a used 650 and the pipes are pretty rusted over. Rather than throwing down $$ for a whole new set, I was looking into hacking off the mounting plates and welding up a new set.

How exact are they tuned? If I stayed to the same diameter and length (and used the muffler which for the most part isn't rusted), would I be in good shape?

Tuned may be slightly too correct. Though they are set for restriction / back pressure, they are not "tuned" in the sence that a two stroke exhaust can be tuned for cc-displacement, RPM range, and harmonics.
On a four stroke, your main concern will be correct back pressure. If you are using the stock mufflers, any additional length that you may add to reroute the pipes is going to have little if any affect on your driveability, as it pertains to needing any special resets on the carbs. The one thing to keep in mind is that you dont want the down pipes on two cylinders to be TEN feet longer that the other two or use 4" ID pipe on one side and 1/2" on the other...:? obviously over-stated in my examples, though you get the idea. Ideally, all down tubes size and length would be exactly the same.

[waterman]

Rahlberg, welcome to forum. Some of the members here have replaced rotten mufflers with Harley factory units. These HD mufflers can be picked up cheap from HD dealerships where it seems every new owner replaces his stock unit. If you are not close to a HD shop, maybe surf ebay.

As far as tuning, I doubt they will need more than minor tuning. I am not a tuning expert by any stretch, but others here are. Again, welcome to group.

[tconroy]

Your plans of hacking off the rusted part and re welding will not change a thing.The important part is the fitting and mounting.As long as everything matches up you will be fine.Not changing the megaphones backpressure will not change anything. do a google search for a motorcycle junkyard in your area and you may get lucky.These 650 parts like a used exhaust are hard to find.You can get new if you got 400 bucks to throw away.