Question about Supertrapp and 'busa cans.

[Guest]

I moved this over from the Performance Mods section..got 90 views but no answers and I'm going to need to start fitting the exhaust in a few days....and I'm a total motorcycle newb so I need the input.

---[copied but rewritten]

I have a (mostly) '83 GS750ES with stock 4-2 exhaust, stock carbs and air box with Uni filter, CarbTune II on the way... I bought a complete Hayabusa exhaust on eBay for the cans and mid pipes and it looks like I'll be able to cut and graft the outlets from the 'busa header onto my 4-2 outlets and run the 'busa mid pipes and cans with some bracketry BUT is this going to mess me up at the carbs? I know bikes are much more sensitive to these changes than cars but thats about all I know at this point.


So if I graft TWO canisters from a 'busa onto my GS750ES is it going to breath too easy? I want to replace my rusty and dented megaphones with them but now I'm worried I'm going to be making it run lean or something.

Right now I want to get reliability and worry about adding power later...but since I need a new exhaust anyway....

Does anyone know if the Supertrapp 4-1's I see on eBay now and then fit under the GS750EF lower fairing and/or allow use of the centersand? I also have the EF plastic and I want to be able to go back and forth between ES and EF and I'm not willing to give up a centerstand at this point. I'm talking about the Supertrapp 4-1 listed as fitting the ES (4MSH-50752C). I've asked the seller but he doesn't know. It looks like I might be able to work a 'busa mid pipe and canister onto that pretty easy.

Thanks! I'm trying to learn....really!
/\/\ac

[DMPLATT]

I'd put money on it running different. Not really sure til you read the plugs. WHat I mean is that chances are it may run a bit leaner. But since you are staying with a 4-2, it may not change much. I don't think anyone can tell you for sure. It'll be a trial and error. It could also run richer, just depends on the Baffles in the Busa cans.

Now, as far as the Supertrapp, I got the header and can off e-bay. I already had a 4-1 system from the previous owner, just rusted and dented. I've tuned the Supertrapp using the discs and it still may be a tad lean, but runs great and my plug reads are decent. They are in the "OK" range, so I'm leaving it. The confusing part to me is that when I had my carbs off, they had stock jetting. I've still got the stock Airbox, but by all rights I should be higher on the mains.

Anyway, I was able to keep my center stand. WHat Supertrapp did was supply a bracket where you have to move the right side spring and Piggy Back it with the left spring. So, both of my springs are on the left. My '83 750E doesn't have a lower fairing, so can't help with that. Supertrapp DID answer my e-mail, so you can get the P/N and e-mail them to see if it appies to your bike.

I like my supertrapp, plus it hugs right under the right rear foot peg so it doesn't hit when hitting corners hard.

edit: My only complaint was that after I installed the Supertrapp I had this vibration, almost like a "TINNY" kinda feeling. Only way I got rid of it was to put a heavy duty rubber washer between where the can bolted on to the rearset. It's been fine ever since.

[mark m]

So if I graft TWO canisters from a 'busa onto my GS750ES is it going to breath too easy?

There is pretty much no such thing. A bit of back pressure seems to help wave tuning in the exhaust, but it doesn't take much to achieve that. Your stock header is probably restrictive enough to get what you need in that respect.

I want to replace my rusty and dented megaphones with them but now I'm worried I'm going to be making it run lean or something.

Now, it is entirely possible (even probable) that you will end up lean with the new cans, as they do flow a lot more air than your stock ones ever did. However, since you are stock everywhere else, it should be a simple thing to tweak the carburation to suit. At most, you should need to adjust the mixture screws and shim the needles a bit, and maybe go one size up on the main jets. You are not trying to get a fussy, high HP combo to run with a stage 3 jet kit and filters. All you are doing is fine tuning the factory setup, which has hundreds (maybe even thousands) of hours of development behind it. Once you have tweaked the settings, your bike will run better than it did new, since the factory settings were marginally lean as it was.

Right now I want to get reliability and worry about adding power later...but since I need a new exhaust anyway....

In that case, simply turn the mixture screws out a bit, shim the needles and leave the mains alone. That will get you really good for anything short of all-out racing and it costs almost nothing but a bit of garage time.

Does anyone know if the Supertrapp 4-1's I see on eBay now and then fit under the GS750EF lower fairing and/or allow use of the centersand?

I don't know about your 750, but I know that Joe Nardy has a stainless Supertrapp on his 83 1100E and still has the centerstand. Seems likely that they would keep that philosophy between models, but it is not a certainty.


Mark

[Macmatic]

Thanks guys! Thats the kind of into and feedback I needed!

Nnow to go make some cardboard patterns and trial fit things....

/\/\ac