gs400 help

[78gs400cafe]

First off I'd like to say thanks for all the information i have found thus far. I recently purchased a 1978 gs400x. Bike is clean and runs fine. The previous owner hacked the mufflers off so now it is just running the two headers. To the best of my knowledge i dont believe it has been re-jetted. Are there any negative/damaging side effects to this besides annoyance? Ive been looking into getting an exhaust for it but seems MAC is the only available. If i bought the 2into1 that they offer what would be a good starting point to re-jet it? I dont plan on adding pods. This is my first bike so Im trying to learn as much as possible. Thank you in advance
Trey

[pete]

Welcome to the forums Trey, these little twins are great bikes! I have an '82 450E myself.

As for your pipes, you definitely want to get some sort of muffler on there as the GS' are designed to run with some back pressure from the pipes, and you'll definitely want to re-jet if you're not going to get stock pipes on it.

Currently, with no mufflers and no re-jetting, your bike will most likely be running very lean, which means it will be running hotter than it should and you risk doing ugly things like burning up valves. Best get that sorted sooner rather than later

The Mac's seem to be popular, but that could be due to availability. There also should be Motad ones around the place which are reportedly very good and made in the UK.

Now, speaking of valves, do you have any service history on the bike? If not, one of the first things you should do is check the valve clearances.

Also, the charging system on these GS' tends to be a bit dodgy, and if you have electronic ignition then you definitely want to check that out as the ignitors on the twins seem to be quite susceptible to carking it if the charging system isn't right.

If you have points, then that's a bit of a non-issue except that it will help your battery last a lot longer as well as making sure you don't blow headlight bulbs and things also.

Good luck with it, and I almost forgot to mention we like pic's and lots of 'em

Hopefully a very friendly fellow by the name of BassCliff will be along before too long to give you your mega welcome, and that is definitely worth a good indepth read.

[78gs400cafe]

Pete,
Thank you very much for answering my questions. The people here seem great. If i were to go to the MAC 2into1 what should i re-jet my bike to? I dont intend to run pods so the only modification would be the exhaust. Thanks!!

[pete]

That's a good question actually as it really all comes down to how free flowing it is compared to stock.

You may find little to no changes are required, but you'll need to do plug chops at different throttle openings to determine how it's running before working that out.

One site I'm going to use to determine jet sizes for mine is www.motorcyclecarbs.com. Take a look on the Support page, there are a few tips and things there that should be useful, in addition to all the stuff on BassCliff's site.

Seeing as he hasn't stumbled across this thread yet (you may want to introduce yourself in the GS Owners forum for the full welcome treatment), his site of awesomeness is at http://members.dslextreme.com/users/bikecliff