GS450 with MAC 2-1 carb question

[lookoutdriftmike]

Hello, my name is mike and I just got a GS450S. Looks like someone wanted to make it a race bike or fancy streetfighter or something (oil cooler and tomasselli clip ons, steering stablizer). I got it running but it's hit or miss sometimes it idles great sometimes i have to feather it to keep it running. When I first got it, it would not start and stay running,so I pulled the carbs and after searching figured that they were not synced AT ALL and the idle mix screws were waaay out. fixed that and it runs decent. now I am wondering, it has a stock airbox but a MAC 2-1 pipe on it and there is no baffle installed. end cap is there but no wrap or anything. should I think about re-jetting (it still has stock jets)? the plugs look like it's leaning out a little at the top but it runs really strong, and I mean stupid strong I would swear that the motor has been rebuilt considering there is absolutely 0 blowby and 23K on the clock. I have installed an inline fuel filter to keep muck out of the carbs and the tank is shiny inside. I just pulled the carbs again and checked and there was some gunk in the bottom so I will be reassembling it tomorrow and taking it for another run. I was thinking maybe one up on the main jet just to be sure (can I hurt it by running rich or just foul plugs)? just wanted a second opinion.

 

[IanFrancisco]

Sounds like you've answered your own question. Too lean equals too hot and in the old 2-stroke days holed pistons were not uncommon. This is a similar old school aircooled motor to those RD250s despite being four-stroke. The S is a rare model, hard to find these days, but luckily identical to an E model except for the fairing and bar-end mirrors. Mine even has little black rubber plugs in the standard mirror threads on the perches.

Running a hi-flow exhaust without rejetting is not a good idea, especially if you like to rev it out. I rarely use more than 7.5k rpm. Some would call that short-shifting. Running too fat a jet is as bad as too lean and uneconomical, if that matters, which it does to most of us these days.

I'd like to see some pics of the oil cooler and cafe upgrades!

 

[450FREAK]

mac 2-1

mac 2-1

The Mac 2-1 exhaust was made as a replacement for stock, it should not need to be rejetted. Sounds like the problem is no packing, lack off proper backpressure. You should repack it and reset carbs to factory specs, see where that gets u. I have a 81 450 with mac and pods, k&n pods or others for that matter require jetting, mac pipes did not as they have close to same backpressure as stock. I am currently running with stock air box because only noticable difference with pods was sound of intake and more fuel consumtion not to mention the price of jet kit from dynojet. Waste of my time and money for very very little proformance gains about 4-6%(about 2hp) but about 12% less fuel economy and less reliability. Hope your bike gives you years of enjoyment as has mine. Keep one finger free for all the haters:-D

 

[doctorgonzo]

eh, some people like pods, some don't. I think they
A. Look really, really cool
B. Mean I can pull my carbs in about 3 minutes as opposed to wrestling with the airbox
C. It's all relative, 6% increase on a 90 HP bike (like mine) is a fair bump in HP.