Gs450, suggested jets?

[free99]

Hey guys (and gals),
I've got my bike working pretty much perfectly. It's a stock setup, using the oem airbox, bs34ss carbs, etc. I've changed the gearing though, to reduce RPMs at the highway speeds I drive at.

I'd like to get a bit more power out of her, she's got 115 main jets right now. I'm following the FactoryPro guide, unless anyone has better suggestions.
I'm trying to avoid buying excess jets I may not need, so would anyone have any suggestions on a good size or two to jump up to?

Thanks everyone.

 

[Who Dat?]

Unless you are having problems related to poor jetting, changing jets will not increase power.

The best thing you can do to increase power is to change your gearing back, so you are back into the power band.
Those engines DEPEND on spinning happily at higher revs.

That said, ... because of the ethanol in today's fuel and the fact that the carbs were set lean by the factory, going to a 117.5 main jet, shimming the needle just a bit and turning the pilot screws out about 1/2 turn won't hurt a bit.

 

[free99]

Alright Who Dat?, I ordered 117.5 and 120 main jets just to see how far I can get it. I've previously adjusted the pilot screws using a single colortune, that helped quite a bit though I'm still a noob at getting into the minutae of the carbs.

Re: the RPMs, I'm sure I need a bigger bike, but for now I wanted to reduce the RPMs at 85mph, as seems to be the going speed in SoCal.

 

[Guest]

I'm surprised the 450 will even get to 85, let alone stay there.

It has been a while since I have been out there, I did not realize that the speeds on the surface streets had gotten that high. I can only imagine what it's like on the freeways.

 

[free99]

I'm surprised the 450 will even get to 85, let alone stay there.

It has been a while since I have been out there, I did not realize that the speeds on the surface streets had gotten that high. I can only imagine what it's like on the freeways.

Oh, really? It's possible I get my bike just past 102mph per a GPS speedo and my phone every now and again. But I might be theoretical, just to avoid any legal issues. The 450s have quite a bit of juice to them, just need a little more. Famous last words.

 

[Grimly]

It's the 250 that will barely get to 85mph, not the 450.

 

[zuluwiz]

You don't need a bigger bike, you already have one. Get that 1000G up and running and you'll have all the power you can use safely on the street.

 

[Gorminrider]

...I've changed the gearing though, to reduce RPMs at the highway speeds I drive at.

...and thereby reduced your "power". Better to rev high. Max power from the engine is somewhere around 7500 rpm . You can't get blood from a stone and it's not a Harley.

 

[free99]

...and thereby reduced your "power". Better to rev high. Max power from the engine is somewhere around 7500 rpm . You can't get blood from a stone and it's not a Harley.

Don't worry Gorminrider, I made that choice consciously. There's a small feeling of resonance at speeds I tend to ride at, reducing the RPMs a little has helped tremendously. I don't really care about launching off the line at top speed.

Thanks again Who Dat for the advice on the jets, I'll be giving them a shot; you'll all be the first to know of success (or problems).

 

[free99]

Happy thanksgiving everyone. I've just cleaned and reassembled my carbs. Should I balance and adjust idle, air mixture, etc first with original jets, or do all that after installing new jets?

 

[free99]

Never mind, why wouldn't I do that stuff after a carb change. :watermelon:

 

[Guest]

I do believe you have just answered your own question.

If you set your mixture, THEN change the jets, you will have to set your NEW mixture.

 

[free99]

Hmm.. I've swapped only the jets, up to 117.5.

She runs ok at high RPM, until I hit WOT, then starts sputtering a little. If I relax my wrist by even a little bit, she's good. Lower RPMs, also sputtering, and difficult to keep running. Slightly better with choke.

Gonna check for air leaks, but this is pretty weird. I used my colortune on cylinder 1 (didn't have time for cyl2), she's misfiring almost every other cycle, even popped hard enough that my vacuum line popped off.

Sheesh.

 

[KiwiAlfa156]

Spluttering at WFO is rich on the main jet. Rolling off brings the needle jet metering back into play and back into correct mixture. A WFO plug chop will confirm. You only need bigger jets to compensate for more air. Unless you've modified the engine to flow more air, bigger jets will reduce power because the fuel air ratio is now sub-optimal (not enough oxygen to burn the extra fuel). Jetting sets the fuel/air ratio and is like Goldielocks -too rich bad, too lean worse, has to be just right.

 

[free99]

It's the strangest thing. I've put the original jets back in, tested for air leaks by spraying with starter fluid.. she's having a really rough idle regardless. Argh!

Colortune is showing a mostly blue, blue-green flame, I moved the balance around between carbs until I could get max RPMs at idle. Not sure what could be wrong, other than a clogged idle passage? She'll idle roughly for a while, but the rpms slowly decrease on their own over about 2-3 minutes until the engine coughs and dies.

 

[Hokano12]

Did you ever sort the issue? Are all the passages on the carb cleared out? I assume you have played around with the idle screw along with the fuel screws? How many turns out are the fuel screws? On my gs425 I have in 1 size up on the pilot jets (25), and 2 turns out on the fuel screws. Any more is too rich and any less the idle is lean and I?ll get some slight popping on decel.

 

[free99]

Found there are a few strange things on my bike that were modified by P.O, sorting those out to be sure I'm not starving the carbs of fuel.

For example the gas cap has a weird ball bearing valve inside it for ventilation, but it rattles like crazy and I presume it's missing a spring. Reason I know the PO got to it was the JIS heads on the plastic of the cap were stripped bad.

I'll keep you posted.