GS450 with K&N, which size main jets?

[Guest]

This winters project is installing K&N pod filters on my -81 GS450ex (the old air filter box was a mess!)

Question is: At what jet size do I start trying?

I know this is trial and error, but maybe someone of you have done something similar?
The bike is stock, except from new filters and unspecified, megaphone type slip on's.
Oh! and its BS34ss carbs w/117.5 main jets orig.

[KEITH KRAUSE]

I would say 135 mains would be a starting point. Don't forget the jet needles. Yours are not adjustable, so you'll need a jet kit. You spend the majority of riding at 3/4 throttle and below, so the needle circuit is too important to forget. If you don't raise the needle a couple of positions, you WILL run very lean at these throttle positions. You may also have to adjust your mixture screws a little.
With a jet kit, they provide you with a choice of mains and they give you jet needles,etc.

[robinjo]

Keith, those non-adjustable jet needles that you speak of, is that so for all countries or could it be US specific? Every bike that I had the carbs apart of (750,1000 and 1100) had adjustable needles as stock. I never had my 450 apart, because it blew the engine, it was a Canadian import so I would have been interesting.

[first timer]

my 550 (USA) had cv style carbs and they did not have adjustable needles, try to find a jet kit, k and n may still have some left for cheap. a kit would make your life alot easier, or maybe some of the other guys who bought jet kits for a 450 can give you a parts list and you can order every thing in peices.

ryan

[KEITH KRAUSE]

Very good point Robin. I forgot about him living in Norway. They may be adjustable. He needs to check his needles. I suggested the needle changes because he did'nt sound aware of their importance. He seemed to only consider the main jets.
blo, if you don't have adjustable needles, get a jet kit and let us know what the "base setting" suggestions are. If you do have adjustable needles, try raising the needles 2 positions by LOWERING the e-clip 2 positions/notches. Make sure any spacers/washers go back on the way you found them. Install larger main jets. Make sure you don't have any intake leaks from loose clamps, bad o-rings in the manifolds, etc. Synch' your carbs and test. Get plug reads. Let us know what happens.
Thanks Robin. Two heads are better than one.

[Billy Ricks]

He probably needs to drill out the plugs over the idle screws too. Be careful drilling them out so you don't ruin the threads. Synching and adjusting idle settings is easy on a 2 cylinder bike. You don't even need the tools you would normally need. Just run the bike on one cylinder at a time by pulling the cap off one plug. You'll have to turn the throttle stop up to make it run on one cylinder. One carb will have it's own idle speed adjuster. Adjust that carb last. Make adjustments for the best idle with the idle screw and check idle speed. When you adjust the carb with it's own idle speed adjuster you want to have it end up running at the same idle speed as the first. You need a kit for the needles to ever get things right.

[blo]

Some historical facts: in Norway 1981 the emisson regulation were not all that modern/strickt. This meant that the CV carbs came with all options, such as access to both idle screws and adjustable needle.
As fore my knowlege of carbs, I know how to sync., adjust float height and general maintenance. I've been reading up on tuning from these pages, and other sources. Unfortunaltely I'm currently writing my master degree in a university, while my bike is somewere else in winter storage. It will therefore be some time before I can work on it.

This said, the reason I brought up the jet size question is that the first jets I recieved from my supplier were wrong(to large diameter), and he had sendt me 122.5 jets wich to me sounds to small. I therefore wished to have someones second opinion on it before ordering new ones.

Thank's for the most wanted help!

[Dink]

blo you need to be aware that all jet and needle manufacturers dont use the same numbering system a 112.5 Suzuki jet may be only 102 in a Dynojet kit for instance (BTW I am NOT saying that the crossover is as stated)
Dink

[blo]

Really?
I didn't know that, thought all sizes were the same. Something like the diameter....
Maybe my dealer is right?
Anyone?

[KEITH KRAUSE]

Hi. My suggestion for 135 mains is for Mikuni main jets. If you don't have adjustable needles you'll need a jet kit and they supply you with a choice of their own main jet sizes. My 135 suggestion is of course a guess. You should always error on the richer side when jetting. In this case, I'm guessing the closest I can considering I've never actually re-jetted your model. Good luck and let us know what works when you get to it.

[Detman101]

Keith, those non-adjustable jet needles that you speak of, is that so for all countries or could it be US specific? Every bike that I had the carbs apart of (750,1000 and 1100) had adjustable needles as stock.

My Gs750L didn't have adjustable needles stock. I had to use a Dynojet Stage-3 Kit on the carbs.

Dm of mD

[Anonymous]

blo you need to be aware that all jet and needle manufacturers dont use the same numbering system a 112.5 Suzuki jet may be only 102 in a Dynojet kit for instance (BTW I am NOT saying that the crossover is as stated)
Dink

Dink's right, Mikuni's number system is different from Dynojet's. Found thet out the hard way 8O