GS650 Tuning help

[Guest]

I've been rebuilding GS's for a while and this 1981 GS650 has me a little puzzled. The air box on the bike was shot so I put on the individual after market filters. The bike starts fine and idles nicely but as soon as I increase throttle, it bogs down. It sounds like it's sucking air hard. I checked the carb to intake boots and had one leak, fixed that. Is there some adjustment I need to make since I ditched the air box and went to individual filters? thanks in advance.

[BigD_83]

Yup,

just like any of these GSes, removal of the airbox is going to result in a large increase in the amount of turbulent air they are gulping. You're going to have to up the mains at least two sizes, possibly more, to compensate, and fiddle a bit with the A/F mixture, as you are probably going to find you are a bit lean at idle.

Your best results will likely come from getting a tapered needle (a la Dynajet)

[Charlie G]

What he said ...or find or fix an air box.

cg

[koolaid_kid]

BTW, what brand of aftermarket filters did you select?

[tom203]

You'll will likely need decent pod filters and a dynojet kit to simplify tuning and get it to run nice.

[bjrpkr]

Thanks for confirming what I suspected. I ended up getting some KN knockoff filters which probably was a mistake. Does KN make a replacement with 'restriction' I guess you'd say? My old air box was shot, deformed. Thanks again.

[koolaid_kid]

Unfortunately, pods = jet kit. The CV carbs require an aftermarket kit, DynoJet is the most popular. APE also sells K&N style pods for a bit less coin. All the other knock-offs have been found to be extremely difficult to dial in, jetting-wise.
If you do not want to go through the hassle of re-jetting (and it is a hassle) then try to find a gently used airbox and go back to stock.

[bjrpkr]

I should kick myself for throwing out the old box, I probably could have salvaged it, oh well. That sounds like the way to go because I really don't want to mess with rejetting.

[tom203]

I always tell the pod wantabes to save their airbox stuff. Hard to find for someone having second thoughts. There are a couple 650 airboxes on ebay now, but neither had the matching air filter box from what I could tell.

[Winterstein182]

Jets or not?

I put pods on this morning just to try (they were free), and the bike runs good enough. Should I go up to 120's or let sleeping dogs lie. It's a 650L and I have 110's currently. Let the controversy begin!

[BigD_83]

Plug chops are your path to enlightenment

[gustovh]

I might have a stock air box.
V

[Winterstein182]

Plug chops?

[koolaid_kid]

From BassCliff's site: Plug Chop method
Although it refers to VM carbs, it is very similar to the method for CV carbs as well.