New to me GS850 jetting questions

[qwqb]

Hey guys,

Just got my hands on a 1981 gs850. The previous owner installed a 4-1 exhaust and 4 separate air filter pods, however he did not increase the jet sizing. I am wondering what I should look into buying to accomodate for the exhaust and air filters.

I also have the stock airbox... is there a performance advantage to having the 4 separate pods? or is it mainly aesthetic?

Thanks!

[almarconi]

Welcome to the forum.

If you have the airbox .. use it. IMHO on that bike the performance gains from pods are not worth the hassle and added expense of rejetting. If you haven't already, check your valve adjustment and make sure your carbs are clean.

[qwqb]

That may be the route I end up taking. Can the factor jet sizes be used with the aftermarket exhaust?

Also, the bike does not currently run, so I am going to be tackling cleaning and rebuilding all the carbs pretty soon and hoping that does the trick.

[kdo58]

found this on another site,
We jet our sets for pods and aftermarket pipes. We use #122.5 main jets, #17.5 pilot jets and the jet needles 5DL31-3.

[almarconi]

That may be the route I end up taking. Can the factor jet sizes be used with the aftermarket exhaust?

It really depends on how restrictive the after market exhaust is. Your best bet is to perform all the routine maintenance on the bike (adjust valves, clean carbs..etc) and then see how it runs. If you need to make any jetting changes do some plug chops to see where you are.

[Octain]

That may be the route I end up taking. Can the factor jet sizes be used with the aftermarket exhaust?

Also, the bike does not currently run, so I am going to be tackling cleaning and rebuilding all the carbs pretty soon and hoping that does the trick.

If you're trying to run the bike with aftermarket exhaust you MIGHT be ok running stock jet settings but if you're using pods and aftermarket exhaust you'll be very lucky if the bike even starts up.

If you dont wanna spend the money on a Dynojet stage 3 jet kit then put the stock airbox back on the bike, with a good/new filter. Assuming its in good shape.. Be sure its sealed correctly.

Did you replace the O-rings on the intakes?
These bikes have very touchy intake systems.

Im not sure the pods actaully have any performance gains but they sure do look better that that uglyass stock airbox.(my opinion)

One more suggestion, search your questions. This subject has been beat to death.

[Steve]

#2 son's bike (see sig) has a header of unknown origin and stock airbox. I am currently running 120 mains (stock is 115), stock 15 pilot fuel jets, stock needles shimmed about one full notch. Have not done full plug chops, but it runs very well.

Note that the stock needles are not adjustable. What is necessary to lift them for a richer mixture is to get some small washers (the smallest washers in the assortment pack at Radio Shack work well), determine how many of them are the same thickness as the nylon spacer at the top of the needle, then use half as many. Usually, it's four washers for the full thickness, so just use two. If your header is rather free-flowing (no baffle, or LOUD), you might use just one washer.

.

[qwqb]

what is this plug chops you guys are talking about? im assuming it is some form of examining of the plugs to see how lean/rich the mixture is?

[Steve]

Explained somewhat in detail on BassCliff's site, click here.

Basically, you mark your throttle like this:


The markings are idle, 1/8, 1/4, 1/2, full

Warm up the bike, go for a ride, take your spark plug wrench with you. Hold the throttle at the 1/8 position, ride as long as you can in that position. Might need to use a higher gear on a back street with no stop signs, but you might need a mile or so. Without moving the throttle, hit the kill switch and pull the clutch when it is safe to do so. Remove the plugs and observe the color. Next, go for another ride with the throttle held in the 1/4 position. Might need a small hill to climb to keep your speed in check, but feel free to use a higher gear, too. Repeat the process for the half and full positions, but you don't need to hold those positions as long. One good long blast at wide-open throttle should be enough for that one.

.

[boingk]

I have the same modifications on my GS850 and am currently running #130 mains, with everything apart from the 4-1 exhaust and individual filters left stock. I've tweaked the idle and mixture screws to suit, but thats about it.

I'd suggest starting off with #122.5 or #125 mains and seeing how it goes from there. In my experience, the #125 mains I started off with for the first step were still way too lean. The original #115 mains only let the bike rev to 4,000rpm!

Cheers - boingk

[almarconi]

The original #115 mains only let the bike rev to 4,000rpm!

If your bike is stock and can only rev to 4k rpm's you've got a carburetor problem.

[boingk]

Sorry, thought I made that clear in my original post but it doesn't look that way when I read it again... second times the charm hey?

After fitment of a 4-1 exhaust (with a pretty free-flowing silencer) and then individual pod filters, my 850 would only rev to 4,000rpm because it was so lean on the stock #115 mainjets. Fitting #130 mains cured this, although I've yet to fine tune this.

Cheers - boingk

[qwqb]

Thanks for all your responses guys, I appreciate it a ton. This is a very helpful forum. Where is a good place to order new jets from?

Also, what do you guys think of this kit as far as rebuilding? - http://www.sportingforless.com/servlet/the-56/Detail

[Octain]

Thanks for all your responses guys, I appreciate it a ton. This is a very helpful forum. Where is a good place to order new jets from?

Also, what do you guys think of this kit as far as rebuilding? - http://www.sportingforless.com/servlet/the-56/Detail

You dont need that kit.

[Octain]

#2 son's bike (see sig) has a header of unknown origin and stock airbox. I am currently running 120 mains (stock is 115), stock 15 pilot fuel jets, stock needles shimmed about one full notch. Have not done full plug chops, but it runs very well.

Note that the stock needles are not adjustable. What is necessary to lift them for a richer mixture is to get some small washers (the smallest washers in the assortment pack at Radio Shack work well), determine how many of them are the same thickness as the nylon spacer at the top of the needle, then use half as many. Usually, it's four washers for the full thickness, so just use two. If your header is rather free-flowing (no baffle, or LOUD), you might use just one washer.

.

MIne has 165 mains in it, lol.

DJ 165 mains that is..