1980 gs850 jetting

[KEITH KRAUSE]

Stock mains were 115. I started at 165DJ and it would bog terrible in the higher Rpm range.. The lower I went with the jets, the less the problem became. I am also running Emgo filters, not K&N. I have left the remainder of the DJ kit intact. I don't mind fiddiling with these carbs some more if some one has a better set up. In the dyno-jet directions they suggest the top end flat spot to be a rich condition and to drop the jet size

Interesting. Just "ballpark" guessing from my own experience, I'd allow 4-5 full sizes (5 is a full size) for the pods and 2 full sizes for a quality pipe. So we're looking at a range of 30 to 35 increase. In Mikuni numbers, that would be either 145 or 150's from the stock 115. Since DJ rates their jetting sizes using a different method, a 150 Mikuni main is approx' the same as a 160 DJ main. So a 165 DJ does seem a little rich and you said it is very rich. On the other hand, your increase of 27.5 (5 1/2 sizes) seems a little lean and you do say performance isn't as good as you expect. Interesting how other 850's with similar mods accepted larger mains. But jetting can vary bike to bike.
First thoughts that come to mind are the condition/quality of the pods, the pipe, valve clearances, how clean the carbs are, how the carbs are adjusted/float levels, even the possibility of mismarked DJ mains (I know, not likely)...just trying to think of things that could limit air flow and cause you to need a little smaller mains than what is usually used for your mods.
Did you test at full throttle and chop off and read the plugs?
What were the 1/3 throttle position (jet needle) reads?
Generally, you choose the main that delivers the highest top speed under same conditions. I often do that, but, some bikes will perform well at top end but a full throttle roll on at approx' 60 in top gear may show some momentary bogging. That situation may be that the bike can't handle the overlap from jet needle to main during a roll on. If that's the case, then I always consider the jet needle more important to general riding and I test and make sure the jet needle is spot on first. Then I go up as large on the main as I can without it starting to bog again. This may be "backwards" jetting according to some sources but it has worked for me on some bikes.
Your jet needle position is what surprises me more than anything else. If you did test and get good plug reads at 1/3 throttle, again, it seems like your bike is lacking flow and it needs leaner than usual jetting. The plug reads are what's important here.
I'm not trying to cause you work, just trying to figure this bike out.

[stain]

Agreed that the mid-range settings are most important--considering that the bike is now mainly driven by my wife who never exceeds the speed limit or "wrings it out". I was wondering if the lower budget Emgo filters were the culprit here, limiting air flow. I might be able to borrow a set of K&N's and see what happens
Carbs have been cleaned with all new gaskets and jets. Bike starts and idles great. Actually I been commenting to my friends that I have never ridden a bike that is so smooth--of the four bikes that I have this is the oldest and by far the smoothest!!! I can't believe how vibration free the engine and whole bike is in general. I find this amazing for a 27 year old machine. I rode a GS850L in my junior year in high school but don't remember{did't pay attention?} to the lack of vibration
I may if I get a chance pick the needle up 1 clip and recheck my plugs---it has been a very hectic summer though with barley enough time to even ride let alone tune!!

[KEITH KRAUSE]

Allrighty then. Enjoy the bike.
Just try to get some throttle chop plug reads at minimal throttle (pilot circuit), 1/3 throttle (jet needle), and full throttle (main jet) before long, and do what the plugs say.

[stain]

redid some plug reads at @ 1/3 throttle and the plugs are leaning toward the lean side, they are very light brown will pick up needles soon as I get the time. Do you think 1 clip or two?
Keith, thanks for taking the time to read and respond to this thread, back and forth discussion in a civilized manner and real world know how is what makes this site great!

[KEITH KRAUSE]

redid some plug reads at @ 1/3 throttle and the plugs are leaning toward the lean side, they are very light brown will pick up needles soon as I get the time. Do you think 1 clip or two?
Keith, thanks for taking the time to read and respond to this thread, back and forth discussion in a civilized manner and real world know how is what makes this site great!

And thank you for saying thanks. I spend a lot of time here sometimes trying to help and I feel like a fool when the person just disappears or doesn't acknowledge the attempt at helping.
It's very hard to guess what to exactly do with the jet needle when I can't see the plugs in person. You say performance is pretty good except for a little hesitation that I think is lean related and most likely jet needle related. I'll throw out past thoughts about your jet needle position and strictly go by "the very light brown color" you say a solid 1/3 throttle test showed.
I sure don't want to cause you extra work by not guessing correctly the first try. You did the right thing by doing the jet needle test since you can see it's on the lean side. I'm actually thinking a 1/2 position change may be enough. If so, then you need to remove the e-clip from the 2nd position from the top and move it to the 3rd position from the top and then place the jet kit supplied jetting spacer directly on top the e-clip. This will result in position "2 1/2".
I really think there's no way you need to go 2 positions richer, based on your plug read info.
That would leave the possibility of 1 position richer being right or "1 1/2", but if you have a light brown color (light tan) right now and your test was done correctly, I think that would be too much also.
So I'd try the 1/2 position change and test.
Hope it works and the slight hesitation problem is gone and you're done with it.

[D.T.]

Brought this one up from the archives....

Interesting reading. I'm trying to tune a 1980 850 and I just read the stage 3 dynojet instructions. Drilling the slide hole to 7/64" and 4.5 turns out on the "fuel mixture screw."

I have a bog in the 1/8 throttle range and roll ons with bog are a lean condition I assume. Today it did it badly for a while, then it died on me. Turns out I was low on gas. Filipped onto reserve and I was back on track..

[stain]

Problem was solved by changing the Emgo filters out for a set of K&N filters and rejetting to Dyno-jet specs.

[grayskull]

Help with install kit

I AM FIXING TO PUT A DYNO JET KIT IN MY SONS 650.WHAT IS THE DRILLS FOR.My kit did not come with some detailed instructions.i got the jet and needle part figured,but drilling and the big screw.i hhave the cv carbs its an 83 gs650.

[grayskull]

put the kit in the 650.the small drill was for drilling the small hole in the bottom of the slide next to the needle.it was easy took needle off drilled hole out installed new needle.Then changed jet set air/fuel mix to 2.5 turns. put it on an walah runs great.