1980 gs850 jetting

[stain]

I know this topic has been hashed to death but anyway----My 1980 GS850 project is oh so close to being done and all I have left is to jet the carbs. I have a vance/hines 4 into 1 and emgo pods. Any quick clues on a jet combo? I really don't want to buy the dyno-jet stage three kit but will if it comes to it. Reinstalling stock air box is not an option. Any help is GREATLY appreciated.

 

[gs_kiwi]

dyno

dyno

as i dyno turner my self don't waste your time it is too hard to fully load the bike up and jet it riding on the street you will save money have more fun riding and the bike will run right all the time. trust me i see it all the time you will save money doing a dyno

 

[RobGS850L]

Having rejetted my 850 with a kit I can tell you that if you did what you said to your bike you need to also adjust the idle mixture and getting those screws to move may be a real adventure. The advantage of the Dynojet kit is the new adjustable needles, the air restrictors, the right drills and the jet assortment. Plus the "how todo's". I'd say leave it stock and save your money but it's too late for that. Check the screws and see if you can get them to move and if not they will most likely have to be drilled out. I tried to run my bike without moving the idle mixture screws and it was not too good to say the least. Not trying to rain on your parade but it's better to know what you may be up against than not.

 

[stain]

All the screws are free on my bike. anyway I said heck with it and purchased the dyno-jet kit. After looking at the kit ,the stage three settings are quite detailed. I don,t think I could have come up with a similar set up my self in a timley manner

 

[RobGS850L]

Love to hear that the mixture screws were loose. You lucky dog. Mine were glued tight and it cost me about 150 bucks to get it all fixed. Add the kit and I was sunk to the tune of 250 samolians. I'm sure you will be happy with your performance increase. The 155 jets from the Dyno kit seem to be good for me but I started high and worked down. I didn't want to start lean and start getting the engine too hot and blue the pipes real bad. One cool thing is getting the carbs in and out with the pods is a whole lot easier. Good luck and have fun.

 

[stain]

Did you use the 155's and leave all the other settings as instructed? I started with the 165's and it is way to rich even with the clips in the 2nd groove. I was going to leave the clips and try the 160's but am interested in your settings.

 

[stain]

Well I just installed the 160DJ jets with needle in #2 position. It's raining out and don't really want to test in the wet, will report back later
​

 

[Zooks]

Well, what happened????

 

[stain]

I went with 142.5 mikuni jets and left the clips in the # 2 position. It runs almost perfect with a VERY slight bog above 75mph and whacking the throttle wide open. Backing off to about 7/8th throttle takes care of it. I am probaly not going to fool with further as my wife has comodeered the bike!!! This also made me sell my FZR400 as she would rather ride the GS!!
Come to think of it Ijust installed a complete DYNA ignition upgrade and should see if this helps:-s

 

[KEITH KRAUSE]

I started with the 165's and it is way to rich even with the clips in the 2nd groove. I was going to leave the clips and try the 160's but am interested in your settings.

I don't know why you're combining main jet and jet needle performance. They are separate. The main controls 3/4 to full throttle, the jet needle approx' 1/4 to 3/4 throttle. You test each circuit at the throttle position it's intended to regulate.
I'd do yourself a favor and take some positive plug reads after running in the appropriate throttle position. I think you're running lean with the jet needles in position 2. I also think your main jet choice is too lean. Just saying from experience.
Lean mixtures can ruin your motor.

 

[stain]

Not combining needle with main jet circuits---thats just where I ended up after repeated tests. Plug checks look good, a nice coffe brown.
Thanks for the input--your opinion is respected.

 

[80GS750]

the dynojet kit is the way to go. i will always buy this kit now... after messing with my 750 it was just way too easy not to

the kit makes it easy and is way worth it

 

[stain]

I bought the dynojet kit and it was WAY to rich. I was surprised because I too have had good luck with these kits.
I am running the 142.5 mikuni jets in the Dynojet kit instead of the recomended jets.

 

[KEITH KRAUSE]

I went with 142.5 mikuni jets and left the clips in the # 2 position. It runs almost perfect with a VERY slight bog above 75mph and whacking the throttle wide open. Backing off to about 7/8th throttle takes care of it.

OK. But just for your consideration, your bog description suggests a lean symptom. Also, you're partly describing the classic "roll off" test of determining jetting. If you roll on the throttle fully and it bogs, but backing off approx' 1/8 throttle IMPROVES performance, that's a classic lean symptom, since rolling off the throttle this way actually creates a temporary richer condition.
Another old school way of thinking, if a symptom is as noticable as you describe, you're not even within 1 jet size of being correct yet. Your bike shouldn't be doing what it's doing, not if it was really jetted right.
Just curious, what mains are stock in your models carbs? I realize you don't want to play with the jetting anymore, but I'm just curious because I have a pretty good idea of what the typical increase is for your specific mods.

 

[stain]

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

 

[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.