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gs850g cafe racer tunning

  • Thread starter Thread starter loxslhelm
  • Start date Start date
L

loxslhelm

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I have a 79 gs850g that I have been building for the last year and a half. At some point I'll post all the build picks but right now I'm dealing with some tunning issues that I need some help with.

The bike has a full 4-2 exhaust with glass pack mufflers(will be re doing it as a 4-1). The head has been port polished. The ignition has been upgraded with a dyna s to eliminate the points and the dyna coils and suppression wires with ngk plugs. Filters are pods. As for the carbs I have 22.5 pilot jets(also have 20's), the needle is at the stock location and the mains are 112's(also have 120's).

I started off with the 20 pilot but switched to the 22.5 which brought up the bottom end although I think I need to adjust the mix screws in as the bike will almost stall when coming to a stop but if I pop the throttle it will settle. My big concern is the top end. The last 20% of my throttle the exhaust note changes. It sounds like its screaming but feels like its got less power.

Thoughts?
 
here is a pick of it still in the build process. some has changed but not much
 
loxslhelm said:
Thoughts?
Click to expand...
1. Put the stock #15 pilots back in.
2. Raise the needle (lower the clip) all the way.
3. Install the 120 mains, but be ready to go to 122.5 or even 125.
4. Turn the pilot fuel screw (the one on the bottom) out one full turn.
5. Turn the pilot air screw (the one on the side) out two full turns.

That will get you going. Eventually, you might need to fine-tune the needle by dropping it a notch, but it definitely needs to be richer than stock. There is no difference in airflow at idle speeds, so there is no need to increase the pilot jets. Even if you did need to change, you would only go ONE size, not two or three.

Then, when you get to the fine-tuning stage, ONLY CHANGE ONE ITEM AT A TIME.

.
 
Ok gives me some stuff to try however I have some concerns. The local shop was the ones to re-sync the slides and they were the ones who told me to bump the pilot one or two steps. Also stock was 19. Only other concern is the fuel and mix screws. It is my understanding that you dont touch the fuel screw on the bottom of the carb(was reset to stock by local shop)

Im new to carbs with this bike. More of a fuel injection guy but you work with what you got. Just for clarification as i understand it the carbs are fully manual/michanical and the stock settings were pilots #19 mains #102.5 (have to double check the main) needle in the middle and air mix 2 1/4 turns out.

Thanks for the help shoo far just need some more
 
I'd love to help with carb tuning, but I'm still learning, myself. I just wanna say, that bike looks awesome! Nice work!
 
Well, there's no such thing as a #19 pilot jet. Mikuni jets come in 2.5 increments, so a 15 or 17.5 should be stock

As for the local shop resetting the fuel screws back to stock, what methodology did they use for this? A flow bench is used at the factory and all 4 screws can be slightly different settings

That said, with pods and different exhaust, you need to open up the fuel screw
 
I stand corrected on the pilots sorry about that its been some time since I looked at them. As for the fuel I think he set them using what the manual specs said but he might have a flow bench. Gonna try these recommendations then I'll let you know how it goes.
 
Ok set them up as described. Seems local shop never chainged the fuel screws so they were just all over the place from when I put then back in after cleaning out 22ys of bad gas. However I have a misfire in cylinder 4 now. Also the mid range is different. I put the needles one down from all the way up. Friend said as I left it was way rich. At idle you hear the miss in the filter but rev it a little and it will backfire. Top end still screams but feels like it's got less then mid. I think the mid feels maybe better but still off compared to the bottom end.

I take it since I had to pull the bar outta the slides to get the needls out I have to re sync it? I didnt touch the adjustments for them just where they mount to the bar.

I would kill for fuel injection.
 
Hard to help when your posts make no sense. Did you do what Steve advised?

He knows his stuff on carbs.
 
Thats what set them up as described means.

Now the bike just sounds all over the place. Where as before it was just the top end that was really off. The fuel screws were all messed up before though.
 
loxslhelm said:
Thats what set them up as described means.

Now the bike just sounds all over the place. Where as before it was just the top end that was really off. The fuel screws were all messed up before though.
Click to expand...

The fuel screws have nothing to do with top end.

They do sell fuel injected bikes. They work great.
 
Welcome to the world of plug chops

Give us a better review of your problems

You opened the fuel screws (underneath the front) to 1 full turn?
Where do you have the air screw set?
What pilot jets?
It sound like you lifted the needles by lowering the clip
What main jet?

What throttle opening is causing the backfire?
 
Hey man, It sounds like youre having some of the same problems I was having with my bike when I first got it. These problems MAY stem from the carbs being gummed up. When was the last time these carbs were FULLY disassembled and cleaned/dipped? Have you at least run Seafoam through the engine yet? Give that a try??:confused:
 
Ok let me start over. I have been building this for the last year and a half. It was my grandfathers and is the first time I've ever bothered to mess with a carb. The entire engine was rebuilt by me and everything c hecked as it was reassembled. The carbs had 22yr old gas in them and were frozen solid. It took six hours with the worlds nastiest concoction just to get the slides out. Once I had them apart and cleaned I sent them to a local shop to have them cleaned again and resynched and jetted. When I got them back I threw them on and it fired right up as if it was brand new.

I did as steve suggested and put the #15 pilots back in and the #120 mains. The needle is one notch from raised all the way. The fuel screws are 1 turn out and the airs are 2 turns out.

Problems are as follows.
1. at idle there is an occasional miss in the cyl closest to the timing pick up.
2. When reved a little it will backfire in the same cyl.
3. Low throttle feels good but mid throttle sounds like its doing a lot but feels the opposite.
4. Full throttle sounds even more intense then mid but has even less power.

Hopefully this clears up some confusion.
 
Steve when I clicked "here" it didnt come up with anything. It says no matches.
 
Okay

the #4 carb has a plugged pilot jet or circuit -it's skipping and popping because it's lean

Did you replace all the O rings in the carbs? The ones between the head and the intake boot?

We'll work on your symptoms one step at a time
 
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