1980 GS850 Carby Jet Sizing and Tuning

[Guest]

Hi from Aussie,,,,,I have a 1980 GS850 ,this bike has the standard Air Box fitted and a 4 into 1 exhaust fitted ,
Can someone please tell me what size Jets I should fit and also the Mixture Settings
All so ,My Carbs only have a Mixture Screw at the top ,,they DO NOT have a Air Screw that I can see,??

I have cleaned the Carbs and fitted new needles and seats ,New Gaskets ,New Inlet Manifold O-Rings , New Mixture Screws springs,washer and tiny o-Ring,,
and I set the Float's at 23 mm ,measured from the surface where the Gasket sits ,the Needles are on the 3rd groove up ,,Mixture Screws are 2 1/2 turns out ,,
The Bike Runs very badly at the moment ,,
I have not Balanced the Carbs because the Bike will only run on 3/4 Choke ,and if you touch the throttle the Motor just cuts out ,,
thanks in advance for your help,, regards Phil

[tom203]

Here's a chart...

http://members.dslextreme.com/users/bikecliff/images/carbspec_float_height.html

proper carb cleaning is a must for these critters to run nicely.....How did you clean yours?

[Steve]

Float height at 23mm is within tolerance, but it's on the leaner side.
It also depends on where you measured. There is a step in the float from the mount (close to the pivot) to the round part. You measure at the bottom of the step, not at the top.
The 'height' you are setting is the distance from the carb body where the floats will stop fuel from entering the bowl. Because you are setting the height upside down, a higher number actually means a lower level in the bowl, resulting in a leaner mixture. The specified setting is 22.4mm ±1.0mm. I prefer to set them about 22mm or so.

Needle setting. I'm jealous, you have adjustable needles. 3rd notch is good.

Mixture screws (Suzuki calls them "pilot screws"). They might end up in the 2 1/2 range, but I start with them rich at 3 turns out. The richer mixture lets the bike start easier and a richer mixture burns easier than a lean mixture, so it's easier to tune.

Probably the most important thing is to answer Tom's question: how did you "clean" the carbs? Everything else you mentioned sounded really good, but did not notice details on the cleaning. Did you remove the pilot jets and make sure the tiny little hole in the end is clear? Did you soak the carbs in any chemicals? (not sure what you have available there) Did you spray carb cleaner through the small passages between the pilot jets and the mixture screws? THOSE are the most-critical passages for running at idle.

.

[phil007]

Thanks very much for you advise ,, I bought and installed Brand new Carby Kits ,,including 115 Main Jets , 40 Pilots , 1.8 Air Jets ,,New Gaskets ,I Set the Floats at 23mm from the top of the little raised piece where the Gasket sits ,,(So that looks as if that is wrong) , So I will go back in and re-set the Floats at 22 mm from the lower part where the Gasket sits,, The Needles are on the 3rd clip , When I cleaned the Carbs ,,I removed every part from the Carb body's ,including the Emulsion tubes and cleaned out every Hole ,,I then sprayed the Carb Body's with very strong Cary Cleaner ,making sure I cleaned all openings about 3 times over a 2 hour time frame ,,Also blowing 120 pound of compressed Air through everything as I went ,,,I will re-set the Floats to 22 mm and see what happens ,,
and will advise,,,,THANK YOU for your help ,,regards Phil

[Big T]

If it won't idle, your carb passages aren't clean.
Strip the carb bodies and give them a long soak and n carb cleaner.
Ultrasonic cleaning is even better
I assume you pulled the mixture screws and replaced all of the O rings?

[phil007]

OK yes I replaced the Mixture Screws ,Springs ,Washers and O-Rings ,,,, I Removed the Carbs today and Re-set the Float Heights at 22 mm ,I set the Mixtures at 1 1/2 out ,, I also hooked up my Morgan Pro Carby Balancer and started her up ,
She started up ok ,, I balanced the Carbs and is now running not to bad ,,Not Perfect ,But pretty good ,, I did notice that my Air Jets are 200 not 180 as I stated before,, Is 200 to Big????
She is coughing a little bit on number 4 ,"Blowing Back" occasionally , It shot the Balancing Tube off #4 once ,, But has since settled down now ,,
I think my next Job is to check the Shims ,,I have bought a second hand set of Shims and Buckets off eBay to use a spares ..They arrived today,,,But I noticed that 1/2 of the Shims are 265 or higher ,but Hopefully they will come in handy,,
I also bought a Shim Tool that should turn up in a day or so,,
So all is good , When I hit the Starter and the Bike starts straight up an Idles pretty nice ,
QUESTION ,,When I do check the Shims , Will I need to replace the Rocket Cover Gasket ????, It looks in good condition from the out side ,,
THANKS AGAIN for all you help ,,,
I am sure ,,with out your help ,my Bike would still not be in Running condition ,,So thank you very much ,,,,,,cheers Phil

[Grimly]

QUESTION ,,When I do check the Shims , Will I need to replace the Rocket Cover Gasket ?

Chances are 50/50 it will come off in one piece and be re-usable, but you don't know at this stage what the PO stuck it on with (if anything).
Before doing the job, get a spare valve cover gasket in stock, just in case.

[Steve]

... I set the Mixtures at 1 1/2 out ...

When the carbs were new, the factory might have set them close to 1 1/2, maybe 1 3/4, but over time, we have found that was optimistically lean to start with, and the quality of fuel (ethanol "enriched") is a bit less, so you might need to go between 2 to 2 1/2 turns out. I always start with 3 turns, as the engine will run better with a slightly-rich mixture than it will with a slightly-lean mixture. Once it is running well off "choke", you can fine-tune the mixture screws for best idle.

And, ... if you do have to change any shims, you will have to re-balance your carbs.

.

[phil007]

OK ,,I removed the Rocket Cover which came off real easy and the Gasket also looks in great condition ,,So that was lucky ,
I checked all the Shims and I found that 5 of the Shims in spec at 0.04 BUT the other 3 Shims are 0.10 ,,0.10 ,,0.11

So it looks like I will need to replace these 3 Shims with a 0.05 bigger Shim , than the Shims that are all ready in the buckets at the moment ,
I measured all the Shim Measurements with the Shim Lobe facing STRAIGHT UP ,, Lobe up opposite the Valve ,,IS THAT CORRECT ????
I am still waiting for my Motion Pro Valve Shim Tool to arrive ,,so I looks like I will just have to wait until it arrives before I can see what size Shims I require ,,
But I still have lots of small Jobs that still need doing on the Bike so that is all good ,,
I will post a few Photos of my GS850 once I get her all back together ,
thanks again for every ones advise ,, regards Phil

[phil007]

OK great Thanks ,I will set the Mixtures to 2 1/2 Turns out ,, regards Phil

[phil007]

You need to go between 2 to 2 1/2 turns out. I always start with 3 turns, as the engine will run better with a slightly-rich mixture than it will with a slightly-lean mixture.



OK thank you Steve ,,for the info ,,I will set my Mixture Screw's at 2 1/2 turns out ,,,regards Phil

[cowboyup3371]

I’m just going to ask to be safe but are those measurements in inches or MM? If in MM, the correct range is .03 to .08 and you want to be more on the .08 side

[phil007]

Yes might have put that down wrong,,,,,,Measuring in MM ,, As I stated 5 of the existing Clearances are 0.04 which are in spec ,,,But the other 3 Clearances are 0.10 which is way to big,, ,,, cheers Phil

[Steve]

I checked all the Shims and I found that 5 of the Shims in spec at 0.04 BUT the other 3 Shims are 0.10 ,,0.10 ,,0.11

So it looks like I will need to replace these 3 Shims with a 0.05 bigger Shim , than the Shims that are all ready in the buckets at the moment

Many of us will run as much as .10mm. It helps the valve run a bit cooler and give better fuel economy.
Don't worry too much about those shims at the moment, but please see the next statement.

I measured all the Shim Measurements with the Shim Lobe facing STRAIGHT UP ,, Lobe up opposite the Valve ,,IS THAT CORRECT ????

NO!!! All three manuals have the same goofy, confusing picture that shows cam lobe positions, only the Suzuki manual explains in detail how to check the valves.
1. Start on the left side of the bike. Using the 19mm nut on the right side of the crank (under the ignition cover), position the lobe for EX1 pointing FORWARD, EX2 will be pointing UP.
2. Measure EX1 and EX2 without moving anything. Record those values.
3. Rotate the crank 180°, you will find the IN1 will be pointing UP, IN2 will be pointing REARWARD.
4. Measure IN1 and IN2 without moving anything. Record those values.
5. Rotate the crank 180°, you will find EX4 pointing FORWARD, EX3 will be pointing UP.
6. Measure EX3 and EX4 without moving anything. Record those values.
7. Rotate the crank a final 180°, you will find IN4 pointing UP and IN3 will be pointing REARWARD.
8. Measure IN3 and IN4 without moving anything. Record those values.

If you look at those positions carefully, you will see the reasoning behind them. Neither lobe on that side of the cam will be pushing on a valve. If it were, it will push the cam a bit sideways in the bearing, which will give a bit of false clearance on the other valve on that side of the engine.

Other than improper technique, you seem to have a handle on the situation, but I will still invite you to take advantage of the offer in my signature. The Excel spreadsheet will help you record the values and suggest shim sizes. It tracks what you have done over the years (and miles/kilometers) so you can possibly stretch out the valve clearance check interval.

.

[cowboyup3371]

Like Steve alluded to, that .04 is TOO CLOSE to being too tight. Once you re-check them properly and if they are still at the same settings then I suggest bumping that one up and leave the others where they are or you'll potentially (meaning may not but is closer to likely) burn up your valves too soon.