1980 GS850 Carby Jet Sizing and Tuning

[phil007]

OK a bit more work done on my 1980 GS850 ,, ,,
My Motion Pro Shim tool arrived ,I removed every Shim , one at a time to see what size each one was and recorded it ,, At this time all the Exhaust Valves are .04 mm
On the intake side I have .08 , .04 , .03 ,.04 , I do not have any Shims to make them all to around .08 ,, I will have to Buy the shims I need and fit them once they arrive in couple of weeks time ,
So I put the Bike back together and Started the Bike up ,,,
The Bike is not running very well ,It seems to be starving for Fuel when you Rev the Motor ,,
If I pull the Choke 1/2 out ,while I am Revving the Motor , the Motor Picks up and Motor Revs up pretty Cleanly ,,
BUT If I do not Pull the Choke half out while Revving it ,is splutters and coughs and pops and will not Rev out much at all ,
I was thing that my Needles might have been a bit low ,so I dropped the Clip down one ,but this did not make any difference at all ,,
The Motor still splutters and pops as you Rev it up ,unless you pull the Choke 1/2 out ,,
The Bike is idling fine
The Bike set up is
Tank has been Sealed with Tank Sealer ,(it is like New inside)
New Fuel and Vacuum line
Standard Air-box
4 into 1 Exhaust
40 Pilots
Mixture Screws 3 1/2 out
Floats 22 mm
115 Mains
200 Air Jets
Needle Clip 2nd from bottom
Do you think the 200 Air Jets are TO BIG ??? , I think standard Air Jets are 170 ???
Or are my 115 Mains Jets to small ???
Would the slightly Tight Valve Clearances of only .04 mm be a problem ???
All the Jets are Brand New ,New Needle and Seats ,New Gaskets , New Mixture Screws ,Washers and O-Ring ,,
The Rubber Diaphragms are in great condition ,,
Any ideas what to do next to get her to Rev up Cleanly ,,
THANK YOU once again for your help,,,
regards Phil

[Steve]

If that was my bike, I would change three shims. The one that is at .03 and the two that are at .04. Don't worry that the two will go to .09, that is still OK.

As for jetting, ... my chart shows that the US models came with two settings. One has 40 pilot jets with 180 air jets, the other has 42.5 pilots with 200 air jets. Both have 115 mains. We never had adjustable needles, but many of us "shim" them to raise them, so lowering your clip one notch is not a bad idea.

In your most-recent starting of the bike, do you have the airbox installed? If not, that is the source of improper running.

.

[cowboyup3371]

Steve, you wouldn't touch the exhaust side since those are also at .04mm?

[bwringer]

One thing to stir in to this mix:

Somewhere in a crack in the garage of my old house are probably the crappy aftermarket imitation junk fake dog#### jets, needles, o-rings and mixture screws from carb kits.

After chasing weird carburetion issues for months, I finally figured out the hard parts in the kits were only pitiful imitations. Once the light dawned, I threw them into the trash so hard they bounced out and disappeared. Not that I cared to look for the damn things.

Fortunately, I had saved the original brass parts. After careful cleaning, I replaced them and my carburetion problems were over. Or at least I was then able to move on to the next set of issues...

The only usable parts in carb kits are the bowl gaskets; if you must replace any other parts, you have to find OEM hard parts, and o-rings from Robert Barr at http://www.cycleorings.com

[Steve]

Steve, you wouldn't touch the exhaust side since those are also at .04mm?

Yeah, they could be done, but at least they are all the same clearance, so it's not quite as imperative.

The issues with hard starting (especially when cold) are related more to the intakes than exhausts.

.