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1985 GS300L - Fuel screw adjustment

cdahl383

cdahl383

Forum Apprentice
What is the factory setting for the fuel screws on a 1985 Suzuki GS300L?

My Dad recently bought a 1985 Suzuki GS300L from my neighbor and I'm in the process of going through it and getting it road ready. The bike starts, runs, and rides as is, but it doesn't run 100% right. It's very cold blooded, but once warmed up it runs well.

Yesterday I took the gas tank and seat off to have a better look at the carbs. I found one choke plunger was frozen up in the carb, which was not allowing the choke to be used. I was able to free it up, cleaned it out, and lubed it so it works properly. I also went through the other one just to be sure both were working well. I reassembled the choke and now it works properly. That should help the bike start and warm up easier.

The other thing I checked were the fuel screws. One carb had only 1 turn out while the other carb had 2.5 turns out. I did some research online and found they should be somewhere around 2-3 turns out stock. Is that correct?

I helped my neighbor go through the carbs as previously the bike wouldn't even start or run. The carbs were gummed up with green residue from ethanol fuel. I cleaned them thoroughly, replaced the pilot jets, and we also replaced the intake manifold o-rings. I told him not to use ethanol fuel if the bike was going to sit for a while.

The bike starts up and idles nicely. It just has a hesitation off idle that is kind of bad until it warms up really good. Once it's warmed up well it will run good and go down the road in 5th gear at 55-60mph no problem. I'm guessing the off idle hesitation has to do with that one fuel screw only being 1 turn out.

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There is no set point for the pilot screws. At the factory, Suzuki tuned them with an emission sniffer for EPA compliance. For us, all these years later, you should set them to about 2 turns out, then tweak them until you achieve the highest idle setting. Try to get the screws within 1/2 turn of each other. And do a vacuum sync.

That bike looks nice. Please check the Newbie Mistakes thread linked in my signature, so you know what to look out for.
 
Thanks!

Ok I'll try 2-2.5 turns or so at first and tune from there.

I tried clicking on that newbie mistake link in your signature but it says that link cannot be found.
 
cdahl383 said:
Thanks!

Ok I'll try 2-2.5 turns or so at first and tune from there.

I tried clicking on that newbie mistake link in your signature but it says that link cannot be found.
Click to expand...

The links in my signature must have suffered from the new forum software migration. Anyway, fixed them... Sorry about that.
 
I tried 2.5 turns out but it still runs kind of goofy until it really warms up good. Once it’s warmed up good it runs perfect with no issues. Seems like you have to give it more throttle to take off compared to other bikes I’ve ridden.

I might try 3 to 3.5 turns out tomorrow just to see if there is any effect on how it runs until it’s fully warmed up.

Only other thing I can think of is maybe the jetting is just too lean now for today’s fuels? I know I replaced the pilot jets with 40 size which is stock.

The choke works now but it doesn’t seem to want full choke. It was about 75 degrees out so not really that cold. It will idle nicely when cold but when you open the throttle it hesitates a bit. Once warmed up it’s perfect. Very strange.

I got my 550 out today for a little bit. It ran just fine. Usually takes a couple minutes to warm up then it’s good.

IMG_7952.jpeg

IMG_7951.jpeg
 
You can try lifting the needle a little. That should help the bike warm up faster. These old GS's are known to be cold blooded, particularly the later year variants and twins.
 
Nessism said:
You can try lifting the needle a little. That should help the bike warm up faster. These old GS's are known to be cold blooded, particularly the later year variants and twins.
Click to expand...
I got it running great now! I turned the fuel mixture screws out to 4 turns out and pulled the choke out a bit while it was warming up. I let it warm up for a couple minutes and then took off down the road. Zero hesitation or bogging now. Idles nicely, cruises nice, no flat spots or anything, just nice smooth power all the way up to 55mph or so in 5th gear that I tested. After a short trip down the road I pushed the choke in and the idle came down a bit and it ran perfect!

I know 4 turns out is quite a bit, so I'm going to try going back to 3 or 3.5 turns out and see how it runs like that. I just wanted to see if turning them out had any effect on how the engine ran. It completely cleaned up the previous lean spot coming off idle to cruising when taking off.

I also dumped in a couple gallons of fresh ethanol free fuel in the tank too.

I'm so happy this bike runs good now! I sort of talked my Dad into buying it off of my neighbor since it was such a nice clean low mileage bike, but I was really hinging on myself being able to get it running better.

The funny part is when I cleaned the carbs for my neighbor last winter when he owned it we got it running, but it was cold blooded. I suggested we turn out the fuel screws more but he was really adamant about not fiddling with those. That was likely the issue the whole time, as well as the choke plunger being stuck. I fixed those two things and now it runs great. Go figure.

I have to put the front tire on still, so I'll remove the front wheel and take it up to the bike shop to get the new tire mounted today. Then the bike will be ready for my Dad!

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