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GS425 starting mixture setting?

  • Thread starter Thread starter baytonemus
  • Start date Start date
B

baytonemus

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The Clymer manual says that all GS400, 425, & 450 models manufactured after 1978 have the mixture screw pre-set at the factory and are not adjustable. This obviously is not the case with my friend's 1979 GS425. I assume this description was written to satisfy emission regulations. Earlier bikes had a starting setting of 1 & 1/4 turns out. Is that where I should start, too?

Thanks.
 
If you have had your carbs apart for cleaning, start with them at three full turns out.

Then, when the bike is warmed up, slowly turn each one in, listening for any increase in engine speed.
There is a chance that you won't hear an increase, so just turn until you hear a decrease, then turn them back out about 1/8 turn.

They might end up around 2 to 2 1/2 turns out, and your bike will run a LOT better.


I remember reading a magazine "back in the day" that was trying to enhance the driveability of the 425, but on an EXTREME budget. They swapped the positions of the washers on the needle, putting the thin metal one above the clip and the thicker nylon one below the clip. That might be a bit extreme, but it seemed to work for them.

.
 
Hey, Steve. Thanks for your reply. Actually with these carbs, there is no washer on the mixture screw. Here's a pic from another thread. The one on the right the is the complete package.

picture.php


Does seeing that impact your three-turns-out recommendation?
 
No change for the mixture screws, the washers in question are on the needle that sticks out the bottom of the slide. :o

.
 
Got the bike running this morning and worked a bit on tuning it. However, my mixture screw settings are all way too far in and I think I know why. I had a heck of a time finding the correct o-rings. They appear to not be available from Suzuki, and (I think) are different from the ones sold by Robert Barr. I ordered three different sizes of Buna o-rings from McMaster-Carr but none of them are quite right. the diameter of where the o-ring rides on the screw is about 3mm. a 1mm thick o-ring is too small but a 1.5mm is too big.

Right now I've got the 1mm rings installed and I think it's probably sucking a little air there. Starting at 3 turns out and slowly turning in as Steve recommended, the right carb ended up at 7/8 of a turn out and the left one at less than 1/2 turn. Honestly, it ran best with the left one turned all the way in.

Anybody know where I can find an o-ring that will fit properly?
 
baytonemus said:
The Clymer manual says that all GS400, 425, & 450 models manufactured after 1978 have the mixture screw pre-set at the factory and are not adjustable. This obviously is not the case with my friend's 1979 GS425. I assume this description was written to satisfy emission regulations. Earlier bikes had a starting setting of 1 & 1/4 turns out. Is that where I should start, too?

Thanks.
Click to expand...

Sorry to threadjack this but I'm also working on a '79 GS425 and it is running rich. I'm trying to find the mixture screw on the carbs and do not see it anywhere. On my GS500 it is underneath near the drain plug. Can you tell where yours is located at?
 
seamax said:
Sorry to threadjack this but I'm also working on a '79 GS425 and it is running rich. I'm trying to find the mixture screw on the carbs and do not see it anywhere. On my GS500 it is underneath near the drain plug. Can you tell where yours is located at?
Click to expand...

The screws are on the sides of the carbs facing outward on both sides. They're just on top of the " throat" that slides into the rubber intake manifold.
 
baytonemus said:
The screws are on the sides of the carbs facing outward on both sides. They're just on top of the " throat" that slides into the rubber intake manifold.
Click to expand...

I'm a little confuse. I got these pics from another gs425 build..can you tell me exactly where they are. Thanks.

10.jpg


11.jpg
 
cowboyup3371 said:
Post up a picture of the opposite sides. I think you have them turned around.
Click to expand...

No both of those are the outside sides of the carbs...you can see the choke lever on one side and on the other you can see the idle adjustment screw in the middle.

Are these the the air/fuel mixture screws I circle in red?

13.jpg


12.jpg
 
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