The Little GS125 Carb Issues

[GSXJosh]

I know they aren't a popular choice being a small cc bike but this nugget that I have needs some help to get back on the road.

It's a 1982 Suzuki Gs125es. Single cylinder bike runs a Mikuni slide carb, later models ran a Mikuni round? Carb.

I'll start this off with the bike has a cheap eBay pod filter. The original air box was not with the bike when I bought it.

I have rebuilt the carb with genuine parts. The carb was cleaned out, everything was spotless.

I've seen videos of these bikes running without air boxes. This one doesn't want to play nice.

It will start with choke, but when revved has a hanging idle, when choked with my hand or choked again with the choke on the carb the idle will come down. I have adjusted the fuel mixture to within an inch of its life, I have richened the slide needle to maximum but it still wants more fuel to run properly.

I believe that genuine parts even if old are still better than Chinese eBay carbs and I don't want to go down that route... Yet.

The bike is going to be a commuter bike so I need reliability in it. Are slide carbs known to have issues if not restricted correctly with a filter compared to a newer Mikuni carb? Have I got a worn out carb? Are they thongs or flip flops... These are the great questions....

Cheers Josh from Oz.

 

[Big T]

First thing to check is, does that cheap filter block the openings on the mouth of the carb?

Buy a better filter with an integral bellmouth, or, better yet, an airbox

Your symptoms and testing indicate an air leak, lean running condition

The mixture screw only controls idle mixture, set it per spec

Some people progressively add tape over the filter to achieve the proper fuel mixture. It's the same as putting your hand over it, or using the enricheners ( choke)

 

[rphillips]

You didn't mention jet sizes. Not familiar with the GS125 but most any bike that goes from OEM airbox and filter to Pods will need LARGER jets. If you are trying OEM jets, good chance they won't work right... Just my opinion.

 

[GSXJosh]

Jet sizes are original and I can't see any identifying marks on them. I don't really want to stay with a pod but I'm finding it hard to get an air box in good condition.


I'm trying to see if any other air boxes will fit but can't find a guarantee yet

 

[rphillips]

I tried looking up an "82" GS125 at the parts places over here but didn't see one. If you can find a parts diagram for your bike and carb, it should show the OEM jet size. See'ins as nobody with carb. knowledge has chimed in, I'd recommend trying a main jet about 3 or 4 sizes above the OEM to see what happens. Keep hoping somebody with more carb experience will show up .

 

[Rich82GS750TZ]

Cmsnl shows an ‘82 GS125
https://www.cmsnl.com/suzuki-gs125-...gdom-e01-e02_model13415/partslist/FIG14A.html
fiche shows a few different jets and their sizes.

 

[GSXJosh]

Unfortunately that carb diagram is different to my bike, according to a local parts guide main jet is a 95.

Looks like early gs125 ran the slide carb that mine has, later versions ran the round carb with diaphragm.

 

[rphillips]

Well, if you go up 3 sizes, that'd be a 102.5 it should tell you something. Like said from the bikes I've fooled with, never a 125, when installing pods you always need bigger jets... I'm no mechanic nor carb guru, just say'in what I've seen.

 

[gustovh]

Not to change the subject, but have you checked the valve clearances, tight valves can mimic a vacuum leak. I found that one out the hard way.

V

 

[rphillips]

Hey, I never remember hanging idle ever effected by jet size.

 

[GSXJosh]

I'm going to see if another Suzuki airbox will fit the frame mounts and try and use it, I'll see what a factory filter does for the hanging idle etc.

 

[GRich]

What other maintenance has been done to the bike? I saw the valves were mentioned earlier, but what about the carb mounting boot & oring?

 

[GSXJosh]

Finally got an airbox for it.

Pulled the carb again today and went through every port cleaning with carb cleaner and some compressed air. However the bike still wants to rev to infinity.

If I use the choke the revs come down and it acts like a normal bike again. There are no air leaks, all clamps are done up, boots are soft and pliable.

I managed to get a copy of the service manual for this carb as well and it's all done to spec.

I'm abit lost with it.

The carb turned out to be a vm24ss Mikuni slide carb.

I've looked at the carb diagrams and I don't know how I would get into all the hidden ports and channels in the carb without specialised tools.

By specialised I mean some bristles from a stainless steel brush pushed into a matchstick.

I would prefer not to get a Chinese eBay carb.

 

[GSXJosh]

Okay I have an update. Bike now starts and idles however after a rev the idle still hangs. I've done a spray test all around the carb and boots etc and there is no leak. However.. how can I test if the slide has an air leak around it?