GN125 small running issues, mildly puzzled and no mechanic will touch age and cc

[zapblam]

Problems that have always existed since I owned bike (5 years):

• When warm, the air screw does nothing, can be turned all way in and still runs the same as turned 3 turns out.
  • needle, spring, washer and oring are there
  • unsure of oring size as no one could find when I lost the original
  • found a guesstimated oring that seems to fit the same as the old one
• Absolutely no oomph in 5th gear.
  • Will accelerate good through 4th
  • then 5th can sometimes hold speed if no wind, otherwise just slows bike down
  • shift back to 4th accelerates great, then 5th no oomph again

Other Symptoms

• when hot has high idle, blipping throttle returns to normal most often but not always
• speedo is not accurate but no big deal, made own marks following wife van

Things done:

• dismantled, dipped, cleaned and inspected carb, every year as its stone simple to remove and do so.
• repaired leaks with new intake boot, oring and clamps this year, no leaks detected with wd40
• compression is very good
• new oiled air filter
• new spark plug and wire
• Spark plug appears normal when doing high speed and cutting engine then pulling plug. Tested when bogged in 5th and in normal in 4th separately.

Bike runs great otherwise, just attempting to tweak these issues out. If only it could maintain 100-110 km/h in 5th instead of reving out to hold in 4th. Would be good for the back highway at least for another year and for wife to learn on

Was a very good city commuter, zippy enough and very nimble and light.

Am going to be selling most likely this summer as now my commute is mostly highway. 125 and highway scary combo, wont even try again. Got my target set on a Vstrom 650

Oh yea bike is a 1985 gn125, 15,000km

[hampshirehog]

Hi. Sounds like she's running lean. Have you checked your fuel tap and made sure that the float valve filter is clean (if fitted)? Also worth checking float level plus the o ring on the airscrew.

[Steve]

I will also go with "running lean", but will go so far as to speculate that maybe the tip of your mixture screw is broken off and stuck in the carb, because you are seeing no difference when you turn it.

The "new oiled air filter" also concerns me, it might be oiled a bit too much.

.

[Flyboy]

Welcome to the forum.
I have another take on it, because it pulls strong in all gears except 5th and you say the plug chops are good.
Are you sure it has stock gearing on it?
The previous owner may have changed sprocket ratios by putting a smaller rear or bigger front sprocket on to try and get the RPM down during highway driving, and over done it.
I would check there first.
+1 on what Steve said about the needle.

[BassCliff]

Greetings and Salutations!!

Hi Mr. zapblam,

I can only add this; If there is an intake O-ring between the head and the carb boot, it won't hurt to replace it to ensure there are no air leaks there.

Anyway, even though not much of this will apply specifically to your bike, let me dump a TON if information on you and share some GS lovin'.

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Here is your very own magical, mystical, mythical, mind-expanding "mega-welcome". Please take notice of the "Top 10 Common Issues", "Top 15 Tips For GS Happiness", the Carb Rebuild Series, and the Stator Papers. All of these tasks must be addressed in order to have a safe, reliable machine. Now let me roll out the welcome mat for you...



Please click here for your mega-welcome, chock full of tips, suggestions, links to vendors, and other information. Then feel free to visit my little BikeCliff website where I've been collecting the wisdom of this generous community. Don't forget, we like pictures! Not you, your bike!

Thanks for joining us. Keep us informed.

Thank you for your indulgence,

BassCliff

[zapblam]

Would the air screw and gear problems be related? I do not think they are but maybe I am wrong.

Every spring I have taken everything apart to try new things I read here in GS Resources, nothing has solved my 2 remaining problems. Fixed many other issues though in the process.


This bike has always had the 5th gear problem, just chalked it up to it being a little 125cc. Never was a problem as it will go 60km/hr easy in 4th in city which was the highest speed limit anyway. But now that I had slight hope it could run the highway, with no 5th gear not even a chance.

• Have no idea if the gearing has ever been changed.

Carb issue:

• The carb-engine boot and oring are brand new, as there was a wd40 leak there. The oring was flat and hard.

• The needle tip appears fine, can see it in the carb throat when its turned all the way in.

• Will have to seek out tiny orings for the needle

• Will have to find and try other tiny orings to see if any other sizes help.
• would that part be the same as other thumper suzuki models such as the gs250 and gz maurauder.

This gn125 is darn near impossible to get dealers to find parts for, everything discontinued.

[zapblam]

by the way, I am Vern from Saskatoon Canada. Been reading these forums for 5 years now, somehow my account got reset or something.

You guys helped get this bike in near tip top shape from sitting in a shed for 10 years full of gas. Can take this carb out and apart almost blindfolded thanks to these forums.

Just the air screw turned all the way in and it still runs still stumps me now. And the gear thingy.

[BassCliff]

Hi,

After doing a bit of research, it seems your bike should have a 14 tooth front sprocket and a 42 tooth rear sprocket. Is that what you currently have?

This is the parts fiche I was using: http://www.cmsnl.com/gn125-1983-d_model13339/partslist/

That's the only online parts fiche I've found so far.



Thank you for your indulgence,

BassCliff

[JEEPRUSTY]

according the spec on the wiki article the bike is sposed to have a top speed of 79 MPH. No doubt it takes a while to get there.

[zapblam]

Best I can get is 90km/h (55m/h) in 4th.

I know she will always be slow, but there should be a full rpm range in 5th right?

I will count sprockets tonight. Pretty sure they are original though, the chain was. Changed chain when I got bike, not sprockets though.

[Steve]

Chain and sprockets should be changed together, as a set, but would not prevent reaching top speed.

I still think your MIXTURE (not "air") screw is broken, but that won't affect anything over about 1/4 throttle, either.

And the brutal reality that it is only an 125, there's only so much that it can do.

[zapblam]

Giving up on the lack of any 5th gear oomph, after 5 years of research and trying.

Wife agrees its way to dangerous of a bike on highway. Max 90km/h in 100+ speedlimits.

Selling. Downpayment for a newer proper highway utility bike, VStrom650

[Flyboy]

Good choice of bike, I am sure you will love it, as far as I know, there are a few members here who have VStrom's and they rave about them.
So if you want to ask any questions about them, maybe post in the off topic section, or in the GS discussion forum, not everybody visits off topic.