GT250k carb tuning - lot of questions

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xevious
Still in the Driveway
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Joined: Wed May 03, 2017 3:19 pm
Country: Switzerland
Suzuki 2-Strokes: GT250 K

GT250k carb tuning - lot of questions

Post by xevious »

Hi all,

First of all I'm new to this forum so I'll do a quick presentation.
I'm from Switzerland, 26 years old and I've always been interested in mechanic.. so I bought a motorcycle (I knew nothing about it before). I like to learn the hard way ;)

I am working hard during my spare time and I already fixed a lot of stuff (brake, electrical, fuel tap, rust in the tank, ignition) but now I'm struggling to set the carbs propperly.

For info:
- the carbs have been cleaned and different elements were replaced with the appropriate Keyster carb kit.
- I have the GT250 Haynes manual but the carb version in it is slightly different and they use part name different than in the schematics (slow running screw for example..still not sure which one it is)
- Throttle cable is new and working well

So..now time for the questions

Does anyone of you have a good procedure/manual/video/anything showing the process of adjusting the carb on a GT250K?

Haynes manual says that you should adjust each carb separatly by removing the spark plug. Can I just disconnect the spark plug cable?

I have 3 "screws" avaliable to set the carbs:
Pilot air screw (n°17 on the GT250 parts catalog or here)
Adjuster cable (n°4)
Screw adjusting (n°6)
Which one is also called the "slow running screw?
Can you please explain me the effect of moving these 3 screws?

In advance, thank you very much for your help. You'll save my beginner's ass ;)
Zunspec4
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Suzuki 2-Strokes: T500R, SV1000S, TS125, Seeley T500
Location: Trowbridge UK

Re: GT250k carb tuning - lot of questions

Post by Zunspec4 »

Hello xevious,

Pilot Airscrew (slow running screw) - This controls the amount of air mixing with the fuel at very low revs, such as tick over. typically as you screw it in you reduce the amount of air effectively richening the mixture. The manual should tell you how to set it, usually about 1.5 turns out from fully (but lightly) screwed in. From here you can fine tune it by disconnecting a plug lead (taking the plug out lets the engine turn over more easily when running on one cylinder) then adjust the Pilot Air Screw and you will notice you can affect the engines running speed. Adjust for the highest rpm, then repeat for the other cylinder.

Screw Adjusting - I looked at the parts diagram you posted and I'm afraid I don't know what this is supposed to do :( . I first thought it would be for setting the tick over by setting the height of the slide when the throttle is closed but it is orientated differently to carbs I am more familiar with.


Adjuster - Takes out any slack in the throttle cable. it is the adjuster you use to synchronise the throttle slides so they both open together.

Cheers Geoff
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dorT500
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Suzuki 2-Strokes: '75 T500M since '93 Ridden it over 100,000 mi
Location: Galveston County, Tx.

Re: GT250k carb tuning - lot of questions

Post by dorT500 »

Welcome to Sundial Moto Sports xevious.

Sounds like you are moving right along and here is hoping you have everything sorted out in short order.

Zunspec4 wrote:............ I first thought it would be for setting the tick over by setting the height of the slide when the throttle is closed but it is orientated differently to carbs I am more familiar with......Cheers Geoff
You thought right,

Earlier carb........throttle valve (slider) stop rod runs through it from what I gather....I've never tinkered with one of these carbs either.

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Zunspec4
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Suzuki 2-Strokes: T500R, SV1000S, TS125, Seeley T500
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Re: GT250k carb tuning - lot of questions

Post by Zunspec4 »

Hello dor,

I think I can see how it works now :up: . An unusual way of doing it though, but if it works.

Cheers Geoff
xevious
Still in the Driveway
Posts: 3
Joined: Wed May 03, 2017 3:19 pm
Country: Switzerland
Suzuki 2-Strokes: GT250 K

Re: GT250k carb tuning - lot of questions

Post by xevious »

Thanks a lot for these answers, I'll be working on it tomorrow!

An other question.. When the throttle is off (engine idling), what should be the height of the valve throttle (the cylinder that slides up and down in the carb). Should it be fully closed or not?
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dorT500
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Posts: 253
Joined: Mon Jun 12, 2017 12:01 pm
Country: USA
Suzuki 2-Strokes: '75 T500M since '93 Ridden it over 100,000 mi
Location: Galveston County, Tx.

Re: GT250k carb tuning - lot of questions

Post by dorT500 »

xevious wrote:..........An other question.. When the throttle is off (engine idling), what should be the height of the valve throttle (the cylinder that slides up and down in the carb). Should it be fully closed or not?
Just leave them lowered for now....this looks about right.....Image you will know when/if you need to adjust the rod to keep the engine running as you fine tune it at operating temperature with the the pilot air screw on each carb. Check to make sure there is no throttle cable hang up at the cable splitter tube before you start. JUST IN CASE something causes the engine to rev out of control now or in the future and cutting the ignition off does not stop it, then quickly engage the enrichment circuit lever (choke lever). That should kill the engine. As you have probably noted from your manual but just to be sure....the throttle valves have to enter the carb at the same exact time (sychronizing section in manual)....hence...they should bottom out at the same exact time. If not, then adjust cable barrel nut as needed to one or the other carb so they do. Also, from what I understand, if a throttle valve stop rod is bent just a bit, it could cause some interference for the throttle valve on its way down. With the air box off you can confirm good operation of all this before even starting engine by just using a hand mirror and watching from the side as you turn the throttle grip back and forth. Make sure the slides are clean and it would not be a bad idea to go ahead and just mist them with WD40 beforehand until you get the engine running. You can then re-install the air box/clean filter and start your carb tuning.

Also, not sure if they could even be put in the wrong way on this model but make sure you have the 'cuttaway' or high side of the bottom rim of the slider FACING the air box.......

Well here....you probably don't need this for illustration purposes but maybe it will come in handy for someone in the future...

http://teamghettoracing.com/bikes/road/ ... and-carby/" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;"


If you did not use genuine Suzuki or Mikuni parts you may consider doing so once you at least get the bike running.


Others with more experience specific to your bike will probably be along to help you if needed as you progress along.


Good Luck
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xevious
Still in the Driveway
Posts: 3
Joined: Wed May 03, 2017 3:19 pm
Country: Switzerland
Suzuki 2-Strokes: GT250 K

Re: GT250k carb tuning - lot of questions

Post by xevious »

Wow! :shock: Thanks for all these precious info!
I'll tell you tomorrow how it went :up:
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dorT500
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Posts: 253
Joined: Mon Jun 12, 2017 12:01 pm
Country: USA
Suzuki 2-Strokes: '75 T500M since '93 Ridden it over 100,000 mi
Location: Galveston County, Tx.

Re: GT250k carb tuning - lot of questions

Post by dorT500 »

xevious wrote:....I'll tell you tomorrow how it went :up:
uh oh..... :| I hate it when that happens. :(



:wink: :lol:
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