GT250B carb tuning

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GT250Mike
Still in the Driveway
Posts: 6
Joined: Sun Apr 18, 2021 4:28 am
Country: United Kingdom
Suzuki 2-Strokes: 1977 GT250b

GT250B carb tuning

Post by GT250Mike »

Hoping for a bit of guidance please.

Busy working my way through some problems on a GT250 B 1977 I have just bought which I dont think the previous owner ever had on the road. The bike starts up first kick and idles fine but is a bit more sluggish than I would expect up to about 6000 rpm when it takes off. The manual I have has the adjustments for the 250A but the carbs on mine seem different so I am after a bit of help. The mixture screws are set at 4 turns out on the left carb and 4 and a half on the right carb. The air filter had just an offcut of dry foam in so I have new filters on order. Also the baffles were missing, which I have just replaced with the correct wading.

Any help appreciated.
dollydog
Yeah Man, the Interstate
Posts: 545
Joined: Fri Aug 11, 2017 7:09 am
Country: england
Suzuki 2-Strokes: several gt250 ramairs

Re: GT250B carb tuning

Post by dollydog »

mixture screw? presume you mean the pilot air screw? shouldn't be anything like 4 turns out, more like 1.5 or 1.75 turns out. what jets do you have in? i use #30 pilot jets and 112.5 main jets with the standard airbox in it. 4 turns out will make the engine run very lean, screwing them in will richen the mixture. hope this helps :D
cheers, dd.
GTS250 road registered. TS250 engine, Ramair frame.
GT250 big bang road registered. Both pistons fire the same time. USD forks.
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karl pa
To the on ramp
Posts: 377
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Country: us
Suzuki 2-Strokes: GT
Location: southeast pa

Re: GT250B carb tuning

Post by karl pa »

The 76 GT250A used a 92.5 main jet, after some issues with top ends burning up, Suzuki went with 95 main jets in the rest of the A & B model. The 95 main jets are on the rich side, but they are on the safe side, for the way these bikes like to run, wide open.
Is 4 turns on the screws where the bike wants to run or is that just where they were set ?
Are the slides in the correct carb with cutouts toward filter ?
The GT250A & B don't really like anything below wide open, so you won't have much low and mid range.
76 GT185
77 GT250
77 GT380
76 GT500
73 GT550
73 GT750
74 GT750
71 T250 scrambler
75 T500 cafe
GT250Mike
Still in the Driveway
Posts: 6
Joined: Sun Apr 18, 2021 4:28 am
Country: United Kingdom
Suzuki 2-Strokes: 1977 GT250b

Re: GT250B carb tuning

Post by GT250Mike »

Thank you both for the replies.

Just about to have a proper look so your advice is appreciated. I think its running a bit rich but not had a proper run since I bought it. Picks up fine when you wind it up but anything below 5000rpm is a bit boggy. Trouble is, I haven't ridden a 2 stroke since 1987 so nothing to compare it with. will check jet sizes and try tuning the carbs.

Thanks again.
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