Assistance with baseline carb set up, 1970 T250 w/pipes

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tz375
Moto GP
Posts: 6091
Joined: Mon Nov 03, 2008 10:47 am
Location: Illinois

Re: Assistance with baseline carb set up, 1970 T250 w/pipes

Post by tz375 »

That's good to know. I have found a few times that changing main jets more than a few steps starts to influence mid range. Needle jet and needle are modulating flow form the main jet during partial throttle conditions. Change the main jet and it changes fuel flow at part throttle.

We also found on the dyno that needle changes still change full throttle fueling an a Keihin carb where the area through the needle jet was many times larger than the main jet and even allowing for the extra air and frothing, that was quite noticeable. I have not tried the same thing on a Primary type needle jet to see if that affects them as much.

IIRC, on the old Rotax 256 AFI Aprilias the rule was more than one size main jet requires a different needle. More than two requires a change in needle jet as well. Those were strange devices though.
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frappy
On the main road
Posts: 103
Joined: Wed Oct 15, 2008 1:36 am
Country: USA
Suzuki 2-Strokes: T500M, T250-II, GT750J
Location: Scotts Valley, CA - USA

Re: Assistance with baseline carb set up, 1970 T250 w/pipes

Post by frappy »

In looking for float height specs on my bone-stock 1970 T250-II, I located at a trusty resource used about 10 years ago when I restored a 1975 Suzuki T500M; an Aussie racer, Suzuki fanatic, and all-around good guy by the name of Murray Barnard (a.k.a. Muzza). The VM26SH carb spec info that I needed was buried in Suzuki 2-Stroke Service Bulletin #11 dated June 1, 1976 that Muzza has uploaded to his OZEBOOK website with assistance from other Suzuki fanatics (diamondJ, H2Rick) here on this forum. Joy in mudville - thanks guys. :clap:

Here's what I found in the said bulletin:

Bore Size: 26mm
Main Jet: 110
Needle Jet: 0-2
Jet Needle: 5CN3-4
Cutaway: 2.5
Pilot Jet: 35
Air Screw: 1-1/2
Float Level: 17.3mm
'75 - T500M
'72 - GT750J
'70 - T250-II
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