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

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

Post by falcon »

I have a T250 that I am ready to fire up but when I got the bike it had the carbs in pieces with lots of various jets. I don't know what the baseline should be for stock, and since I am running JEMCO's and Uni-Filters it will be even more off. I have what I believe are VM26's but I am not %100 sure. There is conflicting information out there and I can't be totally sure.

As of right now I have

5CN3 Needles set 2nd from the lowest clip (rich)
Unknown needle jets (can't find a marking
30's in the pilots
110's in the mains

The bike just had a stock top end rebuild, and with JEMCO chambers and Uni Filters can anyone give me a decent idea for initial start up? I know they will need to be tweaked but I am somewhat nervous that I might run it too rich and wash the cylinders.

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

Post by falcon »

13 views, no replies. Story of my life.

Anyone with a 380 with pipes? What are you running on your carbs? Even a 350 and I can tweak.
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Re: Assistance with baseline carb set up, 1970 T250 w/pipes

Post by Vintageman »

Google Suzuki gtresources or Ozebook vintage suzuki to get what jet sizes are

Odd no writing on needle jets


Jemco chambers for a T250. What kind, do they run under the frame? He has a kit but you have to weld up. Maybe that's what you got. If so they are tuned pretty radical.

Jetting. Well IMO always a little more pilot over stock one or two steps ( 30 now 32.5 or 35) if you like to have small throttle opening performance. Aslo good idea if you let off from higher rpm or going down hills

If you were running stock air box then jetting would be easier may only one or two step larger than main. if 110 was stock 120 maybe 130.


The fact you have pods will make it more difficult versus stock. for example if 110 maybe 130 - >180 depends on how restrictive ai box was, If real large main then Maybe have to enrich jet needle one clip pos.

If those are race type pipes they probably wont hit until 7000 or more RPM. Party over at 8500-maybe 9000 unless bigger carb and/or porting. Not 100% sure about this for don't know what ya got here, curious

I have a Jemco kit for a GT185 and that is how those are (7500 RPM they hit with a bang). Below 6000 it sucks versus stock I have a pick somewhere of his GT250/T250 kit same idea IMO, Sharp cone angles, fat short belly.

I run D&G for and RD on my T350 and Gt250. Work a little better than stock everywhere. NOt same affect as on RD though, but still OK

I have jemco for a GT380 too. Everything is stock on that bike. Even jetting. I have thousands of road miles on that bike just like that, spot on perfect everywhere. Nice tan plug color. if I drove WOT for extended time I would up mains a step or two.
Those pipes are a bit more street than road race kits
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falcon
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Re: Assistance with baseline carb set up, 1970 T250 w/pipes

Post by falcon »

Thanks for the reply, yes they are the u-weld kit from Jemco.

Image

I dont' know if the jets that are in the carbs now are stock or not, and can't find sure information as to what they are supposed to be. I'll check out those links you said to search and see if I can find the info I'm after. I don't have an airbox (the bike didn't come with one) but if it makes that much of a difference I could always try to locate one.

I'll try to find the stock jets and post them up here.
falcon
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Re: Assistance with baseline carb set up, 1970 T250 w/pipes

Post by falcon »

Perhaps a bit of success. I found an old picture of a Suzuki technical manual.

Here is what it lists for the T250

26mm bore size
5cn3-2 needle
02 needle jet
110 mains
25 pilots
p.c. height 8.2mm (what is p.c. height?)
air screw 1 1/2
starter jet 80
float level 13.7mm


So looks like I have slightly richer pilots, the correct needles and the correct mains for stock. I set the float height to "level" with the flange (as I used to to with my old 4 strokes if I didn't have the float height) so I will check that. I didnt' see a removable starter jet so I assume that is pressed in and doesnt' matter?

I will order a few pilots and mains. Thinking, 25, 27.5 and mains 120/135/145 ish? Then find if I need to fine tune after getting it close? What would you suggest?
falcon
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Re: Assistance with baseline carb set up, 1970 T250 w/pipes

Post by falcon »

So i ordered sone 122.5, 130, 140 mains and a pair of 27.5 pilots. Is the needle height the last number on the needle spec? -2? Would that be 2nd from the top of the needle or bottom of the needle?
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Re: Assistance with baseline carb set up, 1970 T250 w/pipes

Post by ja-moo »

falcon wrote:So i ordered sone 122.5, 130, 140 mains and a pair of 27.5 pilots. Is the needle height the last number on the needle spec? -2? Would that be 2nd from the top of the needle or bottom of the needle?
Since you have a modded motor, the stock setting are out the door. Needles are numbered from the top (1) I would go to 3 to be safe.
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falcon
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Re: Assistance with baseline carb set up, 1970 T250 w/pipes

Post by falcon »

Ok so I'll throw the needle on 3, run the 27.5 pilot and throw a huge main I'm there for pilot/needle tuning. I read in a few places this is the way to go so when you're tuning 1/2-3/4 throttle you know that main jet size isn't restricting anything. Then the last thing to do is size down the main once everything else is perfect. Does this sound right?
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tz375
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Re: Assistance with baseline carb set up, 1970 T250 w/pipes

Post by tz375 »

Yes. You can even take the main jets out completely to test needle jet sizes. :shock: At idle only the pilot jets are working, so get them right first.

Then get the mains right for WOT top end and then fine tune the mid range. If the needle jet/needle combo is too restrictive, it might be possible for them to artificially lean out the top end, but that is unusual (but possible).

Always start rich and work back down.
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Re: Assistance with baseline carb set up, 1970 T250 w/pipes

Post by ja-moo »

Well, the main jet "usually" holds the needle jet in, so there could be big problems if they come loose. Big jets is the usual way to go....

And I start at the pilot, needle and then mains.
Visiting from the "K" camp...........
falcon
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Re: Assistance with baseline carb set up, 1970 T250 w/pipes

Post by falcon »

Thanks for all the help guys, I'll be possibly doing some tuning this weekend if my jets show up tomorrow. I'll let ya'll know how it goes and I'm sure I'll have some more questions.

-Aaron
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tz375
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Re: Assistance with baseline carb set up, 1970 T250 w/pipes

Post by tz375 »

ja-moo wrote:Well, the main jet "usually" holds the needle jet in, so there could be big problems if they come loose. Big jets is the usual way to go....
No arguments there

ja-moo wrote: And I start at the pilot, needle and then mains.
That's a good way to get it running but the OP has to understand that changing main jets may well change the needle/jet setting as well. It's an iterative process. I know you know that JA :)
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Re: Assistance with baseline carb set up, 1970 T250 w/pipes

Post by ja-moo »

tz375 wrote:
That's a good way to get it running but the OP has to understand that changing main jets may well change the needle/jet setting as well. It's an iterative process. I know you know that JA :)
I don't, I'm not getting it? Unless you are talking an extremely small main jet........
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tz375
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Re: Assistance with baseline carb set up, 1970 T250 w/pipes

Post by tz375 »

Interesting. Do you mean that if you set the needle and NJ before you get the main jet sized, that you never have to change the NJ setting after you zero in on the right main jet?

I find that if I try to get the NJ right with a "wrong" main jet, that I have to go back and fine tune the NJ again.
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Re: Assistance with baseline carb set up, 1970 T250 w/pipes

Post by ja-moo »

tz375 wrote:Interesting. Do you mean that if you set the needle and NJ before you get the main jet sized, that you never have to change the NJ setting after you zero in on the right main jet?

I find that if I try to get the NJ right with a "wrong" main jet, that I have to go back and fine tune the NJ again.
I haven't had that problem. As the needle taper is what is controlling the amount of fuel, until 3/4 or so throttle, when the main takes control of the metering. Until then, the main (unless extremely small) can't really have an effect. Now, moving the needle up or down can effect the pilot system a bit.
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