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2T carb tuning

  1. #1
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    2T carb tuning

    I'll preface this by saying that I know my way around bikes and carbs and am typically pretty good at tuning them, but this issue has me stumped.

    The bike: 1986 Suzuki RG250 two stroke oil injected twin that I imported from Japan. It has Mikuni flat slides with pod filters and stock exhaust. In Japan it was at similar elevation and was someone's daily rider that got put in storage for a few years until I bought it. I got the bike here, fully cleaned and rebuilt the carbs (not changing anything) and went through everything else on the bike (everything you'd do on a new-to-you or fresh from storage bike).

    The bike runs and rides MINT. Idles perfect, doesn't foul plugs, no flat spots, zero hesitations...it's awesome. EXCEPT it doesn't cold start for shit. I'm talking choke on, cranking the throttle, 500 kicks and it's not even thinking about starting. A squirt of ether and it stumbles to a start and if you can keep it running for ~30 seconds you're good to go for the rest of the day.

    With the fact that it was a regular rider previously, I've resisted changing anything, thinking it might be a problem that would fix itself. I've now gone through this process a bunch times and put about a tank of fresh gas through it with no improvement. Because it runs so well everywhere else on the spectrum, I'm scared to change anything. And because it's a cold start issue only, it makes trial and error a pain (you basically get to try one theory per day).

    Anything jumping out at anyone? My next plan of action is to fatten it up a tiny bit and see if that makes any difference.

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  2. #2
    Backwoods lobster boy number9's Avatar
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    Re: 2T carb tuning

    I have absolutely no help to offer whatsoever, but I would love to hear more about the importation process! What it cost, how long it took, paperwork to jump through etc.

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  3. #3
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    Re: 2T carb tuning

    Quote Originally Posted by number9 View Post
    I have absolutely no help to offer whatsoever, but I would love to hear more about the importation process! What it cost, how long it took, paperwork to jump through etc.
    Hah, yeah I've done it a few times and have seriously considered making it a more serious side hustle. There are plenty of people importing mint, high-dollar bikes that look good in your living room (https://iconicmotorbikeauctions.com/ and http://www.moto2imports.com/, among others), but I'm convinced there's a market for the "working man's grey market bike"...that is to say a cheap rider, maybe a little rashed, needing tires, whatever.

    Anyway, yeah, the bikes can be had pretty cheap. I typically buy them on Yahoo auctions. This RG was like $700 IIRC. Granted it's pretty crusty, but Iconic sold a nice one recently for about $10k. I have a contact in Japan who can do some or all of the work for you. In my case, I pay him to collect and crate the bikes and bring them to the boat. For that he charges somewhere around $5-700. Shipping and tax varies widely, but a very rough estimate would be like $1200 per bike usually (I'll dig up my paperwork on the last two I brought in and confirm). I run all my bikes through the Vermont registration process, which is as easy as it gets. Tax and reg fees are usually <$150/bike. From there I can legally sell to anyone and they'll get a title (if they're in a title state).

    So all in on this particular bike I'm probably at like $3-3500 and it's probably worth $5k because it's not perfect. Not super lucrative for the headache entailed, but the more you do, the better the economics work out. I'd like to a 20' container with about 20 bikes in it, but that's more capital than I really care to invest right now.

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  4. #4
    Mophead going grey dontpanic's Avatar
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    Re: 2T carb tuning

    Sounds very tempting! I may ask you for your contacts. <evil grin>

    The starting issue: are the choke plates synched up? If it's cable operated, is the cable functioning properly?

    Edit: just remembered about the flat-slides. I don't know anything about them. Never mind.

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    Last edited by dontpanic; 04-21-21 at 05:37 PM.
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  5. #5
    Soul Rider Paul_E_D's Avatar
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    Re: 2T carb tuning

    which carbs specifically? Look here for the basics. https://www.mikunioz.com/tuning-tips...v=7516fd43adaa

    I think your idle circuit is not tuned for the weather we have now.

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  6. #6
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    Re: 2T carb tuning

    Quote Originally Posted by Paul_E_D View Post
    which carbs specifically? Look here for the basics. https://www.mikunioz.com/tuning-tips...v=7516fd43adaa

    I think your idle circuit is not tuned for the weather we have now.
    Good point on the weather. It’s been exhibiting this symptom across all seasons here. The weather in Japan isn’t all that different though.

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  7. #7
    Senior Member MHenry600's Avatar
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    Re: 2T carb tuning

    My gut feeling is that one of the pilot circuits are just clogged up still. Even with a really good cleaning, it's easy to have a little crud blockage somewhere.

    Have you blown them all out with compressed air too?
    I feel like that usually helps to move things once loosened up with cleaner.
    Or maybe there's another port/passage you've missed somewhere?

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  8. #8
    Backwoods lobster boy number9's Avatar
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    Re: 2T carb tuning

    Quote Originally Posted by nick5446 View Post
    Hah, yeah I've done it a few times and have seriously considered making it a more serious side hustle. There are plenty of people importing mint, high-dollar bikes that look good in your living room (https://iconicmotorbikeauctions.com/ and http://www.moto2imports.com/, among others), but I'm convinced there's a market for the "working man's grey market bike"...that is to say a cheap rider, maybe a little rashed, needing tires, whatever.
    I'm aware of Iconic; their stuff is usually pretty amazing. But, of course, you pay for it. I don't think I was aware of Moto2; they had some cool stuff on their website.

    Honestly I'd probably be looking at the popular stuff: Aprilia RS250, RVF400, or RGV250. I assume everything has to be at least 25 years old to import it?

    So all in on this particular bike I'm probably at like $3-3500 and it's probably worth $5k because it's not perfect. Not super lucrative for the headache entailed, but the more you do, the better the economics work out. I'd like to a 20' container with about 20 bikes in it, but that's more capital than I really care to invest right now.
    If you ever want to talk about the economics of it, let me know...

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  9. #9
    Changes come butcher bergs's Avatar
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    Re: 2T carb tuning

    I'd check for an air leak/ lean condition. Perhaps you're onto something with fattening up the tuning a bit.

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  10. #10
    Lifer nt650hawk's Avatar
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    Re: 2T carb tuning

    if it sounds like this you are o.k.
    https://www.facebook.com/groups/5787...4266451681772/

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    Gino
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  11. #11
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    Re: 2T carb tuning

    I bet you filled the tank with e10 gas. JA-pan does NOT use ethanol, especially in 30+ year old bikes. Drain the tank and try 100% gasoline. Low effort, no carb drama.
    Where you located?
    I too am interested in joining this side hustle. Wanna join forces?

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  13. #13
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    Re: 2T carb tuning

    You didn't answer which model carb it is? The RS has a cold start circuit of some sort. If that's the model you have, I would start there. Since it runs well after you finally get it going, I'm not sure if a clogged pilot is the issue.

    I do aggree though that pressurized air is needed whaen cleaning carbs that have sat with fuel in them these days. Maybe try again and blow everything out?

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  14. #14
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    Re: 2T carb tuning

    Quote Originally Posted by PurplePackage View Post
    I too am interested in joining this side hustle. Wanna join forces?
    Me first!

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  15. #15
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    Re: 2T carb tuning

    Quote Originally Posted by number9 View Post
    I'm aware of Iconic; their stuff is usually pretty amazing. But, of course, you pay for it. I don't think I was aware of Moto2; they had some cool stuff on their website.

    Honestly I'd probably be looking at the popular stuff: Aprilia RS250, RVF400, or RGV250. I assume everything has to be at least 25 years old to import it?

    If you ever want to talk about the economics of it, let me know...
    You can bring stuff in that's younger than 25, but all the cool stuff is older than 25 anyway.

    There are occasional deals on Iconic. They recently had a KR250 (2 crank shafts!) that went to $3900 but didn't hit the reserve.

    - - - Updated - - -

    Quote Originally Posted by Paul_E_D View Post
    You didn't answer which model carb it is? The RS has a cold start circuit of some sort. If that's the model you have, I would start there. Since it runs well after you finally get it going, I'm not sure if a clogged pilot is the issue.

    I do aggree though that pressurized air is needed whaen cleaning carbs that have sat with fuel in them these days. Maybe try again and blow everything out?
    I'll grab the model, but I think you're right that it has that cold start circuit, which maybe I don't know enough about.

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  16. #16
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    Re: 2T carb tuning

    If you want to get absolutely nothing done for the rest of your day, click on this: https://auctions.yahoo.co.jp/list1/26308-category.html

    Conversion is about 100:1

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  17. #17
    Backwoods lobster boy number9's Avatar
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    Re: 2T carb tuning

    Quote Originally Posted by nick5446 View Post
    If you want to get absolutely nothing done for the rest of your day, click on this: https://auctions.yahoo.co.jp/list1/26308-category.html

    Conversion is about 100:1
    Dude I've already found a stock Ducati 888...

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  18. #18
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    Re: 2T carb tuning

    Quote Originally Posted by nick5446 View Post
    If you want to get absolutely nothing done for the rest of your day, click on this: https://auctions.yahoo.co.jp/list1/26308-category.html

    Conversion is about 100:1
    About half of them will accept returns. Their super polite culture sure is strange.

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  19. #19
    Backwoods lobster boy number9's Avatar
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    Re: 2T carb tuning

    Did you get this thing going yet?

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  20. #20
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    Re: 2T carb tuning

    Yeah I've been ripping it around for a bit...kind of finally fixed itself. I'll have it out for a decently long ride later this week.

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