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Replacement Carburretor

Discussion in 'Technical and Troubleshooting Torque' started by mattb, May 2, 2010.

  1. G'day All.

    I'm going to buy this carburretor to put on my SR500 with its grey SR400 engine:

    I'm in contact with a Japanese fellow who's helping me work out, from forums in his country, what jetting etc is standard on the SR400, as nobody in Australia seems to know (we only got the SR500, with its VM34, as opposed to the SR400's VM32). I want to start with standard jetting and work from there. I'm assuming that a carburretor, which may fit various different bikes, will yet have different jettings for those different bikes, and hence that what I get in a new universal carb won't necessarily be correct for my SR.

    Between his poor English, my non-existent Japanese, and our wealth of ignorance about things like carburretors, our progress is slow. He sent me the below exploded diagram of the SR400 VM42, and if I can tell him what numbers / things i need the specs for, he can ask on a Japanese forum.

    I see from carbs for sale on the net that there's often a lot of specs given, eg.:
    Main Jet 200, Pilot Jet 35, Needle Jet Q6, Jet Needle 6DP17, Throttle Valve 3.0, Air Jet 2.0, Needle Valve 3.3

    Do I need to request specs for all those things? If not, what specs should I be asking for?


  2. Mikuni jets are pretty universal. I've got them from Ian William Tuning in the past.

    That takes care of the main and pilot. After that Mikuni parts get a bit harder to find, but you should be able to get a pretty good tune just by setting the main and pilot jets, float height, needle height and pilot screw.

    btw 200 seems like a massive main jet. Particularly for a 32mm carb. That sort of jet I would expect to see on a 40mm carb on a hot GSXR1100.

    but don't rely on my call on that because I've never had to tune a main jet on a single.
  3. Thanks for that. Somebody sent me this, which hopefully answers the question of jet specs: http://translate.google.com/transla...://www.yamaha-sr400.com/bike/kyabutyousei.htm

    Main Jet # 280
    Jet Pilot # 25

    So I guess I'll plug them in and start from there. I'm going to keep this as simple as possible: standard jetting, remove the K&N and put the stock airfilter back in, but keep my slightly open pipe. Hopefully it'll be a slight enrichment that's required for a satisfactory tune. Then, maybe I'll consider going back to the K&N and further stuffing about.

  4. Seemed huge to me too, but after thinking about it, an 1100cc is basically 4 x 275cc... That said, Ive only played around with carbs on twins.

    MattB, there may be a jet kit available for the 400, maybe check out the DynoJet website. Should give you a starting point at least
  5. Just checked Dynojet out and they don't have one. The trouble is the SR400 was never exported out of Japan new, so there's basically no English info on it or local knowledge about it.

    Another option I have: I've been loaned a carburretor off a 2001 SR400. The trouble is, I cannot work out what to do with all the hoses, and again because nobody outside of Japan is familiar with the 400, nobody on the forum knows. Given the guys on there don't know - and many of them are very knowledgeable otherwise - what hope have I got? Do I block them off? Connect them? Or...? I've currently blocked them off with blutack, and from 3000rpm on, stationary but running, the bike lightly backfires constantly. The hoses which confuse me are circled in red.



    Porca miseria!

    I actually came across a late model SR400 in Peter Stevens today, wit hthe same carb. I tried to work out where these hoses went, but the salesman wasn't too keen on my poking about. They disappeared under the tank or seat, out of sight. He just kept saying they're for breathing for the petrol, and when I questioned what he meant, mumbled that sort of repitition that essentially means, "I don't know, I'm bull-shitting."
  6. Mmm, reminds me of the old lady who got run over on the pedestrian crossing. The police couldn't figure out if the radiator or the carburettor.
  7. JAYCAR have a mixture indicator kit for about $15.
  8. I broke something, I can't post what I was trying to post, I'll send you a PM MatB.

    Edit: No I won't, that didn't work either...
  9. Try this again:

    The problem with that kit is you need an engine with an oxygen sensor in it, I doubt the SR has one built in, you can buy them, but the cheapest I've found is about $90...

    If all else fails, get yourself kit #'s KC-5485, KC-5486 from Jaycar & a Bosch LSU4.2 from here http:// wbo2. com/lsu/sensors.htm, the one you need is prt #7200.

    (You'll need to remove the spaces from that link, for some reason Netrider didn't like it)

    I have both the kits ready to go but sensor as yet.

    Is the engine the same as the SRX400? http://www.srx400.co.uk/srx4-srx6-table.sxc.pdf has some jet sizes, if so.
  10. Wreckers? ebay? I was under the impression that any single wire sensor would be fine.

    Personally I was just thinking of doing kit 5195
  11. Lack of money!
    5195 does a pretty rudimentary job, good & cheap though. It probably does just use a single wire sensor, if that's the case it will be a lot cheaper!

    The other one gives you a read out, between 11:1 & 20:1.
  12. Try this again:

    I've got one of those cheapo Jaycar kits and I got a new single wire sensor off Ebay for $24 inc postage. Now I just need to get a boss welded into the DR's (stainless, allegedly) downpipe, so I can get a baseline mixture reading before I start playing with EFI.
  13. Keep us posted on that Pat. I'll be doing similar, but I'm still a couple of months away on the project.
  14. Hello PatB, haven't seen you around here for a while!

    Let us know how it goes, I am curious to see how handy it is.

    I have all the bits for the other one apart from the sensor, so I'll post up a review when I get it going.