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Thread: Confuddled by jetting

  1. #1
    Join Date
    Oct 2013
    Posts
    52

    Confuddled by jetting

    Hi chaps and chapesses.

    Earlier this year I bought a nice 1200R with full SS Akrapoic and K&N in the stock air box. Bike sounded and went lovely, but when in Germany at a Zed rally, for a bit of fun, I stuck her on a dyno and she was running pretty lean across the board and the perceived wisdom, from those in the know, was that she could be making a fair bit more power. TBH at I'm pretty happy power wise, though a few extra horses never spoiled a day, but am concerned about the lean running. The bike came with an Ivans kit which I didn't bother to fit as she seemed so sweet and I have a workshop constantly bursting at the seams with old bikes needing surgery.

    Last night I finally got around to taking the carbs off and taking a look at the supplied kit, I was disappointed to see that the only jets supplied for not butchering the air box and binning the intake duct etc was 2off #92 mains. The carbs had #98s inside and #95s outside so slightly up on standard.

    I have exhausted the sticky thread on pipes, jets etc, but couldn't find anything with my set up which is basically stock with open Akra (no baffle) and K&N. the instructions with the Ivan's were unhelpful IMHO. Looking at the thread, my gut feeling is to go up two sizes on the mains and jump a slot on the needles and depending on the air screw possibly get a size up on the pilots.

    Any thoughts? Given what a bastard it is to get the carbs in and out I want to minimise the number of times to go though last night's pain and grief 😂 Thanks

    Ralph
    Ralph Ferrand

    ZRX1200R 2004, Z900A4 1976, Z1000A1 1977, Z1300A5 1983, GPZ1100A1, 1983, H2C 1975, DT175MX 1981, RD250B 1975, YZF R6 1999
    www.bikerstoolbox.co.uk

  2. #2
    Join Date
    Jul 2017
    Location
    South from the Deep South
    Posts
    1,860

    Re: Confuddled by jetting

    Heat up the rubber boots with heat gun a bit to soften rubber and get hose tool that looks like screwdriver with 90 deg bend to install them. Gets easy after that.
    Bloody Foreigner

  3. #3
    Join Date
    Jun 2014
    Posts
    8,739

    Re: Confuddled by jetting

    Ralph,

    Are you sure ivans jets are equivalent to standard as I know dynojet are bigger for a given size (I am sorry but I have no knowledge of ivans nor could I find anything on the web).


    Also may be worth asking John (johnnyrep) what PDQ jetted his to as his is the same spec as yours and was only done a month ago (they said his was running very lean) and may just save a lot of cost and time.


    I wouldn't touch the pilots though as they are only for slow running and if you increase I suspect it will give you a very wooley bottom end.




    Just had a look at one of the dynographs for his earlier Rex that PDQ set up for him (again same spec as yours) and they fitted Dynojet 108's and 110's which would be a Keihin equivalent jet size of Outer Carbs = 112 and inner 115 that would give you a good starting point I would of thought.
    Last edited by ZRXNige; 9th October 2018 at 02:16 PM.
    What Goes Around..........!!!

  4. #4
    Join Date
    Jun 2014
    Posts
    8,739

    Re: Confuddled by jetting

    Just re-read the first post and noted you have the snorkel (intake duct) still fitted and as such wouldn't of thought it needed jetting per se


    What I quoted was for it being removed so would think you are fine with what you are running if you are already jetted up but it wouldn't harm to go up one size (and maybe one dynojet washer under the needle) to give you piece of mind if you are concerned.


    As you have none standard jet sizes fitted, are the jets fitted dynojet or Keihin - ive linked the size comparison for your perusal https://yamaha-enduros.com/index.php...nversion-chart
    What Goes Around..........!!!

  5. #5
    Join Date
    Oct 2013
    Posts
    52

    Re: Confuddled by jetting

    Thanks for the info. How would I tell if they're Dyno jet or Keihin? The only Keihin jets I have here , that I know are Keihin are very different (much longer), but they're from a set of CR29s so they might be different anyway. I have tried to add a pic of one of the jets it came with. It looks as though it has a bit of a 'K' on it, which I couldn't see until I blew up the pic on the computer. Eyes aren't what they were
    Rex-Jet.jpg
    Ralph Ferrand

    ZRX1200R 2004, Z900A4 1976, Z1000A1 1977, Z1300A5 1983, GPZ1100A1, 1983, H2C 1975, DT175MX 1981, RD250B 1975, YZF R6 1999
    www.bikerstoolbox.co.uk

  6. #6
    Join Date
    Jun 2014
    Posts
    8,739

    Re: Confuddled by jetting

    I think that be a keihin jet sir and IIRC the dynojet have them stamped/etched on the face of the jet.
    What Goes Around..........!!!

  7. #7
    Join Date
    Oct 2013
    Posts
    52

    Re: Confuddled by jetting

    I ordered up two #102s and two #100s last night from Cradleys, so they should give me two options; up one or up two using the #98s I already have. I think I'll probably go up one and raise the needles one slot, depending on where they are currently and then praps take it to the dyno to see where I am. I'd like it right!
    Ralph Ferrand

    ZRX1200R 2004, Z900A4 1976, Z1000A1 1977, Z1300A5 1983, GPZ1100A1, 1983, H2C 1975, DT175MX 1981, RD250B 1975, YZF R6 1999
    www.bikerstoolbox.co.uk

  8. #8
    Join Date
    Jun 2014
    Posts
    8,739

    Re: Confuddled by jetting

    If you can take your needles up a slot then they are not standard and can only guess they are Ivans (if you have not fitted DJ) which may go some way to explaining things


    I think Nigel (aka z1racer) had an Ivans kit but fitted dynojet in the end IIRC



    I also think this over-jetting the two inner cylinders is a farce (it wasn't that way on the 11 nor many 12's that have been tuned) but as their appears to be no proof either way then hey ho
    What Goes Around..........!!!

  9. #9
    Join Date
    Oct 2013
    Posts
    52

    Re: Confuddled by jetting

    As you say there are no slots on the needles so I stuck a washer under each one that came with the Ivans needles. I'll get it on a dyno when I have time/money and see what it looks like. Given how well it rode I can't think it was massively far out. Fingers crossed eh. Hope I don't have to take the carbs off again; it's a long way from being a pleasure. Still got to have another go at getting the spring clip thing around No 2s air intake rubber to the back of the carb - fiddly bastard that it is!
    Ralph Ferrand

    ZRX1200R 2004, Z900A4 1976, Z1000A1 1977, Z1300A5 1983, GPZ1100A1, 1983, H2C 1975, DT175MX 1981, RD250B 1975, YZF R6 1999
    www.bikerstoolbox.co.uk

  10. #10
    Join Date
    Jun 2014
    Posts
    8,739

    Re: Confuddled by jetting

    If ever there was an advert for pod filters
    What Goes Around..........!!!

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