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Thread: MIKUNI Choke plunger seat replacement and Air corrector jets for GS fours VM's

  1. #1
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    Default MIKUNI Choke plunger seat replacement and Air corrector jets for GS fours VM's

    Here's a little sideline retirement/beer fund gig i've been doing for the Z1 Owners Club GB and Z650 forum over in the UK and a couple of GSR members who have had this done with positive results thought it will be of interest to folks here who are having trouble with rich running and low mpg etc so invited me over to post a thread.

    Choke plunger seat replacement for almost all MIKUNI choke plungers.

    Suzuki GS 550,750,850,1000, GSXR. GSX, Katana . Kawasaki Z650 /900 /1000, ZXR, ZR , ZRX , YAMAHA XS, XJ, XJR, FJ, FJR, RD and most other singles, twins, triples, fours etc that use 8mm head rubber tipped plungers.

    The worn plunger seats are replaced using my own custom built tooling with a unique installation technique that is unavailable elsewhere that inserts the new full size Viton seats without disturbing the brass plungers original rolled securing edge.

    Originally developed for repairing the obsolete and no longer available plungers on early Z1 Mikuni VM28SC round slide carbs i can also replace those on the later VM22, 24, 26 and 28 SS etc as fitted to the Z650, Z900, Z1000 and GS 750/1000 etc Suzukis that are also discontinued including CV carbs and almost any Mikuni plungers that have 8mm diameter heads.

    The rubber seats go hard with age or degrade with ethanol and cause imprecise choke operation as well as being the often overlooked and now widely recognized cause of previously unsolvable rich running, poor MPG and erratic idle issues...

    ONE THING IS CERTAIN.

    If your carbs are running the original plungers they ARE leaking and adversely affecting carburation and fuel economy to some degree.

    Whether you wisely use my one of a kind worldwide service or not i strongly recommend that the plungers are replaced or repaired BEFORE installing aftermarket carb repair kits or parts needlessly as it is highly likely that it's the leaking plungers causing the issues and not worn carb internals as many misguided restorers are lead to believe.

    Once done the results will restore the chokes full function and seal..

    The price is £12.50 each (£50 per set of four etc ) (Paypal Friends/Family or bank transfer) + £3.00 return to UK and £11 worldwide tracked and signed.

    This is not an exchange service.

    You will need to send me your own bare plungers to re-seat which also keeps your resto as original as possible and you will receive back your own original plungers with new VITON seats installed.

    Reply on this thread or Email me at zed.1015@yahoo.co.uk for further details.

    Also some important advise for anyone sending their plungers from overseas.

    Please be sure to send them marked as a GIFT and declare either zero or a low value of £39 or under to avoid vat and customs charges.

    Anything marked commercial over £15 attracts vat which has to be paid before the package is released and will have to be added to YOUR cost..
    And gifts marked over £39 attract the same.

    I don't have the same issue when sending them back out.

    They just go as a tracked and signed letter ( "00" size padded jiffy ) and have always got straight to the destination without any
    charges.

    They should be sent to me bare with the springs etc removed.

    I recommend they are taped to a piece of card at the very least to secure them on their journey.

    Turnaround - Plungers are usually done and back in the post the day after i receive them..

    For clarification -
    The attached pics are of the worn plunger seat that gets replaced .
    imagesW5QHW1BY.jpg


    Thanks.
    Last edited by zed1015; 11-14-2020 at 09:07 PM.

  2. #2
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    Also as an addition to my previous post i also make air corrector jets for use when running open carbs or pods which negates the need to play with pilot jet sizes and lift the jet needles in a crude attempt to correct the fueling.

    Again copied and pasted from the Z1 forum.

    Air Corrector jets for Z650,Z1,Z900,Z1000 and Suzuki GS 750,850,1000..
    They are for VM 24, 26 and 28mm round slide Mikunis and are essential when ditching the airbox and running pods, velocity stacks or open carbs to cure the off idle flat spot and improve overall performance.

    A brief explanation of their function and use for those who don't know.
    These are for use with pods, open carbs and velocity stacks Ö NOT to be used with airbox ( unless it has been cut open and offers virtually no restriction ).
    They simply screw in the air bleed to needle jet tube in the mouth of the carb ( You tap this m5 at 8mm deep . No drilling required )..

    They do NOT go in the pilot air bleed ..

    See attached pic for correct positioning ( 4 o'clock on the left pair and 8 o'clock on the right .This is always opposite the bleed for the air screw )

    Fit and forget then make adjustments as normal to the main to suit engine size/tune..
    Keep the stock pilot jet and jet needle in original position..
    If the jet needle has been lifted as usual in an attempt to mask the issue it MUST be returned to the stock position.
    They compensate for the extra air flow and higher venturi pressure at low speeds that results when removing the airbox which then weakens the off idle mix and causes the flat spot and bogging at around 2k rpms..
    Helps improve running throughout the rev range and gives an average increase of 2 to 6 HP overall Ö
    Beware of using cheap pods as these can be restrictive. Use only good quality K&N etc.

    They are £32 a set posted within the UK + £28 per additional set on same order .

    Overseas shipping at cost which is currently £9.35 to US but will round that down to £37 a set posted with additional sets as above at £28 in the same package.

    Items will be sent tracked and signed for..

    Reply on this thread for more info or email zed.1015@yahoo.co.uk .
    Thanks, Rob.

    carb jets ledar.jpg
    Last edited by zed1015; 11-14-2020 at 09:08 PM.

  3. #3
    chuck hahn's Avatar
    chuck hahn is offline Forum LongTimer Past Site Supporter
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    I havent looked at what new ones cost but i will always go with the most economical route. Where do your reconditioned ones rank compared to new? Also it would be nice to have a link available instead of just click on your email.....cant bookmark the email address from my end to keep you in my favorites list.
    MY BIKES..1977 GS 750 B, 1978 GS 1000 C (X2)
    1978 GS 1000 E, 1979 GS 1000 S, 1973 Yamaha TX 750, 1977 Kawasaki KZ 650B1, 1975 Honda GL1000 Goldwing, 1983 CB 650SC Nighthawk, 1972 Honda CB 350K4, 74 Honda CB550

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    Quote Originally Posted by chuck hahn View Post
    I havent looked at what new ones cost but i will always go with the most economical route. Where do your reconditioned ones rank compared to new? Also it would be nice to have a link available instead of just click on your email.....cant bookmark the email address from my end to keep you in my favorites list.
    My re-seated ones are functionally as good or better than new as i use modern VITON for the seats.
    The originals were/are not ethanol resistant.
    New ones were never available as a separate part from Suzuki ( if you look at the parts book schematics they came as part of the carb body) and are also discontinued by Kawasaki and Mikuni.
    Keyster do include a pattern plunger in their £50 per carb Tornade kits but they don't have the metering needle on the end.
    They are not very precise in their action because of this and many users who bought them and then later opted to have their originals re-seated have reported difficulty with idling, syncing and other issues.
    What do you want a link to ?
    I have a thread just like this on the Z1 site and an Ebay listing but the Ebay price is £15 higher to account for their fees etc.
    If you need a bookmark then i would link to this thread.
    Thanks.
    Last edited by zed1015; 11-14-2020 at 09:09 PM.

  5. #5
    bwringer's Avatar
    bwringer is offline Forum LongTimer Bard Award Winner
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    Excellent! Thanks!

    What are the odds of offering the same for the CV carbs?

    From the Carb Cleanup Series:




    1983 GS850G, Cosmos Blue.
    2002 DL1000 V-Strom, Dark Metallic Space Blue.
    2005 KLR685 - Turd II.3, the ReReReTurdening

    Eat more venison.

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    Quote Originally Posted by bwringer View Post
    Excellent! Thanks!

    What are the odds of offering the same for the CV carbs?
    The odds are certain looking at those pics and i'll change my first post and thread title to include them too.
    The hard work was developing the tooling and the compression insertion rig for successful repeat operations.
    It looks like most if not all Mikuni plunger heads are 8mm dia with the main difference being in the stems so it won't be a big deal and i can always make different mandrels to suit if there's any major differences.
    I only concentrated on the SC's and VM's because that's where the demand was in the Kwak Z1 club due to them being discontinued.
    I have no idea what other model plungers are no longer available and wasn't actively looking but if the demand is there i'll do it.
    Last edited by zed1015; 10-17-2020 at 12:58 PM.

  7. #7
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    I stumbled upon Robís service by accident on eBay a few weeks ago. I sent mine out to him and they made the round trip from California to the United Kingdom and back in 12 days. The whole process couldnít have been any easier. My plungers were so degraded that I could press my fingernail into them and it left a permanent indentation. Iím sure this didnít help things with my over fueling issues. Iím blown away that my plungers look like brand new factory parts. Truly top notch work. I just got them back today and Iím really looking forward dropping them in my Ď78 GS750 and seeing how it performs. Iíll report back when I get some saddle time. Thanks again Rob!

    Matt
    Last edited by mattd1205; 10-08-2020 at 12:30 AM.
    1978 Suzuki GS750

    Past bikes owned:
    1979 Suzuki GS750, 1980 Suzuki GS850, 1977 Suzuki GS550, 1969 Honda CB350, 1976 Harley Davidson SS175, 1979 Motobecane 50V, 1978 Puch Maxi, 1977 Puch Newport, 1980 Tomos Bullet, 1978 Motobecane 50VLA, 1978 AMF Roadmaster

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    Please keep us posted, Matt-Thanks! My interest has piqued.
    '78 GS750E (currently undergoing TLC).

  9. #9
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    Quote Originally Posted by 748cc View Post
    Please keep us posted, Matt-Thanks! My interest has piqued.
    I did notice some things right off the bat when I put Rob’s rebuilt plungers in my carbs. When I’d blip the throttle, the engine would always dip well below my set idle speed before recovering. That’s gone now. the throttle response seems much more responsive than it’s ever been. Also gone is the the idling muscle car smell while sitting at a red light. Mind you this is with no further tuning. I haven’t gone far enough to have an exact number on fuel economy yet but I wouldn’t be shocked if that’s improved as well. All in all I’m quite satisfied.

    Matt
    1978 Suzuki GS750

    Past bikes owned:
    1979 Suzuki GS750, 1980 Suzuki GS850, 1977 Suzuki GS550, 1969 Honda CB350, 1976 Harley Davidson SS175, 1979 Motobecane 50V, 1978 Puch Maxi, 1977 Puch Newport, 1980 Tomos Bullet, 1978 Motobecane 50VLA, 1978 AMF Roadmaster

  10. #10
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    Quote Originally Posted by zed1015 View Post

    I have a thread just like this on the Z1 site and an Ebay listing but the Ebay price is £15 higher to account for their fees etc.

    Thanks.
    Hey Rob,

    This is a bit of a logic leap but as you work with carbs... there are two screws on the arm assembly on my carb set that were locked solid and had obviously been attacked previously by someone with JPS screw drivers so they were scraped round. In the end i had to cut a slice in them to use a flat head impact driver to release them. I can't see a part number and wondered if you had any of those laying around for sale? Poor description but there is only really one 'arm' that comes away from the set of four carbs. Cant get to an image at present.

    regards
    Mike

    Harley Davidson Fatboy
    BMW R1200GT
    BMW F800GT (wife's bike)
    GS550 1978 Project bike

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