83 XL600R twin flat slide carbs

Discussion in 'Thumpers' started by cyclewizard, Dec 9, 2007.

  1. cyclewizard

    cyclewizard Long timer

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    I got a 83 XL600 twin carb, I'm thinking of putting twin flat slide 32mm carbs on it. Anybody done this or knows of a site that has info for the swap?
    #1
  2. Gregster

    Gregster Been here awhile

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    I havn't read of that swap yet, but this site or http://www.thumpertalk.com/ would be your best bet for the info in North America.
    Here are a couple other sites you could search, but you might need http://babelfish.altavista.com/ to do some translating:
    http://www.xl600.de/site/
    http://www.hondaxl.it/
    There is also some good stuff here:
    http://justxr.com/justxr.html
    http://www.xlintperformance.com/index.htm
    http://www.oldrice.com/xl_page.htm
    Good luck on your quest.
    If you figure it out, please post a report here.
    #2
  3. Cordless

    Cordless Two Wheel Addict

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    The main problem with this conversion is that the intake has two ports for each of the carbs--you will have to match the twin carbs to low and higher volume air. You might be better off modding the existing Honda carbs.
    #3
  4. Reposado1800

    Reposado1800 Juicy J fan!

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    I think it would be better to swap in a XR600R head and single carb from something parted out on Ebay but I am no expert.
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  5. Gregster

    Gregster Been here awhile

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    Single carb heads are very difficult to make work on the XL600R frame because the rear shock is dead centre, with one carb intake boot on either side of it. Single carb frames have the rear shock offset a bit to one side to accomidate it.
    #5
  6. Reposado1800

    Reposado1800 Juicy J fan!

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    OOPS! My bad.
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  7. cyclewizard

    cyclewizard Long timer

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    Is there any good carb mods I can do instead of swaping out for the 32's.
    On my 83 model the primary carb has a 125 main an the secondary has a 112 main. Would 120 mains be better on both carbs?
    How could I get the second carb to open at the same time as the primary carb? Also this bike has a reed valve, should I get rid of that?
    It seems like you shouldn't need it since the 84 an up did not have one.
    The bike runs great, But I would like to get all the performance I can out of the ole gal. I'm also going to get my exhaust jet hot coated.
    For a 125.00 bucks I think it's well worth it.

    thanks
    Pop's
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  8. Tech23

    Tech23 Been here awhile

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    What you have is a 2 stage carb, this allows for higher intake velocity (vacuum) and better fuel atomization at low RPM, (= better throttle response) while on the primary carb. As opposed to a single larger carb which would decrease intake velocity (vacuum) at smaller throttle openings, and give poor throttle response. You then have the secondary (right side) carb that starts to open at about 1/2 throttle. You end up with a larger carb at wide open settings than if you had a larger single carb. Trust me a single 60mm carb would not work as well as your 2 stage (dual 30mm = 60mm) carb. The reed valve between the two intake ports, function is to deliver an air/fuel mixture through both intake valves while on the primary carb. without it you would only be supplying air/fuel through the left intake valve from idle to 1/2 throttle. This would cause the right intake valve to run hot, because there would be no cooling effect of the incoming air/fuel mixture on the intake valve, and this would also not fill the big 100mm bore evenly. Also the jetting on each carb is different because each carb has to handle different throttle openings. There is some overlap in their operation. Essentially you have all the benefits of a large carb at full throttle, and all the benefits of a smaller carb from idle to half throttle.
    I had an early "83" that I bought new, and could not get the bike off the dealers lot, due to persistent stalling at idle. I mean the bike would shut off if left to idle for 2 minutes. The bike would also stall when chopping the throttle approaching a red light. There was a technical bulletin on the "83" XL600R for "slow speed drivability". The update included if I remember correctly, new needles for each carb, a new insulator (intake manifold) which had a passage between both ports, a new CDI box with a different ignition advance curve. They then removed the limiter cap from the mixture screw and adjusted the mixture. These bikes were so lean they would not idle from the factory. I believe the bikes that received the slow speed drivability update from the dealer were to have a center punch mark on the engine next to the engine serial number. I dont know how many bikes were involved, but they were performing this update on "83's" in dealer inventory prior to delivery. Or at least they were supposed too. It was rather dangerous having a 600cc kick start only bike shut off in traffic. But the update combined with a supertrapp slip-on made a huge difference.
    I hope this helps some......Tech23
    #8
  9. cyclewizard

    cyclewizard Long timer

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    That's some great info, I'll check for the update an see if it was done.
    Thanks for your help.

    Pop's
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  10. JStory

    JStory Long timer

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  11. Gregster

    Gregster Been here awhile

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    Behold, the beauty of the twin carb thumper.
    It was a damnd shame they couldn't have tweaked the hardware a bit to make them a little easier to set up.
    When they are working properly, they make better and more easy to use low end, while having a stonking good top end.
    [​IMG]
    #11
  12. Tech23

    Tech23 Been here awhile

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    You are welcome, and thank you Gregster, for the technical features page from the back of the factory manual. I wonder what was different about the "84" that the reed valve cross port was eliminated. May have been the update manifold with the connecting passage.
    If the update "kit" and/or the parts that comprise the kit are no longer available, and your bike was not updated... and you are not experiencing slow speed drivability/stalling as I described. I dont think I would sweat it. I would be curious if the bike fell into the VIN range for the update though. Some tech bulletins are handled on an "as needed basis". So a letter was not mailed to owners with the potential issue. These types of technical updates often have an "expiration date", as to how long the dealers will perform the work, and factory will issue the parts.

    I had an obvious problem, that I was able to show the dealer repeatedly. I struggled to keep the bike running at delivery, and trying to be careful with how I was breaking in my new engine (with lots of moving parts inside). I rode down the street to the first gas station to top up the tank for the ride home. I had the engine stall when turning into the gas stations lot and coasted over to the pump. I started the bike, rode over to the gas station exit and it stalled again. I caught a red at the next light and again coasted to a stop. I turned around and went right back to the dealer. I started the bike, and let it idle on the kickstand for them to watch, and six times it shut down. I have to admit that I did not have to wait long for the phone call to bring the bike in for the update, so Honda knew there was an issue with their first year XL600R. The fact that I had a Yamaha XT500 prior to the XL, kept me from getting killed in traffic. I was most times able to refire it while coasting. Gotta love manual decompresors. So yeah, I was releived when the issue was addressed.

    Also I would think the primary carb (left) would have the smaller main jet, and the secondary carbs. main would be larger. More air filling the big bore when the secondary carb is open. My shop manual went with the bike when I sold it.

    After you research the VIN/update post your findings....I am curious.
    Tech23.
    #12
  13. cptoversteer

    cptoversteer drooling oaf

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    Also I would think the primary carb (left) would have the smaller main jet, and the secondary carbs. main would be larger. More air filling the big bore when the secondary carb is open. My shop manual went with the bike when I sold it.

    no, actually, that's correct per what honda claims in the chop manual....the 125 in the primary carb and the 112 in the secondary. one major feature of drivability kit was richer pilot jet....sorry, don't recall exact #s but maybe a 65.

    i'm about to find out effect of having em swapped, as i just learned on carb teardown that prev mechanic put em in backwards. :huh

    your reasoning is correct, tho....most multi-venturi carb arrangements (single carb or multis) use bigger throat in sceondary
    #13
  14. apex

    apex /////

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    my '87 XL600R in all-stock form ran better than most XR650s Ive ridden. I kept my '85 XL250R, match ported it to accept XL350R intake manifold and installed an XL350R primary and XR350R secondary, I used XR500R float bowls, they have easy jet access/change "ports". the dual-carbed Hondas reved so high it was easy to meltdown and crack the head due to lean mixtures. I dialed mine in with an O2 sensor and LED mix indicator.
    #14
  15. Tech23

    Tech23 Been here awhile

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    cptoversteer....is that right? I did not intend to mislead, It is a wonder I remember any of this from 15 years ago. I cant even remember what I had for breakfast this morning. Thanks and ride safe......Tech23
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  16. apex

    apex /////

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    I just looked at the XL600R manual/ '84 is 120/120, '84 CA is 118/118, '85+ 118/115 hope that helps. FWIW from the XL250R manual '84 is 108/122, '85 is 102/100, '86 is 102/105, '87 is 105/105 intresting! I dont have an XL350R manual, anyone? now I gotta find my old notes.. DUAL CARBS!
    #16
  17. cptoversteer

    cptoversteer drooling oaf

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    Apex, you're correct.....i forgot that they changed jetting for later years. from the #s, it almost seems like they were doing trial and error like we have to! i was referring to spec for an '83 like i have.

    my general perception is that like virtually every jap bike from early 80s, it's substantially leaner than ideal from factory and could do with some richening. in my case, less so as i live at 4000'+ and what's way lean at sea level ain't too far off here. i'm initially reassembling my carbs with stock jetting and needle but shimming the needle up about .020 to slightly richen midrange. i'll let you know results when i get it back together this weekend.

    another XL600R bug i recently learned of: the seals between carb insulator plate and head go the way of all rubber and shrink/ossify, even worse than most due to the heat they must endure. when my bike was cold, this made it run lean due to the vac leakage this allowed....but it sealed up once it warmed up even slightly and things expanded. made for really hard-to-find starting woes....every morning i would get it to run a little bit at a time and then it would stall, until it eventually sealed up and ran right. spend the $ and replace these whenever you have carbs off, even if you get o-rings at Ace Hdwe.
    #17
  18. oprahrider

    oprahrider Pissed Off Primates Racin

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    WORST STARTING BIKE EVER MADE PERIOD!:knary

    Cold = 5-7 kicks
    Hot = 3-5 kicks

    Warm = 10-50-F'n who knows kicks:eek2

    No shit sometimes we would leave them running and chained to a pole if we had to run into a store for a few minutes. It just wasn't worth the chance that it would cool off to the WARM stage....To make things worse my Dad was 53 years old,5'11" and about 360 lbs. Meaning I would usually have to start 2 of these bitches:eek1 Everyday for 3 weeks so he wouldn't have a heart attack and croak on me in Mecky-Co.

    23 years later and my insole of my right foot still hurts....LoL....but still it was a great trip.
    #18
  19. Seikkailu_R

    Seikkailu_R Been here awhile

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    XL600r, its not hard to start if carbs and ignition are ok.
    And kicker is knowing what he is doing.
    Cold,warm or hot, dosnt matter.
    Max few kicks and it was running.

    With faulty ignition and carbs, few to hundrets kicks...
    #19
  20. Gregster

    Gregster Been here awhile

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    With a new Ricky Stator and everything else in good shape, mine starts on the first or sometimes second kick every time hot, warm, or cold.
    #20