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  1. #1
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    Best Merc Carbs for High performance 2.5 ?

    What are the best Merc carbs for a 2.5 that is cut to 260 specs? I currently have WMH-39s on my FRANKENMERC motor.

  2. #2
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    don't know about best but
    I run the wh-46 carbs that came on the carbed merc race motors,,,sst120..140 and modvp
    these have baffles and slosh tubes from merc in them
    they also came on production motors late 80s to early 90s but with no baffle/tubes
    Im running them on 260+orted motors,260/80 pistons,crosported 7 pedal intakes,260 electronics and wheel,260 divider and tuner, 34cc heads
    with crossported intake gotta drop the idle circuit to a smaller jet and larger for main
    hope this helps
    Last edited by johnmiffco; 07-03-2015 at 04:55 PM.

  3. #3
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    are those different than whats on 245's my idle and bottom end is kinda soggy

  4. #4
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    wh 20,39,41 ,46 are old style dual float bowl and good to use
    just the 46 was the 1s merc chose to come on their race carbed motors
    the 245s all had single float carbs
    lots of the time the crossported intake will make the motor soft at throttle up slowly window
    as air speed is not pulling good fuel through the jets
    from the extra hole sucking through 2 throats
    really good tuning will take most away
    the old wh carbs flow more fuel through the idle circuit in my opinion
    but also I know them well from racing with them for so many yrs
    Last edited by johnmiffco; 07-03-2015 at 06:23 PM.

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  6. #5
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    so its possible to tune these 3310's and make bottom end lean idle and richen main jet
    or find set of dual float and jet them accordingly

  7. #6
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    when u lean down the idle
    u have to back off the idle timing for rpm wanted
    and that makes it worse when u hit throttle
    a lot of air with no fuel till rpm hits and pulls fuel through mains
    tuning is everything to find the happy spot for every motor
    there is plenty on this site that know the single bowl carbs
    I never messed with them as I learned all I needed on the old style for my 120 boat and drags yrs before that

  8. #7
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    all idle timing does is move timing arm forward advanced or back retarded ,my thinking is retarded for top end like automobile engine , yes/no?

  9. #8
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    idle timing is not top end rpms,,,,so don't understand that ,,,,
    just me personaly have found is
    when idle timing is less than 0 the motor is lean and trying to rev higher so back off timing
    to get desired idle say 1,200
    but if u add fuel motor needs more timing advanced to burn it
    thus raising idle timing up to desired rpm
    now the hot rod motor is a lot happier
    and when hit throttle there is fuel there to help with the transfer rpms from idle jet to main
    stock motors from factory are usually lean and timing backed off for less smoke and epa reasons
    as why when 10% alcy was added lots of older motors melted
    u have to find out what works for u if ur doing all ur own tuning
    with the wh style carbs I learned a lot over 30yrs to get them to fire on 1 compression stroke of 1 cylinmder
    as off the dock reaction meant everything when racing 120/140/formula150 classes
    Last edited by johnmiffco; 07-03-2015 at 09:54 PM.

  10. #9
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    if I try and set mine to 0 its a plain dog if I advance idle timing which moves timing arm forward it runs better less smoke

  11. #10
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    over internet have no clue where ur fuel to air mixture is
    sounds like ur already fat down low
    if u advance idle timing and runs better /less smoke
    just as I described adding fuel must raise timing to get idle up
    may want to try bigger jet for less fuel
    as u might be puddling too much fuel making it a dog when hit throttle
    carb tuning is a learning thing going from 1 way to another to find ur spot
    compression,oil mix,float heaight,timing,jets,setting flys,pick up tube,lots of variables to gat all synced

  12. #11
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    Wow lots of great info, can You give me an indicator when I have the correct Idle mixture screw adjustment?

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