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07-03-2015, 04:24 PM #1
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.
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07-03-2015, 04:52 PM #2
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 helpsLast edited by johnmiffco; 07-03-2015 at 04:55 PM.
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07-03-2015, 05:41 PM #3
are those different than whats on 245's my idle and bottom end is kinda soggy
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07-03-2015, 06:12 PM #4
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 yrsLast edited by johnmiffco; 07-03-2015 at 06:23 PM.
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rgsauger liked this post
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07-03-2015, 08:06 PM #5
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
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07-03-2015, 08:37 PM #6
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
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07-03-2015, 09:15 PM #7
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?
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07-03-2015, 09:48 PM #8
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 classesLast edited by johnmiffco; 07-03-2015 at 09:54 PM.
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07-04-2015, 12:04 AM #9
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
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07-04-2015, 12:38 PM #10
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
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07-04-2015, 09:08 PM #11
Wow lots of great info, can You give me an indicator when I have the correct Idle mixture screw adjustment?
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