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how high do you rev your datsun
Topic Started: Sep 27 2006, 04:23 AM (2,520 Views)
ocphangaz
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Datsun Taikor
my previous mod on the stock carb was superb. better FC, better power delivery, better drivability...

max rev was higher... but still no 6000... free rev can 6.5k la... stilljet too small actually. but 14.4cents/km on highway was superb!

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sam1741
Expert Driver
what mod you have done on the stock carb?
can teach us?
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ocphangaz
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Datsun Taikor
few things to do and get the idea

carb is most efficient if the air is flow "straight" down the throat and venturi. this will improve the throttle response and fuel efficiency.

second the performance of the carb is measured by the air flow rate aka CFM

FIRST - improve flow and reduce turbulence
turbulence will reduce the efficiency of the carb. so you need to...

polish the internals - stock carbs are casted... there are sharp edges that you can sand down with sand paper.

remove unecessary parts - like choke... choke plate creates turbulence

change screws - look at the screws holding the throttle plate.. it's actually 0.5mm too long and protruding out. this will cause turbulence

Venturi - make sure the venturi are straight... that means must be perfect 90degrees vertical.

Air movements.. - look down the carb from above.. you notice that the 2 silver tubes are actually obstructing the air from moving straight down the venturi... it's about 0.8mm thick.. shave it! i shaved it until knife edge alike... it might be sharp.. but i can see the jets from the carb throat now.

bell mouth - notice that the mouth of the carb are quite thick? about 1mm thick.. take a dremel and shave it into "trumpets". instead of || become |\ (keratan rentas).. i hope you understand. other than "straighten" the airflow... it also incease the suction area. (more CFM)

radiused all internal edge... - rounded all edges. this will reduce turbulence.

throttle plate - i remove it and shave the edge to 45 degrees on the edge touching the carb throat. this will improve throttle response as the plate open significantly earlier (without the bucu to block the air) and also reduce the turbulence as the egde become aerofoil design during WOT (wide open throttle) becareful not to reduce the diameter of the plate. or you'll face high idling rpm. just shave the edge touching the carb throat away from the shaft.

CFM - increase the air flow
to increase the airflow you need to increase the surface area for the air to move. with less obstruction, there will be less airflow lost due to turbulence.

Bell throat - outher than straighten the air flow.. it also increase the suction area... this is why trumpets are so effective.

trumpets - same reason as above

remove choke plate - if you notice, even with the plate open, it's obstructing 15 - 20% of the primary throat. remove it. make sure you block the hole after that with epoxy or screw. remove all of it.. even the shaft holding the choke plate.

throttle plate screws - by changing the screw to appropriate (shorter) screws, you remove access screw that will obstruct air flow and create turbulence that will reduce your CFM

other mods

there are many other mods can be done... but without precision tools and time (i did all in less than 2 hours), it's hard for me to do...

1. at the shaft holding the throttle plate. you can shave the back between the screws about 1mm to furthur increase air flow. --|------|-- become --|-____-|-- "|" are screws

2. cut the whole silver tubes... how it affect the carb? dono... but it doesn't need to be that long.

3. clean and polish the carb internal fuel delivery holes... if you got the tools why not? this will improve the fuel delivery at high rev.
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fendy_kjg
Super Driver
3-4 je lah
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sam1741
Expert Driver
wow.. ocp
thanks
i will mod that on my carb also...

too bad i not have dremel tools...
must find one...



btw
look down the carb
there r 4 cooper color tube..
dono what is that.. blocking the intake
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dongdong0507
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Super Driver
float chamber vent?
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washabushi
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Datsun Taikor
wah...
so many things OCP had done on its previous carb...
y dont u just sell ur carb to us?
lol...

*headache too technical*
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ocphangaz
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Datsun Taikor
sam1741
Sep 6 2007, 02:05 PM
wow.. ocp
thanks
i will mod that on my carb also...

too bad i not have dremel tools...
must find one...



btw
look down the carb
there r 4 cooper color tube..
dono what is that.. blocking the intake

the copper ones are the one that squirt fuel... leave that alone...

washabushi... i sold my carb to eject120Y for RM350, together with a newer K&N filter, whole set of carb internal parts, trumpets and also K&N recharge kit.

city driving my FC drop from 0.17/km to 0.16/km
highway the lowest was 0.144/km from kl to penang and sg petani... manage to travel with another guy and full load trunk, kl - sg petani (baling exit) then back to penang for dinner with 1 tank fuel... still got slightly less than 1/4 tank of fuel left.

the carb become like weber... got to press lightly then only got power. press too much the carb flood. but the throttle responds was way better. and have 3 stage of acceleration compared to 2 before mod.

std carb. initial power (using primary jet), additional power (secondary)
modded carb, initial power (1/2 of primary jet), additional power (second half of primary throttle.. pickup almost same with secondary jet pickup on std carb) then third power when secondary open.

power delivery more linear... feel like ;

power rating

modded carb
1 - 2 - 3

std carb
1 - 2.5


with power gain, but lower FC. if DID CAI last time sure FC will go lower somemore to 13sens region.
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dongdong0507
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Super Driver
wow! a good investment too! how mush have to spend? DIY?
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ocphangaz
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Datsun Taikor
spend erm.... RM5 for the trumpet cup.. the rest all DIY

TIPs:
for the throttle plate screw.... you can use the screw from computer motherboards... the screw to lock the mobo to casing...

same size, same thread... and the length is ngam ngam the shaft. it'll not protrude out.
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sam1741
Expert Driver
wah.. thanks for the tips ocp bro
i got few of the motherboard screw lying around.. :D :D

btw.. i going to buy another carb to mod.. and bolt it on straight away.. to leave the current one intact...
dono how much it will cost.
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Jee1
Super Driver
For those who complain engine damn bising, u can do something to overcome the problem. Just change to electric fan.

Benefits - engine will be lighter ( alot of difference )...engine cooler even if stuck in jam & on air cond..
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sam1741
Expert Driver
yeah
i have been thinking of that also
since our fan are drive by the belt...
it uses the power of the engine
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abubu
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Datsun Taikor
how much if mod to electric fan?

wad jobs nid to be done?
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ocphangaz
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Datsun Taikor
i bought my carb new from tanchong for RM510...

electircal fan (use Sunny 130Y as it's thinner) about RM20-40 from kedai potong... mod.. find welder to do. electrical, you need to use a 10-15A fuse to your ignition. so when you "ON" your engine the fan already running.

welding costs me RM30 to mod bracket and also make steel plat eto cover the whole radiator as 130Y radistor is only half of ours.

advantage is the lighter engine... but cooling at higher rev is worse than our stock fan.

another way to reduce engine vibration and engine noise is change to electronic ignition.
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