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PostPosted: Wed Dec 21, 2011 9:16 pm 
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Joined: Thu Nov 10, 2011 2:30 pm
Posts: 11
hi all
just bought a second hand dcoe 45 for my l18 and it runs like sh*t
hoping someone on here has a similar setup and can give me a good strarting point where it runs ok

excuse my ignorance with these carbs but this is what i have found
with the jets under the cap in the centre of the carb body the 2 outer jets i haven looked at yet but the 2 inner larger ones are made up of 4 pieces
the top part where the screw driver removes it has no markings
the next piece has 175 stamped on it
the middle piece has F2
the bottom piece has 120

my engine is an L18, ported big valve head with a 272 grind cam
was running ok on twin su's.
idles ok, initial response off idle is ok then it turns to sh*t and feels like its running on 2 cylenders and wont rev past 5500rpm just really slow and rough
pulled plugs after a 20km limp hope at 70-95kph in 4th, very very rich fouled....
aparently engine the carbs were off was a l20 with l16 head and ran good
spoke to the owner and he assures me carbs are good just need tuning
any ideas?
thanks in advance


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PostPosted: Wed Dec 21, 2011 9:37 pm 
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Joined: Sun Mar 09, 2003 8:11 pm
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Location: South Adelaide
Why waste your time and money to get a "good starting point"?
Id just take it somewhere and get it tuned professionally with correctly sized chokes and jets to suit your motor combo.


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PostPosted: Wed Dec 21, 2011 10:29 pm 
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Posts: 228
Location: The Gap Brisvegas
The smaller screws under the centre round cap are your idle jets, what are these, theyll say something like 45F9

On the body tubes, up near the butterfly plates will be a approx 1cm round screw in plug with a screwdriver slot, undo, and pull out tje 4 cm long with a thick bit in the middle, these are your pump jets, theyll have like 50 on them, what afe yours?

Next inside the centre bore main tube, ie the 45 mm diameter bore, halfway down, are rhe Auxilliary venturi, held in by a screw underneath, it will be something like 3.5 . Whats your?

Behind this is the choke, it is a narrowing venturi, no need to remove, you will see a figure, like 36. What is yours?

What are your cam opening and closing degrees, ie how much overlap do you have?

And is your engine a stock L 18 at stock capacity?
Are you running twin webets or a single?

Lots of questions, but the webwr documentation will give an indication of what you could aim for.

A decent air fuel sensor and wide band display, with car running under load, will help a lot.

Or

Yeah, a tuning shop! Whats your suburb/location, there may be some on hete that could guide ypu towards a shop more suited.

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Yep, i race a Datsun, and I drive a truck, sometimes I get confused, and then the truck goes fast, and the Datsun gets a lot of boxes shoved into it. AWW GEE


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PostPosted: Wed Dec 21, 2011 10:43 pm 
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Joined: Thu Nov 10, 2011 2:30 pm
Posts: 11
dat2kman wrote:
The smaller screws under the centre round cap are your idle jets, what are these, theyll say something like 45F9

On the body tubes, up near the butterfly plates will be a approx 1cm round screw in plug with a screwdriver slot, undo, and pull out tje 4 cm long with a thick bit in the middle, these are your pump jets, theyll have like 50 on them, what afe yours?

Next inside the centre bore main tube, ie the 45 mm diameter bore, halfway down, are rhe Auxilliary venturi, held in by a screw underneath, it will be something like 3.5 . Whats your?

Behind this is the choke, it is a narrowing venturi, no need to remove, you will see a figure, like 36. What is yours?

What are your cam opening and closing degrees, ie how much overlap do you have?

And is your engine a stock L 18 at stock capacity?
Are you running twin webets or a single?

Lots of questions, but the webwr documentation will give an indication of what you could aim for.

A decent air fuel sensor and wide band display, with car running under load, will help a lot.

Or

Yeah, a tuning shop! Whats your suburb/location, there may be some on hete that could guide ypu towards a shop more suited.
thanks dat2kman will check all thoswe things an report back,
Im pretty rural here (bega nsw) so dont think a tuner is an option otherwise it would have already been there
closest is prob canberrra 250-300km so that s y im after a starting point "nick"
cheers


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PostPosted: Thu Dec 22, 2011 11:50 am 
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Joined: Thu May 13, 2010 9:52 am
Posts: 15
Location: NSW South Coast
Muddie.

Pip Barker at Kalaru Automotive should be able to sort it out for you.


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PostPosted: Thu Dec 22, 2011 9:57 pm 
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Joined: Thu Nov 10, 2011 2:30 pm
Posts: 11
Claude wrote:
Muddie.

Pip Barker at Kalaru Automotive should be able to sort it out for you.
thanks claude ive spoken to pip today and he's said he'll take a look early in the new year
cheers


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PostPosted: Thu Dec 22, 2011 11:23 pm 
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Joined: Fri Jul 16, 2004 11:46 pm
Posts: 399
Location: 3910 Another Peninsula Boy
45mm twin throat Webers have 4 accessible jet sets - the 4 brass "tubes" under the jet cover. Each jet set consists of a fuel jet (bottom), an air jet (top) and a mixing section in the middle (emulsion tube)

1 The "idle circuits" are the 2 smaller jets sets under the jet cover. Used in starting, idling and progressive throttle openings up to about 2500/3000RPM, fuel is fed from these jets through tiny holes around the edge of the butterfly. Typically this circuit is used for 90% of the running time.

2 The power jet circuit (the bigger set of jets under the jet cover). Comes into action after 2500/3000 rpm, feeding fuel through the auxiliary venturi in the centre of each bore.

To temporarily fill the gap between these two jet "circuits" when the throttle is suddenly opened, before the revs are high enough to suck fuel from the power jet circuit, an accelerator pump jet squirts fuel into the intake to fill the fuel "gap" between the idle jet and the power jet.

Airflow
The size of the chokes fitted in each barrel determine the maximum air flow that the engine will draw through the carb. If the chokes are too big the engine wont get enough fuel when the throttle is suddenly opened, and it will cough, splutter, backfire, or die. If they are small it should perform reasonably well at low and medium speed but it wont rev out.

It sounds like your idle circuit is 'OK' to get your engine started but the power circuits and/or pump jets aren't right?

To give you the best chance of driving the car at low throttle openings, you may be able to improve your low speed performance by simply adjusting the idle mixture screws.
Start with the mixture screws opened out 1.5 turns from fully shut. Start the engine and allow it to warm up. Slowly adjust one idle mixture screw weaker(clockwise) or richer (anticlockwise) until the engine reaches its highest idle speed, lower the engine speed using the butterfly stop screw and repeat the adjustment on the other idle mixture screw. Repeat until you have the idle speed at around 700RPM with the lowest possible throttle (butterfly) setting. If your carbs have anti pollution idle bypass air bleed screws (covered by "whitish" plastic "hats"), fully close these before setting the mixture screws above.

The chokes will also be a factor, as will the accelerator/pump jet which give a dose of fuel to fill the gap between the idle jets and the power jets as the engine revs build up under quick throttle opening, before the power jets take over at around 3000RPM .

You can refer to weber tuning books that will tell you where to start with choke sizes. My guess is 34mm or 36mm would be OK for a single carb setup on a stock L18.

Auxiliary venturis, which are in front of the chokes and the first thing you see in each barrel, inject the fuel from the power circuit into the airstream. The right size for your application (3.5 or 4.0?) can also be determined from a tuning book.

Fuel/air jet sizes can also be determined from Weber tuning books (Des Hammill's is a good one), but these are starting points only as each engine is different. Webers should be fine tuned to get the best out of each particular engine, depending largely on gas flow characteristics, using a gas analyser.

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RichardC
SSS016


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PostPosted: Fri Dec 23, 2011 9:44 pm 
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Joined: Thu Nov 10, 2011 2:30 pm
Posts: 11
its a single 45
it runs on PULP
ALL 4 plugs were evenly fouled from overly rich mixture
air corrector is 175
emulsion tube is an F2
main jet is 120
idle jet is 55F9
pump jet is 45
chokes are 34mm
aux venturi has a number 2 on it

ran car for less than a minute on brand new plugs and yeah completely rich fouled again
have checked float level needle and seat etc all seems ok
have checked venturi and both appear to be as you described they should
cheers


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PostPosted: Tue Dec 27, 2011 11:15 pm 
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Joined: Fri Jul 16, 2004 11:46 pm
Posts: 399
Location: 3910 Another Peninsula Boy
First, I think the 34mm chokes are OK to run the engine, but too small for big power at high revs.

The idle jets seem OK with big inlets such as yours. However I can only assume the idle circuit is the cause of the over fueling?

On the power circuit I am struggling with an answer to the rich mixture problem, given the smallish sizes of the your fuel jets. The air jets seem large in comparison to the fuel jets, suggesting it should be running lean. You may have a partial fuel blockage or fuel supply problem at higher revs. Could be the aux venturies are too small, causing low fuel flow, or possibly one has a blocked fuel supply, as you say it sounds like its running on two cylinders when revs increase. Can you see fuel being injected into each airstream through both the auxiliary venturis when you open the throttle? Are both aux venturis fitted with their outlet orifice facing inwards towards the butterfly - rare to be incorrectly fitted backward, but worth checking. 45mm weber aux venturis numbers range from 3.5 upwards (4.0, 4.5, 5.0 etc), so you need to check out your number here. Take each one out to check if you are looking at the correct number (and look for any blockage).

"Baz" says F2 emulsion tubes were used on methanol powered minis - which used a single weber on a 1310cc 4 cylinder engine. He says F8 emulsion tubes are usually used on a Datsun L series. Baz says the F8/9 is a bit "crisper". However, my twin 45mm weber L18 has F2 emulsion tubes, and they work well on it. My weber reference book also describes F2's as richer than F16, F11s, but leaner than F8's and F7's. That is, F2's are THE mid range emulsion tubes - the rest run in numerical order from F16 (lean) to F7 (rich) - no logic here - they are Italian!

If you have lean emulsion tubes you get hesitation in the transfer from the idle circuit to the power circuit (2000-300RPM) , the book says go one range richer in emulsion tubes to smooth the transition.

I found descriptions for 2 engines fitted with a single 45mm DCOE weber twin throat carb.

Here are the settings for a big ported 1300cc mini using a single 45mm weber on high octane petrol (11.1 compression ratio).
38mm chokes
4.5mm aux venturis
F2 emulsion tubes
165 mains
170 air correctors (note these are only one size larger than the mains (fuel) )
45 accelerator pump jets
45F9 idle jet
This engine revs to 8500RPM

For a 1900cc MGB using a single weber
36mm chokes
F16 emulsion tubes
55F9 idle jets
140 main jet
175 air corrector
4.5mm aux venturis

My gut feeling in the power circuit is your fuel jets may be too small relative to the air correction jets.
I am stumped on over rich running. The idle circuit you have is jetted close to those that run well on other engines of similar size.

Persist as it is worth having a weber fed Datsun motor. Try and find others who have a similar set up to yours and compare their jetting.
Anyone out there?

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RichardC
SSS016


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PostPosted: Thu Mar 30, 2017 10:00 am 
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Joined: Thu Mar 30, 2017 7:37 am
Posts: 1
I know this is an old post but I thought I would share some of my data.

Standard L18 block with A87 head and standard cam
Single 45mm Weber
Links cross over manifold
HM21C extractors, 2.5 inch exhaust.
Main Venturi 42mm I had these custom made (just buys 2x 40mm)
Aux Venturi 5.0
Main jets 185
Air correctors 190
Emulsion tubes F16
Idle Jets 50F12
Pump 55
Needle and seat 2.25
Weber ram tubes (100mm?)

We tested this setup on a very long hill doing ~30 sec runs point to point pulling from 2000rpm to redline over a set distance to find the quickest time in 2nd gear (maybe it was 3rd, I forget now). We tried a number of emulsion and jet sizes with runs repeated to get consistent average times for each setup. I have graphs of this somewhere.

I still remember the sound of this bouncing off the hills up at Warburton late in the arvo at the end of summer with cool air temps. :thumbsup:

Also I recommend removing the standard fuel pump. Get an electric fuel pump off an 80's Nissan L series. Throw away both of the right angle fuel fittings and buy some straight fittings (note: I drilled mine to a bigger internal size) of correct thread size and mount in the boot. Upgrade the fuel lines one size too. I had fuel delivery issues when I started playing with webers, I could empty the carb fuel bowls quicker than I could fill them in track days until I went to this setup.


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