Your mother could suck start a Harley with a straw...

[batesy]

Okay, so ignoring my father's interesting review of dear old ma's venturi action, I'd like to ask you - the great unwashed masses of Ratsun - if it is worth putting my brother's set of twin 45 Weber's on my stock L20 auto?

 

It currently has a 32/36 on it. But I want moaaarr roaaarr.

 

My issue is 'will it be drivable with twins and the auto behind it?'.

 

Currently my 32/36 is pretty laggy off idle. I've had a bit of a play with it *snigger snigger* but I'm guessing that most webers have this delay unless you idle them right up.

 

Will the twin 45s be worse in this regard, with an auto?

 

Does any of this make sense?

 

And do you even fucking care?

 

Thought not.

[banzai510(hainz)]

40s would be better if possible. I have 44s Mikunis on another car and rather run 40s.

But dont the shift points come from manifold vaccume or soemthing like that. and most sidedrafts you might have 1 port to run this unless you drill out each runner then manifold them together to 1 input.

 

I would try a 38/38 weber if you just got to try this if you can find a used one.

Best to stick with the 32/36 I believe.

 

I never really seen a L series with sidedrafts here with a auto behind it

[batesy]

Yeah, I think I might be too keen. That's the problem with having access to something that's free.

 

You are right, Hainz. Sticking with the 32/36 probably is the smartest idea. Best bet is to probably whack a manual box on a toss the auto. I've got two four speeds sitting here.

[DanielC]

Very basic carburetor theory.  Unlike fuel injection, carbs know only one thing.  How fast is the air going through me.  If the air velocity is too slow, the carb venturi cannot create enough vacuum to accurately measure the gas, for the amount of air going through it.  This can also happen if you open the carb too fast for the engine to respond.

 

Another thing about carbs.  Many carbs have off idle transition ports, that are just above the throttle plate, at idle.  If the idle is too fast, the throttle plate is already partially above the port.   Many times you can actually get better off idle response if the idle speed is slower.

[tr8er]

I had the 38/38 with auto for years. It was not great at the bottom end. But great top end. Can't help with twins though. Seems a bit out of range.

[batesy]

Another thing about carbs. Many carbs have off idle transition ports, that are just above the throttle plate, at idle. If the idle is too fast, the throttle plate is already partially above the port. Many times you can actually get better off idle response if the idle speed is slower.

Thanks, Daniel. I might have another fiddle with the carb. Less maybe more by the sound of it. I reckon it ran better before I re-tuned it!!

[KoHeartsGPA]

I run a single side draft 48mm mikuni, it was very tricky to tune it but with my dad's knowledge and experience with them we were able to get it tuned and I was able to track down some different sizes of jets (that you will need to have) for when the ever changing wants from the engine calls for them.....and it will....I'm not familiar with Webber but mikuni settings will vary depending on atmospheric pressures and altitudes, the good part is the setting of the mixtures haven't needed adjustments, but i did find myself changing jets to give the engine what it wants, with that being said....expect low mpg, I get about 15....on highway!, but it's a blast to drive :thumbup:

[datzenmike]

Don't judge all carbs by what you have right now. The current one may be a big POS.

 

Automatics are always 'in gear' and can't be revved up to overcome a poor idle start. They need a good solid high vacuum at idle. The 32/36 is not a vacuum secondary that comes in only when needed. It's progressive, and almost always tipped in way too soon manually. Too much carb open drops the intake vacuum and air speed past the venturi.

 

Look down the primary with the engine off and pump the throttle. If the accelerator pump is working properly, you should see a strong squirt of gas come out. This is needed to transition from idle to primary jet running. It's also the point where the air speeds is too slow and the mixture tends to be lean. The accelerator pump is designed to add the missing fuel to make the mixture richer and remove this 'flat spot' until the primary can take over.

[Ratwagon1600]

Short answer Batesy (sort of short anyway).

 

Twin Weber's will give you that wonderful throaty L series fuel sucking roar on your stock L20 auto, with piss poor driveability unless you have the accelerator pedal pushed through the firewall, and a fuel bill the size of some small thirld world countries national debt.

 

Im not saying it cant, or shouldnt be done, just that its a lot more complicated than bolting the buggers onto the motor.

 

As others have posted, jetting, tune etc all play a big part.  You could certainly get the twin setup to work effectively, however, to get them jetted, choked, balanced properly could but a significant dent in your wallet.

 

FWIW, with your current driveline I second the 32/36 option.

 

Also, unless you only have one leg, or are totally enamoured with the auto tragic gear box, if you have the time and inclination to swap it for a manul box thats a good option imltho.

 

Relatively easy to do the swap as long as you have the right bits, and theres still a lot more 180b's than 1600's around so parts shouldnt be a problem.

 

And, I care, but thats the kinda guy I am (you drive an auto 180b, you need all the caring you can get :) )

[batesy]

Don't judge all carbs by what you have right now. The current one may be a big POS.

 

 

 

Look down the primary with the engine off and pump the throttle. If the accelerator pump is working properly, you should see a strong squirt of gas come out. This is needed to transition from idle to primary jet running. It's also the point where the air speeds is too slow and the mixture tends to be lean. The accelerator pump is designed to add the missing fuel to make the mixture richer and remove this 'flat spot' until the primary can take over.

I'm able to screw the idle mixture screw all the way in without the engine stalling. Maybe someone put on a bigger jet than what I need?

 

I could just take it to the weber workshop down the road but I hate not knowing how to tune it, given that the carbs are a pretty simple design.

 

Unfortunately, the design of my brain is even simpler!

[datzenmike]

http://www.redlineweber.com/html/Tech/carburetor_set_up_and_lean_best_.htm

 

 

http://www.webercarbsdirect.com/v/vspfiles/images/Weber%20Trouble%20Shooting%20Guide.pdf

[Jester]

For what it's worth, I printed out the pages from the second link that Mike poste about a month ago. Followed everything to the letter and my truck has never run better. 

[batesy]

For what it's worth, I printed out the pages on from the second link that Mike poste about a month ago. Followed everything to the letter and my truck has never run better. 

 

 

Gonna give it a go again this afternoon. Start from scratch.

[scooter]

I don't know why these guys are saying it'll be shitty, my webers don't eat that much more fuel than stock just cruisin, when your wailing on it it eats more, but it goes faster.

 

I'd say run small chokes and buy the recline jet kit and go have fun. Enjoy the weber roar.

 

[tr8er]

The comments are related to the ratio of airflow and throat size. If the throat is too big for the displacement, the Venturi effect will be inaccurate, difficult to dial, and generally not desirable. I'm not putting down Weber, just putting down that much weber.

[MicroMachinery]

I never really seen a L series with sidedrafts here with a auto behind it

http://community.ratsun.net/topic/4473-zerows-610-4-door/

[scooter]

Even if you went down to like a 30mm choke? Hmmm..

 

And i want MOAR carb on mine, id be willing to sell my 45's so i can buy 50 or 55's.... Bahahaha

 

Not that i need it, but im running 40 mil chokes right now and i think i could get a better venturi with the bigger carbs with a similar sized choke.... Im looking into annular boosters like the aftermarket downleg ones you can buy for holleys, i feel the dcoe's boosters leave some to be desired regarding fuel atomization