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Single downdraught carb help


whitefoxxx
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Hey team

 

I am wanting to swap the carb out on my Toyota 4k-u.

 

Motor has only had small amount of work (mild cam, free flow exhaust, and full internal freshen up)

 

I have currently got a Weber 32/36 on it and personally im not a fan, needs rejetting and some modification to the throttle linkage to make it feel nicer on the pedal and drive as it should.

 

I thought about just rebuilding a factory aisan carb but they are crap out of the factory anyway so dont see the point.

 

I dont want to spend huge money.  I have been looking into a nikki carb off the likes of a mazda b2000 or similar (because they can be bolted onto a factory manifold with little to no modification to manifold or throttle linkage) but i cant find any info out on factory jet size or venturi size to compare to the aisan or weber carb specs.  Does anyone know the specs of these nikki carbs? My google searches have found little to no relevant information

 

Or any other suggestions to carbs that would be well suited as a small upgrade. heard datsun l18 carbs are worth looking into aswell

 

Any information or feedback appreciated

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poorly adapted factory bits usually work epic, one dosn't want to over-complicate things too much.

 

32/36 is probably one of the better options without the expense of a side-draft set-up.

 

unsure on jetting for your usage, only ever supplied the adaptor and mainfold, or used them on bigger engines without changes.

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Yea the cam is pretty tame and being a 1.3 i feel the carb is a bit big anyway, only put it on as seemed to be a popular option. I just used a bit of metal to bolt the 2 throttle peices together but its by no means flash. Would rather somthing more similar but slightly bigger than factory carb.

Not looking for flash performance, more reliability with a slight hp gain & straight foward maintence. Its only a weekend car but id like to know its ready to drive no trouble whenever i felt the urge to

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I'm happy with the Weber 28/36 i fitted to my 5k. It was fitted to Anglias/Cortinas and was a popular upgrade back in the day. Mechanically activated secondary choke and removable venturis to suit approx 1000 to 1600cc motors. Worth a Google for more info

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Yeah, I read that that is a much better weber to suit the k series motors, they just seem to be a bit harder to get hold of.

 

By the looks of it tho everyone is saying weber, i think stepping down to the 28/36 looks to be my best option since there is alot more information on them than the nikki i was looking into.  Still have the issue with making up some god awful accelerator cable bracket / linkage tho haha :(

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i say fuck the weber, i build heaps of these things, and webers are a pain in the arse to fit/tune/fuck around with for little to no gain, factory carbs work mint if they are jetted right, make sure you go for the latest model 4/5k carb with the bigger venturis, remove the vacuum opereated butterfly and plug the holes for mechanical secondarys,  you can also use one of the 2tb twin carbs on its own, bigger venturis, bolts straight on , vacuum secondaries but can be easily modded for mechanical operation. 

webers can be made to work, but for the hassle and expense its far easier to either work with something factory, or just bite the bullet and go sidedrafts or bike carbs etc.

a guy in oamaru done a 14.5ish 1/4 mile on a modded factory carb on a well worked 1430cc 3k race car (factory carb cos class restrictions)

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Thanks for the feedback phatt20

 

Your feelings about the weber are very similar to mine in regards to hassle and f'ing around

 

i was looking at somthing other than the factory carb purely to have the bigger venturis, and since im not racing it i can do what i wish haha.

 

What advantages is there to having mechanical secondarys over vacuum?  I have a couple of k series carbs at home but not sure how to identify if it is the later model with the bigger venturis (h had read there was a bigger 4k/5k one) but no where said how to identify it.

 

I had never thought of a 2t carb, does it require any modification to hook up accelerator cable? and does it require rejetting or are the factory jet sizes ample for small gain.

 

Thanks for all this feedback guys, i'm sure it will not only help me but it will give some good information to the next person like me trying to google search their options for upgrades on these motors :)

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its a single one of the pair of 2tb twin carbs, 2/3t single carbs have bigger bolt spacing. yep they require a bit of jet work.

have a look down the top of the carbs you have and the venturi size will be stamped on the venturii , use a good torch cos they are sometimes hard to see.  

mechanical secondaries are better for throttle response , vacuum secondaries are good for driveability/economy etc. 

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Thanks ill have a gander when i get home.

 

Have you used any of these carbs and know of appropriate jet sizes for either.  Probably more after throttle response than economy. 

 

Cars off the road at the moment about to get some more rust taken out before next summer (ke20 2door sedan) so its prefect time to sort this all out.

How do i go about converting to mechanical? is there a linkage kit to use off somthing else or aftermarket kit or is a bit of a custom jobby

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I prefer vacuum as they don't open when you don't have the airspeed for the secondaries. Its super dependant on the carb though.

 

Seriously though spend the $200 and get a wideband, asking people for jet sizes doesn't work, you need to tune the carb for your engine. People always go on about how shit XYZ carb is when they haven't even tried to get it running properly for their engine yet. If you have a cam you may need to mod the idle circuit to deliver more fuel/air as you may/will have less vaccuum, is the accel pump shot too big/small? how's the fueling on primary & main jets? these are things you have no idea until you put something on and measure it. If you find you cannot tune the carb to be nice on your engine after that then throw it in the bin. 

 

I am also a +1 on using a factory carb, they are great units and if tuned to your setup will most likely work better than the webber. 

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Thanks Spencer, i will look very seriously into getting a wideband sensor. If i can find the bigger venturi factory carb from the later model model i will probably look at using that as this will most likley give me what i want out of the car.

 

Now to try and spot these venturi size numbers haha

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