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Banjo

Aisin Carby Alternative

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Lots of people seem to have troubles with the aging Aisin carbies, we were provided with on our early Rollas.

I know there are other carbies been taken up over the years, both upright & side draught, but many are expensive.

Query came to me over the weekend, that I thought someone may have already tried.

A mate, which I haven't seen for 12 months called by, & drove his daughters Mazda 121, which he had been working on.

I had not seen it previously, & when he lifted the bonnet, I commented that it was naturally aspirated, as a carby was what I would have expected to find under an air filter housing looking like that depicted below.

image.png.e9367e9c91634ae6530b9ba691c8482d.png

However, the answer was no, & when the filter was removed, what was in view looked like a carby, but was in fact a single injector EFI throttle body, that looked like a carby.  The injector is in the throttle body proper, under that dome in the venturi.

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The Mazda 121 engine it was fitted to is a 1.3 litre, like our 4Ks.

Now this looked a lot simpler than the single injector EFI setup on the Starlets, & I wondered whether anyone on here had ever investigated trying the Mazda one out, on a 4K Rolla engine ?

Cheers Banjo 

 

Edited by Banjo

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How does it determine fuelling?  Is there some sort of rudimentary ecu?

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Yep !   Just like the rudimentary one, I guess, came on the Starlets.

I believe it has a TPS incorporated, & a MAP sensor.

Will do a bit more research today.

Edited by Banjo

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Found this on www.drive.com.au website review.

"Right from the word go, the Mazda 121 of 1990 captured the attention of Australian small-car buyers.

It immediately attracted nicknames (not all of which were complimentary, on the surface at least) and it's bulbous little body was not only the hot topic of discussion for a while, but also encouraged plenty of imitators.

It was probably that unconventional shape that was mostly responsible, but the biggest thing in the 121's favour was that it was seen as different.

And when you think about it, it was different. Even at its most basic level, the 121's design strayed from the well-trodden path by being a four-door sedan with a distinct boot, when just about everything else was either a three or five-door hatchback.

According to Mazda at the time, the all-new 121 was the world's smallest four-door sedan, and compared with the stodgy old 121 it replaced, the new car was also one of the grooviest around.

And despite being externally tiny, the bulbous roofline and upright accommodation meant the car was actually reasonably roomy inside. Certainly, it was better than it appeared from outside and the boot space shamed many a bigger car. Despite the small opening, the boot could hold enough gear for a small family and the large, wide-opening doors made getting in and out less of a drama than it often is in small cars.

"Like the car it replaced, the 121 sedan used a 1.3-litre, four-cylinder engine, but that's where the similarities stopped in their tracks. The later car's engine was a completely new design and used four valves per cylinder operated by a single overhead camshaft. Electronic fuel injection was still far from universal in 1990, and the littlest Mazda used single-point injection (basically an electronic carburettor) to put out 54kW of power at 6,000rpm and 106Nm or torque at 3,700rpm."

At around-town speeds, the car felt pretty lively, but stretch the cruising speed and there wasn't always a lot left in reserve for overtaking or battling headwinds.

Mechanical thrashing and noise was another downside of the 121's engine, and while it was no worse than most small cars when really wrung out, it still managed to make lots of racket when really pushed.

At least Mazda stacked most of the performance reasonably low down in the rev range, so the engine didn't need to be worked too hard to deliver.

The five-speed manual gearbox made the most of what was available under the 121's bonnet, although a lot of buyers gravitated towards the optional four-speed auto, which is never as satisfying to drive and makes the driver work the engine harder.

One area where the 121 led the field was in its handling. Relatively low-profile tyres and reasonably firm suspension meant it was pretty tidy dynamically, at the expense of some ride comfort over bigger bumps and train tracks.

The first shipment of cars missed out on power steering, but later batches had this feature as standard and it will be appreciated by any driver without Charles Atlas forearms.

In fact, non-power-assisted cars can feel a bit brutish to drive, which is at odds with the car's intended role in life, so power steering is worth the extra money and will be easier to resell. Braking was taken care of by a standard-for-the-time front disc/rear drum set-up that performed more than adequately. The quoted kerb mass of less than 900kg obviously helped in that department.

Equipment levels weren't terrific and a radio-cassette is about all you can hope for.

All in all, the 121 sedan broke some important new ground for really small cars and showed that they could be both innovative and classy."

Cheers Banjo

 

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I think the Chaser SX80 was like a Japanese version of our Cressida ?  Think they had a 1.8 liter engine, so maybe the throttle body would be a mite big for a 4K engine.

The Mazda 121 appealed, as it, like the 4K, is 1.3 liters, so could work well, despite the 121 having crossflow head & 16 valves (we wish).  All that could possibly be needed, may be a simple adaptor plate to mate it, to the 4K inlet manifold ?  

I might chase up my mate with the Mazda 121, next weekend, & have a very close look at the setup. Maybe the little ECU, that I assume drives the injector on the 121, would work, just as it is.

Once I finish this distributorless 5K, I might get a 121 throttle body/carby thingo, & have a play.  It might ultimately keep a lot more 4Ks rollin along a lot more efficiently, & smoothly, for a few more years.

Cheers Banjo

 

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Hi Banjo

Curious to the outcome of this.

My son has a 4k in his 25 and always complaining about the Carby.

If this works i believe it could be a simple solution.

Do you think it would cope with a worked 4k also?

Or would he be needing a bigger unit?

Gizzys25

 

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Curious to the outcome of this.

My son has a 4k in his 25 and always complaining about the Carby.

If this works i believe it could be a simple solution.

Do you think it would cope with a worked 4k also?

Or would he be needing a bigger unit?

Gizzys25

Well,  after all this time, I finally have come across one of these Mazda 121 single injector carbies.  It should be here in the next few days, so I'll pull it to pieces, see how it ticks, & see whether it really is an easy task to adapt it to the K series inlet manifold.

Cheers Banjo

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Thank you for that.  That will make it easier, when I do the 'inquisitive kid" thing, & pull it all to pieces, to "see how it works".

image.png.319f66ef467512020ef1670d0e58d03a.png

http://mazdaepc.com/parts/121/AEDA03/C2/1364/

Just looking through that parts list, it has all the necessary sensors to hook up to an ECU.

Air flow Sensor   P/N 13210B

Throttle Position sensor   P/N 189101

Idle Solenoid    P/N 13XKX

Looking promising for a 3K / 4K Aisin standard carby upgrade.

Cheers Banjo

Edited by Banjo

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Four of them..   laid way over on their side almost upside down on a custom  quad-carb manifold straight into the 4K head!

Even two of them would do!

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Had one of these Mazda 121 "Injector Carbies", delivered to me last weekend, by a mate of mine.  It came off a car at a wreckers that were closing down, so only cost $ 20. I haven't cleaned it as yet.  The pics below, are just as I have received it.

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The little red/orange/black wires, are ones I've attached to the TPS (Throttle Position Sensor), so I could test it with my Speeduino ECU.  It worked perfectly.  It has an idle control valve, MAF Sensor, & the injector built-in, with leads & plugs already attached.  Just have to get a plug for the TPS & AFS.  The injector appears to be a low impedance one, as I measured it at around 2.0 ohms, with my multimeter.

So now I'll strip it, & give it a good clean, & see how it ticks", inside, & then design a mating plate, which will allow it to be attached to the K Series inlet manifold flange, in place of the original Aisin carby.

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 Cheers  Banjo

 

 

Edited by Banjo

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Interesting.. what diameter is the barrel?  Asian are using a dual-choke for the same size engine. Put two of them on a 3K twin manifold!

We want before & after dyno graphs!!   Even smartphone GPS ones on the same bit of road...  Car weighs 860kg, even lighter than a KE70.

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Barrel diameter is exactly 40mm.  Certainly got possibilities.  Certainly a lot simper in design, because the injector can provide a very wide range of fuel control.

My guess is, that when I open it up, & look inside, there will be a lot less little passageways, particularly in respect to the idling circuit, which is so problemomatic on the Aisin carbies, when they get old, & block up.

What I thought was a fuel cut-off solenoid, I just realised is an idle actuator to control air around the butterfly, which closes totally, when at idle.

I'll take some more pics, once I get it dissembled.

I found these comments in a review of the Mazda 121, on line.

"Like the car it replaced, the 121 sedan used a 1.3-litre, four-cylinder engine, but that's where the similarities stopped in their tracks. The later car's engine was a completely new design and used four valves per cylinder operated by a single overhead camshaft. Electronic fuel injection was still far from universal in 1990, and the littlest Mazda used single-point injection (basically an electronic carburettor) to put out 54kW of power at 6,000rpm and 106Nm or torque at 3,700rpm. At around-town speeds, the car felt pretty lively, but stretch the cruising speed and there wasn't always a lot left in reserve for overtaking or battling headwinds.  Mechanical thrashing and noise was another downside of the 121's engine, and while it was no worse than most small cars when really wrung out, it still managed to make lots of racket when really pushed.   At least Mazda stacked most of the performance reasonably low down in the rev range, so the engine didn't need to be worked too hard to deliver.   The five-speed manual gearbox made the most of what was available under the 121's bonnet, although a lot of buyers gravitated towards the optional four-speed auto, which is never as satisfying to drive and makes the driver work the engine harder."

Cheers Banjo

Edited by Banjo

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