90AETO carb details

[ThunderPie]

Hello,
I am from Southafrica and have a pair of 90AETOs in use.
My plan is to convert those engines to a fuel injection (Simple throttle body low pressure injection)

In case that I work in Europe I dont have access to my engines right know and need some techn. details, maybe someone here can help me.

Vital info I need is the inside diameter of the 90AETO and the 70AETO carbs.

I run this project together with a german engineer, who already has the electronic hardware (ECU) for this application and did some ULV airplane engines conversions to fuel injection (Hirth 2 stroke 3 cylinder engines)

So please take this request serious and please stick to the facts in this thread.

kind regards
Stephan Mester

[boscoe99]

That will be an interesting project. I have long thought about converting a Yamaha with multiple carburetors to a single throttle body EFI version. But I was thinking of a four stroke conversion and not a two stroke conversion.

What EFI system have you selected? Kits over here in the US are quite expensive and seem to be tailored to engines with much greater displacement. Don't think that ours would work on a smaller displacement outboard. Cost of the conversion here would exceed the value of the motor in most cases and might be very complex from a technical perspective given the differences between a Yamaha outboard motor system and an automotive type system.

But to answer your question, the only way that I know of to determine the ID of a carburetor venturi is to measure it. I have never seen specifications published by Yamaha. Keeping in mind that they don't make the carburetors and would have no reason to even have this information available. Maybe someone reading your post will have a 90 Yamaha and can take a measurement or two.

Keep us posted on the project please.

[robert graham]

Just curious, but is your reason for this fuel injection conversion for motor efficiency and/or economy?....will there be a provision for cold start fuel enrichening?....good luck and keep us posted on your progress!...

[boscoe99]

A benefit of EFI is that it automatically enriches the fuel supply during a cold condition. Actually, it makes automatic adjustments for all operating temperatures from stone cold to hot as hell.

My EFI cold weather starts today are instantaneous. Being an old dog, I remember having a hellava time getting a carbureted motor to start in cold weather. Automatic or manual choke. Then there was the issue of forgetting to push the manual choke knob in. A cloud of gassy smelling black smoke would follow the car down the road.

[robert graham]

So maybe he gets a bit more power and/or fuel economy for his time/money/effort?....

[ThunderPie]

We use a simple ECU and stick to the OEM ignition system, which runs independant.
The goal is to eliminate mechanical parts and make those engines more fuel efficiant.

for prototypes we will use throttle bodies from motorcycles such as Triumph Speed Triple.

We will run those engines with a Lambda wideband con*****er LSU4.9D
that will automaticly adjust with the ECU the fuel mixture ratio
(in theory that is not a big problem at all)

Problem is the hardware, f.e. the right throttle bodies

So again we really need to know which inside diameter the 70/75/85/90 hp carburetors of those engines have

[boscoe99]

So do you take the area of the each throttle body, multiply times three, and then find an EFI throttle body that will support that area? Maybe go up a tad in area to compensate for an EFI throttle body typically having a larger diameter than a carburetor would due to the carburetor having a venturi?

How do you engineer/manufacture a manifold that transitions from one throttle body hole to three intake passageways?

I had not thought of converting a motorcycle EFI system to an outboard motor but I like the concept. How does the ignition system get separated from the fuel delivery system? Seems to me they go hand in hand and would need to be processed by the same ECU. Maybe I am misunderstanding what you are saying/doing.

[boscoe99]

So maybe he gets a bit more power and/or fuel economy for his time/money/effort?....

More power, better economy, better throttle response, less engine wear possibly, more user friendly, easier starting, less problematic, etc. It just takes time and money. Sometimes lots of it.

I see where Holly (the carburetor people) offer a retrofit system to convert from a carburetor to an EFI system in cars and trucks.

https://www.holley.com/products/fuel...uel_injection/

[TownsendsFJR1300]

Holleys had that system out for a very long time....

In any case, for the OP, (if it helps), newer Harley Davidson's are fuel injected with ONE THROTTLE BODY and a single manifold that splits to both cylinders. Their TB's, I believe are Mikuni's.

Even thou their engines are larger displacement 4 strokes, the stock HD engine might put out 60HP (in your ball park).

[SeaDawg3]

More power, better economy, better throttle response, less engine wear possibly, more user friendly, easier starting, less problematic, etc. It just takes time and money. Sometimes lots of it.

I see where Holly (the carburetor people) offer a retrofit system to convert from a carburetor to an EFI system in cars and trucks.

https://www.holley.com/products/fuel...uel_injection/

Boscoe, I`ve used the Holley Pro-jection set up years ago. Holley used the tach signal as a reference for injector pulse rates. stand alone fully adjustable ECU. That was long ago back in the early 90`s.

The stand alone EFI systems today are insane! I wouldn`t hesitate again to use such a system given I was back into restomods.

OP, cool idea!

[boscoe99]

Holleys had that system out for a very long time....

In any case, for the OP, (if it helps), newer Harley Davidson's are fuel injected with ONE THROTTLE BODY and a single manifold that splits to both cylinders. Their TB's, I believe are Mikuni's.

Even thou their engines are larger displacement 4 strokes, the stock HD engine might put out 60HP (in your ball park).

The thing I like about some of the Holley stuff is that mostly all of the sensors/rheostats/potentiometers/thermistors are mounted on provisions on the throttle body itself. Makes a retrofit easier. I like the thought of using a motorcycle/watercraft/snowsled EFI system but God only knows where all of the sensors are located. Would make the conversion a bit more difficult. But, finding a crashed bike might enable one to pick up a complete EFI system for not much money.

With 3D printing available some one, some where, will figure a way to print an intake manifold that will interface with the engine on one side and the throttle body on the other side. Technology today is insane and becoming more insane all of the time.

Mr. OP, keep us posted please. As you may note this is interesting stuff to read about for a number of us. Thanks. Photos would be a bonus.

[ThunderPie]

Well it looks like no body here has the informations we need,
this thread is now turning into a useless discuss about some Harley engines and Holley aftermarket kits.

I leave and try to find out those details somewhere else.

best regards

[boscoe99]

Some might think that it is useless (and stupid) to do what you are considering doing.

You seem to be looking for some information without the understanding that the information for which you are seeking might not even be needed.

We have a saying here "don't let the door hit you in the ass on your way out".

Best and kindest regards.

[rodbolt17]

agreed.
dunno what kinda anganeeers are tying this but they forgot that carbs have a venture, EFI does not.
that would make measuring a carb throat totally useless.
my self I would use a single shutter design air valve and 3 injectors.

but first ya gotta do the math on air displacement,volumetric efficiency and air speed past the shutter to come up with a shutter large enough to flow but not so large as to allow to much air.

at the end of the day it comes down to a 14.7/1 a/f ratio at all engine speeds.

[SeaDawg3]

W O W ! ya think with his knowledge he would have already figured out the size/area needed.
but if it were me and it was an experiment with user data/log to make changes, I`d probably go with matching the CC`s of the outboard with a similar size, already in production throttle body set up with injector rail from a jet ski.

the 2 stroke yamaha GP1300R`s were EFI, I know as I`ve had fuel con*****ers and remapped ecu`s for that machine. That motor could pull past 7400 rpm`s with the stock Bore TB``s. Then there was this guy Ross who bored them out for more flow...
plus there are the other TB`s from the 4 stroke yamaha engines, the FX series... and on and on and on...
an adapter could have bee made or is probably out there to go from the carb base profile to a rubber boot/clamp configuration to hold the TB`s... simple as I see it...

I remember back in the day aftermarket TB`s were avail with a hug cost, I don`t think that company is around these days or producing the same TB``s offered in the 80-90`s

oh well...