carb question.

Hi Big B, 3 times the gas seems like an awfull lot. Sounds like
a lot of the extra gas might be going out the tail pipe?

What makes a Tillotson worse? I've been thinking about changing
to one of these carbs for a long time.

Here's a pic of an Ibea slide carb:
2qdwu94.jpg


Got bad feedback on this on another forum. Looks perfect to me,
but a bit expensive. I think I've also come across 3 jet Ibea carbs,
would those be easier to tune for idle?
 
Those kartcarbs aren't efficient with fuel. You proably got negative feedback, because nobody know's how they work.

You got the 2 screw and 3 screw version. The 3 screw version is one with powerjet. Like on the pic you posted. No need for power jet on scooters :)
 
Bram: Why does it take much more fuel than regular "floater" carbs?
Cause exessive fuel would mean a drop in power, and I dont think you would drive like that.
Or is it on lower rpm and throttle opening that the engine runs very rich?

And another question, does these cart carbs carry a small amount of fuel or does the fuel go directly from the pump to the jets?
What I am wondering is if the carb cuts the fuel delivery to the air the moment the pump stops pumping or if you could drive a short period with fuel left in the carb (like on floater carbs when you cut the fuel delivery to the float bowl).
 
Last edited:
mt5-ronken said:
Bram: Why does it take much more fuel than regular "floater" carbs?
Cause exessive fuel would mean a drop in power, and I dont think you would drive like that.
Or is it on lower rpm and throttle opening that the engine runs very rich?

And another question, does these cart carbs carry a small amount of fuel or does the fuel go directly from the pump to the jets?
What I am wondering is if the carb cuts the fuel delivery to the air the moment the pump stops pumping or if you could drive a short period with fuel left in the carb (like on floater carbs when you cut the fuel delivery to the float bowl).
Click to expand...

No if you run out of fuel in your gastank it's over. The fuel line is your floatbowl :p

I don't know why it uses so much fuel. I think it has to with what you said, about the richness of fuel on low rpm.
 
So if you cut the fuel delivery to the carb at WOT will the engine die instantly or will it run for a few seconds more (risk leaning under that period)?
 
mt5-ronken said:
So if you cut the fuel delivery to the carb at WOT will the engine die instantly or will it run for a few seconds more (risk leaning under that period)?
Click to expand...

It will run a few seconds, because there is fuel in the fuel line.
These carbs have a membrane, and that's why they need vacuum.
 
Big B NRG said:
It will run a few seconds, because there is fuel in the fuel line.
These carbs have a membrane, and that's why they need vacuum.
Click to expand...

Maybe I'm going far off topic now, if so please say so...

What I want is to cut the fuel delivery to the air right off, with maybe a max of half a second where it continues to deliver fuel.

So if you cut the fuel on the fuel line right in front of the carb fuel inlet and cut the vacuum too, will it still run for a few seconds on fuel still present within the carb or will the engine die instantly?

I'm trying to find a way to make two separate fuel systems which you can very quickly switch between during the ride.
But that also means that the primary fuel system (carb maybe) will have to begin working the moment you switch from the secondary fuel system.

So far the only way I've come up with is EFI with two separate injectors, but that would be too hard to make I think...
 
mt5-ronken said:
Maybe I'm going far off topic now, if so please say so...

What I want is to cut the fuel delivery to the air right off, with maybe a max of half a second where it continues to deliver fuel.

So if you cut the fuel on the fuel line right in front of the carb fuel inlet and cut the vacuum too, will it still run for a few seconds on fuel still present within the carb or will the engine die instantly?

I'm trying to find a way to make two separate fuel systems which you can very quickly switch between during the ride.
But that also means that the primary fuel system (carb maybe) will have to begin working the moment you switch from the secondary fuel system.

So far the only way I've come up with is EFI with two separate injectors, but that would be too hard to make I think...
Click to expand...


The moment you remove the vacuum, the engines stops.
The moment you cut the fuel to the carb, it will run for 1 sec. Maybe less. Because it does not have a fuelbowl. Just a membrane that opens and closes on the pulse of the engine.


What is your purpose for such a system?
 
Hmm, it might work with a cart cab then...
I'll have to make som tests with such carb someday...

I want to have a primary fuel system with usual fuel (ethanol in my case) to drive with on usual occations, but when I need extra power I want to be able to swith over to an other fuel system which will deliver a more powerful fuel (most likely methanol+nitromethane) for a few seconds.
Now that fuel is not good for either the engine, yourself or you wallet for long time use, but when used during short periods of time during the ride I see not much problem with it.

It would then be some kind of the "power on demand" like nitrous oxide systems have, although rather than just injecting gas and more fuel I would totally disable the primary fuel system and just use the carb at WOT to draw air through and run solely on the secondary fuel system for a short period of time.
But the moment you disable the secondary system the primary system has to start working like normal again.

If the secondary system only would be used at WOT you could quite easily make a simple injection system which would spray a constant amount of fuel to the inlet air.


But first things first, how to disable the primary fuel system (most likely floater or membrane carb) and then make a quick and smooth switch to the secondary fuel system and then back again.
 
That might work, if the valves to the different fuel lines are positioned directly in front of the carb inlet it might work cause then the fuels won't have much time to blend with each other.
The extra amount of secondary fuel needed could be injected using some kind of injection system.

With a membrane carb that might work, but I wonder how well the parts handles methanol and nitromethane.

I am more fond of floater carbs, but the float bowl carries too much fuel to allow a quick switch between the fuels without allowing the fuels to blend.
Maybe I could decrease the volume in the floatbowl and use a membrane fuel pump to keep the fuel level right?

Btw Bram, do you still use your membrane carb or do you use a floater carb now?
 
mt5-ronken said:
That might work, if the valves to the different fuel lines are positioned directly in front of the carb inlet it might work cause then the fuels won't have much time to blend with each other.
The extra amount of secondary fuel needed could be injected using some kind of injection system.

With a membrane carb that might work, but I wonder how well the parts handles methanol and nitromethane.

I am more fond of floater carbs, but the float bowl carries too much fuel to allow a quick switch between the fuels without allowing the fuels to blend.
Maybe I could decrease the volume in the floatbowl and use a membrane fuel pump to keep the fuel level right?

Btw Bram, do you still use your membrane carb or do you use a floater carb now?
Click to expand...

No I'm not using my membrane carb anymore. Just a floatbowl one.

Why can't the fuels mix?
 
Have you tried running the alternate fuel, to see what other
tuning changes might be required? Might be more complicated
than just switching fuels on the fly.
 
Bram: okey, was the tm28ss better?

well, because methanol and nitromethane carries a fair amount of more oxygen than ethanol. When you engage the secondary fuel system that wouldnt matter much, it would just run rich for a short period of time cause the engine keeps getting ethanol.
But when you disengage the secondary fuel system the spray of extra secondary fuel stops, but the carb still has a small amount of secandary fuel inside itself that will cause it to lean off in a very not so good way :/
Hopefully it leans so much that the engine cant ignite that fuel, but you can never know...

Even if it's in a very short period of time I don't want to drive super lean at high rpm...
Maybe should make the disengage of the secondary fuel injection delayed by a second or so, so it will richen the mixture the moment you switch back to the primary fuel...


StepVino: Nope, but I know what I will have to do, pour a lot more fuel into the engine, maybe twice as much as now (and now on ethanol i drive with around 45% more fuel than on gasoline)
The methanol and nitromethane both burns very slowly (on rich mixtures which I will run on) so I don't have to bother about the ignition system more than I have to make sure it can ignite this fairly wet mixture.
Because of the higher energy released I will lower the compression ratio and take a little higher squish just to be on the safe side.

The thing I don't know is if things in the carb can handle the fuel or not, but that maybe don't make much difference when it's only going to be there in a very short time...
 
mt5-ronken said:
Bram: okey, was the tm28ss better?

well, because methanol and nitromethane carries a fair amount of more oxygen than ethanol. When you engage the secondary fuel system that wouldnt matter much, it would just run rich for a short period of time cause the engine keeps getting ethanol.
But when you disengage the secondary fuel system the spray of extra secondary fuel stops, but the carb still has a small amount of secandary fuel inside itself that will cause it to lean off in a very not so good way :/
Hopefully it leans so much that the engine cant ignite that fuel, but you can never know...

Even if it's in a very short period of time I don't want to drive super lean at high rpm...
Maybe should make the disengage of the secondary fuel injection delayed by a second or so, so it will richen the mixture the moment you switch back to the primary fuel...


StepVino: Nope, but I know what I will have to do, pour a lot more fuel into the engine, maybe twice as much as now (and now on ethanol i drive with around 45% more fuel than on gasoline)
The methanol and nitromethane both burns very slowly (on rich mixtures which I will run on) so I don't have to bother about the ignition system more than I have to make sure it can ignite this fairly wet mixture.
Because of the higher energy released I will lower the compression ratio and take a little higher squish just to be on the safe side.

The thing I don't know is if things in the carb can handle the fuel or not, but that maybe don't make much difference when it's only going to be there in a very short time...
Click to expand...

It's going to be hard to realize that.
I found the TM28SS more precizer to adjust. It runs much "cleaner".

The Ibea was just big hole, much fuel+much air and go.
I think it had to do with the fuelmembrane thickness. It's used on 100cc engines and those give a stronger pulse. But I never got that fare to test.
 
That it is going to be hard I already know, question is if it is worth the job if I get it right...
I have wanted to drive on that fuel for a long time, but the fact that it is really nasty and expensive has made it impossible for me to drive it as primary fuel, but just for short periods of time it would not be a problem, except meking it work for that period, which isn't going to be easy...

That is what I have been thinking about membrane carbs as well.
Maybe I will do better with a floater carb and perhaps try to decrease the floatbowl volumea little...
 

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