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Electronic FMU?

Old 01-28-2004, 10:30 PM
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Default Electronic FMU?

Alright I need some clever thinking here. I'm trying to figure out a good fuel management setup for my Banshee Project so I can get that done. (If you don't know its a twin carb, 2 cylinder 2 stroke 350cc motor) Since its carb'd I just can't throw an FMU on the thing becuase there is no fuel return. So I need something that will control a fuel pump that can raise the fuel pressure per pound of boost. Or if anybody has another fuel setup I'm open for suggestions.

Or maybe Turboedit can come out with something for this motor Or even if anybody has any suggestions on how to do an EFI system that would be great.
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Old 01-29-2004, 04:53 PM
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Default Re:Electronic FMU?

I once saw an article in dirtwheels I think where a banshee had macanical alcahol injection . In the right side case (siting on the bike) a pump was run off the motor from the inside. I dont know how they did it .

My 2 cents. If you enclose the carbs in a box you will have a better time tuning the thing (I think). By pressurizing the air around the carbs you keep the carburators happy because all they need is a higher pressure on the outside to work. Its like going way way below sea level when the box is pressureized. The carbs see that a huge amount of air going past the vanturi because of the pressure differential outside the carb vs inside. They will automatically deliver more fuel.



I read somewhere that carburators are flow based and richen according to air flow through the venturi. I take it that this ment that there isnt a lot you have to do but maybe change jets. You will have to refrence your gas tank to boost I guess so the fuel will flow into the carbs
because when you pressureize the carbs it will blow the fuel back into the tank. I dont think that you can boost directly into the carb it self because they need a pressure drop in the venturi to pull fuel from the bowl.
Am I making sense? You could draw throught the carbs but its not a good way to do it. Fuel pressure wont do anything for you but flood the motor and possibly make a big bomb.

Look up Paxton superchargers. They are where I am getting my knowledge from. Paxton makes craburated supercharger kits for cars. www.paxtonauto.com

I hope that I have helped a little I am really curious about how it will turn out. I want to see 80 foot boosted rooster tails.
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Old 01-29-2004, 05:05 PM
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Default Re:Electronic FMU?

I understand your logic and yeah it makes sense. Pressurizing the gas tank is not going to be a problem becuase we are putting a fuel pump on the fuel line so when boost does kick in the pump will force more fuel through the jets. We're using a pressure switch to activate the pump, my problem is that I need a way to increase that fuel pressure in a ratio with the boost.

construction has a good chance of starting this weekend and maybe fuel management won't be a problem on this bike. The way I look at it, the thing is at WOT 99% of its life and if you ever ridden a Banshee it revs like hell. So the majority of its life will be under full boost and therefore fuel tuning might not be a problem becuase if it runs rich on inital spool up and runs fine at full boost thats all that matters. The bike is manily used for hillclimbs, long trail riding and on the street.
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Old 01-29-2004, 05:51 PM
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Default Re:Electronic FMU?

I dont follow you with the fuel pressure and pump. The carbs supply fuel based on flow not fuel pressure.
All that needs to be done is make sure that the float bowls stay full and that the carbs are big enough to handle the demand . It might be benificial to have slightly more pressure on the feed line to the carbs so that the fuel is for sure flowing into the carbs too much pressure might over flow the bowl.
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Old 01-29-2004, 05:58 PM
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Default Re:Electronic FMU?

You can run fuel pressure into a carb. East Coast ATV has a turbo Banshee and their fuel management is a variable jet and a fuel pump on stock carbs. The trick is to force more fuel through the jets. I don't know how but they had a variable pressure regulator and I want kinda the same thing. The fuel pressure started at 1psi and at full boost it was at 15psi.
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Old 01-29-2004, 06:13 PM
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Default Re:Electronic FMU?

You lost me. In normal form carbs on banshees are fueled by gravity. The fuel is drawn out of the bowl by the vacume inside the venturi.

I guess if you were forcing the air through the carb inlet directly you would have to pressurize the fuel inlet that way. You will have to do a bunch of stuff to make the carb work right though. The fuel will be spraying through the jets and possibly it will make a big bomb under you butt. :P I am curious at how that works because it goes against the way the carb is supposed to work.
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Old 01-29-2004, 08:16 PM
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Default Re:Electronic FMU?

there is such thing is an fmu for carbs. A dude i know runs one on his turbo vw rail.
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Old 01-30-2004, 06:46 PM
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Default Re:Electronic FMU?

on the www.toohighpsi.com website, there are some pics of a guy boost referencing his fuel pump. I don't know what a banshee fuel pump looks like, or if you can do it. but, boost pressure was supplied to the fuel pump. A fuel pump sees X amount of pressure over reference. Which is usually ambient pressure, 14.7psi at sea level. So, if you supply the carb with 7psi, and you are running 6psi of boost, then your carb will only see 1psi......But, if you send 6psi to the fuel pump (on the top of the diaphram, not the bottom where the fuel is), then your fuel pump will put out an extra 6psi ontop of the 7psi, making 13psi total coming out of the fuel pump. it's going to fight 6psi of boost, so the carb is going to see 7psi. I think I confused myself already.

anyways.. tap a boost pressure line into the air side of your fuel pump, and your carb will always see the right psi. Becuase of the way venturi's work, you shouldn't need to do any work to the carb except fine tuning.
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Old 01-30-2004, 06:49 PM
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Default Re:Electronic FMU?

http://www.toohighpsi.com/BudgetTT/tthowto.htm

Here's the page.. it's half way down, you can see two pics of the fuel pump modified.
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Old 02-02-2004, 01:48 PM
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Default Re:Electronic FMU?

Just install EFI, it's way worth it. Carbs suck.
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