how to build a blowthrough carb for your turbo bike

[turbonate]

had a few people ask me how i got mine to work right, so i figured why not just post a thread about it. i've been building turbo cars with blowthrough carbs for years and decided it was time to do a blowthrough bike. i've put almost 12000 miles on it and ridden it all over hell and creation with no issues other than getting some trash in the needle and seat outside of slidell la once.

the bike

[turbonate]

i'll try to list everything in the right order as the pictures

the first thing you need is an electric fuel pump, i use a frame mount pump from an 89 f-150, they are available at any parts chain for about a bill. you can also see the fuel feed port i added to my tank in this picture.

you'll also need a good quailty return style boost referenced fuel pressure regulator, i use an aeromotive since i've had great success with them on my race cars

, i guess it goes without saying that you'll need a return port in your tank as well, i used the stock pickup location as a return port.

next you need to seal all the atmospheric vents on the carb and drill and tap it somewhere above the fuel level, i built a 4 into one manifold and used an old zenith i had.

[turbonate]

this has nothing to do with the carb, but you are going to need an oil feed and return for the turbo. i drilled and tapped both camshaft oil pressure galleries in the head and tied them together and ran that to the pressure side of the turbo.

next i drilled and tapped the case above the oil level directly in front of the cam chain and fed the returned oil from the turbo into it.

[turbonate]

now here is the key to the kingdom that makes this whole mess work right. i installed a pitot tube into the charge pipe with a flared end directly in front of the compressor outlet. now tie the hose from this into a y that feeds into the pressure port you put into the side of the carb, and the fitting on your boost referenced fuel pressure regulator. what this does is the flared tube creates a restriction in the intake path and the higher pressure generated is carried to the float bowl and fuel pressure regulator creating about a 1.3 to 1 float bowl to carb throat pressure differential causing a self enrichening condition under boost that will keep your pistons from having a thermonuclear malfunction. on my bike i'm making right at 10psi so i limited my total timing at 8 degrees shy of the stock max, it's been a couple of years since i set it all up, so i don't remember the exact numbers.

[ibuiltmine]

you have a video fo this bike running? I like turbo stuff

[turbonate]

you have a video fo this bike running? I like turbo stuff

i sure don't,i don't even own a video camera.

[Randeezy868]

Cool man thats a pretty sweet setup.

[gmp]

awesome i have a few 14b's laying around and i have always wanted to do this to a sr500 nothing like hearing a turbo'd motorbike.

[turbonate]

awesome i have a few 14b's laying around and i have always wanted to do this to a sr500 nothing like hearing a turbo'd motorbike.

except riding one

[Randeezy868]

I think im following you with the carb mods. Are you using anything in the carb? Or just using it basically as a throttle body with fuel injection. I cant tell if your using the carb for idle fuel and using thefuel pump to boost fuel(sort of like an extra injector controller) or did you basically go full fuel injection with the fuel pump running fuel at idle and at boost. Also, any problem with crushing the floats in the carb. Ive heard boost will squash them and not allow them
To work properly. Ive done some turbo cars but nothing with a carb.

[ibuiltmine]

except riding one

Im looking for a Yamaha Warrior. That is going to be my first turbo build.

Have you done any EFI turbo stuff?

[turbonate]

I think im following you with the carb mods. Are you using anything in the carb? Or just using it basically as a throttle body with fuel injection. I cant tell if your using the carb for idle fuel and using thefuel pump to boost fuel(sort of like an extra injector controller) or did you basically go full fuel injection with the fuel pump running fuel at idle and at boost. Also, any problem with crushing the floats in the carb. Ive heard boost will squash them and not allow them
To work properly. Ive done some turbo cars but nothing with a carb.

i've got the carb working just like a normal one, all the circuits function normally. the pitot tube provides about a 1.3 to 1 float bowl to carb throat pressure ratio to cause the air fuel ratio to enrichen under boost, the fuel pump runs at all times, and the fuel pressure is set at 1 psi at idle so as to not overpower the needle and seat, the electric fuel pump simply provides a pressure increase under boost so that fuel will keep flowing in the the carb and not get blown back into the fuel tank. i'm running stock brass floats unfilled, i've not had any problems with them up to 10psi, but anymore than that and i'd find some carbs with nitrophyl (foam) floats. if you have anymore questions i'll be more than happy to help any way i can.

[turbonate]

Im looking for a Yamaha Warrior. That is going to be my first turbo build.

Have you done any EFI turbo stuff?

warrior bike or 4 wheeler?
i've built and programmed 3 megasquirts, but never on a bike. been playing with the idea of converting the kawi to fuel injection, but i don't really want to have to add an intercooler since i won't be getting the cooling effect that a blowthrough provides when the fuel atomizes.

[ibuiltmine]

warrior bike or 4 wheeler?
i've built and programmed 3 megasquirts, but never on a bike. been playing with the idea of converting the kawi to fuel injection, but i don't really want to have to add an intercooler since i won't be getting the cooling effect that a blowthrough provides when the fuel atomizes.

Yeah, a bike.
When you do decide to convert to EFI, let me know. I have a complete 04 gsxr750 with a spun main. Id sell the entire wire harness/throttle bodies, computer, fuel pump, etc.....
I even have a power commander PCIII Brand new in the box

[turbonate]

i was beating on my poor turbo bike this weekend in the shop and broke the chain, which slapped the clutch pushrod, which in turn broke the case. luckily i have a spare engine, and yes, i'm drunk in the picture.

[SOKfab]

i just read the steps u posted, and they were extremely helpful, thanx i have some questions, but i dont have time now ill try to get back on tonight.

[turbonate]

i'll be glad to help any way i can

[SOKfab]

ok im a little confused on where to drill and tap the carb exactly?

[turbonate]

you want to drill an tap it above the fuel level so the pressure picked up from the pitot tube will help force fuel into the carb throat. you might look into how the overflow vent is set up on yours, that will work just as well as long as you are sure to plug all the other atmospheric vents.

[SOKfab]

Ok im gonna post a pic of my carb and just let me know where,