slide carb

[dwilfong]

I am going to try and mod a small slide carb to run on the big nitro engs.

http://www.ebay.com/itm/180666477460?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649

Cheep enough to play with at $25 shipped to the house.

Also many different needle jets and needles available for this carb design.

going to remove the main jet and put a fuel control valve thew the bottom of the bowl controlled by the 3rd channel.

Will use a design like the fuel doctor set up with a slot to control flow.

This way all adjustment will be done with the servo. From full flow to no flow with just the servo.

Will post some pics as I go with this project.

David

 

[dwilfong]

don't need the pump that is on those carbs. there metering system is reliant on vacuum signal to pull the needle seat off. It can get confusing trying to set it up.

This carb is simple and have tuned many of this kind of carb on my dirt bikes.

Also for $25 can mess a few up and not get in over my head in cost.

Like a slide carb with a needle. Many Different needle jets or emulsification tube as I call them and needles are available for this carb.

I like the premixing of the fuel and air before it is sucked in to the venturi.

Will all depend on the size of the whole carb if it will fit in the boat.

Here is a pic of the carb broken down.

 

[Tom Foley]

It's mixed in the venturi as its sucked up the needle jet that protrudes into the venturi of the carb . Pilot jet will be way too small I'm thinking right off the bat , heavy also . you like tinkering !!

 

[dwilfong]

Their will be no pilot jet screwed in to the bottom of the needle jet . It will be replaced with the slot valve controlled by the 3rd channel. the pilot valve will be full adjustable.

You know when you pull out the needle jet and it has all those little holes drilled in it.

That is the holes the air enters the needle jet tube and mixes with the fuel before it is sucked in to the venturi. the air is controlled by the air bleed jet or orifice in the front of the carb venturi.

All most all carb have a emulsification chamber to premix the air fuel before it is put in to the venturi.

The zoom carb dose this in the venturi with the holes drilled in the spray bar.

The idle circuit will probably be blocked off as are eng don't really idle. well if you call 10000RPM idle then thy do. the carb slide will be opened to far to use this circuit any way at this RPM.

 

[Tom Foley]

Yes the air bleed holes in the Needle jet forgot about hose little devils !. Also thinking about the spring pressure on the slide . We need video for sure !

 

[dwilfong]

Ya those little devils. :lol:

That is the whole reason for using this carb. It is amazing what thy will do to the fuel droplet size.

The spring is no big deal. If a servo can turn the rudder at 80+ the spring will be nothing.

I will have a video don't worry.

Waiting on the calibration plate for the flow bench to be made to do some bench testing with the strobe light at night.

Now the wife will be jealous playing in the dark with the strobe. :unsure:

 

[tnrcboatracer]

Make sure that the rubber and plastic parts are compatible with alky/nitro. MAny of the gas motor seals are not!.

 

[dwilfong]

Ya that plastic float my have to go. Thy make a rebuild kit with a brass float.

Have bin tossing this around in my head and think the first build will be with no float bowl.

I will just put a fuel nipple on the bottom of the needle jet in place of the pilot jet and hook the line from the BV needle to it.

Will also not use the idle circuit.

Want to keep it simple to start the testing.

 

[dwilfong]

Here is the first attempt. Removed every thing that was not needed. choke assy ,idle circuit,bowl and needle seat. got a little carried away and got in to the slide chamber and also the main jet air bleed cavity. But that is alright now I know where thy are now.

Weight is 3g more than a stock carb.

Have a 10-32 90deg fitting to put on the bottom of the main jet tube. This will go to the BV needle for the first try.

I will fit in my SGX 90 boat with a adapter plate on the RS 1.01.

That will be next to adapted it to the eng.

Then the cable linkage to the servo.

David

 

[dwilfong]

Mounting done. no modifications need to the RS back plate. Will just need to counter sink the carb before I mill off the air horn.

Looks good will fit under the cowl of my SGX.

Cable next.

 

[dwilfong]

 

[dwilfong]

Fuel nipple done new carb cut down and mounted.

Getting close.

 

[dwilfong]

Well did some testing on my flow box mock up and found that a pressurized fuel delivery will not work with the emulsification tube .

The fuel will spit out the air bleed in certain low flow high pressure situations. When you back off the throttle and their is pressure built up in the tank. It is most pronounced when the tank is almost empty.

Will test a separate float chamber set up next like thy use Europe.

This will keep the needle settings constant.

Could use some measurements on some float chambers from those that use them.

Like the CMB chamber but not sure of the size of the unit?

 

[Michael Caruso]

Well did some testing on my flow box mock up and found that a pressurized fuel delivery will not work with the emulsification tube .

The fuel will spit out the air bleed in certain low flow high pressure situations. When you back off the throttle and their is pressure built up in the tank. It is most pronounced when the tank is almost empty.

Will test a separate float chamber set up next like thy use Europe.

This will keep the needle settings constant.

Could use some measurements on some float chambers from those that use them.

Like the CMB chamber but not sure of the size of the unit?

Very cool.

I would like to know if you are trying to use pressure in the tank?

Mike

 

[dwilfong]

Well did some testing on my flow box mock up and found that a pressurized fuel delivery will not work with the emulsification tube .

The fuel will spit out the air bleed in certain low flow high pressure situations. When you back off the throttle and their is pressure built up in the tank. It is most pronounced when the tank is almost empty.

Will test a separate float chamber set up next like thy use Europe.

This will keep the needle settings constant.

Could use some measurements on some float chambers from those that use them.

Like the CMB chamber but not sure of the size of the unit?

Very cool.

I would like to know if you are trying to use pressure in the tank?

Mike

Yes it was a pressurized tank.

Used a needle on a T fitting to control the pressure in the tank. then hooked up my BM flow meter to set the pressure to 4psi witch is about 220 on the BM meter.

Then ran the system on my make shift flow box at 25 CFM.

I am building a float chamber that will fit in my SGX rigger and will test the setup on the box to see how large of a chamber will be needed to keep up with the carb.

the chamber will be clear to set the fuel level and see how this affects the fuel delivery in the carb.

 

[Joe Warren]

I am going to try and mod a small slide carb to run on the big nitro engs.

http://www.ebay.com/...984.m1439.l2649

Cheep enough to play with at $25 shipped to the house.

Also many different needle jets and needles available for this carb design.

going to remove the main jet and put a fuel control valve thew the bottom of the bowl controlled by the 3rd channel.

Will use a design like the fuel doctor set up with a slot to control flow.

This way all adjustment will be done with the servo. From full flow to no flow with just the servo.

Will post some pics as I go with this project.

David

Novarossi ran these for years on the Short stroke SS .21.... I might even have one?.... the barrel valve carb was a improvement. On Many Big engine carbs it is important to keep the Spary bar in the middle of the open hole. Thats why CMB uses progressive twisting type barrel valves. reguardlesss of what the opening is the Spray bar is in the middle of the air stream..... B)