[NitroFreak]

Hi Guys,
I´m Max, 19 years old, and a 2 stroke small engine enthusiast.
I´ve built several small single and twin cylinder reed case engines for RC Cars.
Here are some pics of the twin cylinder reed case. It has 57cc with 2x 36mm bore x 28mm stroke.

And it works fantastic.
Here is a video
https://www.youtube.com/watch?v=OyyjH-jTLXY

Here is my newest project, that i have some questions about.

It is using two 32mm bore cylinders with 28mm stroke to make a 45cc twin, having only a single carburator.

The Reed blocks are built-in to make sealing the crankcases easier.
Carburetion is the part where i scratch my head.
In those small cc engines, we normally use "pumper" diaphragm style carburetors, as the fuel tank sits below the carb. I can´t use those in that situation because the diaphragm can only be connected to one crankcase.
So, while one cylinder sucks the mixture that was just enrichened by the fuel that the crankcase pressure just pumped into the carb, the second cylinder will run the carb empty because the first cylinder has already drawn all the gasoline out.
I think it has to be a float bowl carburetor as those dont have an internal fuel pump.
I was thinking of delivering the fuel either by an electronic fuel pump or by pressurizing the gas tank using the pipes.
Has anyone got any experience with a twin cylinder engine running on a single carb?
I was hoping, by using a slide throttle carb the fuel supply would be very steady, and with both cylinders sucking air through the carb, the airflow would be very steady, helping with fuel atomisation and preventing double rich mixtures.

Thanks,
Max

 

[Morph0906]

Dude awesome first post welcome to the site, a moderator had to approve your first Post ! I have no idea what would work best but am subscribed to this one, welcome to E2S

 

[dANbOT]

Sweet dude.
I am a former r/c car enthusiast, although I spent my time with the nitro engines.

What is the application for this engine? HPI Baja twin?

 

[John Tice]

Damn MAX, You’re good. My company uses Solid Works, how about some pictures on the equipment that you use to carve out the parts?
You have promise for the next generation, what can I do to help? How about a liner instead of that plating job. An iron sleeve will give you many change options which you don’t have with the plating.
:thumbsup:
JT

 

[John Tice]

Hello again Max; Please tell us more about yourself & how you’ve been educated at such an early age. You are a fascinating young gentleman who I’m sure we all would like to know more about. I’d love to have you do some additions to How it’s Done.
Keep up the Good Work
JT

 

[toydoc]

Hi Guys,


Here is my newest project, that i have some questions about.

The Reed blocks are built-in to make sealing the crankcases easier.
Carburetion is the part where i scratch my head.
In those small cc engines, we normally use "pumper" diaphragm style carburetors, as the fuel tank sits below the carb. I can´t use those in that situation because the diaphragm can only be connected to one crankcase.
So, while one cylinder sucks the mixture that was just enrichened by the fuel that the crankcase pressure just pumped into the carb, the second cylinder will run the carb empty because the first cylinder has already drawn all the gasoline out.
I think it has to be a float bowl carburetor as those dont have an internal fuel pump.
I was thinking of delivering the fuel either by an electronic fuel pump or by pressurizing the gas tank using the pipes.
Has anyone got any experience with a twin cylinder engine running on a single carb?
I was hoping, by using a slide throttle carb the fuel supply would be very steady, and with both cylinders sucking air through the carb, the airflow would be very steady, helping with fuel atomisation and preventing double rich mixtures.

Thanks,
Max

Nice stuff.

I'd use a Keihin CDKII 28mm with a remote vacuum fuel pump (AKA, any stock Kaw 650 jet ski fuel system 87~90). Tap a nipple for pulse line in one cyl case and go.

How the cyl is orientated with one side feed for intake maybe a issue. It wont have time to flow / fill each side evenly. Then it tricks the motor to thinking the far ports are only booster ports and runs lean on the far side. Then the exhaust pulse is used as a valve. It pushes against in rush of fresh air charge. But the air charge isn't even "push" so more wacky things can happen.

If I offset a reed intake, say 20mm to one side. I have to limit / buffer the near side to keep the air charge "in time" from side to side.

I'd lay the motor on it's side. Feed both cyl through the crank (what's the bottom case now).

The double mixture issue should have been cured with your addition of reeds. R/C race motors use a lot port overlap. So the piston port race motors suck air and push air over the venturi and double carburate on one power stroke. The reeds stop any "push", you won't have that gas fog in front of the carb when running.

 

[John Tice]

Max: I ran pumpers for years while racing Karts. You might use a slide valve carb while having an auxiliary pump tapping each crankcase. Walbro & others make auxiliary pumps; we used to call them Sissy pumps. With one pump on each case, 2 pumps on the engine you should have plenty of fuel for each carburetor. As far as carb size goes, a friend running an 8.2 ci West Bend engine ran 4 Tillotson carbs on each engine with alcohol fuel. He stated that he couldn’t over carb the engine running alcohol.

Back then, we mixed 4oz. per gallon of Green label Castrol castor oil with each gallon of methanol.
This should be easy to scale down for your engines. We hooked the carbs together using bicycle spokes in the linkage. Spokes are small strong & easy to find.
I hope this helps some
JT

 

[NitroFreak]

Thanks!
I´m not worried so much about the distribution of fuel mixture in the heads regarding the position of the ports and boost ports as the mixture will have time to come to a rest while it is at TDC and then spread evenly to the ports and boost ports.
Two fuel pumps, each with their respective cylinder supplying fuel to the carb may work, but then i have an extra two pumps that take up space? The idea was to make it simpler by using only one carburetor.
Is it not possible to just use the exhaust pressure to deliver fuel? That would be the easiest?
I can´t lay the engine on the side because of the way it is built into the car.
John, Yes liners is the way that i want to go. At the moment i use cylinders that are available on the market, and all of them have a plating.
The engine i want to build soon will have my own cylinders with cylinder liners that i hope you will make for me.
I just haven´t finished the design yet.
About me, Its really just me craving for more power and finding ways to get it.
It starts off with your basic port job that you do to the standart engine (22.5cc (32mm bore x 28mm stroke)) that comes with the car, you´re satisfied for some time, but then again you want more. I got a big bore kit (28.5cc (36mm bore) that i ported from the start on, Again i was satisfied for some time, but you tend to always want more.
I got a twin engine that was on the market (heavily aftermarket, needs special install kits), but they all are only piston ports.
At that time i had no idea about CAD, but had a friend who did, and he was also into the RC thing.
We had plans /ideas to make our own reed twin, but he never really got around to do it, so eventually i got sick of waiting for him and got my own copy of solidworks, and started teaching myself how it works (Quite easy, with youtube tutorials, and that kinda thing) Not too hard, just time consuming to get used to all the features.
I started doing the designs for the fist version, continually tweaking it until i was happy.
I then got a friend to mill them for me.
At that time he used a smaller mill, But now he has a big machine that has awesome tolerances.
I´ll have to find some pics of the single cylinder reed case he milled for me recently, the machine work is outstanding, Night and day difference to the pics in the first post.

 

[NitroFreak]

 

[John Tice]

Yes Man

I’d love to be on your team. Most of us are like you, we’re happy for a while but then want more. For us work a day folks, most of us are too busy to take up the self education which you are doing. I’m sure that most of us folks who can contribute to your projects would love to throw in a wrench or two.
Go for it man, with plenty of pictures.
:Cheers:
:NodYes:

 

[ktm550]

nice work. mikuni has many kinds of small pumps. i think you might need to use a float style carb though. vaccum line could be tapped in to the crankcase or transfer port or side of the intake area

http://www.mikuni.com/fs-carburetor.html

 

[NitroFreak]

Okay. The smallest one is 14 litres / hour, isnt that a bit much? the prototype drank fuel at about 2 litres/hour.
Dellorto also has small pumps.
Do you know of a float style carb with a 15-16 mm venturi , apart from the dellorto?

 

[ktm550]

no im not familiar with them real small engines. im sure theres a forum for that type of engine

 

[TrickedCarbine]

I'd imagine you would be able to get a carb from the chainsaw world to do what you need. I've seen lots of large scale RC guys use walboro diaphragm pump and carbs. Definitely consider a carb that has some type of bowl. As stated above, just tap a barb to feed the pump a pulse.

Side note: You sure are talented for a younger fella. This definitely puts you ahead of 90% of your generation. What you are doing requires some dedication and talent. I can't imagine the stellar stuff you will be producing later in life.

 

[John Tice]

& E2S brings us all together
:thumbsup:
JT

 

[seattle smitty]

Racing outboards have had "siameezed" (1-into-2) inductions systems forever, both on opposed and alternate firing twins. Lots of guys used crankcase-actuated fuel-pumps, lots of guys just ran a line (through a check-valve) from the 'case to pressurize the tank. I've used both systems, either one works fine. A pressurized-tank system is maybe a little touchier in that you can't have any leaks (vacuum or pressure) and the check-valve has to be in good shape, but seeing the kind of work you do, I wouldn't expect you to have any such problems that are due to sloppy assembly or maintenance.

Very cool stuff!!

And FWIW, let me do a little selling job here: A hands-on, tech-savvy fellow like yourself might sooner or later find outboard racing to be of particular interest. There are various kinds of outboard racing, but I am referring to small (125cc thru 1100cc) fuel-burning (including nitro, if you can make the engine live with it) outboard hydroplanes and runabouts as used in the PRO (Professional Racing Outboard, a misnomer because as yet there is little money in it, alas) category of the APBA (American Power Boat Association) and USTS (United States Title Series).

Unlike most or all motorcycle and kart racing, alky outboard racing has very open rules, which is why it appeals to creative mechanics. You're limited only by displacement, and your fuel has to be liquid in a tank and not something in a pressure bottle, and you can't use a mechanical supercharger. But you can use any engine you want, from the Italian-made and nearly state-of-the-art GRM and VRP racing outboards, to converting motorcycle or snowmobile (or whatever) powerheads, to up-dating obsolete engines to try to stay with the new stuff, to building your own motors from scratch. This is a form of 2-stroke racing where the tech-masters are considered the REAL racers . . . although somebody who is merely a "checkbook racer," and just buys all the latest gear and is "merely" a driver can hardly be sneered at because these boats, most of which weigh less than the driver, go very fast.

Here's one scratch-built engine project by an old ex-racer who is making an oversized version of a classic racing outboard, just to have fun with: www.boatracingfacts.com/forums/showthread.php?14110-Building-A-Looper-Beast/
First go to page 45 to see the engine on the boat.

www.apba.org/pro
www.ustitleseries.net/
www.hydroracer.net

 

[seattle smitty]

Oh, darn, I didn't notice your location . . . in Spain?? Well, the Europeans have the same sort of outboard racing.

Okay, try this video of a European O250 250cc hydroplane championship race:

www.youtube.com/watch?v=Y3xVyTzvKrU