ZM 2000,
I believe you are right about the cooling method on the sprayer, you would expect the hot air to be directed away from the operator. so there may be a fan on the output end of the shaft.

However, all this still does not address cometravi's problems, and I think that unless you are an engineer with your own equipment, or have a friend who can do the job, it all could be rather expensive and needs to be balanced against importing a weedeater motor, (maybe secondhand? ).
If you persevere, I'm sure you will find an answer, your enthusiasm should carry you through.

Volksman,
50cc motorcycles would make great aircraft engines except that the cranks are normally full circle types which are extremely heavy, and of course you might have to change to a pumper carb as you say.

HI Guys,
Thanks for your interest!! I think i may be pretty close to getting a Walbro carb. I have located a local supplier who can supply the carb of a 35cc gasser meant for RC!! Well the catch is that its as expensive as the engine :-)!! and it'll take a month to get here.

Just one thought though.
Is the hp of the engine, to a large extent, determined by the carby? At the moment, this engine gives 1.5Hp with the carby it uses. Will the Walbro carb improve this?

I think the colling of this engine is done by the fins to a large extent. But the fins look like very big to me. Can i look at reducing the fin size to reduce weight?

Type 2 Stroke, Single Cylinder
Displacement (cc): 35
Bore (mm): 35
Stroke (mm): 36
Fuel: Petrol
Compression Ratio: 6:1
Spark Plug: Mico-W175Z\ Champion PL7YC
Power:
KW (HP): 1.1 (1.5)
Speed (RPM): 7000
Starting: Rope
Dirn. Of Rotation at PTO: Clockwise
Ignition System: Fly Wheel MagnetoCB\TI Optional
Weight (kg.): 4.7

In their stationary engines, the cylinder is made of Cast Iron. I'll find out today what the cylinder for this engine is made of.
I have attached a pic of the engine mounted on a sprayer:

Cometravi

The carburetor of about 9-11 mm venturi will be enough for it. HP depends on many things and a still bigger carb will not improve it.

The weight is too much but you need to see the actual weight after you get rid of everything that is not required for a flyer. My Ryobi weighs 65oz while Zenoah G23 weighs about 50oz.

You will also need to replace the spark plug with a "R" vesrion like Champion R7Y or similar to avoid radio interfrence otherwise a suitable capacitor will be needed but I do not recommend that(more parts, more risk of failures).

The fins are usually about 1/2" deep, if your engine have bigger ones then do not reduce them at this stage, I suggest leave them till you try it once in aero mode and then decide taking into account engine temperature with prop on.

Good Luck.

Cometravi,
The reason for using a pumper carb such as the Walbro, is so the engine can be used in any position. This carb will not make the engine any more powerful unless it has a larger bore, if it has a larger bore, then the inlet tract on the engine will have to be matched up to the carb,
Also, because the mounting method may be different, you may have to make an adaptor of some kind to suit the carburettor, making sure that the inlet tract remains the same length as before. This is because this length is worked out to suit the piston port, and is quite important.
You will also have to drill a small "pulse hole"down to the crankcase from the carb adaptor somehow, to correspond with the "pulse hole" in the carb. ( if you have a problem a small hose could be a possibility). This hole transmits the alternating pulses from the crankcase to operate the pump diaphram in the carb.
So it's not just a matter of bolting on the new carb and "hey presto"!

Don't remove any material off the cooling fins ( unless you have definite proof that the engine is running too cool), - don't modify anything without a very sound reason! and some knowledge of what you are doing! - I said earlier to give things a try, but didn't mean you should do it without thinking about it carefully beforehand!

Do you have a good knowledge of the basic operating principles of the two stroke engine? If you are interested ( let me know ) and I probably can find you some links to good sites on this subject, and although many of them tend to be for racing etc. they give you a much better understanding of the subject.
There is a good book by a guy called Gordon Jennings, who sussed out the two stroke, and passed on the information to us all. An old book now, but is still as relevant today as it was 20 years ago, and in many peoples opinion has never been surpassed.
Sorry for the sermon!

ZM 2000
Looking at the engine mounted on the sprayer, I notice that it drives a large centrifugal fan, and it looks to me like some of the air is bled from this to cool the engine, what do you think?

Looks like you and I sent in a post within seconds of each other, hope I didn't repeat, or contradict anything you said.

Willdo

I figured exactly the same that cooling comes from some outlet of the fan.

No you havent contradicted anything. I mentioned the same about the fins and also the pressure pulse in my earlier posts.

Hi guys.. just a quicl update... no walbro carb yet...
A thought did cross my mind though...
If i use something to pressurise the fuel tank and ensure that fuel flow is maintained to the engine, can i use the float or any other type of easily available carburettor? I think ZM said that the float type carby may overflow..

A couple late thoughts from left field. Check out the Walboro web site so that you under stand how a Walboro works. Make a large two needle R/C model carb, get a repair kit for and large Walboro and use the parts to make a regulator. Use crankcase pressure to move fuel from the tank to the regulator.
If your engine MUST run CW then using a production pusher prop mounted on the front will work. Of course you will need left thrust built into the firewall.

I sure hope the sprayer version has an all aluminum short block. Otherwise, you're gonna have a very tough time finding a plane that will fly with a 35cc engine that weighs 4.7kg (10lbs).

The description says the PTO runs C.W. so if you make a prop hub for the flywheel side a conventionat prop will work. Many older light planes had the fuel tank mountd just ahead of the windshield with a wire going through the fuel tank cap with a cork on the bottom. this was the fuel gauge. Conventional float carb. Don't see why it wouldnt work as is in a Cub, Champion. etc.

A float type carb should work so long as you don't try to fly upside down, and as long as the fuel can get to the carb float bowl, ( eg gravity ).

The engine could be lightened by removing the heavy flywheel and having an aluminium prop hub made, (or if the original flywheel hub has the contact points cam on it, you could use that instead), then use a battery pack instead to supply the power, this battery pack mounted in the tail could be used to counterbalance the heavy engine up front. (If the cylinder barrel is cast iron, there's not a lot you can do about it, just don't go chopping off fins)
An aircraft with a short nose would also help, (you'll probably be looking at a high wing slow flying aircraft for this engine).
I think that your wing loading would need to be around 29 or less. - Someone please correct me if I'm wrong.
There's no harm in trying things but be prepared for the odd failure, it's all good experience, but always think carefully before you change anything permanently.

The plane I had in mind for this was a SPAD CLT (Cub Like Thing). And thanks for the encouraging words on the float carby. The walbro carb is impossible to find in this part of the world.

So the Q stands, If a maintain the fuel supply using a fuel pump for e.g. like the the one used for fuelling, rather than gravity, will that suffice? There is a way to feed fuel using a simple tank and pump arrangement like the one used to pump water to the windshield. But using this kind of arrangement, wont the float carb overflow if the pressure is greater than the one exterted in typical gravity feeds?

Is there any other type of easily available carby used in bikes, automobiles etc which is not too tempramental to odd aircraft attitudes? I was thinking, these stunt dirt bikes go all over the place and yet keep running... dont they use a float type carby?

Cometravi ! !

Welcome back.

Let me clarify regarding float type carb and fuel pump.

1. You can use high tank and gravity fuel flow.

2. You can use the flaot type carb with certain reservations. The problem is fuel level that will be frequently disturbed due to bank and pitch of the plane, even if it is a floater type of plane. This upset happens in motor cars and bikes as well but they can live with it because the engine is connected to wheels that keeps it turning. In airplanes such upsets can stop the engine and you need to land immediately. So better go ahead and give it a try. Let us also know the results.

3. You cannot use the windshield washer pump because a) the material might not be compatible with petrol b) they dont have a system to stop & work on demand.
The fuel pump in motor cars can be used but they are too heavy for a model airplane. Pressure is no problem, the float type carb is made to handle it.

Good Luck.

Hi ZM,
Just Wondering, if the pressure is no problem, then why does the windshield washer system need to stop and work on demand?
So i take it that there is no other type of automobile carb that is not too tempremental to odd aircraft attitudes (bank roll etc)

Hi Again,
I have located a local supplier who can supply Sthil carburettors for about $60. The problem now is which carby!!! What kind of carby should i look for. According to him the carby can be used on 30cc engines.
As far as throttle control goes, do these carby's have throttle control built in or does that vary from carby to carby?

WIll it be easy enough to fit the carby to the engine mentioned?
I asked the price for the Sthil engine but its prohibitively expensive:
its like USD400 just for the engine!!!!! so i'll stick with the local sprayer engine only!!!

If you are willing to pay $60 for a carb, how about just buy one from a vendor here in the USA and ship it over there? I've bought them off E-bay for as little as $8 a piece. Shipping can't be that expensive to India.

I agree with Volfy, - can't be too expensive that way.

Car pumps ( too large for your purpose ) will have a relief valve built into them so that when the needle closes, the relief valve will open, the mechanical ones run constantly.
Tank in the centre section of the wing as in full size high wing types could be an answer.

Best solution? listen to Volfy! buy one from Ebay, maybe buy a kit for it too. but don't forget it won't just fit straight on as I said somewhere before.
Need to check your inlet tract size too!

Carb on the Stihl will be a Walbro, Tillotsen, Zama etc. the engine makers don't usually make their own carbs.

Cometravi,

To calculate approximate correct carb venturi size:
D = K x Square Root(C x n)

D = carb diameter, in millimeters
K = constant between 0.65 and 0.85 (determine smallest & largest D for engine)
C = cylinder displacement, in cubic centimeters
n = RPM at peak power/1000 (be realist, dreaming only will make you try carbs far
bigger than the correct, with results below your needs)

For a Ryobi 31cc running @ 8000

31*8=248
15.75*.7=11.02 carb dia in mm

From your specs 35*7=245 .....> yeields 10.17 to 13.30 mm diameter

Hope this helps. It is just something I saved from another post, forgot who's.
On the engine: What size /shape is the intake port? (May give you an idea of sizing of alternate carb)

Many automotive fuel pumps are a solenoid pulling a diaphram inone direction and a spring returning it. when the carb is full the diaphram just stops. The early Spitfires had float type carbs. When an ME 109, with fuel injection, shoved the stick ahead to dive, with a Spit on his tail, if the Spit did the same thing the fuel would go to the top ot the carb and flood. Had to roll over to dive. To late by then. Went to fuel injection real quick.

Dang, Willdo and Volfy have the right idea. Unless this sprayer engine you are looking at lays around in heaps over there in India, I would be looking to get an engine/carb/something shipped over. UPS operates in India don't they?

Is there some sort of restriction on personal importation of stuff like this?

(btw-the constant vacuum carb from the Suzuki bike is still a float type carb. The diaphragm in it is for control of the throttle slide and mix needle. CV carbs won't do any good for all position engines. Bikes get away with float carbs because the carb is so close to the CG and the fuel tank is still 'above' them in cornering loads etc. Flypaper's example of the Spit having to roll to dive is a good indication that if the carb isn't too far out in polar moment of inertia the only real problem is pure inverted or negative g situations)

The last two guys sum it up well, can't argue with any of that, thanks for the help!

Hi all thanks for your inputs. Yes John there is a restriction on personal importation. Its the customes duty u have to pay and more than that its the headache one has to go thru if the customes guys stop your parcel at the dist center. A carby could maybe slip through but a full engine is out of question!
But i get the idea, try getting the tried and tested engines, and only if you absolutely cant, then go in for the sprayer.

.cheers....

Cometravi ! !

Looking at your enthusiasm, I offer you for free, one 25cc converted engine with Walbro carburetor. Tell me if you can have it collected at Dubai.

Best Regards.
ZM

YES ZM!!!!I think I can have that arranged!!!!!!!!! But u sure!!!!!!?

Yes ofcourse I mean it.

Give me the Dubai contact and your contact in India on my email [email protected]. I will take/send it to Dubai on next opportunity and advise you when it is done.

Wow! And there I though India and Pakistan don't exactly have the warmest regard for each other.

ZM2000, my hats off to your for your generosity.