Two Engins one carb

[alan white]

Sure would be hard to design a manifold when the engines are identical rather than mirror images of each other, unless one faced one way and the other the other way, putting the shafts at opposite ends. You could do that if a jackshaft ran between, but then they would rotate oppositely and the ignition advance on one would be backwards, not to mention the start cord.
A simple idea to try out to synchronize the carbs would be to put a limiting valve on a common fuel line and run both engines at various rpms until both quit at the same time when the limiting valve is slowly closed. That will index the carb needles, whose screws could be turned by a screwdriver with a wheel on top to count turns.

A.

[Frosty]

Jeees,-- every motorcycle on the planet has to have carbs synchronised. Its no big deal.

Each( both) carbs intake vacuum will be meaured and the throttle opening set acordingly.

Just google motorcycle carb synchrinising or something like that.

Your all making more out of this than is necessary. many multi cylinder engines run single venturi carbs.

Which brings me to saying that its a silly idea anyway --a 200cc engine or 300 will be smaller and lighter than 2 x100.

[Bergalia]

Originally Posted by jack frost

Jeees,-- every motorcycle on the planet has to have carbs synchronised. Its no big deal.

You obviously never rode my old BSA A60 Jack......

[alan white]

Throttle opening is one thing and involves air, but fuel mix is not easily measured. Usually involves counting identical turns on adjustment screws.
This is like my old BMW boxer 750--- 2 carbs, no cross-over.
Actually, it ran fine, even with nothing in common except the air filter.
I think it's a no-problem problem anyway. Racing machines must have all sorts of methods of determining peak output from two sources, like exhaust pressure gauges, etc.. But that's when the last drop of power is vital to winning.

A.

[tuantom]

Some of the prototype ultra low emmission vehicles within the last ten years or so played with heating the gas before entering the cylinder. If it's vaporized prior to entering the cylinder, it'd burn cleaner. I haven't heard of this in several years now, so I'll assume it's gone the way of the dodo.

As for connecting two engines to one carb, I don't see why not. multi-cylinder inline motorcycles do essentially that. I have an old Honda cb750 that has the 4-carb setup; but I've seen aftermarket setups for this bike that are only two carbs. It's simply an aluminum Y-shaped manifold that connects two cylinders to one carb via rubber (similar to the original intake manifolds) couplings.
It seems to me these longer intake runners might affect lower rpm performance; but the setup is advertised as high performance - aka high rpm.

The logistics of actually pulling this off depend on the geometry of the engines and intakes locations, but it is possible. If it were me, though, I'd shoot for two identical carbs - maybe some old moped carbs. You could sync them individually to make up for internal differences in the engines. Even tuning by ear will get you pretty close to in sync.

[Frosty]

Air intake and mixture sychrinisation --same thing.

Turn the mixture screws for highest vacuum then equalize them.

There are lots of things to spend your money on. Fitting single carbs to a twin carb set up is one of them.

[Frosty]

Originally Posted by Bergalia

You obviously never rode my old BSA A60 Jack......

Sorry Berg iether an A50 or an A65

Simple 500cc 650cc

[Bergalia]

Originally Posted by jack frost

Sorry Berg iether an A50 or an A65. Simple 500cc 650cc

Nah, nah Jack. You're being pedantic. Obviously you were never a BSA man. Always referred to in rounded numbers. On your 500cc - 650cc....how do you explain the B31; B32...M20...M40 ? 310cc? 320cc? 20cc ? 40cc?

[madtech]

well......... where to starrt

the tubes that go from the carb to the engines i think some one called it a maner fold (please dont bother to correct me.) are the same length and the same diamiter. the engines run lovly with one carb the only troble is the starting on one engine. so now i pull start both engines together.

iv found an old elegro car rpm counter and i need to attact it to the low out put side of the magnito of somthing ill do the same for the other engin and the ill have a constant read out

some one said that when the engines rev up to thier working loads one may take 45% and the other 55% but the rpm will stay the same this is not exactly correct the engine rpms will vary as both engins are run through thier own clutches(with the idea to stablize the load rpm and thus efficiency) the prop rpm will increas to a maximum of the highest reving engin.

it is very important to me that these engines increase thier rpm and power output equaly. as i need every ounce of power from them

any one know the pitch of seagull 4 bladed fan prop or how to find out the pitch of these straight bladed props

cheers guys

[madtech]

another thing guys so far iv spent 100pounds on this project its not cos im a skin flint im just skint so far iv got a cannoo, two identical engines without carbs, two seagull bearboxes(you know the bit the prop goes on) and all the cogs and chains and metal for 100pounds. ill post some pics up in about a week and show you what iv done but if you can imagin two engines laying side by side their conected to compression clutches. they run 10toothed sprockets which are chain linked to a 28 toothed sproket is linked to a upsidedown seagull gearbox that goes into the other gear box which turns my prop well wait for the pics

[alan white]

Hi Madtech,

Just pointing out that beyond a low RPM when the clutch springs are overcome by the centrifugal action of the weights in the clutches, the RPMs are exactly identical usless your clutches are slipping, in which case they should be replaced.
It is correct to say that of the two engines, each, until perfectly tuned, is producing a different amount of power.
They can be considered a single engine with two cylinders once the clutches are engaged, though out of balance most of the time.
The way you are using two clutches is also going to make your powerplant sound different each time you run it, so it would make sense to phase the motors together 180 degrees apart by means of sprockets to a common jackshaft, and then put a clutch output onto the jackshaft to power the prop shaft. One engine can start the other that way. More compression, but phased right, it should divide the compression strokes to be sequential. This brings up another point, which is that until the engines are phased correctly, the carburator, if shared, will probably do different things each time you run the engines. Sometimes both engines would take in at the same time. Other times, not.

[Frosty]

[quote=alan white;142465]Hi Madtech,

Just pointing out that beyond a low RPM when the clutch springs are overcome by the centrifugal action of the weights in the clutches, End Quote.]

What wieghts? its a comon wet compression clutch.

Why would the wieghts if it had them. overcome spring pressure at LOW rpm.

Some larger motorcycles using dry clutches have wieghts this is to increase spring pressure at higher RPM when max torque is requested. Never to --overcome.

The rest of what you said is practicle. Using 2 clutches will as you say mean the engines firing order will be different each time.

Its not a good idea. Sorry and all that but I have already said buy a 200cc.

Your throwing money at the engines just to sychronize them.

Scrap the idea buy a single motor and move on. Im trying to save you money!!

[alan white]

Wet plates or no, the principle's the same. I would guess they are not wet plate clutches on 97cc engines, but I could be wrong. Maybe they are manual clutches.
Anyway, you're right about one thing. Two engines add complication and if possible, a 200cc engine would be a better choice.

[StianM]

It should be the same rpm as long as they are driving the same load.

If you running two engines but on two diferent loads the rpm would be more dificult to match. A smal PLS picking up signals from the ignition and giving up the diference in a 4-20 mA output driving the trotles would be one option.

[madtech]

Originally Posted by alan white

Hi Madtech,

Just pointing out that beyond a low RPM when the clutch springs are overcome by the centrifugal action of the weights in the clutches, the RPMs are exactly identical usless your clutches are slipping, in which case they should be replaced.
It is correct to say that of the two engines, each, until perfectly tuned, is producing a different amount of power.
They can be considered a single engine with two cylinders once the clutches are engaged, though out of balance most of the time.
The way you are using two clutches is also going to make your powerplant sound different each time you run it, so it would make sense to phase the motors together 180 degrees apart by means of sprockets to a common jackshaft, and then put a clutch output onto the jackshaft to power the prop shaft. One engine can start the other that way. More compression, but phased right, it should divide the compression strokes to be sequential. This brings up another point, which is that until the engines are phased correctly, the carburator, if shared, will probably do different things each time you run the engines. Sometimes both engines would take in at the same time. Other times, not.

now this is the info i need. the clutches were copresion cone clutches, as in two cone fit inside each other and are pressed into each other to activate or seperated to deactivate. any way i welded the clutches and orrientated the engines so that one piston is right up and the other is rightdown. this should mean that the engines pull thier air/fuel mix at opposit times. and should give me two power stokes per revolution. this should keep the carb opperation simple and the same each time i start it

i already had a jack shaft powered up on a 2.8:1 from the two engin sprokects. this then turns my first seagull gearbox(with is own toothed greared clutch powered down 4:1) this takes the drive from horizontal to vertical. that then drives the seconed seagull gear box which is powere up 1:4 giving a final 2.8:1 power increase and a 2.8:1 reduction in final rpm.

i know this is a long way of going about it but i could nt source a 1:1 90degree bevel gear to go from horizontal to vertical so thats why iv dun it

any one know how to run and electric rpm meter from the electrics on these small lawnmower engines

pics soon i promise it will all become clear bloody bluetooth device cant handle windows vista argh