jasona

Hi everyone!

So I have a 45cc twin cylinder (two carbs) petrol (gas) two-stroke engine in my 5th scale Spitfire. It's VERY hard to start: Symptoms suggest it's struggling to get the fuel through, so I wanted to try a fuel pump.

Which pump would you suggest for a large gas engine?

The engine runs beautifully and flawlessly once it starts, it can just take an hour to get it started. Today we tried for two hours until all our batteries were flat and it wouldn't start, it just runs off the prime and then stops.

Set-up: Fuel tanks has three exit tubes: One for filling, one connected to the exhaust as a pressure pipe and the other that goes off to the engine: That pipe splits into two via a T-piece to go off to each carb.

It ran beautifully and started easily on the test bench and HAS fired up and run in the airframe, but at best it takes about an hour to get it started.

So, 45cc twin cylinder petrol/gas two stroke: Which fuel pump? I did see the Perry Pump VP40SG but I get the impression that's not intended for really large engines.

This the engine: http://www.meiss-motoren.de/Reihenmotore/45_R/45_r.html

Thanks in advance for any responses or suggestions!

STUKA BARRY

Gasoline/petrol engines have a diaphram type pump already in the carbuetors. You don't need a pump, you need a choke or spray the carbs with starting fluid which you really shouldn't need to do if the engine is tuned properly.

jasona

Thanks for replying and thanks for the insight about the carbs.

I got through a whole can of Easy Start today trying to get it started! I was spraying it in to the carbs on each attempt: It would run only off that prime then stop.

Once it does start though, it runs perfectly, making me think the settings on the carbs must be not far off.

jasona

Would a larger pressure nipple on the exhaust help? Or an extra pressure line coming off the exhaust? Large diameter pressure pipe from the exhaust?

spaceworm

Try rebuilding the carbs. Sounds like they are not pumping properly. And/or, solder shut the bleed hole in the choke plates to maximize the draw at startup. You so have chokes, right? Also,l make sure the cylinders are wet before you try to start. Stick your finger in the carb intakes, they should come out wet with petrol. Gas engines need to be almost flooded to start, unlike glow engines. Are you using magneto ignition or ECDI? Make sure you batteries, if CDI, are up to voltage. Search here on RCU in the Gas engines forums for starting help. Good luck.

rexbirk

Are you running muffler pressure into the tank or carb? Correct me if I am reading this wrong.

You need a crankcase port to the carb to provine the pulses for the carb pump to work. Muffler pressure would not be strong enough?

I have never seen muffler pressure used on a gasser.

av8tor1977

My Feedback: (6)

That's because all the ones that used it blew up!!

AV8TOR

acerc

ROTFLMAO! My thought's exactly!

3136

If you have a nipple on the muffler it's probably for smoke.
Take your cowl off and post some pictures. There should be a nipple on the crankcase somewhere that connects to the carb.

jasona

Dear All,

First of all, thanks so much for all your kind responses and help.

Apologies for my ignorance, but this is my first ever gas engine (many years of aeromodelling, but all glow engines up until now!)

Yes, on each carb there are two pipes: The one coming from the tank and an extra one coming from a nipple on the crank case.

So you don't run muffler pressure on a gasser? I didn't even know that! Do you think the fact I am would cause problems? Yes, I'm currently running muffler pressure to the tank.

It's electronic ignition, not magneto.

The engine is new: Barely run in (test bench running before putting it in the airframe)

Oh, and the question about does it have chokes? That I'm not sure of: Certainly not manual chokes like on a motorcycle (excuse than comparison - I rode 2-stroke motorbikes for many years), but would it have chokes of some other sort? If so, whereabouts on the carbs would they be?

The fuel IS getting through, but the engine's acting like it's not: When I stick my fingers over the carbs and turn the engine over to prime it, both fingers DO get wet, but at best the engine will fire just a tiny bit: Just one or two pops.

When I spray Easy Start (ether) into the carbs, the engine will run for a second or two and then stop, so it's only running off the Easy Start.

Knee-jerk reaction to all this is wanting an extra way to force the fuel from the tank to the carbs a bit more, hence my starting this thread asking about a fuel pump.

So, to muffler pressure or not to muffler pressure? Will it help or hinder in this case?

Thanks again.

jasona

P.S. Been doing some more research: At the moment I have a single clunk in the tank and a single fuel line that then splits into two at a T-piece and goes off to each carb. For a twin cylinder, it appears I'd be better of with two clunks in the tank and two individual fuel lines, one for each carb: That would ease the flow of fuel, surely?

3136

No never run pressure to the tank from the muffler.

Petrol/gas is much more volatile than glow and it can ignite/blow up potentially from the exhaust.

Have you connected the fuel line correctly ie not to the wrong pipe on the carbs?

Take some pictures and post them.

Javier-RCU

My Feedback: (6)

Take a look...

http://www.hobbyocean.com/index.php?...fob4muiv3ubi55

RichardGee

My Feedback: (156)

Jasona,

You MUST be able to choke the engine. This requires choke plates over both carburetors such that you can close the carburetor intake, flip the propeller 6-8 times with IGNITION OFF and throttle at least 50% OPEN. This should suck a good slug of raw gas into the crankcase and up into the cylinders.
THEN..
IGNITION ON - leave the chokes ON (carburetor intakes covered)
Throttle at IDLE, plus two clicks up
FLIP the prop until the engine "barks"
Leaving EVERYTHING exactly where it's at,,,, OPEN the choke plates
Now, flip the prop until the engine starts.

THIS entire procedure should require NO MORE than 60 seconds (90 seconds if you're slow).

IF your engine will not start using this procedure, then as has been suggested, you probably have a carburetor diaphragm pump problem.
However, IF, as you say, the engine runs flawlessly through an entire tank of gas once it is started - ALL THROTTLE SETTINGS and ALL ATTITUDES - then I would NOT suspect the carburetor pump diaphragm.

My guess would be that you simply are NOT sufficiently choking the engine to get it started and to keep running once started.

Obviously, your tank lines must flow freely with NO cuts or holes anywhere in the entire fuel system.

There are some good electric fuel pumps available - Volgelsang sells one that most of the Moki fliers use - BUT IMHO, this is putting a band aide on a known problem.
Your gasser should NOT require a pump to start and run properly.

IF all else fails, call the manufacturer and look for guidance.
Good luck,
Richard

OliverJacob

My Feedback: (12)

Do not use silicone fuel lines, gasoline will eat them up.
There should be a choke on each carburetor to draw enough fuel.
Once the engine fires, you open the choke all the way, it will not run with a closed choke.

Also - take some time to set your needles right. It'll start up a lot better when done properly.
And use no muffler pressure, the exhaust gas is a lot hotter then from a nitro engine, you
do not want that in your gas tank...

earlwb

Are the carbs above or below the engine? If below the engine then you will have a heck of a time trying to prime the engine to start as the fuel won't go uphill into the engine easily. If above the engine then the fuel prime will more easily get into the engine for starting.
Are you able to choke the engine? Usually thecarbs have a extra choke plate on them. You close the choke, flip the prop until the engine sputtets ot coughs, then unchoke the engine and it ought to start right up then.

With Walbro style carbs that have built in pump regulators, you do not need to use muffler pressure. It is not required or needed. If the engine is running Ok once you get it started, and the carbs are under the cylinders and not above the cylinders, then you will have to get creative on how to get the engine primed to start. One way is to use a large electric starter. Maybe another way is to invert the plane, flip the prop and choke the engine to get it primed good, turn the plane back upright and then try flipping the prop to start it.

Actually using muffler pressure is not a problem with gas engines, if the carburetor is setup for it. NV_engines GX40, Evolution 10gx, and Evolution 15GX all use muffler pressure and none of them has blown up. I have been flying the heck out of a NV_Engines GX40 with muffler pressure and it has not caught fire or blown up on me. Technically to get ignition to occur inside the fuel tank you need a very specific air/fuel ratio. Normally the fuel tank is filled with gas vapors that push the air containing oxygen out as the gas evaporates quite readily. Then the exhaust gasses have little to no oxygen in them too.So it is very unlikely you'll get the contents of the fuel tank to ignite. Now I am not saying it is impossible as some very unlucky individuals managed to set their glow planes on fire before using glow fuel, So anything is possible.

vertical grimmace

My Feedback: (1)

You do not have the fuel pulled up to the carb with the lines full of fuel. That is why you need to choke the carbs. This is also why the prime burns off and then will not fire. If nothing else, choke the carbs with your fingers until the fuel is pulled up (lines full of fuel) to the carb. Have the ignition OFF when doing this. Then try to start the engine.

That will really suck if that engine has no chokes. Just sayin'

cjgillette

My Feedback: (15)

Hi Jason -

Couple of things. First, without any doubt whatsoever, you do NOT need a fuel pump. The link posted by Javier-RCU is for a fuel pump used to fill gas cans. Your carbs run off a diaphragm that pumps the fuel to the carb if set up properly. You do NOT need muffler pressure and as others have indicated, that could be an explosive mistake. So - let's think this one out. If the engines run properly once started, sounds to me like the carbs are fine once gas is getting to them. It's the fuel set up that's probably an issue and it is likely that somewhere there is an air leak that is preventing gas from easily getting to the carbs on startup, in which case choking the engine won't really help either. I always use three line set ups from my tanks. One line straight from the clunk to the carbs. One line from the tank to an external vent. And one line from an external fill port to the tanks. There's lots of good posts on fuel tank setups and some people have no problems with two line setups.

I would try replumbing your tank before messing with taking the carbs apart or anything like that. It's usually something simple like that and I remember having the same issues when switching from glow to gas. Make sure you use tygon or Viton tubing - not silicone - and make sure your tank has a proper stopper made for gas.

Hope this helps. If it doesn't maybe some pictures and more info on your brand of engine might help. Don't give up on gas - it's definitely the way to go IMHO.

Chris

spaceworm

Make sure the "VENT LINE" is unplugged for engine startup and flight. Run the vent line up over the tank and then to the back of the tank and then down and out of the plane. As suggested several times, read the forum on gas engines here on RCU. All we have said here is a repeat of that forum[8D]

ec121

My Feedback: (2)

Check and see if the vent line on the crankcase is used for the pump impulse line. You might not have it all hooked up correctly. Some carbs use an external impulse line and some have a hole in the base of the carb. I wouldn't expect external lines on a twin carb engine, but you never know. Also just for my curiosity, what brand of twin has two carbs. Most boxers have the cylinders fed from the crankcase with bypasses.

av8tor1977

My Feedback: (6)

Please forgive me for having some humorous fun rather at your expense.

What would help a lot here is if you could post several nice clear photos.

AV8TOR

Javier-RCU

My Feedback: (6)

I don´t think so, if you read carefully you will find in specs: "Full Metal Shielding, anti-interference" you mean anti-interference in order to avoid the crash of the can?

Javier

bcchi

Some one better tell Horizen about your thery.All of the new EVO small gas engines have muffler pressure going to the fuel tank.I have run muffler pressure to the fuel tank on many gas fueled engines never had a problem. Just lucky I guess.
BCCHI

speedracerntrixie

My Feedback: (29)

Being that it was easy to start on the stand I'm wondering if starter fluid was used there too and if so what effect it may have had on the carb flexible parts?

3136

You missed the word potentially, I don't think I'm alone in that theory either.

I once had a disagreement with someone, he said he could throw a lit match in a open full bucket of petrol/gas and it wouldn't blow up. The crazy ******* did it, he said if you hover the match above it will blow but you can throw it in quickly and your fine.
Maybe so, but still a little silly. I lost a $50 on that.

Anyway to the OP post some pictures