Webster Build

[Longboy]

On the model airplane carburetor, start with the fuel mix needle at 1.5 turns open. The horizontal screw under the throttle arm sets the idle speed as a closed throttle stop. The screw in the center of throttle arm into the carb body sets the needle withdraw from the mixture tube as you open the throttle arm. Sight down the barrel to see its position as you open/ close arm. With all three of your hands...Spin Webster over, prime and release with finger tip and adjust mixture as the number of "hits" indicates.

 

[simister]

Thanks guys for all your advise on Fuel mixture.

Also, thanks Longboy on the carby settings. At least I will now have a starting point and I can experiment with settings later.

John

 

[simister]

I have fitted the carby. However, I am not sure if I put it in upside down, as I saw another on You tube the other way around. I have the main thumb screw to the bottom with the fuel feed also from the bottom. My last photo should show how I have installed it.

I have tried to start the engine but with no luck.

I have set the exhaust valve timing so that it just starts to open about 20 degrees before the piston reaches its most outward part of the stroke. I have done all these settings from the plans and all being viewed from the fuel tank side of the engine.

I have set the cam so the the points are closed and just about to open at 15 degrees before TDC.

I have compression.

When I spin the flywheel I can see the fuel being sucked up the fuel line.

I am not sure if the spray bar in the carby should protrude into the throat slightly or be flush with the throat.

The plug doesn't appear to be saturated in fuel.

I don't know how to check and what to look for to see if the carby is set correctly.

Any help on this please.

John

 

[Longboy]

Your carb position is fine. They work in any degree position. Prime to flood the engine, see if fuel is drawing into cylinder and a wet plug. You can remove plug and dribble some fuel in there. You may be able to check the draw through on the removed carb with a rubber tiped blow-off nozzle on the bore of carb with air pressure very low...if you get wet from the manifold side, you have fuel flow. Set your spark right at TDC and make sure the exhaust valve is closed just before TDC. What do you use to turn the engine over? Dave

 

[simister]

Hi Dave,

OK, I will give that a try. I have been turning it over with a battery drill fitting (anti clockwise). The spark plug appears to be getting fuel through to it. I was told that the spray bar should be half way into the throat, but mine is just protruding into the throat. So if I set the spark at TDC, are you saying that the exhaust valve should be open as the piston is moving from BDC to TDC?

Thanks John

 

[Brian Rupnow]

This engine will run either direction, depending on how you set up the valve timing. As the piston is moving from top dead center towards bottom dead center, set the exhaust valve to just start to feel the effect of the cam when the piston is 1/8" before bottom dead center. Once the piston has reached bottom dead center and started back up in the cylinder, that will be your exhaust stroke. Since the points run off the crankshaft, you will get spark both at the top of the exhaust stroke and at the top of the compression stroke. I can't remember now if the cam on this engine has any overlap on the power stroke or not, but it doesn't really matter. Time it to fire at top dead center. You can always adjust the timing after you get the engine running.

 

[Longboy]

Hi Dave,

OK, I will give that a try. I have been turning it over with a battery drill fitting (anti clockwise). The spark plug appears to be getting fuel through to it. I was told that the spray bar should be half way into the throat, but mine is just protruding into the throat. So if I set the spark at TDC, are you saying that the exhaust valve should be open as the piston is moving from BDC to TDC?

Thanks John

Yes...during the exhaust stroke. The ex. valve should be closed coming up to TDC so the in. valve gets a full draw on the intake down stroke. Ignition should happen near TDC, the top of compression stroke. Looking at my Webster crankshaft from the con rod side, the exhaust valve by clock face timing is open at 1 and closed by 9. Regardless of carb setting, if you know you have a fueled cylinder and compression and spark...Webster should show some pops! Dave.

 

[simister]

OK, I think the problem is that I am not getting fuel into the cylinder. I took the spark plug off and blew it out with some compressed air. Next, I started turning it over with the drill, and when I put my finger over the carby intake, I could see fuel started flowing through the fuel line. I could see the intake valve opening and closing but only a very small amount. As I continued, the fuel started dripping out of the exhaust valve through the valve stems. I then took the plug out and it appeared dry. It certainly was not dripping with fuel, as I tried to flood it on purpose to see if fuel was getting through. The fuel is sucking through the lines but I don't think it is entering the cylinder. I put a lighter spring on the inlet valve but with no improvement. I am fairly sure the problem is fuel. If I blow some compressed air into the carby intake I can feel it come through the spark plug hole. So it appears there is no blockage between the valve block and the cylinder. I am not sure what checks to do next to pin point the problem. Would you think that the compression is sufficient given that it is sucking fuel through the lines?

John

 

[Mechanicboy]

Engine need to run:

1. Good compression--> Check there is no leakage in valve, gasket and cylinder/piston (not too large gap of piston ring in cylinder).

2. Good spark from sparkplug--> Check all connections, contact breaker and battery is in order.

3. Right timing of ignition--> Set a ignition timing between 2.5 and 5 degree before TDC as start point.

4. Fuel tank in same level as in carburator (not flooding from tank to carburator, let the engine suck the fuel into engine). If problem to suck the fuel into carburator--> can be caused by too hard inlet valve spring and replace with a softer inlet valve spring.

5. Right fuel/air ratio--> The engine running as petrol engine need less amount of fuel than engine running on methanol due high energy value in fuel. Also adjust less petrol than methanol in same engine. 1.5 turn turns of fuel mix needle is maybe too much for me since i has engine running with fuel mix needle at 0.5-1 turns since my engine is running on petrol.

6. Too much oil from oil cup on cylinder can give fouled spark plug, be careful to adjust a amount of oil into cylinder with adjusting screw. Can you see there is oil in cylinder while the engine is running--> amount of oil is correct. Also not too much oil out of exhaust, little smoke is ok.

 

[simister]

I deliberately tried to flood the engine by holding my finger over the air intake and cranking with an electric drill. I could see the fuel moving through the fuel line. It then started ripping through the exhaust port valve as it was flooded with fuel. Then, when I took the spark plug out it was fairly dry - I would of thought it to be dripping with fuel but this was not the case. There is enough suction on the piston to suck the fuel up the line but it doesn't appear to be getting into the cylinder. John

 

[Mechanicboy]

I deliberately tried to flood the engine by holding my finger over the air intake and cranking with an electric drill. I could see the fuel moving through the fuel line. It then started ripping through the exhaust port valve as it was flooded with fuel. Then, when I took the spark plug out it was fairly dry - I would of thought it to be dripping with fuel but this was not the case. There is enough suction on the piston to suck the fuel up the line but it doesn't appear to be getting into the cylinder. John

Flooded fuel out of exhaust without starting the engine ---> Check the spark is there on sparkplug and check ignition timing is set to 2.5 - 5 degree TDC. Also the egnine is not startet up due lack of spark from sparkplug or the ignition timing is too late after TDC.

You had the finger on carburator and the engine is sucking the fuel into engine---> Replace the stiff intake valve spring with a soft intake valve spring. Stiff intake valve spring will make difficult to start the engine since vacuum in the cylinder is not strong enough to open the intake valve and suck fuelmix into the cylinder.

 

[simister]

Jens, Correct me if I am wrong, but if the fuel was being sucked up the fuel line, wouldn't that indicate that the inlet valve spring was not too stiff? Or, are you saying that it may be opening enough to suck it into the valve block but not into the cylinder?

John

 

[Mechanicboy]

If the engine can suck fuel, the spring is ok. The problem is igniting the fuelmix. Check the ignition equipment. If ok, close fuel from tank. Then give some drops of fuel into carburator and start up. If engine is starting up and running a short time, ignition is ok---> turn the fuel mix up 1/4 each time you are trying to start up engine until the engine is running with correct fuelmix.

 

[simister]

Ok, I will try that in the morning. Actually, I have got a small perfume atomizer spray, which can spray a very fine mist. Do you think that may be better to try than some drops of fuel?

John

 

[Mechanicboy]

Ok, I will try that in the morning. Actually, I have got a small perfume atomizer spray, which can spray a very fine mist. Do you think that may be better to try than some drops of fuel?

John

Yes, you can do it.. Later in this day i can make a movie how do it with the engine then you can learn out how do check and start up engine.

 

[Mechanicboy]

Here is my engine in these movies.. The text is wrote there..

[ame="http://www.youtube.com/watch?v=LD5lRiQ_SL8"]http://www.youtube.com/watch?v=LD5lRiQ_SL8[/ame]

[ame="http://www.youtube.com/watch?v=o1dNPdmGxSE"]http://www.youtube.com/watch?v=o1dNPdmGxSE[/ame]

 

[simister]

Thanks Jens for the videos - a great help. I have sprayed the inlet of the carby with fuel and still with no luck on firing. So, next I purposely turned the engine over while I sprayed a lot of fuel into the carby. I did this to test if the fuel was getting through to the cylinder. When, I removed the spark plug it was dry. I would of expected it to be dripping with fuel and totally flooded. I am now convinced the issue is fuel. I do have suction from the piston but the fuel is not getting into the cylinder.

Tomorrow, I will remove the valve block and investigate why. I feel sure now that there is a blockage between the carby and the cylinder.

I will update the post when I have pulled it apart.

Thanks guys for all you help so far. However, I am not there yet, but it is now narrowing down.

John

 

[Brian Rupnow]

Simister--There is a trick involved here. If you block the carb inlet with your finger and turn the engine over, it will always pull fuel up the fuel line because of direct suction as long as the inlet valve and spring are functioning. However, for the engine to run in a normal manner without being choked by your finger, the vacuum created to suck the fuel up from the tank is created by venturi effect. This is essentially a low pressure area created in the carburetor by a narrowing of the air passage into the carburetor, or a restriction caused by something protruding into the air passage. As the air flows past the restriction, it creates a low pressure area and that is what sucks up the fuel under normal conditions. Did you use a gasket when you mounted the carburetor? If so, did you cut out the hole in the center of the gasket to let the air pass thru? If your ignition timing is remotely close, and you have good compression, then suck up a bit of fuel in an eye-dropper, remove the sparkplug, and squirt it into the cylinder, then quickly put the sparkplug back in, put the coil wire on, and spin the engine. If it doesn't at least "pop" or try to start, then the problem may very well be in your ignition system.---Brian

 

[Mechanicboy]

I can see you has OS carburator. I has same carburator in my OS 10FP engines. Spraybar in my engines is in mid position to create vacuum and make easy to adjust and start up engine. Can you move the spraybar into the carburator to mid position as i am showing your photo of your carburator.

 

[simister]

Thanks Brian for the tip. However, I have found a blockage in the valve block and now it is clear. There is now fuel going into the combustion chamber as the engine cranks over.

Now, I have managed to get it to fire and then stop. Whilst cranking the engine, it is firing and the cylinder is getting quite hot, but will only run by itself for a couple of seconds. I have checked the timing of the spark and the exhaust valve timing and they are correct. I think the problem is a leaky exhaust valve. When I remove the valve block and put my finger over the inlet there is good springy compression when I rotate the flywheel. However, when I re fit the valve block the compression is much less. With the valve block removed I injected some compressed air into the block and there is leakage through the exhaust valve. The inlet valve seems fine with only a small amount of air leaking. So, I think before I go any further I should fix this issue. I am not sure if I will have to remake the valve and guide, or if it can be ground with some abrasive paste.

John