Recently bought a Laser 75 4-stroke. Do some four strokes not start well by hand?
It seems the only way to get it going is to flood it with fuel, turn it to the compression
stroke, add glow juice and flip counter-clockwise. If it doesn't start, I need to immediately remove the glow juice and repeat the procedure. This works only a small percentage of the time. Backflipping (clockwise) doesn't work because the engine doesn't seem to make enough compression backwards. It doesn't seem to have a lot of compression counter-clockwise either, but when it's running it idles and
transitions well without glow power. It wouldn't do this if the ring was shot would it?
All of my 2-strokes start easily by hand so I got rid of my electric starter. Do I need a new starter or a new engine? Ross

I always have no issues with my 2C engines, I only got a chicken stick, I had to buy an electric starter when I went into 4C engines. Once they are properly tuned they will start with a black flip, trust me there is a lot of compression. I turned my 4C engine backwards very gently till TDC with the glow on, it kicked. I do not have much luck starting it counterclockwise with a chicken stick. Back flip is always best.

My TT91 will not start with anything but an electric starter, it idles lovely and got tons of power but she will not play ball to start. My YS110 will always start on a blackflip, save for the first start of the day, the electric starter is required.

The back flip deal is just bouncing it up agains the compression backwards.

The OS four strokes don't have much compression backwards either.

Is this a new Laser? if so, the ring will seat eventually and you will have more compression.

At my age, I just use the electric starter anymore.

Enjoy,

Jim

I've not tried hand-starting my TT91FS but it has almost *no* compression when turned clockwise -- but has plenty when turned anticlockwise and runs fine in every respect. I wonder why it has no compression when turned backwards??

No compression when turning by hand clockwise means no compression when "being turned" anticlockwise by combustion pressure. I was helping a guy last week with a Funtana 90 powered by an ST G2300 with about 5 hours running from new. It was the same - no compression when turned by hand clockwise. We couldn't start it by hand for the love or the money.

I hand start all my engines. I have found all naturally aspirated four strokes to respond well to the backflip method, as long as they are generously primed. The YS .63 takes quite a bit of priming but starts well when flipped through compression (anticlockwise) like a two-stroke. My YS 1.10 when cold (start of day) is the best self primer of all - put the glow heat on unprimed, flip through compression about 5 times and she'll start to fire and one or two flips later, she'll fire up into a nice safe idle.

My TT91 has almost NO compression, then one day it had tons of compression but that was only for a while, once I ran the engine the compression went away, its weird, how can it be like that? I get 10,500 RPM on a 15x4W with 15% nitro ... that means its a very good engine. Weird ...

I find 4 strokes generally more difficult to hand start than 2 strokes. Most ringed engines will seal better in one direction of rotation over the other. This has to do with the placement of the ring gap and overall piston clearance. My Supertigres have good seal in both directions, my OS 2 strokes seal better when turned clockwise with exception of the 140rx.

I'm not trying to be argumentative, but I just don't get this. When the piston is rising toward the top of the compression stroke, the ring has no idea what direction the prop is turning. All it knows is it's moving toward the top of the cylinder.

Is the compression difference perhaps due to the timing of the valves?

Are you sure that the throttle was open when you checked the compression? A four stroke with a closed throttle has almost no compression because the carb is not letting any air into the cylinder to compress.

On all model engines...
Depending at what direction the connecting rod is pushing on the piston when it is headed up in the combustion chamber, (left or right), one or the other of the piston skirts will be against the cylinder wall. With the ring gap to the side and that skirt away from the wall, there will be less compression.

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On some four strokes....
The less compression in the clockwise direction has to do with the cam timing. On a saito, it's almost unnoticable. But some other brands it is very pronouced. One of the valves opens up sooner in the clockwise direction and releases the compression.

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With a four stroke throttle completly closed, and after going trough one compression stroke, most will have no compression on the second compression stroke.

Enjoy,
Jim

Hello; I have a Laser 100 in a Taube that I don't fly very often, to start it I fuel it up then hold a finger over the carb opening and turn the engine over anti-clockwise until I hear the goosh-goosh sound that tells me that the engine is recieving fuel. I then put the glo driver on it and turn it clockwise until it gets stiff, then I just twist the spinner nut clockwise, with the throttle at idle, it usually starts right away. If it fires but doesn't start, I take the glo driver off and prime it again, goosh goosh, and twist the spinner nut clockwise again and away it goes.

One thing with my Laser was that the carb is quite high, being mounted right next to the head with a short intake pipe. My carb is higher then the fuel tank, and without muffler pressure behind the fuel, your fuel hoses have to have a good connection to keep the fuel running to the carb or you'll lose your prime, and it will be difficult to start and run.

Most other flyers at our field have a starter, so if I am having any difficulty starting it, someone will drag their starter over to where I am and offer to spin it over for me. I don't think I have had to use a starter on that engine more then twice in all the time I've had it. It always amazes newcomers to see how easy it starts, and how quietly it runs, and how low it idles.

Thanks for all your replies. Sounds like even easy starting 4-strokes need a starter every now and then. I better put one on my Xmas list... Ross

Many engines have the crank bored off center fromt he cylinder, that forces the piston skirt to one side and the same side at all times, if turned counter clockwise it will tilt to the opposite side and have more or less compression.

To the TT .91 owners. The compression of this engine will go up and down till it is completely broken in. I don't mean the time it takes to run well, but the time it takes to get the best compression possible, probabally 5 or more gallons of fuel. Till then the ring will rotate, differance in how much oil is on it, how thin the oil in the fuel you last used, and other factors will cause the compression to vary.

One of the best four stroke starting methods, is to put your thumb over the end of the muffler and turn it over with the electric starter, take your thumb off the muffler when it starts. The last item is critical. Works on two strokes, but it is possible to flood them and even hydrolock a two stroke, especially if you leave off that last critical item.

Hello; Putting your finger over the exhaust outlet on a Laser engine won't do anything except get your finger dirty. Lasers don't use muffler pressure.