Flymo GT2 (JLO engine) service information

[aesmith]

Hi,

We've picked up an old Flymo two stroke for cutting banks and odd bits and pieces. The mower's marked GT2, but nothing on the mower helps me determine which of several variants it is.

Ours looks exactly like the one in this Youtube video ..

http://youtu.be/Kn0IdqVCgr4

Is anyone familiar with these mowers? I'd like to confirm which exact version as the sparkplugs differ according to the NGK reference. I'd also like to find out how to adjust the carburettor as it's running a bit rich at the moment (sooty plug, but I guess the plug could be wrong).

Other than rich running, and possibly not revving to full speed, it works fine.

Thanks, Tony S

 

[Burnerman]

Haven't seen a small JLO engine for ages!
Anyway, no worries about the plug, but do clean the air filter......in fact run the engine for a while without it to see if there's any difference in pick up.
Is it a brown painted carb, maybe a Dell Orto?
John

 

[Mursal]

Will you still use it to cut the grass, after it making an appearance on U-Tube, might be worth a few bob?

I do love a pull start 2-stroke, saves on the gym membership ........
If it is starting, I'd proceed adjusting the carburetor with caution, and always take note of where you moved the adjustment screw from.

 

[aesmith]

Thanks. It's not mine on Youtube, but mine looks to be the exact same model.

I couldn't see any branding on the carb, it's not painted just natural metal coloured. There seems to be only one adjustment screw, anyone want to make a guess as to what that does? I'd assume fine-tuning mixture, but is it controlling fuel or air (ie unscrewing makes it richer or leaner)?

Starting's easy! Less force than pull starting a four stroke of the same capacity, and twice as many compressions per pull.

Could you clarify what you mean by "no worries about the plug"? Do you mean I shouldn't be concerned about it's colour?

Thanks, Tony S

 

[Burnerman]

There should (could) be two screws....one mechanically holds the throttle open slightly to prevent stalling, and the other (if there is one) will be in the side of the carb and that controls the idle speed mixture. If its there, turn it in gently and back out again one complete turn.
John

 

[aesmith]

There should (could) be two screws....one mechanically holds the throttle open slightly to prevent stalling, and the other (if there is one) will be in the side of the carb and that controls the idle speed mixture. If its there, turn it in gently and back out again one complete turn.
John

I need to have another look. The one screw that I found faces the rear of the mower (carb on the right hand side of motor).

There's no throttle control as such, just a preset slider thing on the underside of the cowling which controls running speed. That's locked by a hex set screw so clearly not intended to be adjusted while in use. I think, without dismantling yet, that the actual throttle butterfly is controlled by a governor from the cooling fan, and the sliding thing sets the governor spring tension.

I might have to disassemble a little, but it sounds as if the one screw I've found so far must be the low speed mixture adjustment.

 

[Burnerman]

I guess that must be the pilot mixture screw, which restricts the fuel supply at low RPM.
Post a pic if you can!
If the engine will run slowly, turn the screw until it just starts to falter, and then turn it back in a fraction.
John

 

[aesmith]

I did a bit of investigation today. There's definitely just the one external adjuster, and that must be low speed mixture as it only affects tickover. I've set that about 3/4 of a turn out, which seems to give the smoothest idle.

I'm more than ever convinced it's running rich, for example if I turn the fuel tap off then I get around 30 seconds of smoother and faster running just before the engine stops. Unfortunately I couldn't see a way of getting the carb off without removing the whole engine, as the float bowl is trapped within the cowling between the engine and deck. So I'm no further forward working out how to adjust the mixture at full speed.

Pictures of the carb from either side here (fuel line and hose to high level air filter disconnected.

Normal running speed is set by a governor balancing spring tension, the governor is preset and locked by the hex set screw visible from below.

 

[Mursal]

Run it hard for as long as possible, working and check the colour of the spark plug. For a good mixture it should have a hint of brown on the earth electrode. Black = Rich, but it must go to full operating temperature before checking.

But if its starting and running well, I'd leave it. If only one screw (nothing underneath), then the float level might be a touch high. Leaving the fuel high, but its not going to be easy to split that, to leave it not running to lean. Switching the petrol off isn't a good indication, but I do notice the change in our own stuff.

 

[aesmith]

Cheers. I agree, in principle, that running too rich is safer than running too lean. The problem is that it's stopping it from reaching full revs, which means it doesn't fly as high or cleanly as it should. The lean running just before running dry clearly show what it should be doing.

I'll double check when I get a chance, but I'm pretty sure it was up to full temp when I checked the plug before. It doesn't take long for a small air-cooled two stroke to get to temperature.

Would there be any other mixture setting apart from float height?

 

[Mursal]

There might be a screw on the bottom of the float bowl, but I'm not sure. What about that choke lever, is the choke butterfly inside open full?
When its running where is that black governor control, is it pulling the engine back, or letting it go on up the revs? Can you attach something to it (wire), to see if the engine will go on up if you give it a bit more throttle.

Edit1:
Forget about the wire, mark the plate (tipex) and the casing in your second last picture where the bolt goes through the elongated hole. So you can go back to original if need be. Loosen with a 10mm spanner and move the plate to tighten the spring, just a little. Try and see if it goes into the revs, don't over adjust or the engine may over rev.

 

[Burnerman]

First picture......does that spring loaded plunger lock down at all - or is it an old fashioned 'tickler' button that causes the carb to flood?
With these two strokes, you cant expect them to run cleanly when not under load....in fact they will 'four stroke' until loads like heavy grass are encountered, and then run cleanly until the load has been overcome.
The other slotted screw is the pilot mixture, usually about 3/4 to 1 turn out.
John

 

[aesmith]

Thanks again. That's a spring loaded plunger, a tickler as you say. Following your previous post I looked at the bottom of the float chamber as far as it's visible, there's what looks like a drain screw in the centre (hex head) and something similar to the tickler except then when you press it upwards it lets fuel out of the chamber. I was hoping that was an adjuster, but it doesn't seem to be. Not that easy to photograph ..

 

[Burnerman]

When you press that off centre pip, you'll get fuel running over your fingers, right? That's because it's a float bowl drain, spring loaded with a fibre gasket on the inside.
The thing I'm interested in is on the top of the carb......what happens when you press that?
John

 

[aesmith]

The thing I'm interested in is on the top of the carb......what happens when you press that?
John

The thing on top is a "tickler", pressing it causes extra fuel to flow into the float bowl. Without dismantling, I assume it just presses the float down as that's how they normally work.

By the way, the throttle's fully open when running off load. I can reach the spindle with my fingers and there's no further travel. I'm trying to think of a way to measure RPM (should be 3800) as maybe it just sounds slow as it's a bit rough.