Lawn-Boy Lawn Mower Starting Problems...Help!!

jwb1 · 24-07-2007 5:40pm #1

I'm trying boards.ie as a last resort....I've been to my lawn-mower repair shop twice already with this problem but to no avail. The machine cost me a fair chunk of change only 6 years ago so I'm reluctant to junk it....

It's a Lawn-Boy Gold Series 6.5hp 2-cycle lawn-mower. Very powerful and sturdy....

Some weeks back, it refused to start so I took it to the repair-shop...turns out the coil in the engine was gone so...after several weeks waiting for the part from the US, I got the machine back last week....they serviced the engine as part of the repair....

Initially, everything seemed fine but I noticed that the machine got progressively harder to start after it had been used for a while (say, 45 mins).

The only solution seems to be to leave it get cold and then start it again.

This is very weird indeed (and not a little frustrating given the very limited windows we're getting these days to cut the grass...)...

Has anybody any notion what might be causing the problem?

JB

seamus · 24-07-2007 5:54pm

Have you checked that there's sufficient oil in the engine? (assuming it needs it). The expansion of the hot engine may be causing more friction than it should.

Other than that, I'd be worried that it wasn't reassembled correctly, and again, excess friction caused by expansion is causing a problem.

10-10-20 · 24-07-2007 6:52pm

With cars which won't start and show similar symptoms, you always look at the engine temperature sender or the fuel lines.
Heat in the lines can cause vapour lock and difficult starting.

Can you describe the starting - does it turn over OK? Does it take more for the engine to 'catch' - as-in is it like it's low on fuel? Are there any unusual noises...?

jwb1 · 24-07-2007 7:40pm

Thanks for taking an interest guys....

seamus wrote:

Have you checked that there's sufficient oil in the engine? (assuming it needs it). The expansion of the hot engine may be causing more friction than it should.

Other than that, I'd be worried that it wasn't reassembled correctly, and again, excess friction caused by expansion is causing a problem.

It's a 2-stroke engine so the oil is mixed in with the petrol. I've checked the oil/petrol mix and it's fine.

I'm interested in this "excess friction". How would that prevent the mower from starting? Would it not also cause a problem when running (when the thing is going, it goes like a dream....no problems at all)?

10-10-20 wrote:

With cars which won't start and show similar symptoms, you always look at the engine temperature sender or the fuel lines.
Heat in the lines can cause vapour lock and difficult starting.

Can you describe the starting - does it turn over OK? Does it take more for the engine to 'catch' - as-in is it like it's low on fuel? Are there any unusual noises...?

No unusual noises. It's like there is no fuel in the tank - which means (I think!) that it is not "turning over"? It's for all the world like you were trying to start it on an empty tank or without priming the engine. Does that help?

Thanks again!

Mailman · 24-07-2007 9:36pm

LawnBoy! That is a quality lawnmower but ferociously expensive to buy and repair.

It's a two stroke so not much to check. Ignition, compression and carburettion. That's all.

Try a fresh spark plug in case it is a dodgy plug or incorrectly gapped. Perhaps you have one from a strimmer or hedge trimmer you can try in it's place.
Perhaps your new ignition module is dodgy too. These can be taken out and checked on a tester but that would have to be done in the workshop.

Pull the engine over and ensure you feel resistence from engine compression. If there is no resistence then it was run without oil at some stage probably.

After that all that you can look at is carburettion. Perhaps there is dirt in the carb bowl. Take off the air filter. Try squirting fuel into the carb and see if it starts any easier.

Other than that ensure that the throttle hasn't come out of adjustment. The lawnboys I remember from my childhood didn't even have a throttle cable, just the one knob/button on the top of the engine.

Lovely lawnmowers but I couldn't justify spending the money on one of these myself.

Is your fuel stale? if so it'll be difficult to start.

bauderline · 24-07-2007 10:41pm

I would say try a new spark plug first, go buy a good quality one from autoparts or agri store and see how you fair with that.

If you do not get an improvement with that then it is likely the carb that requires some "tuning". I doubt it is dirt else the thing would cut out and stutter mid stride.

Anything more serious than that or incorrect assembly of engine parts the mower would not run correctly at all or would be a heap of smoldering junk at this stage..

Also unlikely to be electrics as it would either not run at all or cut out at random when running.

I would be pretty sure its either spark plug or the carb adjustment.

If you have the original manual it should list some troubleshooting steps and symptoms... if not send a mail to the manufacturers and ask for their take on it....

good luck !

baud.

bauderline · 24-07-2007 10:48pm

The more I think about it this is classic symptom of a faulty spark plug, the spark is always much better when the plug is cold but diminished when the plug warms up, though the spark is enough to keep the engine running it will not be good enough to crank the engine from stop. Thus you have to let it cool....

Yup, go get a new plug, make sure you get the right one, if you get the wrong one and its too long.... bye bye piston....

I wated a childhood vandalising these things...

baud.

jwb1 · 25-07-2007 8:54am

bauderline wrote:

The more I think about it this is classic symptom of a faulty spark plug, the spark is always much better when the plug is cold but diminished when the plug warms up, though the spark is enough to keep the engine running it will not be good enough to crank the engine from stop. Thus you have to let it cool....

Yup, go get a new plug, make sure you get the right one, if you get the wrong one and its too long.... bye bye piston....

I wated a childhood vandalising these things...

baud.

I know they've cleaned the plug but I'm not sure they replaced it - I'll check.

They've also cleaned the carb but I'm interested in your comments on carb "tuning" - what could be wrong here and how could it just impact starting?

It might be my imagination but I think the mower is drinking more fuel than normal too. Now, this might be due to all the failed starting attempts....

Thanks for your help....

JB

bauderline · 25-07-2007 9:53am

If the plug has not been replaced since you bought the mower, 6 years I think you said, then cleaning it won't do squawt .... its old and done and needs replacing ....

As far as I remember the two adjustable settings on most of those carbs are idle and air mixture, the air mixture might be the one causing issue, the idle screw should not cause any issues... you will likely need the owners manual to direct you to which screw is which... otherwise you will need to experiment... scary thought !

I also remember on the old two stroke mowers there was sometimes an adjustment at the very bottom of the float chamber on the carb. If this is set too high it can also cause problems when starting...

As I said, try the plug, if this doesn't work I would track down a local mechanic and get him to have a look at it, if you starting messing around with the carb you might well end up with no functioning machine at all !!

good luck. baud.

jwb1 · 25-07-2007 5:48pm

bauderline wrote:

If the plug has not been replaced since you bought the mower, 6 years I think you said, then cleaning it won't do squawt .... its old and done and needs replacing ....

As far as I remember the two adjustable settings on most of those carbs are idle and air mixture, the air mixture might be the one causing issue, the idle screw should not cause any issues... you will likely need the owners manual to direct you to which screw is which... otherwise you will need to experiment... scary thought !

I also remember on the old two stroke mowers there was sometimes an adjustment at the very bottom of the float chamber on the carb. If this is set too high it can also cause problems when starting...

As I said, try the plug, if this doesn't work I would track down a local mechanic and get him to have a look at it, if you starting messing around with the carb you might well end up with no functioning machine at all !!

good luck. baud.

.....and then the pull-cord broke!!!!

Have handed it back to the shop for (more) repair work....they had fitted a new plug...but now they will go over the whole thing again....including both crankshaft seals, carb, etc. etc.....

...thanks for your advice....I will let you know the outcome....

Interestingly, I discovered along the way here that 2-stroke mowers are now a rarity....apparently banned by some EU regulation. People with serious slopes in their gardens (like me) are now using 4-stroke mowers with pumps it seems....saw a nice Honda model today that retails for around 700 euro....wide body, 5.5hp engine...this compares very favourably with the original cost of my Lawnboy in 2001...900 pounds!

peasant · 27-07-2007 12:01pm

I also have a two stroke mower (not a lawnboy). It's set up perfectly and runs really well, but I also have a hot start problem.

If it cuts out and I start it straight away again it works fine. If i leave it for a minute or so, it is almost impossible to start again while the engine is still hot.

I suspect the latent heat affects the carburettor.

I work around this issue in the following way:

If i need to stop just for a little bit, I leave the engine running and when I need to stop for longer (but not long enough for it to cool down) I close the fuel cock and just let it run out of fuel and stop it that way. Doing that (and priming it of course) it starts on the first pull, even when hot.

jwb1 · 29-07-2007 12:27pm

peasant wrote:

I also have a two stroke mower (not a lawnboy). It's set up perfectly and runs really well, but I also have a hot start problem.

If it cuts out and I start it straight away again it works fine. If i leave it for a minute or so, it is almost impossible to start again while the engine is still hot.

I suspect the latent heat affects the carburettor.

I work around this issue in the following way:

If i need to stop just for a little bit, I leave the engine running and when I need to stop for longer (but not long enough for it to cool down) I close the fuel cock and just let it run out of fuel and stop it that way. Doing that (and priming it of course) it starts on the first pull, even when hot.

That's intriguing....I'll give that a go when I get the machine back from the shop....if that fails, it looks I'll be spending something like 1200 euro for a new machine....the consequence of having a serious slope and a large garden!

josephr · 28-12-2008 7:50am

If it's a lawnboy that is over 3 years old you are going to have to pull the plate off of the bottom where the exaust comes out and clean out the carbon build up. It would not hurt to pull the head off and clean it to. These things build up carbon and it makes them a nightmare to start after they get hot. I have one that is four years old and it did the same thing yours is, would not start when hot, and after running awhile the idle would go up and down while running. I just replace my muffler every two years and clean the carbon out of the exaust and head every year and I have had no more problems. Hopes this helps.

jwb1 · 28-12-2008 12:52pm

josephr wrote: »

If it's a lawnboy that is over 3 years old you are going to have to pull the plate off of the bottom where the exaust comes out and clean out the carbon build up. It would not hurt to pull the head off and clean it to. These things build up carbon and it makes them a nightmare to start after they get hot. I have one that is four years old and it did the same thing yours is, would not start when hot, and after running awhile the idle would go up and down while running. I just replace my muffler every two years and clean the carbon out of the exaust and head every year and I have had no more problems. Hopes this helps.

You can imagine my surprise at seeing this in my inbox this morning, almost 18 months after I posted the problem!! Since then, I've been using a makeshift (and, to be honest, grossly unsafe) way of keeping the mower running). I will give your suggestion a try....here's a dumb question: where is the exhaust?

I don't have the idle problem you talk about. In fact, it's when I start it up initially that the idling is a bit erratic but it settles down once the thing hots up....

Apart from this annoying problem, it's a lovely machine and I'd hate to see it go....maybe you've saved me 1200 euros!!!

Thanks - John

josephr · 28-12-2008 11:33pm

Ok, if you turn over the lawnmower on its side you will see a plate with 4 or 5 screws in it above the blade on the bottom of the engine. Have a tube of heat resistane silcone with you. Take the screws off and pull the u-shaped tube out. MAKE sure you take the spark plug out and ground the plug wire to the motor. Turn the motor untill the piston is all the way up top and then shine a light into the two holes you took the u-shaped tube out of and see if there is carbon buildup. I scrape mine out with a screwdriver and then spray it with a can of carbenator cleaner to get it nice and clean. Let this dry. Take the muffler off and make sure it is clean also. If the muffler is over 4 years old it is probably clogged up and you might think of getting a new one. Put new silcon sealer on the plate and reinstall it in place. This process is called decarbonizing the 2 cycle engine. With oil mixed in the gas these motors tend to build up carbon quicker than a 4 cycle motor does. This carbon makes the motor run hot, cloggs up the system, and sucks up the incoming gas onto the head so you really don't get a good burn. On the head you just take the bolts off and take the head off and clean the carbon off the inside of the head and the top of the piston. NOTE, have piston at the top when you do this to the head. Spray some carbenator cleaner on the head and piston to get it good and clean and then reinstall the head. Please use a new gasket and plug. Touque the head bolts to what they should be and your done. If you want to make sure your carbenator is clean take the top cover off, crimp your gas line with a pair of vice grips remove the tank and drain it. There are two large screws behind the foam pad or filter of the carbenator. Back these out and take the whole unit off. BE very carefull as this is a plastic carbenator. Turn the carbenator upside down take the four screws out and you will see a screen over the center jet. Make sure the screen is clean. If you want you can take the jet out and clean out the holes in it with a small piece of wire. Remember this is a plastic carbentor so be very carefull. Check the gaskets to make sure they are good and reinstall it. After you have done this put a new plug in it and start it. While I had the tank off I would drain it and use new fuel. The above is a complete tune up of your 6.5 hp motor. I'm going to do mine in about 2 weeks and if you want I will send you pictures. I know how much I hate paying a guy to tune up my mower and then the thing not running right. Hope this helps you and if this is done every two years you will be able to get alot of use out of that lawnmower. They are a good brand but most people just don't know how to take care of them. PM is very inportant. Got to go eat and mess around now. Let me hear from you.

Lawn-Boy Lawn Mower Starting Problems...Help!!

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