Power Force DYM1481FB Lawn Mower - Help Please

[chris301up]

I have inherited a Power Force DYM1481FB lawn mower which I am currently working on. I am not familiar with petrol lawn mowers and have posted other questions regarding this. Initially I was able to get this to start, but it cut out after a few seconds so, thinking it was a fuel issue, replaced the carb. This, unfortunately, didn't cure the problem so I've now replaced the spark plug and ignition magneto. There is now a good spark and I can get the engine to start, providing I hold the linkages (which I assume connect the governor?) but, as soon as I release this, it cuts out. The revs do not increase when pulling on the handle either, which I assume should? Anyway, I am now at a loss, as I don't really understand how these are supposed to work. Can anyone help please? Maybe point me in the right direction for an engine schematic diagram? Thanks.

[Mick]

Hi Chris, and welcome to TGMF.

I can only apologise for not replying sooner, I've had no PC for a couple of days. Sorry.

I take it you haven't tried the original carb now you have changed the ignition coil? Maybe that's an option unless you know there's something actually wrong with it.

A couple of photos would be helpful, one of the linkage front to back from the side, and one from the top looking down on the linkage, though you'd need to remove  the air filter housing to get a good view and idea of how you've got it set up.

A diagram for that machine I also can't find, but I know it's almost identical to some other Chinese powered mowers, such as some of the Cobra's etc.

[chris301up]

Hi Chris, and welcome to TGMF.

I can only apologise for not replying sooner, I've had no PC for a couple of days. Sorry.

I take it you haven't tried the original carb now you have changed the ignition coil? Maybe that's an option unless you know there's something actually wrong with it.

A couple of photos would be helpful, one of the linkage front to back from the side, and one

from the top looking down on the linkage, though you'd need to remove  the air filter housing to get a good view and idea of how you've got it set up.

A diagram for that machine I also can't find, but I know it's almost identical to some other Chinese powered mowers, such as some of the Cobra's etc.

Good afternoon

Strangely enough I tried the old carb earlier this afternoon. Couldn't get it to start at all, so replaced with new carb again. I had already taken photos of the linkages earlier and are herewith attached. The yellow item sticking out is just to block the air intake whilst the filter is removed. I was going to ask what these do as they don't appear to do anything at all. I have worked on engines all of my life so have a good understanding generally. I just cannot get my head round how these mowers work without a throttle cable? Maybe you can point me in the right direction? Thanks

[Mick]

Nice that was handy having the photos ready.

The first pic the one you plugged with the yellow thing is just a crankcase breather pipe.  Basically the fumes etc from the crankcase are drawn back through the air intake to reburn them.

The second pic.  Behind that tin plate in front of the governor arm there should be a spring (governor spring) pulling upwards so the top of that arm moves away from the carb thus opening the throttle on the carb.  The throttle should be wide open when the engine is not running, and when running the governor arm will move to close the throttle to a set speed set via the tension on that spring.   I notice your throttle is closed which means the spring isn't doing anything.

[chris301up]

Nice that was handy having the photos ready.

The first pic the one you plugged with the yellow thing is just a crankcase breather pipe.  Basically the fumes etc from the crankcase are drawn back through the air intake to reburn them.

The second pic.  Behind that tin plate in front of the governor arm there should be a spring (governor spring) pulling upwards so the top of that arm moves away from the carb thus opening the throttle on the carb.  The throttle should be wide open when the engine is not running, and when running the governor arm will move to close the throttle to a set speed set via the tension on that spring.  I notice your throttle is closed which means the spring isn't doing anything.

Hi Mick. Thank you for the information. I'll have another look at it in the morning and check out what you mentioned. Just as a point of interest I noticed a spring on the governor plate at the bottom pulling forward, which in turn pulls the lever to the rear, away from the carb. But, as far as I can see, it closes the throttle. Totally opposite to what I would've thought. I may just disconnect the linkages and see if it will run without them and go from there. Thanks so much.

[Mick]

I would compare the two carburettors and make sure the throttle shafts are set up the same. One might have the linkage holes on the other side reversing the rotation.  The governor linkage should be holding it open when not running.

[chris301up]

I would compare the two carburettors and make sure the throttle shafts are set up the same. One might have the linkage holes on the other side reversing the rotation.  The governor linkage should be holding it open when not running.

Morning. I have compared the two carburettors and, as you mentioned, the linkage shafts are set up differently and was reversing their rotation. I have now swapped them over so that the governor linkage is pushing forward and holding the butterfly/throttle open. But still nothing. I've also removed the spark plug to check, and that seems totally dry. Was expecting it to be wet from 'flooding'? Fuel is getting to the carburettor at the fuel line and the float chamber. Removing the bottom screw allows fuel to leak which confirms this? I'm not entirely sure now that fuel is getting into the engine?

[chris301up]

Just an addendum. Have disconnected the linkages and, with the butterfly/throttle almost fully closed, got it to finally start up and run. It increases and decreases speed with handle, although quite 'lumpy'. At least I've got something to happen.

I've now replaced with the original carb and got it to run also. Again without linkages and still very 'lumpy'. I'm just wondering now if it could be a timing issue or should I try another carb? Thats the question now.

[Mick]

If it starts and runs with the throttle almost closed it sounds like it's running on the idle circuit and not the main jet.  If you remove the fuel bowl from the bottom of the carb you should see the main jet, it will be either up that chamber where the bowl bolt screws into, or in the side of it.  give it a clean and see if it improves.

Regards timing. If you're sure the replacement coil is the right one it is possible the flywheel key has sheared, but normally that would be caused by the blade striking something solid like a brick or metal object sticking out of the ground etc.

[chris301up]

If it starts and runs with the throttle almost closed it sounds like it's running on the idle circuit and not the main jet.  If you remove the fuel bowl from the bottom of the carb you should see the main jet, it will be either up that chamber where the bowl bolt screws into, or in the side of it.  give it a clean and see if it improves.

Regards timing. If you're sure the replacement coil is the right one it is possible the flywheel key has sheared, but normally that would be caused by the blade striking something solid like a brick or metal object sticking out of the ground etc.

Thank you for the information Mick. I've just given the jets a good clean and nothing has improved. I'm not sure of the history behind this. It could've hit something prior to me having it I suppose? I have taken the nut off the top and checked the keyway as best as I can. The groove in the shaft and key all look in line. I haven't got a puller so unable to remove flywheel (if that's the correct terminology?), but don't think this is the issue? Thanks

[Mick]

Yes, you can usually see if the key and keyways are aligned tbh.

Running lumpy, does it sound like it's running rich? If so just make sure there's no fuel in the oil.  Sometimes this can happen with a faulty carb, the fuel mixes with the oil then the engine breaths it via the breather simulating a rich carburettor.

Was the old coil faulty? I mean no spark.  Also make sure the air gap is set between coil posts and flywheel magnets.  Around ten though, or thickness of a business card or label.     

[Mick]

They normally run quite nicely when all is ok.  Here's a B&Q version which I think is very similar, running after I serviced it.

[chris301up]

Yes, you can usually see if the key and keyways are aligned tbh.

Running lumpy, does it sound like it's running rich? If so just make sure there's no fuel in the oil.  Sometimes this can happen with a faulty carb, the fuel mixes with the oil then the engine breaths it via the breather simulating a rich carburettor.

Was the old coil faulty? I mean no spark.  Also make sure the air gap is set between coil posts and flywheel magnets.  Around ten though, or thickness of a business card or label.   

Yes. It could possibly be running rich? Occasionally I get a backfire. I haven't checked the oil for fuel. I'll check that tomorrow now. Once I changed the carb and it wouldn't start, I suspected a faulty magneto so, just as a matter of course I replaced it, and then the spark plug. Yes I initially used a business card to set the air gap at the magnet. I did then check with feeler gauge afterwards at 10 thou. It certainly seems like a fuel issue to me? I suppose its possible the carb I purchased could be incorrect for the mower? I didn't want to purchase another if its not going to sort the problem.

Just checked oil and all is fine. No fuel ingress there!

[chris301up]

They normally run quite nicely when all is ok.  Here's a B&Q version which I think is very similar, running after I serviced it.

Yes thats a very similar model to mine. Mine certainly doesn't run or sound anything like that 

[chris301up]

Decided to buy another carburettor from Solent Tools which is the correct one for this machine apparently? If it runs? Great. If it doesn't run? At least I'll know for sure that this cannot be the issue and go from there.