Won't start

[srobo2]

Hi, I have a Honda HRG465 C3 which is about 15 years old. It was running normally, then the other day, after about 20 mins use it wouldn't restart after emptying the grass box.

Air filter is good, oil good, I replaced the fuel with fresh fuel, the spark plug sparks (however I replaced it with a new plug), cleaned carburettor and still nothing. I then replaced the carburettor with a non-honda branded one, and still nothing. Fuel is getting to the carburettor, so there isn't any blockage.
Any ideas of what else it could be?

Thanks.

[Mick]

Hi srobo2, and welcome to TGMForum.

Sounds to me like a spark issue, especially as you've changed everything else.

The OPC switch on the left of the engine kills the spark when you release the OPC lever on the handlebars.  I would start there and make sure the switch is being pressed when you hold the lever up.  They have had issues with the cables being slightly too long and after a while the switch isn't being pressed.

Pull the handle on the bars and give the cable a tug with your hand and see if it tries to start.

[srobo2]

Ok, I'll give that a try tomorrow. However, the plug is sparking when I remove it from the lawnmower and pull the start cord with the plug against the metal engine. I did wander if it might be an internally damaged cable that doesn't get the plug to spark when installed, but it works when removed due to the angle of the cable (if that makes sense)!

[srobo2]

Checked the OPC switch, and the bar lever/cable pushes the switch all the way in. Checked the plug again and it is sparking well.
I have attached a photo; when the carburettor etc is removed, this brass coloured button/switch (sorry, I don't know the name of it) is permanently pushed out. It doesn't go back in if I give it a press. Is that normal?

When I look in through the gap where the carburettor normally sits, I can see what looks like an extended piston. I can't get a decent photo as it's too dark. When pulling on the starter lever a smaller (perhaps a few mm diameter) piston moves, but the thing that looks like a larger piston doesn't.

Don't know if that makes sense?
The lawnmower doesn't sound like it is even close to starting.

[Mick]

The brass thing is called a Thermowax.  It's the part that pushes the choke off when the engine warms up.  Only the silver pin in the middle of it should move outwards when it heats up.  When closed like in your photo the choke should be fully closed.

I'm going to suggest you drip a small amount of fuel (or spray some carb cleaner) directly into the air intake of the carburettor and see if it tries to run, if it does then the fuel system is still at fault.

[srobo2]

Hi, I have sprayed carb cleaner in through the air intake, with no joy. Also took the plug out and poured a small amount of petrol in, replaced the plug and still nothing happens.

[Mick]

Nothing at all, not even firing or spitting back?

Does it have any compression?  Is the valve cover dented in at all?

[srobo2]

I'd say there is a bit of spitting back after pulling the starter chord several times, but nothing like it trying to fire up.
There is compression - you can hear (what I think is) pistons moving after pulling the starter.
As for the valve cover -.I've attached another photo of what I think you mean, and yes it's prety beaten up!

[Mick]

OK.  I've seen it a few times where the valve cover is dented in so much that it rests against on of the valves inside and keeps it open slightly, therefore spitting back instead of starting.

It's got to be something like this, I mean you've changed checked everything else.

The cover is held on via four bolts but it's also glued on with with pretty strong sealant so needs prising off carefully to prevent bending it out of shape.  Then bash the dent out and refit with fresh sealant.

[srobo2]

It works again! Thank you so much for that.
I removed the valve cover and bashed it back into shape, resealed it and left it overnight.
Topped up oil this morning and it started. It's running at a higher speed than before, but it works!

[Mick]

Cool, that's great to hear.    Always tricky doing these diagnoses when you can't see and hear what's going on, but we got there in the end.