Mountfield lawn mower engine valve issue?

[wazzag]

hi,

I've been having a lot of trouble with my lawn mower. It's a self propelled jobby with a v35 engine that keeps flooding and obviously cutting out. Fuel ends up dripping from the exhaust box.
I decided to investigate after watching many many YouTube videos and gave got to the point where I have the carb off and the head off and I think I've found something suspicious. When I rotate the flywheel and watch the piston and valves, the exhaust valve opens slightly (not fully) on the compression stroke and then closes with a clicking noise coming from inside the engine. It then opens fully as expected during the exhaust stroke.
Can anyone please tell me whether this is normal and if not what the cause might be?
Many thanks,
Warren

 

[Burnerman]

First thing to do is to open up the tappet cover on the side of the engine.....I suspect that the valve retaining clip or collet has come adrift, and the inlet is interfering with the exhaust valve.
If all seems well there, then it's strip down time but I've never seen camshaft issues with these, and the valve timing is set by marks on the pinions.
Some engines have plastic timing gears which are prone to failure though.
John

 

[wazzag]

Thanks John.

I thought the fact that the exhaust valve opened on the compression stroke was a problem but it seems it may be a feature that makes it easier to start the engine (which doesnt occur when its running) I read this in relation to another engine and just assumed that the same feature may be present on the v35?

If so then I guess this isn't the cause of my issue.

 

[Burnerman]

Are you saying your V35 has an automatic decompressor mechanism?
I'm afraid I can't comment on that one, but why a 150cc side valve motor needs one is beyond me.....I can't say yay or nay!
Anyway.....fuel coming out of the exhaust system means that either the carburettor is flooding ( very unlikely) or the machine has been turned over on its side. Any comments there?
Whether auto decompress or not, nothing should drip from the exhaust with the machine on level ground.
I can't find any records of this motor having auto decompress - can you?
Do post back, have a peek under that tappet cover.
John

 

[Nige F]

The dreaded B+S engine I did some resarch myself and the ex. valve opening is indeed for easy starting - and it stays like that apparently. Stick a new carb on it like I did - £20 delivered from on the net

 

[wazzag]

Thanks chaps. So it seems the behaviour is normal!

For now I'm going to clean the carb and give it a complete service. New oil, plug, filter and gaskets.

If this doesn't work I'll get a new carb. Any suggestions on where to get one from please?

 

[Burnerman]

There's a good chance you'll get one from GHS Ltd - if you definitely need one, that is.
John

 

[Burnerman]

Just looking at this post again.....raw fuel dripping from the exhaust?
Could this not be engine oil due to a) being overfilled or b) the machine having been turned on its side?
John

 

[Mursal]

https://www.youtube.com/watch?v=tceKAAViC1c

It really is another world ................

Watch the petrol on the hopefully hot exhaust, start outside .........

 

[Burnerman]

Thank you very much indeed for that - hardly necessary on a side valve though, with only about 6.5:1 compression anyway!
John