Yamaha 342 mower

19 Feb 2021
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United Kingdom
Could anyone help me by sending a photo of the linkages to the carburettor from the governor on a Yamaha YLM342 or similar lawnmower please?
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Ye gods, thats an old and rare one! Spares nigh on impossible now but you’ll maybe get a blade and an air filter.
I don’t have any diagrams of the governor but I’d expect a rod from the governor to the carb, with a long spring sleeving it......a picture of what you have may help.
John :)
That looks all in order, just needs to be spotless with an aerosol of carb cleaner.
First rod on the top is the choke, the throttle is behind and almost out of view.
Spring loaded screws.....top one is the tickover, next is the pilot or slow running mixture (1 1/4 turns out) and the bottom one is a drain from the float chamber.
Take care not to damage any gaskets if you can - you’ll end up having to make some!
John :)
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Cheers, so the governor should be connected to the further back (top) linkage?
Yep, the one in the foreground is the choke, and connected to the lever on the handlebar - the rear one is the throttle speed, directly connected to the governor.
This linkage should be free to move, and when the engine is off, it holds the throttle wide open.
John :)
Cheers, I guess when it gets going it moves. Thanks for the education
No worries - this machine was a good bit of kit with a very short production run, hence the lack of spares.
So, run it, change the oil and scrap it when it finally packs in.
John :)
Thanks for this - My YLM 342 stopped after 20 years, hadn't been serviced for 5 or 10 as the local supplier shut. Thanks to your pics and some other general help I removed the carburettor dashpot and found lots of crap in there, cleaned out, changed oil but now it's running like a hare, even on the slow tickover. Would that be the governor not kicking in? I don't want to change the screws as it was fine till I stripped it down.

I took the airbox off and it ran slowly again, I can't tell if the airbox is sticking on the governor linkage or just having cleared the carb and mounted tightly it's now over fuelling (I did put the plate and nuts back on to keep all the carb gaskets sealed). One other thought - is it possible I've bent the float?

Thanks in advance - it's the first time I've stripped one down and TBH I amazed my self it's running at all!
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Update - stripped down again and I'd not put the fuel feed to the carb into the plastic clips on the Air filter housing and it had got pushed against the throttle linkage and jammed the governor!
Hi all, after our 342 had been sitting for years we couldn't get it to run. Cleaned the carb but still no luck. Drained the fuel and noticed there was a filter in the tank end of the line. After cleaning this it starts but I need to set mix and idle.
It's only the slow running mixture that is adjustable.....if all is as it should be, set the idle mixture screw at 11/4 turns out from fully in.
Turning the screw anticlockwise richens the mixture - the engine will start to chuff some black smoke.....turn the screw back in slowly until it runs smoothly.
Turning the screw 11/4 turns clockwise weakens the mixture......the engine may speed up a little but may tend to stall when you want to rev up.
Juggle this and the tickover screw until you are happy with it and it idles nicely.
John :)

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