Lawn Mower Advice - Poor Running

Evening All as the .ORG seems to know everything I thought I would ask this here as I can't find much online that is very specific to my problem.

I have a Champion R484 Lawnmower with a SV150 petrol motor. Now I service it every year but not so far this year.

So I go to mow the lawn and start the mower up it runs fine for 5 mins or so and I get about an eighth of the garden mown, then it gradually loses revs and dies, it will restart but revs up then dies. I thought this would be a good time to service it so I change the oil drain out the fuel as this was a little old and clean and re-gap the plug (which still looks pretty poor tbh) I thought I had a spare but turn out I don;t so have ordered one. Because of the running issues I also had the carbs off and apart they were full of crud almost like scale but I cleaned all this out and they were sparkling, whacked the mower back together now it starts fine BUT the engine pulsates badly, as in on lowest throttle it will rev up then back down the back up and down and eventually will die. I seems to not be as bad on full throttle.

I'm thinking as the carbs are freshly cleaned and it has new fuel and oil it has to be the spark plug or possibly the igniter unit which works off a magnet.

Any help/advice greatly received. Cheers

[tigersaw]

They usually have a govener which picks up the throttle as it sences the revs falling off, look for some levers running from the throttle on the carb. If adjusted badly or jammed / kinked thats what happens.

Do you mean running from the throttle levers to the carbs? It was fine last week when I used it that's what's odd.

[tigersaw]

If its like my old suffolk, then the carb throttle is controlled by a rotating bit sticking out, which also has the throttle stop screw. The throttle cable ties in there too, but with an additional bit of ironmongery to govern the revs, it both stops stalling and backs it off if you cane it. On the Suffolk it was connected to a kind of metal leaf that used the air from the flywheel for the feedback.

Originally Posted by tigersaw

If its like my old suffolk, then the carb throttle is controlled by a rotating bit sticking out, which also has the throttle stop screw. The throttle cable ties in there too, but with an additional bit of ironmongery to govern the revs, it both stops stalling and backs it off if you cane it. On the Suffolk it was connected to a kind of metal leaf that used the air from the flywheel for the feedback.

This is my motor:

Attachment 11271

[tigersaw]

difficult to tell, but is part 25 like an aluminium leaf connecting back to the carb throttle somehow, using the air from the flywheel as described?

Originally Posted by tigersaw

difficult to tell, but is part 25 like an aluminium leaf connecting back to the carb throttle somehow, using the air from the flywheel as described?

No number 25 doesn't connect to the carbs at all. I've had the carbs off and in bits today I don't recall seeing anything like you describe.

[tigersaw]

Fair enough - so what is it?

Originally Posted by tigersaw

Fair enough - so what is it?

This is what it is listed as 'AIR VANE SET', now I think about it that z shape tube goes from this bypasses the carbs straight to the airbox. What was up with yours, cloged or something?

[tigersaw]

It didnt move freely, gummed up with grass.