Lawnmower Problem - Advice Please!!

wild handlin

Hi All,

Apoligies if I have posted this in the wrong section, mods please feel free to move if you wish!!

It's not a new mower, had it for a long while but has never given any trouble. It has a Briggs and Stratton Quantum 35 engine and is a fantastic runner. Even after a long period out of use it starts first time!! However, last time I tried to use it it started on the 2nd attempt (nothing unusual I would have thought) and ran brilliantly, however after about 5 mins it started revving up, then down, up and then down further, up and then stopped. (almost as if it was out of fuel). However, I checked the fuel and it's fine. Started it up again and went fine for about another 2-3 mins until it did the same thing - engine revved up, then down, up then down further, up then conked out.

Any help would be great, I'm no expert on small engines (2 stroke or 4 stroke), I did manage to take the strimmer apart right down and cleaned everything out and replaced a few parts, built it back up again and it now works!! but by no means am I an expert!! I've taken a look at the mower, but can't figure out why its all of a sudden started doing this.

Many thanks

bmaxi

Try running it without the air filter. If it runs all right then, clean or change the air filter.

joewicklow

I would say it needs a new diaphragm in the carb. I replaced mine a few weeks ago, the diaphragm gasket only cost €5 or €6.

http://www.youtube.com/watch?v=C5nzigcNTwo

wild handlin

Bmaxi - Many thanks for your useful advice. I had actually installed a new air filter in the mower in August last year, and since then it seemed to perform alot better - it certainly sounded healither - up until last time I tried it!! Many thanks for your help.

Joewicklow - That video is very interesting, many thanks for the link. The mower was throwing out some black smoke now and again and I had put it down to "age", however this could be the problem. Certainly the time before last when I used it it did seem to throw out alot more black smoke than normal, and sounded a little more rough than usual. I had thought it maybe was the air filter (only installed a new one in August) so I took it apart and had a look at the filter, but there was very, very little dust/grass on it at all - if any, so I did wonder what else it could be. A new diaphragm does seem a good bet, I will study the video and see how I get on.

Many thanks for your advice, hopefully it will be back up and running again soon - grass is getting pretty long!!

yop

You might let us know how you get on please. I have a lawnmower which eats fuel for 5 mins, then works away for the next hour+.
It pipes out white smoke every intermittently also.

I have serviced it and put in new air filter but no dice.

mikehunts

joewicklow wrote: »

I would say it needs a new diaphragm in the carb. I replaced mine a few weeks ago, the diaphragm gasket only cost €5 or €6.

http://www.youtube.com/watch?v=C5nzigcNTwo

Sorry for bringing up an old thread, but would like to thank ye kind folk for sorting out my mower, i could not figure out why it was revving up and down until i found this thread so i went and got a new diaphram for 6euro and she is working perfect again.:):)