Mower Engine won't rev (Hunting?)

[Crazy Dazz]

I have a Rover mower, with a fairly standard 4-stroke engine.
It must be almost 20 years old, and hasn't worked for a while, but I thought I would give it the once over before chucking it in favour of a cheap chinese replacement from Masters.

It wasn't getting a spark, so I cleaned the plug, and rejigged the lead which was essentially busted. Put in some fuel, and voila, started with one tug (better than it has in years.)

It's always had a good rev range, but now it won't get above mid-range. Once I push the throttle beyond half-way, this "hunting" behaviour kicks in.

It will start to rev, increasing for maybe 3 seconds, then falter, falling back to previous revs, then repeat. Its very consistent.

It idles fine, and will go as high as a "very fast idle" but once I push it into the mid-range this happens.

It still cuts the grass, just a bit annoying, so thought I'd ask the collective brains trust...

[Mechan1k]

Had this with my Masport with the Briggs engine on it.
ended up being the carby diaphram getting old/brittle .... managed to get the replacement one I needed (pulsa-prime type) ... replaced it ... all thanks to youtube ... and runs like a new one.

Prior to that I changed my magneto/lead and also plug to no avail.

[Trevor 57]

I am not sure this is your problem, but it happened to mine and is a pretty common fault, where the throttle cable hooks on to the carby is at the front of the mower, when we push the mowers around we run into things and inadvertently push the bracket that holds the cable in towards the engine, you need to move the bracket back out to get full throttle again, if this is the problem

As I said not sure if it is the problem, but it happened to mine and I couldn't work out why it wouldn't rev, went to a mower shop to buy a new one and the bloke there told me about the issue, now it runs like it always did, bloody Briggs and Stratton engines (on a Rover mower)

[Mowdit]

Could be as simple as a clogged air filter.

I get this regularly, not enough air and overfueling, won't rev and hunts.

Rip it out and start it to see if this is your problem.

Or as mentioned the bent bracket (although that shouldn't make it hunt)

Also electrical, if as the revs build it loses spark (crook earth, magneto or lead) it will pulse as it fires again only to repeat.

Goodluck

[gossy]

I'm taking a guess at dirty needle and seat in the carby. Had a mower that had the exact same symptoms, cleaned the seat and has worked like a charm ever since. This is on a B&S engine as well.

[burnz]

the rev limiter spring is tangled up, not enough play.

run the engine and observe the rev limiter in action, it could simply be restricted in movement.

[zilo]

it was the same symptom on my mower. ended up cleaning a fuel hose and replacing the filter.

[backbreaker]

I'm with BURNZ.

[Stefan]

I would not get a cheap Chinese mower, I walked into bunnings for a mower and was disappointed in what was on offer. Not even a decent catcher attached, just flimsy net / bag that will probably be torn on the first bush it gets caught on

I bought a 20 year old 50 dollar victa, rebuilt the carby and it has started first pull for the last 5 years. Solid as a rock, built they way a mower should be.

I'd fix what you have if you struggle take it to mower shop to sort. But really these things are simple as.

[Binny]

I hear so many mowers in my neighborhood like that. The OCD in me wants to go over and fix it!

[FPV+fteT3]

I have a very reliable 4 stroke rover when it decides not to rev properly which it has done a couple of times in the last 10 years I unscrew the 10mm (looks like a nut) in the middle of the bowl on the bottom remove the bowl and clean the needle refit turn the fuel on and check bowl has sealed then thrash again for years.

[prydey]

Originally Posted by Mowdit

Could be as simple as a clogged air filter.

try this first. my old boy has a 4 stroke rover which had similar symptoms and i cleaned the air filter and problem solvered.

[The Yeti]

Originally Posted by Stefan

I would not get a cheap Chinese mower, I walked into bunnings for a mower and was disappointed in what was on offer. Not even a decent catcher attached, just flimsy net / bag that will probably be torn on the first bush it gets caught on

I bought a 20 year old 50 dollar victa, rebuilt the carby and it has started first pull for the last 5 years. Solid as a rock, built they way a mower should be.

I'd fix what you have if you struggle take it to mower shop to sort. But really these things are simple as.

I'm with Stefan be VERY carful with the cheep Bunnings masters options, IMHO they are a false economy, I got a GMC with a Briggs n Stratton off Bunnings a few years ago and it was rubbish the base design was rubbish and wouldn't flow grass to the catcher the catcher was also rubbish and wouldn't attaché properly and would fall off for seemingly no reason, in the end my boss was tossing out his old rover because it was seized so I swapped the engine on the base for one that has bearing wheels, the catcher fits and the grass clippings flow in to the catcher

But even the Briggs engine is a low rent version on these cheap mowers

[Spurious]

Wandering revs most likely caused by restricted air intake.

Simple test, remove air filter & see if it runs normally.
If not then most likely a fuel issue, a lack of.
If you lean the mower over to wash the pan then sometime engine oil will back flow to the carby, exhaust &/or air filter. Rovers with a carby mounted filter are prone to this.

If it won't start at all then there's no spark &/or the coil/stater is stuffed.
The ceramic part of a spark plug can crack & cause the spark to earth out on the engine body. Cracking occurs either from age or hosing it while it's hot.

Most mower shops/servicing are cheap as chips. I've never had a service or repair job exceed $120.

[mr smith]

Mine was doing this and I adjusted the govenor arm. Its open to being bent if the mower takes a hit to the front. I will add I really dig my old Victa, it lives outside, cost me $200 bucks (used once by a friends mum) gets basic maintenace and is used for two + hrs at a time. My top dollar Honda = rubbish

[GASWAGON]

Could also be a blocked carby if mower has been sitting around without use for a while.

ULP these days goers stale very quickly and can cause blockages in the carby jets if not used regularly.

[Mechan1k]

Also never use an Ethanol blend if these small engines (I made this mistake and found it caused issue) ... and if fuel is sitting around for a bit ... use a fuel stabiliser as well ... since doing this my 4-stroke Masport and 2-stroke brushcutter have worked better than ever.

[BENT_8]

Ditch it and get a Honda...problem solvered.

[Trevor 57]

Originally Posted by mr smith

Mine was doing this and I adjusted the govenor arm. Its open to being bent if the mower takes a hit to the front.

this is what I was getting at as well

[danzvtil]

Originally Posted by BENT_8

Ditch it and get a Honda...problem solvered.

I bought a victa with a Honda engine, wicked. Heaps of power,uses 25% less fuel than briggs, the only thing I don't like is that it needs 2-3 pulls of the starter to run from cold. My old briggs would always start on first pull.

[mik]

i had a briggs and stratton for about 17 years, it was a beauty , i beat the living hell out of it, i did put rings in it after about 15 years, but again, it worked really hard and did a lot of hours.

it had a heavy built aluminum body on it, still as good as the day i bought it other than a bit of paint degradation, the catcher door was rusted away and catcher had seen better days but was still workable, the ignition failed finally and from memory it was a fair bit of coin to replace so i thought might as well invest in a newy.
i dont really look after my mowers that much ,although it did see a couple of oil changes and a filter and about 3 spark plugs in 17 years ,
the only thing i really do religiously with my mowers is make sure the fuel tank is always chocka block full to the top when i park it up,
less chance i think of water condensing in the tank and causing carburettor/ hard start type problems.

[NTF6]

Originally Posted by Mowdit

Could be as simple as a clogged air filter.

I get this regularly, not enough air and overfueling, won't rev and hunts.

Rip it out and start it to see if this is your problem.

Or as mentioned the bent bracket (although that shouldn't make it hunt)

Also electrical, if as the revs build it loses spark (crook earth, magneto or lead) it will pulse as it fires again only to repeat.

Goodluck

^^^^ What Mowdit said, blocked air filter, mine was doing the exact same thing, checked the air filter and it looked like a doona, cleaned and like new again.

[mr smith]

Originally Posted by BENT_8

Dont ditch it and get a Honda...problems will be worse

Fixed

[mechanic]

Originally Posted by CoolBFWagon

Could also be a blocked carby if mower has been sitting around without use for a while.

ULP these days goers stale very quickly and can cause blockages in the carby jets if not used regularly.

Won't hurt to strip the Carby and clean the jets, but sounds more like governor spring problem to me.We had the B&S agency when I was an apprentice. Some of those old models were rubbish.

[Trevor 57]

I really hate it when a person comes on, asks for advice there never appears again, WHY ****EN ASK!!!!!

[gossy]

^^^^ Maybe he is busy rebuilding the carby???? Hope he comes back soon with an answer.

[prydey]

Probably waiting for his grass to grow

[snowcone]

I gotta tell you, I laughed when I saw Big W selling Chinese mowers a few years ago and thought who would buy one of those.
Strangely enough, I did. My trusty Victa Vortex died and I went mower shopping and found I needed around $400 to $500 to get a replacement.

Walked into Big W and saw the Sanli 4 stroke on special for $250. It was the last one in stock so I got another 20% off for being a display model.
I had a good look and blimey, the engine was a Chinese clone of a Honda. None of those antiquated side valve Briggs and Strattons, this is a overhead cam engine with electronic ignition and full roller bearing wheels

In the past 5 years that I had it it has not failed to start first time every time. I have broken 2 things on it so far. The base plate for the blades cracked and I bought a new genuine one for $20 at a local mower shop. The left front wheel broke from rubbing up against the brick wall too hard - cost me another $20 for a genuine wheel. Heaps of power and never lets me down.

[Mowdit]

Originally Posted by prydey

Probably waiting for his grass to grow

Or lost in the jungle it has become
(A big part of the forum is the SEARCH button, it often helps other people solve a problem without re posting, so I agree, a FOLLOW UP FROM THE OP AS TO THE PROBLEM/FIX SHOULD BE MANDATORY !!!!! )

Bought a Briggs &Stratton powered Masport for Christmas last year, did less than 20 hours work with it and broke the crank an inch above the blade disk.

Took over 9 weeks to get fixed under warranty

Am a mowing contractor, no mower for that long is bad ! Never again !

My local mower shop has since missed out on over $5k of sales because ive since gone elsewhere for better service, and as it turns out better prices also

[Crazy Dazz]

Patience Grasshoppers!

As you'd expect, its a Briggs & Stratton. A "Quantum XM 40."
I'm currently trying to find a manual for it...

I thought I would start with the simplest, whip off the air-filter, and have a gander at the carbie. I'm accustomed to the air filter just being screwed onto the top of the carby, but there is nothing like that on this model. So I'll start pulling the cowlings off and see what I find.

EDIT: OK, the "quantum 2" engines have the filter on the side of the carby... Off to have another look.