OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions On Briggs & Stratton Engines Briggs Quantum Stalling

Took a mower for a good run today - 2003 Masport with xts 50 Quantum

Anyway, back lawn ran great, front verge ran ok, then I left it idling on the path for about 5 minutes. Came back and put the throttle to half - bogged and died.

Primed, started first go mowed for 2 mins, then surge and dead. Fiddled for a minute, primed ran 30 seconds and died. Primed then started and stalled. Repeat and same thing.

"blocked jet" I thought, burnt my finger getting the nut off - clean as a whistle. Good fuel flow once I turned the tap on (fitted one a while ago)

Cracked the sh**s and went and finished the front with another mower.

After cooling 10 minutes, I was able to start (hard but managed) but surged.

Whilst it was running, I stuck my hand over the snorkel - normally this is accompanied by black smoke and a flood. However now it revved hard and wouldn't stall

So this would indicate an air leak downstream of the carby - loose carby or intake at the engine

Will have to have a look

Any other ideas?

Regards
Tyler

Hi Tyler
strange symptoms there, maybe the inlet manifold tube has a hole rubbed through it by the cowl, or the manifold has come loose where it bolts to the head. Come across those problems on several occasions. Haven't come across a Quantam with a snorkel before

Thanks Norm

Damn annoying because it did all the back and 3/4 of the front then died haha

The upper level Masports had the snorkels, and Victa had them as an option - not many people took them up on it unfortunately as its the best thing for a mower

Those Quantums are a pleasant motor indeed. Hope you sort it soon Tyler.

I have a few Quantums with the snorkel ,they are a lot better at keeping dirt etc out of the engine.

If it's not making a popping noise out the muffler or backfiring it sounds like a carby problem ,I've
had a few that the fuel hose was so old it would slowly disintegrate and block the main jet ,I would
remove the fuel bowl and it was spotless but then when you put fuse wire up the main jet it would
dislodged the small rubber fuel line debris ,then the motor would run without a problem.

Here is a carby guide https://www.outdoorking-forum.com.au/forum/u...r-problems-and-solutions.html#Post104746

Cheers
Max

Out of interest Max, the popping noise would be non seating valve correct? My xm50 does it slightly after a hard run

The internal line disintegration was the exact issue with the old quantum 35

I checked the jet, definitely not blocked - ran a jet drill through. Turns out I must have dropped it as there is one missing from my set - bugger

The popping noise can be a non seating valve but usually if this is the case the engine uses a lot more fuel.

The popping noise with the motors I've had is mostly a sign of weak spark meaning the spark plug is faulty
or the coil is faulty,the correct method of checking the ignition coil is with an oscilloscope .

I would change the coil for one that you know is good as long as the plug doesn't have a problem.

If changing the coil still doesn't fix the problem at least you have ruled that out as being the problem.

Cheers
Max.

Thanks Max

That might also explain the similar problem I have been having with my Pop's old mower - Masport MSAA alloy deck with xm50 bought in late 90s (1997?). It had an old champion plug in (and the original red painted plug in a box was in the shed).

The air filter was awful again so last month I gave it a full on tune up - blades and bolts, 2 oil changes, air filter and prefiler, a clean NGK plug, clean and lube linkages, rpm check (was a bit fast)

And once it was hot it was lightly popping. I was thinking valve or timing (considering someone hit a pair of scissors in the grass - thin short couch grass so no excuse).

I will throw in another plug and see

Its doing 2 lawns now so will probably get a 3rd oil change next time I'm there

Just out of interest, do those snorkels fit on most late model Briggs engines? They seem to cover the same area where the air filter cover is anyway.

Hi Sapper

Define late model? Anything OHV, no, and briggs (or any other manufacturer) havent done a snorkel for them as yet

From what I have seen Tyler all the OHV stuff has the carby on the left hand side

Hi Norm

I have seen one of the intek ohv's with a snorkel, but I wouldn't call it a modern briggs ohv. All the newer ones I have seen have carby on the left, with a few upper model exceptions

eg https://gympiemowercentre.com/shop/victa-ultimate-keystart-self-propelled-lawnmower/

But some of these are DOV - which have some special lever arm operated OHV - not straight up and down pushrods

sorry guys, I meant the Quantums (which are not exactly late models).

Yes Sapper - will fit - even the older choke ones I think. They ended up being called 625 series or 675 before they were axed

Tore the cowling off today - I hadn't done it before on this one. Only used it 2 times since I bought it

Had the thickest pile of greasy grass I have ever seen - couldn't even see the governor arm, fins all caked. And it looked so clean on the outside - lulled into false sense of security

Degreased all that - had to scrape out with screwdriver and squirted a bit of water down to get the chunks out. And then I saw the intake - split.

I always like to start the engine after any water near it so put the tube back on, put the coil back on (took off in case of water). Wrapped rope around the pulley and away it went - ran smoother than ever despite the split

Will take to it with the soldering iron and see how it goes.

I was also disgusted by how the gasket between the manifold and engine wasn't even on right from the factory - they missed the bolt hole entirely (gasket bolt hole was triangle still) - they just torqued it down without checking - the edge just sealed it.

Turns out it was made in the first few months of the Chongqing Plant - bugger

Hi Tyler,
I sort of guessed that in my first reply. Silicone instead of the gasket unless you want to make one and JD Weld the crack.

JD welded (actually permatex equiv) the cracks - all cleaned and back together - went first go and ran fine. Will mow this week now our heat wave is gone, and see how it goes

Bet it shi*ts itself again with my luck

Hey Tyler, that crack looks like its from overtorquing or like you said, because there was no gasket under the hole. If you nee a manifold, let me know, ive got a few here, just pay for the postage.
Cheers, Ted

Thanks Ted

I actually found 2 I didn't know I had in one of my parts box - I was thinking they were all classic 35 ones, but turned out 2 were quantum.

Its a great mower, but I have only ever used it 2 times - always felt like something was amiss - now I know why

This is the only photo I have of it - back when I bought it in sept 18. Got the old '93 Morrison the same morning from another tip.

Old thing has a light knock, but just goes and goes (have cleaned it up since this photo)

Hi Tyler,
I have lost track of the number of different types of manifolds Briggs have used, all the same just a bit different. Always does my head scratching through boxes of bits trying to find the one that will fit.

Well, I used it yesterday and was not overly impressed. I needed to give the lawn a slight scalp (They suggested de thatch on Gardening Australia Friday). I didn't take a photo, but it wasn't anywhere a severe one. Plus, I mowed last week, so I am quite sure I wouldn't shock it.

Put on some bentonite clay after mow to hopefully help the sandy soil, and a very light natural fertilize before the thunderstorm we are scheduled for tomorrow (hopefully pelt the clay in further than the sprinkler).

Back to the mower, started first go and mowed the back lawn without any major issues. Got several catchers off.

Then the front - a fair bit harder cut. Full throttle, slow push, stall. Repeat, same. Check full RPM - 3190. Upped it to 3300 - no difference. Ended up cutting 13-20cm strips so it wouldn't die.

The way I see it now (after stalling a Quantum 50 about 8 times in conditions a PT wouldn't have batted an eyelid over) is they are the mower equivalent of a Commodore 4 (the one with the Starfire).
They get along mostly fine in normal use, but its when you need power, you suddenly realize its not there.

It is not a fault in the mower - its just how it is. The thin quick cut blade bar wouldn't have helped its power.

Anyway, I persevered and got it done (couldn't be stuffed getting a PT out with not all that much to go)

To its credit, it worked very hard. I gave it a unloaded run at 2500 for 2 minutes part way through to cool it down. There a slight weep in one of the gaskets which occurred after the last oil change (must have cleaned crap out) so it used a bit of oil, and for the first time I noticed a little oil smoke when it revs up (practically nothing). At the end, it used from full, down to a bit over half way between full and add on the dipstick. Will add some rislone stop leak to the new oil (changed it after the mow - still relatively clean)

Whether it's because of clearances from its chinese manufacture, I don't know. It had semi synth 15w40 in the sump, so maybe a bit of burn when really hot.

Plug burn was perfect - little bit of oil residue

Love the snorkel - was dust flying everywhere - and when finished, the new filter and pre filter was near spotless.

G'day Tyler,

3200-3300 rpm at full throttle is normal for one of these - I have a May 2001 built XTS50 [think it's US origin], on an alloy chassis Masport Maxicatch 550. With the snorkel, too - a very good idea, that.

This one has the Quickcut cutter bar too, and it seems to work pretty well. It does have problems ejecting the clippings in really heavy growth, but doesn't seem to lack grunt, at all. So in these conditions, I just do a first cut at max height setting [or run the line trimmer over it], then a second cut.

With these older-design sidevalve Briggs, they were designed to use SAE30 monograde mineral oil. I have zero oil consumption issues, running Penrite Small Engine SAE30.

From experience, even using a 20W-50 multigrade oil in one of these sidewhackers will result in some oil burn.

Hi Gadge

I had an inkling 3300 was the top - any more than that I though was pushing it. I agree, the main issue is clearing clippings - I actually went up 2 levels at one point with a bit of improvement and then went back over.

Probably more an indication of reciprocating mass than a poor engine I suppose - the little gxv120 on the big bob is 70cc less and will go through much thicker grass (though being a side shooter it is under much less load)

I sometimes run sae30, but I an never get it at a good price - always pushing $30 for 5L. I bought a tonne of Castrol UltraClean 15w40 at autobarn for $12/5L bottle.

I use very short oil change intervals (often change after every mow until I am happy its staying clean) so at $1.40 ish per oil change with the 15w40 semi, it is quite economical. Before I put this oil in, I use the cheapest 15w40 I can find (usually Nulon or gulf western mineral) to flush the muck out for 2 or 3 changes.

In normal use, I notice no consumption. Briggs recommend 10w30 up to 37 degrees - but I reckon thats a bit too thin (can only imaging how much I would have burnt on saturday.
Apparently, 15w40 is the most shear stable multigrade.

Its only in this heavy cutting I have noticed oil consumption. Still, I believe it leaked a fair bit of this.

That being said, a friend never checks his oil so I use sae30 in his.

G'day Tyler,

Agreed, that it's not easy to find SAE30 at a discount - Autobarn sometimes has weekend 'storewide x% off' sales, and I picked up a 5L of the Penrite SAE30 for somewhere in the $20s there, a while back. Lasts me a long time, as I only have two 4-stroke mowers.
They haven't had it for a while, but Autobarn also used to have specials on Valvoline 20W-50 mineral @ $12/5L or less.

My Big Bob is currently waiting on reassembly, after a partial teardown to install some chassis bits from a donor machine. Like you, that machine is my go-to for heavy growth - the 4hp Briggs chugs on through it. Fitting the extra pair of blades seemed to help with that, too.

Hi Gadge

If you only have a few 4 strokes, 30w is definitely the way to go.

Unfortunately, I can't pass up free good condition 4 strokes, so have amassed a fair few. I can see why people go for them - quieter, no fuel mixing, enough power for most. But, they just can't compare in the thick stuff

If I had a lot of time on saturday I would have done a comparison - 2 blade PT V SPFC 160 V 4 Blade Chonda on Honda deck V Masport quickcut with xts50 V Masport quickcut with Quantum 35

I reckon they would finish in that order (best to worst)

Have got 5L of Valvoline 20w50 from a few months ago's special - $9.99. It was ear marked for the Camira, however I grabbed 2x GTX 20w50 last month - again, Autobarn $9.99. Lucky if it does 500km between oil changes though

Last time I used Big Bob, he only had 2 flat blades, but have a pair of low lift blades ready to add for next use. Have to wait for the verge to grow haha. Did your Big bob handles shear?

G'day Tyler,Don't know that fluted 'lift/fan' blades would offer any advantage, on a Big Bob. I just fitted a second set of the OEM type flat blades.

Yeah, the handle bracket fractured, for the second time - on the near side in this pic:



And a FleaBay donor mower @$20, which had the '3rd gen' strut reinforced bracket type, was by far the cheapest repair option.

Just a quick follow up on this, I bit the bullet and purchased one of these masport quadcut discs (plus stiffener ring)

https://www.gaspares.com.au/products/BLH7932?

I put 2 blades to try it out, 2 minute install with the rattle gun. Reconnect plug lead, check oil, new fuel, turn on fuel tap (added that a while back), 4 primes and went with a quarter of a pull. Then settled down so much smoother than before. Quantums are generally quite good, but the big blade disc just completes it

For under $40, its a completely different mower.

I plowed it through a small bit of grass 65-70% as thick as what was absolutely killing it before - now at only 1/2 throttle without any significant bogging. Threw grass to the back of the catcher and packed it much better. Significantly less muck build up on the deck (to be expected).

Ended up putting the top end back to just on 3k rpm - just because it doesn't need the top end anymore but is nicer to have slower idle

Now I just need to work out the old Masport 400 - turns out someone mig welded a victa boss onto the quickcut masport bar. Will probably just throw a Rover disc and boss on that one.

Will eventually convert the other couple of masports I have

Actually, scratch that, I seem to remember the rover being about 5-10mm bigger, so that won't work, just in case anyone tries this in the future

Hi Tyler,
I don't sell a mower anymore with a blade bar on it, the idea is just cheap junk. Sometimes it takes hours to set one up with a proper blade carrier but in the end it is worth it, smooths them out and makes them feel much more solid
Having said that I have had 3 of these small mowers (sprinter type bodies) come back recently with blade problems and no idea why. First one was a Sprinter with a Briggs and I had fitted a Rover blade carrier and the 3 screws holding the base had come out, never had that happen before. Second one is baffling the 2 blades had completely vanished to the point I was thinking did I fit blades to it. The bolts were tight and there was no sign of any bit of blade under the bolt head, both blades missing, defies logic. I know it had blades because she had cut the lawn several times. Third one was a Sanli I had put a Briggs on and used the Sanli blade carrier on it and the blades had become very loose for some reason but the bolts were tight and it hadn't done much work. 3 mysteries I don't have answers for.

Hi Norm

I would never sell a mower with a bar blade on it either - too many issues hitting things. These quickcut swingback bar systems are a step up from that, but still lousy.

When you say the 3 screws holding the base, do you mean the 3 small blade boss screws? If so, I have personally had that happen to me 2x and seen it another 2.

Perplexing how blades could disappear without a trace. Only thing I can think of is poorly heat treated blades, or the 'grain' flowing across the blade - so it practically sheared at the highest stress point; the bolt.