4-stroke Briggs&Stratton mystery

[Stuggi]

I heard something I didn't believe today and I wanted to check it out with you guys as well;

My fathers neighbor has a lawnmower with a B&S engine which sputters and stalls all the time. He talked to some sort of mechanic, and he told him it's due to the fact that if you tilt the mover too much, oil will run down into the carburetor via the combustion chamber and stiffen the membranes.

I find this very hard to believe, as in my opinion the piston rings and the valve train would stop it from reaching the membranes, and the membrane wouldn't make the engine stall as I can't see why it would be doing much on a engine running at a fixed RPM, but then again my 4-stroke engine experience is kinda limited to newer B-model Volvo engines and old VW boxers.

Funny thing was that he opened up the carburetor and took out the membrane, flexed it a bit and reinstalled it, and now it's working a lot better.

Please help me, my father has promised the neighbor a bottle of wine if this fixes one of our older lawnmowers, and I'd hate to see anyone getting free expensive French plonk.

 

[shenion]

Not likely.

If tilted too far, it will slosh into to the breather tube and get dumped into the air filter.

The membrane is a pump, uses two flaps as valves. When they get stiff, the pump stops working.

 

[Stuggi]

Yeah, so much I figured out, but do they get stiff from the oil? These are quite old engines we're talking about, 15-20 years so I would think it would be due to age more than any stray engine oil.

 

[shenion]

No, they get stiff from the gas. Gas gets old, turns into an acid and all kind of nasty things, then attacks plastics, rubber etc and causes rust.

The diaphram/pump membrane only has contact with the gas on one side and outside air on the other. Even if it was sucking oil into the filter, it still would never come in contact with the membrane.

Run carb empty of gas when you store stuff and use gas stabilizer.

 

[Stuggi]

Well, that's what I thought.

The interesting thing is that the neighbors mower is only one year old, but he said the membrane was poking out 3-4 mm to the side, so my guess is that it was mounted badly when it left the factory. Ours on the other hand is from 1987 according to my father, so it's probably seen it's best years.

How much information would one need to get the right rebuild kit for a B&S engine?

 

[shenion]

Some of the membranes do stick out, the use the same on many carbs.

Go on the B&S web site, enter the model # and you can get the parts breakdown and the carb rebuild kit. Find a local supplier or enter the # on ebay.

I have rebuilt many over the last year. Most are 12-20HP that are easier (carb is separate from tank.) Have two more to do right now. The B&S site has all the manuals online.

If it is real old,then B&S may not have the the manual online. There are generic kits available given the HP of the engine.

B&S engines will last a long time if taken care of; especially the older ones as they are likely to have a steel cylinder. As long as the oil is changed or not over filled they work well. I have seen a few that need a new head gasket as they can rust out.

I have bought several riding lawnmowers over the last year. Typical: "Won't start, bought a new one, come get the old one." Almost always carb is plugged up from old gas. Rebuild kit, clean up and sell for 3x what I paid for it

 

[gordon stephenson]

Probabley why all the Honda engine owners refer to them as "Briggs and Scrapem"

 

[R Kraft]

Most of the older briggs have an integrated fuel pump in the top of the tank.
It has a diaphragm that has intermittent engine vacuum on one side of it that with the spring and flapper valves, pumps the fuel.
The pump keeps the little reservoir on the top of the tank full and the extra runs back into the tank.
They also used to have a vacuum controlled choke that was part of the pump diaphragm.
The diaphragms harden with age.
Usually tipping just floods it and overfilling with oil will foul the plug or lock the cylinder.
The most common damage is to hit something with the blade and damage the zinc flywheel key, that will make the timing off and cause heating and poor performance if they run at all.
Robert

 

[MrFluffy]

B&S engines will last a long time if taken care of; especially the older ones as they are likely to have a steel cylinder.

Its the B&S IC (industrial components) series that have the steel liners along with the oil pump on some models and other such "luxuries".
The ally blocked non ic variants have what briggs call "coolwall technology", which they just bore the material of the crankcase casting for the bore. Not nikasil or any other plating finish, just run the piston right in the casting material.
And if you thought that was bad, lets not mention the complete lack of oil pump (they have a bendy bit of metal on the crank which flings oil round randomly). Or the briggs easystart cam grind, which doesnt let the motor get compression up till above a certain rpm, thus letting them fit a tiny starter motor and skimp out a bit more. Great for compression testing and diagnosis too...

The non ic motors are so crap, Im slowly trying to erase any memory of them from my workshop. The last 12hp I had, I ended up boring it on the mill to take a gpz750 liner and flat topped turbo piston I had spare and I think that ones still running against the natural law of briggs longeivity. Theres one left here in my sons little play tractor, and thats developed a trait of being a nightmare to start from cold, but once its running its unstoppable...

I personally hate briggs motors so much they make me twitch. Every single one Ive ever been given has had big scratches down the bore and been completely clapped out... Give me a ohc honda any day of the week, the japs sure can make a good small motor.

 

[jugs]

Lots of B & S info on this site - Davidsfarm

start with -> http://www.youtube.com/watch?v=ZIZg8myJPUM&feature=related

good luck

 

[Stuggi]

Probabley why all the Honda engine owners refer to them as "Briggs and Scrapem"

Well, this is the first one to develop problems, and I have another fitted to a single phase generator that must have over 500 hours on it, as the generator is 12 years old and used to run all day long through the summers. Still going strong after just a couple of oil changes and one new spark plug.

On the other hand, I actually have seen some bigger Kohler engines that surprised me quite a bit, much quieter than a similar B&S engine (HP wise), but then again the riding lawn mower it was fitted to was about 5-6 times more expensive than the one with the B&S engine, so I might be comparing apples and oranges.

 

[shenion]

Yes Honda's are good. They should be as they are twice as expensive. Most are reliable but I see many flogged on craigs list with "needs camshaft'. Seems a few models have some bugs.

Same for Koler, most I see are higher-end engines with an actual oil pump/filter instead of just a sling gear.

B&S makes comparable engines at similar prices. The problem is any product that is sold on price alone will have a low-end B&S engine (Or worse a Tecumsech) with no optional upgrades. Pressurized oil system, low-noise muffler, better carbs are all options on many B&S engines. Most people see are the low-end, aluminum cyl engines that are throwaway engines.

I had a generator with a B&D Vanguard engine that was excellent. MOst of the V and opposed twin engines seem to be real good. My whole-house generator has a 26HP V_twin B&S engine that has been flawless. Just change oil/filter and it keeps chugging along. Real nice setup as the engine runs well below its rated speed and HP.

My biggest complaint with all small engines are the emissions. Most come with fixed carbs that are non adjustable that run too lean. But, that is nothing my #60-80 drill bit set can't fix

 

[stinkbridgenine]

yes hondas are good,i`ve got a 620 v-twin on one of my karts,it seems bombproof at the moment,and yes,it has got a proper oil pump.
my brother has a B&S world formula on his kart,and although obviously not as powerful,it`s taking a good thrasing on a regular basis with no probs as yet.

 

[Stuggi]

Same for Koler, most I see are higher-end engines with an actual oil pump/filter instead of just a sling gear.

Yeah, the one I've been servicing has a really nice full flow oil filter and a whole lot better muffler on it, but as I said, 5-6 times more expensive mower.