Old 3.5 HP B&S runs a few seconds and dies

[turboscrew]

Hi.
My problem is old B&S 3.5 HP push mower engine.
It hasn't been used for most of the summer, because in the beginning of the summer it started to
act up. It starts with the first pull, runs 1-3 seconds with high-ish revs and dies.
I checked and adjusted the valves (probably not done in the last 10 years if ever) and changed the
diaphragm, and in the process cleaned the carburettor a bit.

What could cause that dying?
Leak between the gas tank and the (tank-mounted) carburettor?
Somehow damaged diaphragm (or mis-pre-loaded)?
Leaking or mis-adjusted valves?
(Still) dirty carburettor?
I guess not the tank cap - it probably would run longer then? Minutes?

The gas tank was emptied during the cleaning (and mixed with about a gallon of new gas).

The engine is 1973 manufactured 92902, and I used it (on another mower frame) wha I was a teen (now 51).
It's probably not worth much money, but it has personal value to me, and it's also kinda cool to have
an almost-half-of-a-century-old B&S in active use.

Oh, forgot, the carburettor is Pulsa-Jet Automatic Choke.

 

[mechanic mark]

Replace air filter and spark plug.

http://www.briggsandstratton.com/~/...on_troubleshooting_detail_reference_guide.pdf see failure tables #8 & #9 won't stay running

 

[Fish]

Total cleaning of the fuel system, and probably time to "tune up" or replace the ignition system.... Those points can be troublesome......

 

[turboscrew]

@mechanic mark: Spark plug ans air filter were changed last year and there is very little electricity to adjust - just the airgap, and it looked good.

@Fish: I'll do that.

 

[Fish]

If your system does have points, I would suggest that you just clip the wires to the points under the flywheel, and install a newer electronic coil, and be done with it. An old time mower shop likely has a bucket full of old good coils....Cheap.....

 

[angellonewolf]

im still a bit new to engines as only playing with them foe 2 years and prob only done 10 or sow mowers but will say one of my last and one of my first mowers were briggs engines and both where problems with condenser and points and most sets can be bought from ebay for ｣5 for a new set the last mower i had sparked but did not run took a chance as was told you cant really test a condenser un less got special test stuff replaced and mower runs very good and went to a good home prob will run for the next 20 years all for ｣5 and a bit of carb cleaner

 

[Fish]

Ok......... Not sure what you said, but OK....

 

[angellonewolf]

im still a bit new to engines as only playing with them for 2 years and prob only done 10 or more mowers but will say one of my last and one of my first mowers were briggs engines very old a hayter 12 inch cut 1979 point problem and both where problems with condenser and points and most sets for briggs engines sets can be bought from ebay for £5 for a new set the last mower i had sparked but did not run took a chance as was told you cant really test a condenser unless got special test stuff replaced points and condenser and mower runs very good it went to a good home prob will run for the next 20 years all for £5 and a bit of carb cleaner

if you got a condenser and points replace for new before fault finding as when condensers get old and hot can cause many problems and for the cost of a few pence the first place i would start or as said change to electronic

 

[Fish]

OK, I guess it might be the monetary thing.......

So are you saying that buying the cheapo Chinese points/condensers are good enough, with a squirt of carb cleaner?

And what is L 5 worth in American? Euros? I never got that thing yet. So you are all on the Euro thing, or what?
L 5 means 5 pounds????? gawd I will try and find you an electronic coil "used" in my shop, and mail it to you, so you can open a
new horizon...... I will put it in my e-bay store, and sell it real cheap.... What are the model/type numbers?

 

[turboscrew]

My engine (92902) has (composite) magnetron. The only adjustment is air gap and it's "one piece" - there is nothing replaceable except the whole unit. The spark looks fine, so I don't think the problem is there. It also starts with one pull, but dies right after that (1-3 seconds).

But for those that have points: a car-made capacitor with wowen terminal(s) is usually better. The vibrations tend to wear the contact thread to break. Also the car-made capacitors bear cold weather (frost in winter when in storage) usually better. Then again, the function of the capacitor is to stop arcing between the contacts. The quality (or even capacity) is not very important. Too small capacity or missing capacitor just make too long spark and wears the points fast.

BTW: about the currency rates, I often use this: XE Currency Converter - Live Rates
Now it says (GBP = £):
1.00 GBP = 1.66955 USD
and
1.00 EUR = 1.33999 USD

So 5.00 GBP = 8.34775 USD

There are some countries in EU that don't belong to the monetary unit (euro) but have their own currencies.
Great Britain is one of them, Sweden is another.