Briggs & Stratton Engine Problem

[pheeh.zero]

My thought on the mag being bad...it would take minutes not seconds for it to thermally fail.

[Manjo]

Great page. I looked at my multimeter and it can only handle up to

1,000 DCV. 10,000 DCV would blow mine up.

Manjo

[Manjo]

I don't know anything about magnetos. I have to ask why would it take minutes? Would it take that long for a winding to heat up and separate (if that's possible)? I get a 2,500 ohm reading through the spark plug cap to the body of the magneto. I did visually check the connections and there are only a couple and they seemed in place when I getnly pushed them with a screw driver tip.

Manjo

[dpb]

...

I've not read the rest of the thread but noted you were apparently still searching --

Anybody suggested checking the exhaust screen (I'm assuming it has one) for C deposits? Sounds like it could be clogged w/ buildup which will cause such symptoms...

--

[Oren]

Do a "shade tree mechanic" (G) test. Pull the plug, re-attach the wire on the plug and lay the plug on a good ground (scratch the paint) of metal. Pull the start rope and watch the spark. You want to see a bright blue spark and hear it snap.

(The other method is to hold the plug wire terminal in your hand give 'er a yank on the rope:) BTDT.

The flywheel has two magnets inside (not shown in your .pdf file). They can become corroded and a simply cleaning with a fine sand paper can clean them to a shine.

Magnetos do go bad, but very seldom in my experience.

Look on the last page at part #147 (Seal Needle Valve) and part #118 (adjustment screw), If one or both are damaged, you'll not get the proper adjustment.

Examine the tip of the screw for damage or wear. Sometimes they bend the tip of the screw if the tighten them down to far into the seat.

I'm throwing things out there, because I like/want to avoid pulling the flywheel.

Now, have you hit anything last fall with the mower? The flywheel has a shear pin. It can be a small fracture, but the timing is off on the magneto...just a bit.

[Gary Dyrkacz.]

How about checking around the head gasket for leaks. I had a lawnmower engine that exhibited a similar problem.

[Manjo]

I know it doesn't do much good, but I did do a visual check of the head gasket edges. Nothing unusual, but I'll check it with some sudsy water today. I lent out my leak down tester (I hope to get back soon) so I had to use a standard cylinder compression tester. I got consistent readings of 74 psi with a warm (not hot) engine. I think this is a good reading since it's a small cylinder, unlike an auto engine cylinder. Manjo

[Manjo]

The exhaust has not been checked. I did put my hand near the exhaust canister and I could feel puffs of air as the engine ran at normal rpm. But now that you mention this, the air pressure felt a little low or soft. I'll pull the can and check it today. Manjo

[Manjo]

Good idea to clean the magneto. I've been hesitant to remove the magneto since it seems to be a pretty close fit to the rotor and I didn't want to introduce another problem, but it's time now. The rotor itself has some light rust that I'll sand lightly, too.

I did a similar spark plug test a few days ago. I left the spark plug in the engine port and put another spark plug in the cap and held it to the top of the first and I was able to start the engine. Although it ran a little slower rpm-wise, the engine functioned close to normal and I could see a spark across the hand-help plug gap that looked good. As the engine slowed down, there was more yellow coloration to the spark and then the engine died. I will try this and your test again just to be sure I=92m getting a decent spark after I clean the magneto and rotor.

I haven't chased the valve seat, but I did spray it with carb cleaner and blew it out with compressed air. I checked the idle adjustment needle tip and it looked good: it was straight and did not have any apparent wear or damage to the tip.

I'll check all these things today.

Manjo

[ransley]

feed

If spark is yellow its weak, it should be white to blue white,

[patrick mitchel]

Here's a wild thought; I read that it's a leaf blower. Is there a belt drive in it? Was thinking of a way to power the engine using a drive to spin the motor - with the plug out and grounded. Long enough to see if the coil overheats and breaks down and loses spark. That would at least remove one of the variables. Having gone through a series of question with a 8 hp briggs L head (finally found an intermittent intake valve) that caused me some pondering before I was able to put the thing back in service shredding the freakin ivy wall on the north side of the property. Pat

[Oren]

The crankcase has a breather also. See parts 8 & 9. This allows gases to escape out the crankcase. They can be clogged, but cleaned easily.

[Oren]

If you did have a leak at the head gasket; you might hear a slight whistle sound with the engine running. A blown gasket and I doubt the engine would run, as the power combustion goes out the passage/leak.

[Oren]

If you pull the plug out and test, there is now no compression. Pull the rope and cycle through several power strokes and you can get a better exam of the spark.

[dpb]

A "blown" gasket wouldn't give 75 psi, either... :)

[pheeh.zero]

The engine needs to RUN in order to heat the coil to thermal fault. Spinning has little to do with it.

[jacko]

[pheeh.zero]

You can safely spray WD-40 to run an engine because its propellant is propane gas...and the oil lubricates the upper cylinder. All mechanics know of this...and most use it!

[Manjo]

I live in eastern MA. I also agree with Husky 99%. I went to the leaf blower manufacturer and they only had a four-page assembly manual with no engine information or details. I went to B&S's web site and then called Customer Service. I was told by B&S the only repair manual they offered (to sell me and I bought) was the "Single Cylinder "L" Head (built after 1981) Repair manual". That B&S manual covers plenty of different models and carbs including mine, but it contains no "principals of operation", or explanation of how any of the carbs actually work. My carb experience is limited to motorcycle float carbs, but I was lucky enough at the time to find an expert forum that filled in the bike=92s official service manual carb blank spots.

And that's why I came to this forum. I needed to fill in the big blanks and have been very lucky to learn from all of you and to read Husky's carb tutorial that has filled in a lot of carb blanks, also. IF ANYONE knows of a manual or web site that has an operational description of my carb or a similar small engine diaphragm carb, I'm more than happy and willing to read it and learn.

(The 1% I don't agree with is the implication that I am lazy, stupid, and cheap. I work hard to gather any and all information and data available, I=92m of fair intelligence, and have and will spend money to buy tools and manuals to help and guide me to fix engines and appliances I don't feel it's necessary to pay someone $50 an hour to repair for me. To imply otherwise is unfair and demeaning.)

Have you checked to see if the plug is wet when it dies? ---- YES, IT"S a little wet.

Can you keep it running by spraying fuel (use WD-40, not starting fluid) into the carb intake? ---- No, the starter fluid will NOT keep the engine running, but will start it. But I will try WD-40.

Have you tried running the engine with a spark tester in the plug wire? ---- No. I lost my spark tester and I'm buying a replacement.

With the tank half full, does the inner reservoir fill up after a few pulls of the rope?

----- I DON=92T KNOW. The tank-top carb covers any possible view of the reservoir. IS there some trick to looking into the reservoir with the carb in place??

Are the little "flaps" cut in the diaphragm curling up or laying flat against the side face of the carb? Did you use a new diaphragm, or just reinstall the old one? ----- THE FLAPS are laying flat against the carb body. YES, I did buy and install a new diaphragm, and when I blew out the carb body, the diaphragm and cover were OFF the carb and not damaged.

Thanks,

Manjo

Manjo

[pheeh.zero]

You're doing a fine job of trying to isolate the problem and learn at the same time. This carb is NOT the easiest to understand. It is an amazing design...but it's almost like they got one person to design this...and them put him back in the asylum.