Briggs and Stratton 3.5 hp lawnmower engine problem

onic component of it might be on. I have this 3.5 horse engine on my old pu sh mower. The engine is about 38 years old now but the mower is used very i nfrequently so the hours are not that bad. About 5 or 6 years ago I replace d the old OEM coil that used points, with a used newer electronic type that eliminates the points. The mower is on it's third carburetor, gas tank and second deck but it has always started ok. I tried to start the mower this morning and as sure as my wife said, (I hate it when she's right), "You'll never start that old thing", it wouldn't start. Long story short there is n o HV spark to the plug. It seems as though the coil is bad again. I was goi ng to hit up a few used lawnmower places to try to get a replacement coil b ecause I have no engine numbers on my machine to look up the part but I was wondering if anyone knows if it's possible to bench test these things. Tha nks for any help Lenny

shouldn't be hard to continuity test the coil LT & HT sides. You have a mul timeter?

Beware, connecting & disconnecting the meter on the LT side can cause a spa rk on the HT side.

NT

That reminds me I must wind up my Hayterette mower with Griggs & Stratton circa 1975 for the first time this year. IIRC ignition checks on my repair page

onic component of it might be on. I have this 3.5 horse engine on my old pu sh mower. The engine is about 38 years old now but the mower is used very i nfrequently so the hours are not that bad. About 5 or 6 years ago I replace d the old OEM coil that used points, with a used newer electronic type that eliminates the points. The mower is on it's third carburetor, gas tank and second deck but it has always started ok. I tried to start the mower this morning and as sure as my wife said, (I hate it when she's right), "You'll never start that old thing", it wouldn't start. Long story short there is n o HV spark to the plug. It seems as though the coil is bad again. I was goi ng to hit up a few used lawnmower places to try to get a replacement coil b ecause I have no engine numbers on my machine to look up the part but I was wondering if anyone knows if it's possible to bench test these things. Tha nks for any help Lenny

I admire your avoidance of landfill! If all else fails, go electric, they have come a long way since the flip-over B&Ds back in the day. But! Look f or corrosion around any connections, and look for a bad spark-plug wire, ca rbon tracks or similar. Otherwise, these coils have a limited life in that application.

Peter Wieck Melrose Park, PA

There were a lot of Briggs and Stratton electronic type magnetos that were prone to failure. I use a method to test suspect magnetos before I spend much time trying to find out why there is no spark. Remove the spark plug from the engine so that it turns over easily. Then stuff a rod or something similar into the the spark plug boot so that it makes good contact with the end of the spark plug wire. Now turn the engine over slowly while holding the rod. You should get at least a tingle. If no tingle then try turning the engine over a little faster. If there is a little tingle then the problem is most likely a bad connection. This could be a corroded ground wire. If, even turning the engine over fairly fast, there isn't even a tingle the magneto is bad or the kill wire is grounded. I have used this method for years and it is a really fast way to find out if the mag is probably good or not. Eric

say hi to Darwin for me.

That's what these are for.

Oh phooey. There is no way you can get a dangerous shock from slowly turning over an old lawnmower engine equipped with a magneto. Sheeesh! Eric

Exactly, on a small magneto like this it'll tickle, but this reminds me of a true story:

Many many years ago, a guy I knew was having some ignition work done on his stock Hemi Challenger at my buddy's garage, and brought along a magneto to try just in case. Just rotating it a half turn sent him flying! Those things have balls.

Was the mag the type that winds up when being turned over slowly? I have some old magnetos that work this way. One is on my 1945 Gibson tractor. When turned slowly it winds up a spring inside that lets go when it reaches a certain tension, thereby spinning the magnet fast enough to get a good spark. Those mags will deliver a really good shock. Years ago I had one of these that would only deliver a little tingle. Talking to a guy who knew about mags said that the coil may have absorbed moisture over time, especially since the mag was from a marine engine. He suggested baking the mag in oven at 200 degrees for several hours and then letting it cool in the oven. I tried his suggestion but was dubious. After it was cool I grabbed the spark plug wire and turned the mag over. When it let go I got a really good shock. Made my arm ache. Eric

No, just the type they used in race engines. Something like this:

They must have some pretty strong magnets and the voltage at operating RPM must be VERY high. I guess that's what is needed for really high compression engines. Eric

At one time, I had a '55 Chevy 2-door sedan. With a 437 cu in big block,Hilborn fuel injection and other assorted"make a shit ton of horsepower" goodies.

One of them was a Hunt Magneto.

One day, while hanging out at a local wrecking yard, a guy bet me he could kill my engine by pissing on it.

Heh. "$100 says ya can't."

I opened the hood, by tilting the whole front end forward.

He unzips his fly and I watch the golden stream arch over until it hits the distributor.

My Chevy is still idling, and he's laying on his back screaming "My dick!"

I just walked over to him, "When you're done screaming,you owe me $100."

Typo, 427

onic component of it might be on. I have this 3.5 horse engine on my old pu sh mower. The engine is about 38 years old now but the mower is used very i nfrequently so the hours are not that bad. About 5 or 6 years ago I replace d the old OEM coil that used points, with a used newer electronic type that eliminates the points. The mower is on it's third carburetor, gas tank and second deck but it has always started ok. I tried to start the mower this morning and as sure as my wife said, (I hate it when she's right), "You'll never start that old thing", it wouldn't start. Long story short there is n o HV spark to the plug. It seems as though the coil is bad again. I was goi ng to hit up a few used lawnmower places to try to get a replacement coil b ecause I have no engine numbers on my machine to look up the part but I was wondering if anyone knows if it's possible to bench test these things. Tha nks for any help Lenny

I understand the value of "object lessons". I have 5 grandchildren. But why in God's name would you let someone piss on your engine? Lenny

Because 1. it was worth $100 and 2. It was funnier than Hell.

LOL! The only shame is that you didn't video record it.

This was in the mid '70s. I would have to have had an 8mm camera with me at the time.

Just a random thought.

I used to work as a mechanic at a small engine repair shop. One of the cartoons that found a home on the front counter:

A kid sitting in the driveway with the lawn mower totally disassembled. And his dad standing there looking at him. "I found the problem. It's out of gas."

The caption should have been "You're paying me how much to fix this"?