ALKY
Silver Member
runs fine at idle but misfires at WOT or when PTO is engaged . Is it the coils? It is a b&s 16hp twin. thanks
1641 misfire under load
- Thread starter ALKY
- Start date
would chk simple stuff first - reset spark plug gap (replace fouled plugs as needed), replace/clean air breather element(s).
if still a prob, may need valve adj (see info at briggs website for that engine) or may have some trash in carb load circuit (try some seafoam cleaner) or re-adj carb load jets (see manual)....
if still a prob, may need valve adj (see info at briggs website for that engine) or may have some trash in carb load circuit (try some seafoam cleaner) or re-adj carb load jets (see manual)....
I concur with your diagnosis. One ignition coil is bad. You can remove the spark plugs, plug them into the spark plug wire, ground the plugs then spin the engine over. You should then be able to tell which plug is misfiring. I usually just stick a screwdriver up in the plug boot and spin the engine over. Most people don't like the small jolt received when testing this way.
Zork
Platinum Member
- Joined
- Dec 14, 2003
- Messages
- 984
- Location
- Virginia
- Tractor
- '04 Branson 3520, '51 Fergy, '96 MTD 18/46, '02 Craftsman GT5000/48
Timing; Air flow or manifold leak; Carb adjustment (dependent on air flow) or trash inside. I have seen plugs misfire at higher rpm's- look them over carefully for anything that looks like a crack or line in the porcelain insulator. I dont think it is the coils because they would tend to fail or cause missing after they get hot and not dependent on rpm. I dont think it is the valves because I think that might cause "weak" cylinders or popping in carb or backfires in exhaust.
With the air filter off and the engine at 3/4 to full throttle ( and missing) what happens when you start to restrict or block off the air to the carburetor? If it picks up rpm's and the cyl' it is most probably fuel starved.
With the air filter off and the engine at 3/4 to full throttle ( and missing) what happens when you start to restrict or block off the air to the carburetor? If it picks up rpm's and the cyl' it is most probably fuel starved.
Zork
Platinum Member
- Joined
- Dec 14, 2003
- Messages
- 984
- Location
- Virginia
- Tractor
- '04 Branson 3520, '51 Fergy, '96 MTD 18/46, '02 Craftsman GT5000/48
If it runs smoother with the wire just taken off the plug a little bit but misses with the wire on or completely off I'm most positive that particular plug is bad. I forgot that is a test I used and found it to be pretty accurate to identify plugs that have failed or are failing internally.
Did this problem exist before you put new plugs in it? I have found back in the day that some plugs behaved weired after they were over tightened or the porcelains were jarred when the socket was taken off and the easiest way to find the plugs, short of replacing them, was with ans oscilloscope or when you remove the wire ever so slightly and notice that rpm to pick up and smooth out.
Did this problem exist before you put new plugs in it? I have found back in the day that some plugs behaved weired after they were over tightened or the porcelains were jarred when the socket was taken off and the easiest way to find the plugs, short of replacing them, was with ans oscilloscope or when you remove the wire ever so slightly and notice that rpm to pick up and smooth out.