Briggs & Stratton

Classic model series 90000
Experienced gardeners share their insights in answering this question :
Probably need caeb adjustment turn your fuel mixture screw in a little to see if it runnes better other problem my be a possibllity that the crank key is off a little partially sheared maybe

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Gasoline that contains alcohol has a tendency to ignite easier, which can cause afterfire. Small engine muffler type and manufacture. Carburetor adjustment may not be properly set for correct engine performance. Anti-afterfire solenoid may not be working properly.
If it`s clogged, the combustion chamber may not be getting enough oxygen, resulting in a too-rich fuel mixture that will cause the engine to run poorly and even spew smoke. The solution is to change the air filter, a relatively easy task. Blue and white smoke is the result of oil on the engine.
Black smoke may indicate that the mower is “running rich,” or burning too much gasoline. Your lawn mower`s carburetor regulates the ratio of gasoline to air mixture. If the carburetor isn`t getting enough air, the mixture has a higher percentage of gasoline, which can create black exhaust smoke.
Clogged or Dirty Air Filters

Dirty air filters are one of the most common reasons lawn mowers sputter. Dirt can be present in the apertures that lead from the carburetor and the fuel filter and interrupt the flow of fuel supply to the combustion chamber. You want to be sure to clean or replace dirty air filters.

Backfiring in internal combustion engines occurs outside of the combustion chamber, and is typically the result of an improper air to fuel ratio. An overly lean air-fuel mixture (i.e. an overabundance of air) can lead to a failure to ignite in the combustion chamber, also called a “misfire”.
The main difference between a misfire and a backfire is that a misfire occurs when an engine`s cylinder fails to fire (incomplete combustion) whereas a backfire occurs when complete combustion takes place outside the cylinders.
Spark Plug Issues

Examining the spark plug regularly is essential because a dirty one can cause various problems, and smoking is one of them. If the spark plug is dirty or too old, or if the plug`s gap is too large, it won`t start the mower and will sputter black smoke.

The white smoke is the engine burning off all the excess oil. The fix – drain the excessive oil, and idle the engine until the smoke clears. This may take 5 minutes or so. Too much oil will cause other problems, smoke, poor running, no running, leaks, engine damage.
Common signs include reduced engine performance, black smoke coming from the exhaust, backfiring, overheating, or hard starting.
The main jet is located inside carb then you have to replace a carburetor unit to eliminate this problem. If the black smoke only appears when the car is climbing or carrying heavy loads, then it is the result of a power system on the carburetor that will supply more gasoline thus making AFM richer.
Explanation. Common causes of backfire are running rich (too much fuel going into cylinders) or faulty ignition, possibly a fouled (dirty) spark plug, coil, or plug wire. Pop-backs are usually caused by problems with timing.
Engine hunting and surging at idle is usually caused by a fuel delivery, air leak, or governor system problem. Cleaning/overhauling the carburettor, adjustment of the governor, and/or changing the air filer may be required.
Explanation. Common causes of backfire are running rich (too much fuel going into cylinders) or faulty ignition, possibly a fouled (dirty) spark plug, coil, or plug wire. Pop-backs are usually caused by problems with timing.
Another possible cause of your backfire is a spark plug refusing to “spark” when the exhaust valve opens. If the air/fuel mixture has become too rich, unburned fuel is left in the exhaust system. The misfired spark plug ignites the rich air/fuel mixture, causing a loud “bang” in the tail pipe.

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Engine misfires changed fuel filter

Check the cable from coil to sparkplug to have continuity(measure apparat).Check the other wires as well.Check the ON-OFF switch.

regards savumihai71

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We had a Poulan lawn mower with a Briggs & Stratton engine last year that started with the engine revving problem. The RPMs would go up and down and the fumes coming out of the mower near about killed me. So this year we purchased a brand new Poulan Push Mower – model 961120083. Just brought it home on Saturday – last night we used it for the first time – guess what – the engine revs up and down just like the old one. Almost to the point of stalling and again the fumes are bad. It can’t be a dirty mower it’s brand new. What’s up with their mowers?
ANSWER : There seems to be one common source for gas for the 2 mowers. You could be placing old or contaminated gas in the NEW and OLD mowers. The fumes comment you made leads me to think that the problem is with the fuel itself. Old gas smell horrible. Sniff test the gs can you use for filling the mowers. If it smells awful you know you need to get rid of the contents of the can rinse it and then re-fill it. There may even be water in the gas can that went straight into your new mower. IF you drain the gas from your mower and gas can and start anew and the problem persists then you should immediately seek warranty service for you new mower.

With the 2 mowers having different engines and the same problem it just points to the gas supply as the source of the problem.

Thanks for using Fixya.


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Excessive chain oil coming from oil tank onto the chain.
ANSWER : You possibly have a hole in oil line that goes to the oiler outlet.the only way to repair this is to take the saw all the way apart to get to hose that is located between the housing and the is a real pain in the ****,but it can be do.any questions please contact me

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Excessive smoke when runing oil in exhaust
ANSWER : Sounds like it could be a blown head gasket betwen the cylinder and valves. The gasket is very thin in that area and is a common problem. Not a recommended fix for a novice. Best taken to a shop….. Dwain

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I have a Husqvarna YTH2348 that I bought from Lowe’s last summer. As I was mowing today it suddenly started to vibrate excessively. I believe the problem is in the transaxle. When the brake is engaged there is no vibration, as soon as I disengage the brake it starts to vibrate more than normal. It will move forward and back, but I obviously don’t want to use it if something has come loose inside or an adjustment needs to be made.
ANSWER : There are usually one or two idler pulleys on the belt that runs from the engine to the transmission. Check those, more than likely one has gone bad. the should spin freely with the brake engaged, and the should not wobble.

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Misfiring when motor runs it is not firing properly sounds like it is missing, changed oil, replaced carp needle, cleaned of the rotor head for spark.
ANSWER : Your valves need have take to shop or get a book show you how to do it

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No idea how old this blower is, but we recently replaced the spark plug to get it working and it seems to be working fine, except the vibration is so much that it causes the cylinder to come loose from the block. Any idea what the problem could be that would cause excessive vibrating.
ANSWER : The vibration is almost certainly an imbalance of the fan rotor. The device is very simple, the only thing attached to the motor shaft (and the only thing that moves besides the motor itself) is the fan. See if you can remove the cover over the fan. You will probably find that the fan rotor has some pieces broken off.

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Why excess oil from around exhaust manifold? – Husqvarna 223L
ANSWER : Too much in the fuel mix

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