fired up the mower and cut the grass, probably been a few months since it was cut, started up quick but engine was revving up and down oddly. video attached of whats happening. it did revving up and down after a few minutes and worked perfectly after. what could have caused that to happen?
mower revs going up and down
- Thread starter slybunda
- Start date
- Joined
- Jul 13, 2020
- Messages
- 201
My experience is water in the fuel or bad fuel. I would dump the gas and refill and that usually fixed it.....
There was likely something clogging up your carburetor, perhaps some corrosion caused by ethanol in the fuel (and the water it attracts). Even using stabilizer is no guarantee. Running it a while apparently cleared it out. A while back a small engine guy told me about Mechanic in a Bottle, I was skeptical but tried it on an old chain saw that wouldn't start..got it started right away. A small dose of that in your gas will help (especially nice in 2 strokes that seem especially vunerable). If you know your gas didn't have ethanol in it, it could have been debris in which case you should drain and clean the tank and the fuel filter if there is one. You can drain the gas into a clear container or milk jug to see if there is water in it, since it is heavier than gas it will be sitting on the bottom (they don't mix very well)
Last edited:
ahh this lawn mower has been in storage a long time before it was handed to me, it has not much use on it was stored rough and something dropped on the back and punched a hole in the plate as seen in the video.
no fuel stabilizer has ever been used in this mower. engine oil is clean though.
fuel here is E5 so has 5% ethanol in it. not worth buying something like aspen fuel which is ethanol free but costs a third of the price of the entire mower for 5 liters of it.
no fuel stabilizer has ever been used in this mower. engine oil is clean though.
fuel here is E5 so has 5% ethanol in it. not worth buying something like aspen fuel which is ethanol free but costs a third of the price of the entire mower for 5 liters of it.
Three things are possibly causing the issue:
1. The fuel is old and is causing a run issue (dump out the old fuel and replace with fresh)
2. The carburetor is dirty from sitting with old fuel (will need to be taken apart and the passages blown out with carb cleaner spray)
3. The diaphragm in the carburetor has hardened up from sitting and will need to be replaced.
Start with the first two before replacing the diaphragm.
1. The fuel is old and is causing a run issue (dump out the old fuel and replace with fresh)
2. The carburetor is dirty from sitting with old fuel (will need to be taken apart and the passages blown out with carb cleaner spray)
3. The diaphragm in the carburetor has hardened up from sitting and will need to be replaced.
Start with the first two before replacing the diaphragm.
if it's running fine I wouldn't worry about it but that surging is typically from a dirty carb. Those briggs are easy to clean and rebuild kits are cheap for them. Plenty of videos online showing how to clean them. Donyboy73 has a few that I know of.
I have had good results adding a little Seafoam to the gas when my GVC
Honda 160 motor does that.Maybe i cleaned out deposits from the carburetor?
Honda 160 motor does that.Maybe i cleaned out deposits from the carburetor?
try some B12 in the carburetor and fuel tank. If you are mechanically inclined or like YouTube, taking off the float bowl and cleaning it is probably a good idea as well. Make sure the fuel tank is empty first! Engines do this because of debris in the carb. With it that bad you might need to do a carburetor rebuild.
You may want to consider a fuel filter in the fuel line to keep debris out of the carb.
Just my $0.02
You may want to consider a fuel filter in the fuel line to keep debris out of the carb.
Just my $0.02
Not only one filter, but two!
This is the system which Briggs used for many years on the lowest models. I think it is called the "Pulsajet". The carb is mounted directly on top of the tank so there is no external fuel line. There is a plastic pickup tube reaching to the bottom of the tank and there is a metal screen on the bottom of the tube to keep big chunks of debris from going up into the pump. The fuel pump puts fuel into a metal pocket in the tank under the carb which serves as the fuel bowl. There is no float valve, the bowl simply fills up until overflowing then the excess runs back down into the main part of the tank. The second fuel filter is on the jet pipe which reaches to the bottom of the bowl. It is also a metal screen.
There is a single main jet and no idle circuit. Because of this simplicity it is likely to keep running even in case of dirt etc., but even in perfect order don't expect it to run really steady. This is a low-end product.
I fixed a generator doing this with Techron.
Fired it up today for the first time this year. Took around 25 pulls and it started. When started it did the same thing as the video in my original post. Revs going up and down for a minute then it leveled off and held revs steady.
Will look to getting a new sparkplug for it. Original one it has is a champion one. Is champion any good?
Will look to getting a new sparkplug for it. Original one it has is a champion one. Is champion any good?
Another point is that many of these engines have an air-operated governor.
At the start of the mowing season it's a good idea to remove the air shroud (metal part of the top of the engine with the starter assembly in it) and clean out mouse nests, old grass, etc that block the airflow which cools the engine and operates the governor.
At the start of the mowing season it's a good idea to remove the air shroud (metal part of the top of the engine with the starter assembly in it) and clean out mouse nests, old grass, etc that block the airflow which cools the engine and operates the governor.
It is likely the fuel treatment as high octane won't help a low compression push mower engine that has a fixed ignition.
We discussed that topic with you in the Push Mower High Octane thread.
