Pulled this motor out of the box a couple of weeks ago fitted it on a Deutscher and it started up no problems on the second pull. Went to start it today and it would not start without starter fluid and the auto choke is fully closing. I'm thinking I might have to block one of the holes in the choke butterfly. Bit strange on a brand new motor. Any thoughts?
I only use BP Ultimate with mowers as I have less trouble than with other fuels.,It's a good experiment you drain out all the old fuel replace with BP Ultimate and try to start the motor.
As we know.
The degradation of fuel when exposed to heat, light, and air can occur more quickly than the general shelf life when stored under optimal conditions. While itβs difficult to provide an exact timeframe because several factors come into play, here are some general estimates regarding how quickly fuel can "go off" under these conditions: Factors Affecting Degradation Speed
Heat: Higher temperatures can accelerate the breakdown of fuel. If gasoline is kept in a hot environment (like a vehicle parked in direct sunlight), it can start to degrade within a few weeks. In extreme heat (over 90Β°F / 32Β°C), degradation may begin within one to two weeks.
Light: Direct sunlight can also contribute to the breakdown of fuel, particularly due to heat and the photochemical reactions that can occur. Gasoline exposed to light may begin to degrade within two to three weeks.
Air: Exposure to air allows for the oxidation of fuel, which can lead to the formation of gums and varnishes. With exposure to air, fuel can start to show signs of degradation in as little as a few weeks.
Minimum Timeframe
Given these conditions, fuel can start to go off within two to four weeks when consistently exposed to heat, light, and air. More pronounced effects can typically be seen after one month of such exposure.
I'd drain the fuel /fuel bowl and make sure the fuel side is flowing properly and not gummed up ,I've heard of a plastic flap in the fuel hose spigot in the tank closing off sometimes as it wasn't deburred properly also seen new motors with debris in the tank and carby,
Had very similar issue with a Baumr 750SX mower, dunno if it's a Chonda but certainly has a Honda carb lookalike. Would start with choke on but died as soon as the throttle was opened a smidge.
I'm no stranger to carbs and went through the carb minutely many times, couldn't find anything wrong until noticed the O-ring between float bowl flange and carb body was distorted, almost severed . It was a very thin section O-ring, couldn't find anything in my extensive selection to match so gave it some TLC and managed to "de-distort" the crushed section.
Mower then started and has been running perfectly since. Seems it was sucking air through the distorted bit enough to prevent fuel being sucked into the idle and main jet. Just saying,as they say :-)
Thanks MM, I haven't had a chance to look at it yet. This one the auto choke is fully closing and not the slightest attempt to start without starter fluid, then it fires straight up and runs fine. switch it off and no way \will it attempt to start
went through the carb minutely many times, couldn't find anything wrong until noticed the O-ring between float bowl flange and carb body was distorted, almost severed . It was a very thin section O-ring, couldn't find anything in my extensive selection to match so gave it some TLC and managed to "de-distort" the crushed section.
Mower then started and has been running perfectly since. Seems it was sucking air through the distorted bit enough to prevent fuel being sucked into the idle and main jet.
I would say the fuel bowl o ring being damaged won't make any difference to the way a lawn mower engine will run because the carby already has a breather where the top of the fuel is vented to atmosphere .
The only way I could see a damaged o ring on the top of the fuel bowl making any difference to the way the motor runs would be if the air vent was metered.
In a lawn mower carburetor, the breather or air vent that allows air to enter the fuel bowl is typically not considered a metered air vent.
A metered air vent would be designed to regulate the amount of air that enters based on specific criteria, which is more akin to how certain components in more complex carburetors operate. In a standard lawn mower carburetor, the vent simply allows air to enter the fuel bowl to replace the fuel as it is drawn into the engine, ensuring proper fuel flow without any specific metering.
I've had a lot of mowers where they have a slight carby blockage and they just fix themselves ,Dirt or debris in the carburetor can lead to poor fuel flow, causing hard starting and rough operation. Once the engine runs for a bit, the vibrations can sometimes help loosen debris, allowing for improved fuel flow.
Also had a few mowers with damaged o rings on the top of the fuel bowl and it didn't make any difference to how the motor ran but the fuel bowl would leak a little fuel when the mowers on an angle.or the mower goes over a big corrugation.
Pulled the carby off and gave it a going over, looked like a couple of holes in the tube were blocked, thought that might be the problem, put it back together and no improvement, little squirt of starter fluid and it fires straight up. Got me buggered
Fixed it put 2 pop rivets in the choke butterfly and all good
I have this problem when the fuel is old ,they won't start without fresh fuel or starter fluid down the carby throat but once running the motor still runs well on old fuel, I assume that you have tried fresh fuel already though.
I know some new engines in the past were just an assembly of new components that were quickly put together to ship overseas and once you took delivery of the new engine it would need dismantling and assembling again . (nothing was torqued to correct specifications or put together correctly)
If it's not an old fuel problem ,I'd be checking for a weak spark ,try another plug , check your air gap on the coil as I've seen a few new motors and the coil is 1 mm away from the flywheel .I've had a few new coils that were no good as we know , when the ignition coil is failing, which can result in a weak spark at lower engine speeds. As the RPM increases, the coil may produce a stronger spark, allowing the engine to run smoothly once it starts.
Hi Max, All fixed the choke was letting too much air through so a couple of pop rivets solved the problem. I tried one pop rivet a couple of days ago but it needed two
Good that you have the motor starting cold easily now , it's still a little strange that it was fine a couple weeks ago.
As we know the hole in the choke butterfly allows a small amount of air to bypass the closed choke plate. This can help stabilize the engine during starting, allowing it to run smoothly before the choke opens fully. It prevents flooding and aids in maintaining combustion until the engine warms up enough to run on a normal mixture.
Some old Briggs have a spring loaded check valve that opens after the engine fires cold to help with the fuel mixture on start up.
As we know if the operator opens the choke straight after starting there won't be a problem.
Hi Max, this auto choke is brilliant because you can remove the carb in seconds, unlike the others where you have to remove the 2 studs holding the carby on so you can disconnect the choke rod. This idea is brilliant as long as it continues to work
Hopefully the auto choke opens a little after it first starts otherwise it will be blowing black smoke until the motor warms up a bit.
Mowers aren't worth enough to waste too much time on taking the carby studs out and installing them again.
I just use some small pliers to bend the choke lever to remove the linkage ,you move the carby out a little on the studs at the same time, then after you put the carby back on you bend the choke lever straight again.
Hi Max, All fixed the choke was letting too much air through so a couple of pop rivets solved the problem. I tried one pop rivet a couple of days ago but it needed two
This is why I save choke vanes from old carbs here.
Most time small holes works but I have one time where the opposite was necessary on a handheld blower. Original carb hole were too big and the replace had too small of holes. I got lucky that I had a vane with the correct size holes.
Basic I started with a non start condition unless I hand choke the blower and then with the new carb it was flooding on choke.
When I first started working seriously on small engines Tecumseh engine were bad about choke vane holes being too large. It was recommend solder one of them up. But I prefer some more solid like a new vane with smaller holes.
