Masport 400 rotocut, four stroke B & S motor. Won't start now after previously giving no trouble. But when you tip in on its side and then righten it it will start for a few moments.

Matt, If engine is two stroke and not oil injected then yes you must mix 2 stroke oil and fuel. 4 stroke engine have a crank case which is filled to proper level with 4 stroke engine oil. Check the attached links,instruction and guides, Good luck
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What sort of motor is it? A two stroke or four stroke?
If it is a four stroke it could be a number of reasons why it doesn't go when you give it throttle. It's difficult to help you if you're not providing lots of details. Is the motor by itself or is it a ride-on lawn mower? Usually something like your problem is the result of lack of sump oil and or the timing is incorrect, therefore it can backfire. If it is a two stroke then the carburettor is probably clogged and cannot provide fuel at high revs but just manages to run at low revs.

you need a valve job the hotter the motor the more unseated the valves

take it back as the repairer has not completed the installation of the carby properly
and yes he is correct in that the user manual states in what position not to place the mower or the oil will get to the carby and air filter

Go to youtube On line type step by step assembling masport 400

Judging from what discription you are giving me I would say it is a 4 stroke, so make sure you have either sae 30 or 10/w30 oil in crankcase where it says oil and petrol (gas) in the other tank. 2StrokeJim

Did you get any instructions from the previous owner? If it's a 4 stroke waverunner there will be a dipstick on the engine block, but I'm guessing it's probably a 2 stroke engine because most watercraft used 2 stroke motors clear through the 1990's. The oil will be mixed with the gasoline when you fill it, bottles of 2 stroke oil can be purchased at most stores that carry oil. Your waverunner can be mixed at 50:1, which equals out to be 2.6 oz of oil per gallon of gasoline. On a 2 stroke engine the engine gets lubrication from the oil mixed with fuel and will burn up fast if straight gasoline is used. Let me know if you have any troubles, but try to get ahold of the previous owner to get some more info.
Daniel

HELLO,
You can fix these yourself, all you have to do is to follow the instructions below,
1 Remove the spark plug lead from the spark plug and move away from cylinder head. Always do this before attempting any repairs to a lawnmower.
2 If your lawnmower is a "four stroke" mower (separate gasoline and oil), tip the mower so that the spark plug is pointing skyward. Never tip it on its side with the spark plug to the ground.
3 If your lawnmower is "2 stroke" (oil and gasoline mixed) turn off fuel tap. You can tip a two stroke mower any way that is suitable to you.
4 To change a blade, or blade disc, it is often easier to remove the spark plug and feed a length of string into the cylinder head to 'lock' the piston while trying to un-do the blade bolt(s).
5 Check the motor's "air filter" while doing this sort of maintenance as a dirty or clogged air filter will affect engine performance and increase fuel consumption of your mower. Symptoms of a clogged air filter include inability to start, starting and quickly stopping after several sputters, or a weak idle. You may also see oily or smoky exhaust.
6 If your mower is a "four stroke" model, change the oil at least once a year. When it is tipped over with the spark plug in the air, is a good time to remove the "oil fill" plug and drain oil into an old ice-cream container for recycling.


I hope this will help to solve the problem.....

you likley will need a new air filter and a carb cleaning. when mowers are turned on their side. oil will seep past the piston and if your intake valve was open it can pass thru into the carb and also spoil your air filter. I am assumeing you have a paper air filter. start by taking off your air filter. then you should also pull the spark plug, place a rag covering the hole. then pull the cord a couple times. chances are that you will blow the oil out of the cylinder.