Yamaha majesty 125 2004 won't start! The engine

It might be..(if bike is in good condition or have new engine)
But not more than 30 minutes

If it backfires through the air filter, it may be indicative that the ignition timing has slipped and it is firing too early.

sparks ? compressions 100psi or more ? water in fuel ? injecters clean ?

If a starter is able to crank the engine but it won't start you usually have either an electrical or fuel problem. It's also remotely possibly that it's compression.If an engine has proper fuel, spark and compression, it will start when you crank it. So your challange is to find out which part isn't working right. Start with fuel. Spray a little starting fluid into the air intake while someone tries to start the engine. If it starts briefly when you're spraying starting fluid, you probably have a fuel delivery problem. That could be injectors, fuel pump, fuel filter, relay, fuse... who knows what until you check into it.If it doesn't start with starting fluid, check the spark. Pull a plug wire and attach it to a spare sparkplug and set the plug on a solid metal part of the engine. Have a helper crank the engine while you watch the plug. If you have a good spark, it might just be out of timing.In any case, you'll need to start isolating the problem. Find out which part isn't working then you'll know what to replace/repair.

The only other thing is air. I am not familiar with your engine but it sounds like it's not getting air. If you pull the plug after trying to start it is the plug wet?

hi there mwb15
have you made sure the ignition coil is producing enough voltage to fire under compression load ?

you may get a spark at the plug unloaded but under load it may be breaking down / weak making you think its got a fuel problem ?

does your system use a cdi coil system or point/condenser system ?
spark usually falls into weak spark, no spark catergory

if compression , fuel ( you replaced carb) and exhaust are ok , and you have air and vaccuum tight c/cases only things left are timming and spark

remember F A C T S

F = Fuel A = Air & ( air tight c/cases ) C = Compression T = Timming S = Spark

compression should be about 130- 140 approx if in good running order

take a look and let me know

cheers pauly46

You didn't say what year and model the bike was but on any four stroke engine, you must have three things for the engine to run. You need fuel, spark, and compression. The easy one to check is the fuel. Take your air filter off and make sure you're getting fuel to the engine. Then, check your spark. Pull the spark plug wires off the spark plugs in the head and insert another set of plugs in the wires. Ground the plugs against the engine, turn the ignition switch on and press the start button. Watch the plugs to see if you have spark. The next test is compression. With the engine cold, remove the spark plugs. If you have a compression gauge, connect it to one of the heads and spin the engine over with the starter. If you don't have a gauge, simply put your finger over the spark plug hole. Turn the throttle wide open and press the start button. You should show about a hundred pounds of compression if you have a gauge or the compression should blow your finger off the hole with a good deal of force if you're checking it that way. If you have all three of these and they're timed correctly, the engine should run. If the engine won't run, find out which of the three elements is missing and work from there.

Good Luck
Steve

Check the compression, pull the spark plugs one at a time if more then one. If you don't have a compression gauge, you can put your figure over the spark plug hole, be mindful that before it blows it's going to **** so make sure that you don't hurt yourself leave a little gap so your figure doesn't suction down to tight. If your getting compression it should **** and blow pretty hard. If it seems to have good pressure and suction. You might need to check your timing, also make sure that you can feel air moving out the exhaust, might not be able to with the pipes on it but if it won't start and your getting everything else it needs to run gas,spark, etc. It has to almost be timing or compression.