Engine Trouble Engine loss of power when hot n fourstroking alot

4 tanks threw. Head appears cracked

can't tell from that pic, but that would explain a bit of compression leak

four cu said:

It revs out at full throttle just sounds like a lawnmower. Bore appears to be good and rings are where there soposed to be. Seems like it's not too tight. This advanced ignition issue could it only occur once it's warmed up?

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if the cdi is faulty, or mounted in a bad spot (on the head? i doubt you did that ). that "black box" can sometimes cause issues. its very possible. only way to know is get a new one. mine just died today there is the possibility that a solder join inside is playing up, or it has a dead component, etc etc(unfixable unless you know how to remove potting epoxy?).

it also pays to pop the magneto cover off, and the magneto nut, to see which way the keyway is facing. they say, with piston at top dead center, it should be around 1(13?) oclock. if its at 11 oclock, say...theres the issue! remove and turn it round the other way!

everything else looks fine! (though i see a little bit of scuffing down below the exhaust port?) now that plugs had some use its gone back to black, just like the piston crown. so it is NOT running lean. again. its not running lean. fuel is not the issue...you are running oil arent you? the fact that you CAN hold the throttle fully open...it has enough fuel.

a crack in the head? ditto. cant really tell by the pic, but its possible, very possible.(that line that seems to be just above the plug in your pic and takes off to the left? is there any sign of oil leaking on the other side?) it makes a kind of squeaky noise if either the gasket or head is dud. very distinctive when you know it.

they always sound like lawnmowers! but yeah... copious amounts of smoke from the exhaust are also a good indication its too rich.

once again...is the exhaust clear?

and and and, see that piston...and the lil clips in it? spin them round 90 degrees so those ends point the same way the piston travels in the bore (vertical). i already stated why though its not really an issue if the dirty thing wont run properly! its just the "right" way of doing things


crassius, that info on the "2" sounds about right. i never bother measuring anything, myself

A update. Had to change head due to a crack got mad and drove it Until it barely moved. Problem fixed thing drives good n no power loss when hot yes it'll be because head was changed. Thanks again for all your input.