490 wont start

[Sammundo]

so i bought a yz490. i know, love them or hate them. well as seams a bit of a standard problem it wont start. piston was blown when i got it and has been rebored new piston and head mod done. compression is good, spark is bright, carb stripped and cleaned and set as manual specs but it still wont go. tried all the suggestions i can find so far from laying on its side, blowing into breather, rocking, sissy kicks etc. in fairness i dont weigh a great amount but it does turn over quite well with a good jump on the lever. any other suggestions and things to check or try that dont involve setting it alight or leaving it on kerbside would be greatly appreciated.cheers folks

[bazza]

Crank seal? Compression - fuel and spark so simple,  yeah right

[crossedup2]

With a blow piston before you might check ignition timing also. Crank seals as well.

You may need to borrow someone else's right leg!

Peter B

[mainline]

No mudwasps in the muffler or exhaust blockages? Rag left in the airbox after you cleaned the filter?

[YZ250H]

Crank seals, fuel tap leaking causing flooding, buggered needle and seat (again causing flooding), timing.  All these things have been an issue with my 465.

Have you tried a squirt of "start ya barstard"   

[frostype400]

Yeah I'd be trying some fuel down the plug hole if you haven't already you have to remember the blokes that rode them new were not all big fellas just proper technique I found it easy to start my 400 when I was younger by leaning the bike against a wall or tree so that I could stand up and give it a proper kick.

[Sammundo]

will check timing marks tomorrow.any tips on how to pressure test the seals? tried fuel down the hole and the exhaust is clean through.

[OverTheHill]

Hi, have an "83 490K myself which arrived with a shorn off flywheel key. Might i suggest you check that possibility. Pull the flywheel off to be sure as looking in at the key with nut & washers off can fool you as you 'can' see the key but might be shorn of & moved around so all you're seeing is the top exposed bit. Sorry about the long winded answer. If it's sparking [which it will still do if shorn off] but timing is a long way out, it should at least sneeze every kick or two. Mine kicked back so hard before i discovered the key problem that it broke a tooth off the kick start idler gear. When tightening the flywheel [if you do take it off] make sure it's very tight using a solid holding tool resting on the footrest or something solid & a half inch breaker bar. After all that, if that's not the problem, well, bugger. Had some strange ones over the years in the bike shop--like piston in back to front [big reed cutaway to the exhaust port]. Goodluck.

[torm92]

They are not the easiest thing to start . it is all in the technique . it took me 6 months to learn how to start mine. It can involve trees , fuel drums and aerostart.
I usually turn the engine over until it is on TDC at the brake stay, this way the kick starter will start engaging at the top of it's stroke . Then jump on it like you hate it. Usually starts first or second kick.
Good luck

[YZ250H]

Then jump on it like you hate it. Usually starts first or second kick.

If it doesn't start first or second kick it gets so much easier to kick it like you hate it  . 
If it still doesn't start after kicking it for ages you will actually end up hating it    For a little while anyway 

[Sammundo]

thanks guys. am starting to hate it a little. i think we need some time apart. good news is the timing is set and holds pressure in the crank so it looks like the only thing stopping it is my sore leg.maybe a few days apart to recoop will sort it. and maybe a big hill.

[YZ250H]

If it is like mine used to be it will be a love/hate relationship until you get it sorted.  Then it will be pure love   

[Sorelegs11]

I have had an it490k for over 15 yrs and I find choke on, a couple of slow kicks to prime it and thenn go for it.
Be carefull jabbing the kicker as the idle gears have been made lighter by removing half the body of the gear and are easily broken and you will really hate it, I am up to gear #4 in the last 12 mths.
As some body said before get the kickstarter right to the top so you get maximun stroke, good luck

[Canam370]

I start big 2 strokes like big 4 strokes. Roll it over to top, carefully ease the kick lever past top (you'll feel it drop about 25mm'ish) til you feel the next 'stop'. If you rotate the engine past this point go around and try again. Let the lever return the top rest and then give it a serious PUSH/kick aiming to end the kick well below the footpeg. The aim is to get the engine spinning - jabbing at the kickstart lever won't do it. A half hearted or tentative kick will risk a kick-back - you'll be picking your teeth out of your ankle!