84 500 runs lean when hot

[PEZBerq]

My 84 500 auto seems to run lean when it gets hot. After a 3 or 4 lap race I need to apply the choke to get it run smoothly as I ride it back to the pits. It seems to want to stall without the choke on. While racing it there is no issue - it seems to be when at small throttle openings after the race .  It starts well and behaves quite normally when cold and getting to the start line etc.  I only use it for VMX so haven't used it for extended riding sessions hence it hasnt really been a major drama but I would like it sorted for vinduros etc.

What are the things I should be checking out to sort this Thanks

BTW it's jetted as per Paul Rooneys recommendation for a 38mm Mikuni and is used at sea level more or less.

[holeshot buddy]

sounds like it might be a air leak
check reed block and base gasket

[PEZBerq]

I was hoping an air leak wouldn't be the first thing suggested It would explain it though I agree. But would an air leak typically get worse as the engine heats up?

[JohnnyO]

Try raising the needle a notch or a bigger pilot jet, it may just be too lean and gets worse when hot.

[PEZBerq]

Worth a try before moving on to checking the base gasket. I'll try the needle first and move to the jet next. Thanks Jonny O

[Liqueur]

Crankshaft seal behind flywheel is another.

[huskibul]

   on my huskies it's a real balance between the jetting and the conditions or how hard your running it, i alway run jetting slightly rich for normal riding so you get a good plug colour when conditions are hard and hot,as they say "just off the blubber jet" , check for leaks with the WD leaktest while your at it though before looking further 

[pancho]

 I'd say fix it quick before it melts something expensive.

[PEZBerq]

  check for leaks with the WD leaktest while your at it though before looking further 

WD Leaktest  Do tell more

[pancho]

 Carby cleaner works good.

[mainline]

Spray wd around potential leak areas while the bike is running and see if the problem improves briefly with the spray temporarily 'plugging' the leak

[huskibul]

   Yeah pez as paul said , put an extension nozzle on the WD can and with bike warmed up and at a good idle closely spray  right  around base gasket  and intake flange and gaskets use plenty and really drive it in ! you'll notice a distinct change in  rev's if you've got a leak ! I also do the head whether or not it's needed  ?  works a treat -if nothing move on to jetting/seal etc!  cheers 

[PEZBerq]

Thanks to the brains trust for the WD40 test info. I use a pump bottle rather than spray cans so will be able to get heaps in no worries. Off to the MotoGP this weekend so I'll check for leaks next weekend  The best racing is likely the 125 and Moto 2 but it's still a great weekend and is sure to be wet and cold