Burns363R Posted April 21, 2020 Report Share Posted April 21, 2020 I just rebuilt this stock banshee with 1mm over pistons. It was already .5 over, and .75 wouldn't clean it up enough. Got it bored and gapped and put together. Compression is only 110 on 1 cylinder, and 115 on the other. Im wanting to mill the stock head some to get compression up a little. I want it to be 93 octane still. You think I can take .020 off the head and still not have any detonation issues? Quote Link to comment Share on other sites More sharing options...
Burns363R Posted July 7, 2020 Author Report Share Posted July 7, 2020 Bump for some help. Quote Link to comment Share on other sites More sharing options...
Burt Reynolds Posted July 10, 2020 Report Share Posted July 10, 2020 (edited) Are you holding wide open throttle during the compression test? Stockish bikes only need around 120-125. Not holding the throttle open could bring it down. You want to keep kicking with WOT till the gauge won’t go up anymore,even 20 kicks is fine. Also the engine should be cold. If you have low compression i wouldn’t mill the head to compensate,just asking for trouble. Unless the kicker feels very loose or it won’t start,I wouldn’t worry about testing compression on a fresh build till it is broken in. Your not going to get accurate numbers because the rings have not been seated after breakin 5 psi difference is still ok,as long as it doesn’t go further. Edited July 10, 2020 by Burt Reynolds Quote Link to comment Share on other sites More sharing options...
Burns363R Posted July 27, 2020 Author Report Share Posted July 27, 2020 The engine should be broke in. I have 20-30 min of run time on it. Piston/ring clearances are all within factory spec. Bike just doesnt want to start. Seems that the compression is to low. Carbs have been cleaned and checked 3 times. All jets pulled, all passages verified. Seems to only hit on 1 cylinder most of the time. Switched spark plugs/wires, still same cylinder. I think bumping compression a little will help. Quote Link to comment Share on other sites More sharing options...
kawa110 Posted July 27, 2020 Report Share Posted July 27, 2020 Pressure testSent from my iPhone using Tapatalk Quote Link to comment Share on other sites More sharing options...
bansheesandrider Posted July 28, 2020 Report Share Posted July 28, 2020 A bone stock Banshee new from Yamaha starts just fine without having to cut the head to raise compression! Your problem is somewhere else and you are trying to Band Aid it. Figure out why it won't start(jetting?) and fix it right. Quote Link to comment Share on other sites More sharing options...
Burns363R Posted August 17, 2020 Author Report Share Posted August 17, 2020 110lb on right cylinder, 105lb on left cylinder. Vacuum and Pressure tested engine. No leaks at all. Quote Link to comment Share on other sites More sharing options...
Burns363R Posted August 17, 2020 Author Report Share Posted August 17, 2020 So do guys deck there stock heads for slight bump in power? Or do a head gasket trick like on the trx250r? Quote Link to comment Share on other sites More sharing options...
kawa110 Posted August 17, 2020 Report Share Posted August 17, 2020 Cool head with interchangeable domes to obtain required compression for fuel desired to be used at specific elevations. Sent from my iPhone using Tapatalk Quote Link to comment Share on other sites More sharing options...
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