Just checking if i have this right.Long straight at Pukekohe race track slowing for hairpin back wheel locks bike seized,not to bad as it strarted next kick but on dismantling bad damage to piston and barrel.Anyway,the piston crown is undamaged and has black deposits the spark plug is a ten range and is medium brown no detonation marks to be seen.So my thinking the bike is full race with jha jet kit could it be off throttle fueling maybe bigger pilot jet in conjunction with up a size main jets.(it was the right/front cylinder)what do you guys think?.
Was the major damage to the side of the piston facing the exhaust, and barrel damage around the exhaust ports? _________________ MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball
Im guessing youre running premix? Its very common on dynos for a 2 stroke to seize on the shut off if youre not used to doing them.
Its also common for MX bikes to do it if going down hill on a closed throttle.
With an oil pump on the bike even if you shut off at high speed oil is still feed into the engine. Of course with premix if you shut off not only do you get no fuel, you dont get any oil either.
I think i can see where dave is going with his question tho. _________________ If I have to take the carbs off once more...
You can? Cool, I'm not sure I do... _________________ MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball
Thanks for the replys,thought there would be none.The damage is all round,there are undamaged patches.The main damage was at the exhaust port,not on the bridge.It is only on one side and about 1cm wide most of the damage was superficial and could be polished out with some fine sand paper 1000# but there is a 1cm streak which is about 1/2mm deep which is not viable.The straight is long and i have the JHA carb kit in so bigger pilot jet which should help with off throttle cooling and lubrication.Checked the chart and found that the needle is recomended for the 4th clip,I was running on the second.So my fault guess it got lean on the straight!.Will go up a jet size on the front/200 should do itand go to 4th klip pos to be safe.There was no sign of pre det on the crown,it was quite black.The bike was going well and keeping up with many of the 4 strokes inc the sv 650s,Guess it will be a new barrel then.Still love the NSR and it loves new parts.Thanks,Bruno
You won't need a new barrel if you get that one repaired. I don't know of any in NZ, but it may work out cheaper sending it to the UK / USA and having it repaired than buying new if there aren't any.
Search the web for Nicasil plating before you scrap it! _________________ MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball
I have been racing 2 strokes for nearly 20 years and have never had a seizure on a closed throttle running pre mix.
Apex Leisure in the UK specialise in NSR`s.
Take a look at the following link which shows some info on piston diagnosois and replating of cylinders.
http://www.apexleisure.co.uk/enginetuning.htm
You can E-mail Jo if want any technical info.
I know she visited Pukekohe race track last year on holiday in NZ.
Dave Ett wrote:You won't need a new barrel if you get that one repaired. I don't know of any in NZ, but it may work out cheaper sending it to the UK / USA and having it repaired than buying new if there aren't any.
Search the web for Nicasil plating before you scrap it!
What would be a ball park figure in USD or GBP for Nikasil plating?
In Australia, it can be done for about AU$600-AU$800 <- but don't hold me to it tho _________________ Jerry Lai
NSR250 [MC21SP]
My last barrel - last year - was £103 including return postage! _________________ MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball
That figure was for two. Sorry for the confusion
But it looks like it would be cheaper to send it to Apexleisure to get it done. And at least you'll know it's done properly. _________________ Jerry Lai
NSR250 [MC21SP]
As far as I know, Apex don't do the work in house, they farm it out to someone. You might save even more by going direct... _________________ MC21SP Plaything
BMW F800GS Bumblebee
Triumph 9551 Daytona Big boys toy
FJ1100 Sporting relic
GTS1000 oddball
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