NEW TOP END REBUILD.. ENGINE NOW RUNNING TO HOT

[motorbikes010]

Hello,

I have recently as in yesterday got my bike (Honda NSR 125 R-K) back which had a new top end put in and the last one was melted.
The problem I have is that it is running hot as in the needle is at 3/4 and sometimes going uphill its almost in the Red.

I have check to see the coolant level and its fine. The thermostat works as it was tested.The water pump is working.
Could it perhaps be the 2-stroke oil>? Maybe its bad quality? or could it be something else?

Please help as I have just bought this bike and I am so dissapointed with it so far.

Thank you for your help.

[tonyyzf]

Make sure you have the right grade of spark plug and get the fuel mixture checked, if its running weak it'll heat up and be in danger of seizing.
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[0ddball]

How hot does the radiator get? It's easy to get an airlock in the coolant.

Though, when you say "got it back" does that mean the work was done at a garage? If so take it back and tell them the problem.

[motorbikes010]

What do you mean about the fuel mix? The two stroke to petrol mix? what should the mix be? How would i adjust that?

[mr jamez]

Get the spark plug out and compare it to this, gives you a clue as to what the mixture is like.

https://www.spark-plugs.co.uk/pages/technical/diagnosis.htm

If the bike is running lean, you need to check that you have the standard jets and the collet is in the correct place on the needle, has an aftermarket exhaust been fitted? someone may have messed with the jetting. The lubrication system may be at fault, check the adjustment of the oil pump and you should have a nice haze of blue smoke when the bike is warm.
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NSR 125F > BROS 400 > NC30 > BROS 400 > Trumpet S4 > '97 VFR 750

[motorbikes010]

I will check this and let you know when i finish work today. I cannot go back to the mechanic becuase he's in sailsbury and I live in Oxford. Will try to do it myself. Will let you know what the Plug looks like.
Do you know what else I could try?
Thanks a million

[motorbikes010]

Whilst I am on the topic of asking. What exactly would cause greater top end speed? Higher No of teeth on the back sproket or higher number of teeth on the front sporkets?
Thanks

[robbie21mcn]

check the head has been torque down properly onto the barrel thats a usual suspect also make sure theres no air in the system
run the bike with the rad cap off and squeeze your hoses to get excess air out of the system if your gauge is at red then the radiator when it was like this should have been too hot to touch. the fact you said it was only up a hill mostly suggests a problem with the head or barrel and when under grestest compression any leakage of gas into the cooling system causes the coolant to get hot hence the head also. they are notorious for it but these factors i have mentioned are most likely.
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fzr 600 its yellow but its no banana!!!!!!

[0ddball]

[ZRX61]

It might help matters if you told us why it melted the original piston & what was done (if anything) to stop this happening again with the new piston...

[motorbikes010]

I dont know about that... I have a feeling the person I bought it from ran it without 2 stroke oil.

What I have done is I changed the 2 stroke oil to castrol TT. I re-adjusted the oil pump as I read in the manual. I ran the bike without the Cap on and let some bubbles come out from the system. There weren't many there, Then i turned off the engine topped the coolant level and then i took it for a 20 mile test ride. Went uphill and through traffic and all over oxford. The temp gauge was at the most on half.
The plug was checked and tightened. It seems to be fine now....


I was using sh1t 2 stroke before so it could have been that?

What do you think?

[ZRX61]

[Vin]

Bit difficult to say from what you have described but I do remember having an old two stroke of mine rebored with new pistons and rings etc. It was very tight for the first couple of rides which made the bike run hot.....could be something similar. Take it easy and monitor the situation.

[simon1221]

Does it rattle, piston slap ? Bacause when I put the wrong size piston in miy bike it went into the red in about 10minutes.
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