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geordabroad

Exhaust Discolouration 1st Ride After Engine Rebuild

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Hello

just rebuilt my 06 TXT Pro 300 after new kickstart gears, new piston and rings and new jets in the carb. Also put a spacer on the top of the cylinder to reduce compression to calm it dwn a bit.

Got it going after leaning the carb quite a bit (turned the air screw in 1.5 turns) as the plug was really oily initially. Now there doesn't seem to be any problems, however at the end of the ride yesterday I noticed that the front bend of the exhaust, just after it exits the cylinder, had turned a yellow/ gold colour. Is this nornmal or does it hint at the engine running too hot or some other hidden problem?

In addition I did notice, when I stopped half way through the ride yesterday, that there was smoke coming out the exhaust, as well as coming off the side plastics that had melted against the exhaust. Is smoke from the end of the exhaust normal after a rebuild with new piston and a little Blue Hylomar to keep the head spacer in place?

Cheers

Ian

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You have done things that will increase the temperature of the exhaust gases

Rings bedding in (friction)

Reduced compression (less efficient combustion)

If you have leaned off the carburetion, that will also increase the exhaust gas temp

The exhaust smoke was probably due to oily deposits within the exhaust system being vapourised by the higher exhaust gas temperature. The deposits were deposited when the motor ran cooler prior to your engine work. Once they are burned out with use, the smokiness of the exhaust should return to previous levels (assuming you haven't changed oil type or mixing ratio)

Using hylomar on the head gaskets will not cause exhaust smoke

Oil put on the rings for reassembly would have caused slightly more smoke than a normal cold start for a few seconds

The discolouration of the exhaust can probably be polished off if it worries you

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Thanks for the quick feedback, feet up fun. Was not worried about discolouration, just worried that I might be harming the bike in some way.

While I was riding the fan was coming on and then going off so I assumed the temperature of the coolant must be ok.

A follow up question:

Are there any signs you know of, other than the fan being on all the time, that show the engine is too hot? The reason I ask is that it is relatively cool here at present (20 degrees c) and will be getting much much colder over the next few months (-5 to -15) but I will also ride in the summer when it could be up to 35 or 40 degrees c each time I come out. How can I tell if the engine is seriously overheating?

Cheers

Ian in Beijing

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High exhaust gas temperature does not mean the motor is running hot

If the fan cuts in and out then the mechanical parts of the motor are at the right temperature

Serious overheating = coolant loss from the coolant system overpressure relief valve

If you are fanatical about knowing how hot the motor is, you can use a hand-held non-contact thermometer (laser guided) on the barrel or head. It should not go above about 100 degrees C.

These bikes are fine here in Summer (Australia) and it gets just as hot here as it does in China.

If the bikes's cooling system is working correctly, the rider will fail long before the bike overheats.

David

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Pedantic observation. It's a mixture screw on a gas gas screwing it in will lean it off but it actually reduces air & fuel. Mikuni carb as on Beta is a true air screw this mean screw it in for less air ..i.e richer.

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Hi geordabroad, I cant remember where i saw it but i'm 99% sure i seen a temperature kit that you permanently stick on the side of the barrel that tells you what the engine temp is at, it was similar to the one's you find in offices that change colour as the temp rises and drops. maybe that would help reassure you when your riding on hot days, if i find where i seen it i will post it up.

Cheers Steve

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