hot running

[blacklav]

Ive just rebuilt a 1977 d model with rebore, new pistons, rings and exhaust valves. The problem I have is it seems to be running very hot.

 I have not touched the carb settings.

I cannot remember if it was this hot before the rebuild but it does seem excessive as the wiring above the motor starts to sag and soften due to the heat. Even after a run in 12`C weather it still gets hot. Obviously the cylinder head is the hottest but it seems hot on the cases as well.

Ive checked the oil flow, and there is plenty reaching the head. I`m using 20/50 mineral oil.

The carbs are set slightly rich for the pilot jet but spot on for the main ( according to the sparkplugs).

Any idea`s

many thanks

chris r

[XS Rod]

The only thing I can think of that would cause the engine to run hot would be a lean condition.
Don't know about running mineral oil in your crankcase... but I don't know a lot.

[madmax]

 Check your ignition timing with a strobe at 1200rpm and 3000rpm, the little ears on the advance weights can wear allowing the timing to advance way too far, ie to the point of holing pistons too far.

  There is a bodge repair to the weights but it's only a bodge and won't last forever, new genuine Yamaha advance/retard mech is the best answer.

    Max

[richard]

Max is right check your timing with a timing light to make sure it is not running too far advance at 1200 and 3000. Engines run hot when they are breaking in or seating the rings. So it is wise to make short runs and let the engine cool down between rides for the first 500 miles. There many different opinions on break in procedures. Mine is just one of them. Also any thing you do beyond stock to make the engine breath better without re-jetting the carbs will cause your engine to run leaner and hotter. If you have an air intake leak on you carburetor boots it will also idle high, surge at speed and run lean.

I'm not sure mineral oil is your best bet on lubrication. You are the first Person I've heard of using it. Most people use castrol 20-50 or rotella or some other brand of motorcycle grade oil. I run castrol 4T 20-50 motorcycle oil. I broke my rebuild in by several short half hour rides and let it cool down completely between rides until I reached 500 miles. It didn't feel completely broke in until just over 2000 miles. I have 5400 miles on this rebuild now and all the seeping and blow-by mist on the head while the rings were seating in are gone. it get 37C or 100F here all the time so I run one jet size richer on all my biked on both pilot and mains to help them run cooler. There are people who run wind deflectors on their bikes to direct more wind towards the cylinders in hotter climates.

This is what one guy did www.xs650.com/forum/showthread.php?t=2426

But I would keep it simple until you have figured out why it is running hot.