Overheating xj 700 aircooled

Quite vicious overheating after riding only 6 miles.....
I know I have to work through the possibilities......

Ignition timing
Camshaft Timing
Carburation
As this machine has pick ups and h as such a non mechanical firing system then there is little to check.....however is it possible for the engine to run with the timing 180 degrees out...
When I remove the timing cover the pointer for TDC is the opposite side of the housing to that shown in the workshop manual.

Any help would be greatly appreciated as this is driving me to distraction

 

That's a problem....

what about your valves as well?

 

What bike?

If it runs at all, it's unlikely a timing issue.

Are your valve clearances in spec?

Look at the plugs; is it running horribly lean?

Probably needs a valve adjustment, carb service and then the carbs adjusted.

 

I want to drop back a second and ask... What makes you think it's overheating?

As for the timing, they use a "wasted spark" system supplying sparks to two cylinders at the same time. Since those two cylinders are 180 out of phase, it should work just fine if the timing marks are 180 out.

Fitz, According to the thread title, it's a xj 700 aircooled.

 

that pointer can stop anywhere.
i'll second this....What makes you think it's overheating?

 

What makes you think it is overheating? Its a air cooled engine and cylinder head temps can easily get to over 250 degrees F.

 

Timing 180-Out.
Hard to imagine.

Maybe you checked with the No.-1 Piston at the Top of the EXHAUST Stroke.

If you THINK that you are running hot:

• Check your Oil Level.
• Read your Spark Plugs

 

Sorry my router went TU

Smells hot......no really.....extremely hot....even for aircooled

 

Are your pipes bluing? Are your plugs blistering? Any lean symptoms? Have you changed your oil since you noticed this? If so was it shimmering with little metal flakes? Any overheating symptoms, like self adjusting idle lower, extremely rapid exhaust pinging after shut-down that doesn't rapidly slow down? Pants catching on fire? Just kidding on the last one.

 

If it smells hot, check out your fusebox for wires that have melted. Seems to be an issue with these bikes. I eliminated my fusebox and put in all in-line fuses. As to running hot, like the real mechanics said, check your plugs for color. If they are white, your motor is running too lean. Is the carb system stock or do you have pods? With pods, the motor needs larger jets to compensate.

 

Just an informational question for a previous poster. Why would the idle self adjust lower if the bike was running hot? I have never heard this before. What would be a reliable way to tell if the bike was running hot. Spark plugs blistering?

 

Spark plug condition (not necessarily blistering) and/or pipes turning blue.

Spark plugs are your best indicator of what's going on in the combustion chamber.

 

Agreed, not necessarily blistering, but if it's present overheating is for sure. Bluing pipes are reliable, and if you ever rode the bike when it was normal your perception of changes is the MOST reliable method to know.

idle changes: As an air-cooled motor heats up so does the oil and exhaust gas temp. The hotter oil causes an overall drop in oil pressure, which means it isn't moving or lubricating like it should, this puts a drag on the pistons. The higher exhaust gas temp accelerates it's departure from the mill further leaning out the mix. As I understand it, these two combined will cause an airhead to idle downward before it gets to catastrophic heat levels, but not long before.

 

Blue pipes on the right hand two cylinders as you look at the vehicle from the front........The left hand ones have very little blueing

 

Stock exhaust? If yes then those two cylinders are overheating. The stock head pipes are double-walled and will not turn blue unless the inner pipe is rotted through or the motor is running dangerously hot.

If it's an aftermarket exhaust then it would only indicate that those cylinders are slightly hotter than the others.

Next step would be to check your valve clearances and get a compression test. If all looks good, into the carbs.

 

It's an aftermarket exhaust system

The plugs are as black as the ace of spades.....??????

 

you're not overheating.

it's an air-cooled engine..........it's still going to be hot. don't touch it, you'll burn yourself. Just like on a lawn tractor. They get HOT. You're probably smelling some oil that has squeeezed out, and exhaust fumes, and the hot cheap0 aftermarket pipes, etc.......

Dave F