causes for HEAT....

My bike is running great cold. Not ice cold, but after starting with choke on a 50 degree morning and running for a couple minutes, it feels perfect. After prolonged use (about 10 minutes or so in the afternoon when the temps are in the 80s...) it starts to get hot. It gets that hot engine smell, and performance suffers. In an otherwise well running bike that is properly lubricated and driven normally, would overheating only be caused by a lean mixture? If not, what would be other reasons for this?

thx in advance

kellen

 

Lean mixture will do it along with a few other. I would check the lean issue first. Pull your plugs and take a look at them. Post a pic if you can. That will tell the story.

 

99 times out of a Hundred ... when an Air Cooled Engine is running HOT ... the problem is that the Air~Fuel Ratio is too Lean.

Using the wrong Grade of Oil will cause an overheat.
Timing too far advanced will make an Engine run Hot.
A problem within the Exhaust System.
Fuel.
Oil Pump dying.
Idling in warm ambient temperature (Climate)
Clogged Fuel Filter.
No Air Filter.
A filthy dirty engine with dirt and mud in the cooling fins.
Wrong Jetting / Way-off.
Low oil pressure.

 

thanks rick..... have correct oil, wasn't idling, has brand new stock replacement air filter, new fuel filter, engine clean, oil level is correct.

that leaves oil pump, jetting, timing, and exhaust system.

If jetting is correct, and since i'd like to check the easiest things first, is there anything that could be maladjusted that would cause a lean mixture?

pilot screws only control mixture at idle correct? Is there something else on the carb that controls mixture while on the main jets? Is this why a clogged filter would pose a problem? not enough fuel in the bowls so full amount doesn't get into jets?

Would float height affect lean or rich mixture?

Thanks.... for now i'll assume something is mis adjusted because that should be easier to test then something that is broken. i'll go pull the plugs and take some pictures.

 

Yes. A lot.

 

No. The Pilot Jets are always feeding fuel. If they are too lean and there is some issue preventing the Main Jet Feed from being correct ... you'll run lean.

Usually, this means that the Main AIR Jet mechanism is fouled in some way.
The passage blocked, the Metering Ports in the Emulsion Tubes clogged and the Main Jet Feed is too lean. This condition limits the amount of Main Jet Fuel that can be drawn-up when the throttles are opened.

Other know faults:
Diaphragm Pistons sticking.

Instead of being Opened and the Needle raised to allow the Main Jet Flow ... the Diaphragms stick as they rise ... causing a Lean burn, too.

The Bores for the Diaphragms are easily refinished and the oxidation to the Bores Inside Diameter removed.
Wet sanding with 800 strips wet with WD-40 as the wetting agent will refinish the Bore.
Follow-up 1000 and 1200.
Race Prep by Polishing the Bore.
Dremel Buffing Pad, Jewelers Rouge's #-5 and #-6.

Mirror finishes on those Bores do wonders for performance!

 

sweet.... pulled the plugs. insulators are as white as paper. It pretty freaking lean. I had the tank off a couple weeks ago and checked the pilot screws were about 2.75 turns out. Maybe i'll pull them out a little more and see what happens. I really need to yank the carbs, I just live in an apartment, and will probably have to do the cleaning in the kitchen or bathroom. my wife is gonna be pissed. i'll tell her she can go out and buy a shirt or something.

thanks guys

kellen

 

What number are your plugs from this guide:

Spark plug guide

Will give a good idea of how far out you are and what you should be looking at when things are right.

 

24, but with a whiter insulator. The electrodes don't have any signs of degrading, but i don't ride for long distances so its never been hot for long.

 

yeah 24 says it is "OK", but that is too lean. My 82 550 had these problems as I was a 23 or 24. I found out that the o-rings on the pilot screws were thrashed causing a big air leak around the pilot screws leaning it out. It also caused it to be very difficult to start when hot (for example after stopping to fuel up). After replacing the o-rings, adjusting the screws close to 3 turns and re-syncing, the plugs are all 14 or 16.

 

well... i'll be able to check for that tonight... pulling the carbs in a couple hours and i'm gonna take this rainy weekend to clean and rebuild. I'm very interested to see whats going on in there. i know 24 said OK, but maybe to lean, but i'm sure its not okay, because the engine is getting hotter than it should.

thanks for the help thus far!

Kellen