(this might help someone)
OK, so far we have:

1. Running LEAN (too much air in mixture)
2. Low quality gasoline (contamitaned/low octane)  
   unefficient combustion=excess friction
3. Valves need adjusting (excess/chronic  friction is  
   generated)
4. Not enough/wrong/degraded OIL (watch out for      
   synthetics!)
5. Wrong main JET/carb setup/dirty-obstructed carb
6. Aftermatket EXHAUST (could make motor run lean)
7. Wrong/damaged SPARK PLUG
8. Physical barrier for cooling vents (paint, mud, etc)
9. Buildup on cylinder walls prevents correct lubrication
10. Anything missing?    ....anyone?


ORIGINAL MESSAGE
Hi people, Iīve been doing A LOT of reading at this site lateley and learning much, but still need YOUR help to fix my bike.

Basically I just got a 97ī CA model, with 4,000mi in overall good shape, no rust, that, letīs say, was tampered with for fun by someone who didnīt know what they were doing and got rid of it, and worse, I donīt know itīs history (I found it at a car lot, was a trade-in).

Symptoms + Update:
 
- After 25 minutes of normal riding it OVERHEATS (rich/lean, doesnīt matter) and the torque is gone, nothing drastic but annoying.

- Once hot, during uphills motor behaves like a lawnmower, just WON'T REV UP.

- Regardless of all variables I cannot get it over 60MPH (100kph), I feel the potential power there but just cannot get it out.
Basically it "chokes" on 5th gear, @ 55mph, at about 3/4 throttle, the wind stops me flat. Almost no passing power.
Air filter is fine, box has holes.

- Have the NGK dp8ea installed, Iīll try the no.7 soon.
Or no.9, someone said? (oops, allready bought no.7)

- CARB'S A MESS (no brown goo though) clean inside but abuse marks everywhere, one "arm" tha holds the floter valve's pin is broken (pin stuck to that side), but floters still work well, floter valve ok, and cannot get the jets out (145 main jet kit), theyīre very much STUCK in to place, soak carb in acid or something?

   Just buy a new carb?  $ how much?
   The Mikuni BS40ss or VM?
   (I'll check that right away, thanks Lancer!)

- Just put in fresh oil 200mi. ago (20w50 & clutch stopped slipping!), already jet-BLACK again.  

- VALVES RATTLE some, not really loud metal clinking, but I donīt know what is normal. (Sounds like the workings of a small outboard motor, click click, click. This normal?)
Iīll try to ajust soon, just need right tools and correct know-how, never done it.

UPDATE:
1. Just changed oil (warm), lots of tini-tiny aluminum filings (oil was shiny under the sun, will change again soon to flush the all the burned gunk out for good), installed new oil filter too.
2. Changed spark plug to no.7 (is this bad).
Runs better, burns better, overheats less I think. But somehow harder to start.
3. Old sparkplug came out somewhere between "normal" (tan deposits on tip) and "carbon fouled" (black, fluffy carbon on sides), but not white and nor spots.  hurra!
4. Now I could reach 70mph and "choked" less on 5th gear at about  1 1/4 turns out on the mixture valve, yes a little lean but, again, it chokes less.  
5. I'm worried about the "clinking" the valves make, my gut tells me they're bit too loud.
6. And yes, the jets are STUCK beyond any hope.
7. In the next few days I'll be riding the same road (and uphill) I took when it overheated, let's see what happens this time.

I'LL KEEP YOU UPDATED ON THE JETTING JOB AND/OR
NEW CARB + VALVE ADJUSTENT, coming soon (pics too!)
End of UPDATE.


DIAGNOSE?
Any advice, tips & links appreciated.

Thanks in advance
Richard P.

How does the bike run when cold?
How do You know that it overheats?
Everything sounds like wrong main jet /i'd say too big/.
Just pull the carb out and go step by step, making sure You have the corect set-up. Do the mod's in the same time. I think somebody has overdone all the mod's.

145 main jet w/t after-market pipe is way too lean--no wonder it's blue. If you can get the main jet out, maybe you can use the next size drill bit to open the hole up a bit( I forgot what I used before ???)[glow=red,2,300]with the main jet needle out of the way of course [/glow]. I hope that dude did not burn up the exhaust valve running that lean

You just changed your oil and it is already black again ... engine must be REALLY CRUDDED UP INSIDE ...change the oil again, you have to get the crud out of there and unless you want to tear it down for a rebuild then changing the oil is about the only way to get the crud out.

The main jet is STUCK.  If it is all that stuck in there, then you can bet that the rest of the carb has stuff in there too ... even if there is no brown goo ... passageways are likely stopped up, or at least restricted.  Take the carb off and dissassemble as much as possible, then soak in the best carb cleaner you can get.  You will probably need to leave it soaking for at least a week.  Then try taking the rest of the stuff apart.
If you are up to doing a complete carb rebuild, then do it.  

If you have a stock exhaust/muffler then go up at least one size main jet, 1/2 white spacer mod, and adjust pilot jet screw for proper tune.
If you have after market muffler then go up at least 2 main jet sizes (150), one size larger pilot jet and tune. accordingly, and do the 1/2 white spacer mod.


If you are not up to the carb rebuild and/or just don't want to mess with it, then get a new carb.  A Mikuni VM is the least expensive and will make great power and is very responsive.  Carb kits are available on ebay or on this site.

Stimpy - FSO wrote on 12/31/69 at 16:00:07:


The bowlvent with the hose on it is for the CA model. Is normaly connected to the "Canister" which sits on the exhaust bracket just in front of the rear wheel. There's another hose that runs from the canister to the tank.
Remove hoses and cap, you don't need them.

The other conections on the bowlvents (one on either side) should have a lenght of hose and go up and forward over the carb and end inside the square frametube under the tank.

As for the other problems, suggest you do the valve clearance adjusment and get a 2nd hand carb.

To open-up the main jet you could drill it with a 1.5 mm drill = 150 mainjet.

Greetz
Kropatchek 8)