Conference vmszoo::rc

  Nigel,

  When you adjust the carb., do you actually hear the difference in the
engine?  


           Jim

    Sounds like a valve is sticking.  Does it have any compression after it
    stops?
    
    Charlie
    

Jim, yes adjusting the needle valve does make a difference. I'm not too familiar 
with four strokes, but I read somewhere that you shouldn't try to "peak them 
out" too much. I guess that I run it a little richer than the setting that gives 
peak revs.

Charlie, that's a definite maybe 8^) Again, lack of experience tells here, but 
this motor's never felt like it had too much compression. I thought that maybe 
this was because it's a four stroke, and a bit long in the tooth. I'll decoke 
the valves tonight (if I can figure out how to get the *$&$^ thongs out!).

Thanks!

Nigel.

    Similar to what Charlie said but, check the cam followers. 
    
    Mine have rusted several times and caused poor engine running. 
    (Common on the OS90 4-c)
    
    E.

    How about adjusting the valve clearances?  If its warming up and then
    dying abruptly you may have a valve stem/rocker clearance that is too
    close.  As it warms up, the clearance goes away and you wind up with a
    valve not fully seated.
    
    Will

Thanks again!

I checked the clearances, and they seemed OK. I'll check again. I didn't take 
the bottom end apart (Coward 8^)). I think I'll try the valve suggestions first, 
and then if I REALLY have to, I'll take the bottom end down. 

Wait for the "how the heck do I put this back together??" note!!

Cheers!

Nigel

Nigel,

I'm not a 4stroke guru, but I've had a similar problem with my two strokes. It
turned out to be a kink in the pressure/vent line (muffler to tank). 

The engine would run fine for a while and then die cold. The problem was that 
it would draw until a certain level of vacuum had built up in the tank and then 
it would just quit.

When I pulled things apart it all worked, put it back together and it died
Took a long time to track down.

Definitely worth checking before you tear the engine down any further.

Randy

    .7
    
    He! this is an eye opener. I had this problem with my Royal 40
    for the last year. Never could figure out the problem. It would run
    to about 1/3 of the tank and then die out on me. My friends told me
    that it whas because my fuel tank whas to low, but the middle of the
    tank is at the same level as the crankcase. I will now look for that
    kink in the pressure line.
    
    Jacques

Make sure your muffler pressure tap isn't blocked as well. Doesn't 
have to be the tubing.

    I have seen carbon cause the valve to hang open.  Sometimes you turn it
    over and there is no compression.  These valves are small and it only
    takes a small particle of stuff to hang it off the seat.  Be very
    careful if you disassemble the head on this engine.  The valve seat is
    brass - very soft and easily damaged.  If you do not have experience
    with this, I would recommend against attempting it yourself.  I use
    toothpaste to reseat the valves on my 91Surpass.  Regular valve
    grinding compound is to coarse a grit.
    
    Charlie
    

    If nothing else helps, I have suggestion that fixed an older SAITO
    and OS also.  We tried everything that is replied to here with no
    change at all.
    
    What fixed BOTH engines was to add a Perry micro-oscillating pump in
    serieis with the fuel line between the tank and carb.  We even added a
    glow driver to light the plug at low throttle.  The ONLY thing that did
    anything at all was the pump.  I think the part number is OP-20. I
    don't have an RC mag here to look it up.
    
    The older 4 strokes did not have as good fuel draw as the new ones do.
    The going price here in New Mexico is $19.95.  They also work GREAT on
    fussy 2 strokes also.
    
    Good luck,
    
    Ron

Thanks for all the help!

(There's nothing gets people going better than a problem engine! 8^) )

I finally figured out how to get the valves out, and discovered a LARGE amount 
of carbon in the exhaust valve (surpise, surprise!). I removed this carefully 
(using a piece of plywood as a scraper where necessary), and put it all back 
together. I've only had time for a quick test run, but it looks better. I also 
decided to throw away the bit of fuel that I had left in my can, and use fresh. 
All being well I'll fly the beast tonight, thanks again for all the help!

Cheers

Nigel

    A point that is worth noting on some OS 4-strokes is that the hole that
    the carb needle slides into is sometimes made of brass, from what I can
    see. If the needle gets knocked by, a cowling etc, the brass hole can
    get damaged around the edges, making it difficult to lean the engine or
    even peak it where you want to.
    
    This has happened to me in the past on my OS-91's. Symptoms are not
    being able to screw in the carb needle anymore. If one is using the
    finer carb needle you can change to the coarser one and things improve.
    Best solution is to prevent it by allowing for clearances for the
    needle in the cowling, especially with soft mounting techniques where
    things then to wobble more !  I guess we all learn by our mistakes.
    
    Regards,
    
    Eric.

Well, thanks again for all the ideas!

The test flights yesterday went well, the engine is back to it's old self. It 
looks like the problem was carbon around the exhaust valve. 

It's nice to fly with an engine that doesn't quit just at the end of the strip!

Cheers

Nigel.

    It's nice to fly with an engine that doesn't quit......
    
    Quick, Sell it to Joe M.!   ;-)
                                  

    Yeah.  I could use one of them thar engines that run for more than a
    minute!!!
    
    One good thing about short engine runs, though.  I get in many more
    flights per tank. ;-}
    
    Must be Friday or I am sniffing too much castor fumes.
    
    Have a good weekend.
    
    -Joe