Cota 247 Running Lean and Overheating

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brownie
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Re: Cota 247 Running Lean and Overheating

Postby brownie » Thu Aug 26, 2010 1:21 pm

G'day Andrew,
So you can at least cross the carby off the list, poor old amal much nicer carby than a mikuni :shock:
few things you could try [or maybe you already have]
have you tried disconnecting the kill switch wire at the primary wire connection to take it out of the equation
HT coil really well earthed no paint,rust between it and the frame
LT coil could be breaking down test it with a ohmmeter [ most likely problem]

Doubt your exhaust would cause any problem unless it was the only earth between the engine and the frame.With the collar coming loose just wire it up so it can't loosen or a hose camp on the pipe hard against it



keychange

Re: Cota 247 Running Lean and Overheating

Postby keychange » Thu Aug 26, 2010 2:25 pm

Ross

I thought that maybe it is sucking air back in through the exhaust .... yes - no ?

I have in the past removed kill switch - I have removed paint from frame under coil connection. I haven't tested LV coil - not sure how to go about that - what am I looking for

Cheers

Andrew



bestrcpilot
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Re: Cota 247 Running Lean and Overheating

Postby bestrcpilot » Thu Aug 26, 2010 3:19 pm

So we know that it is not the Carby. My 348 use to do the same thing. Run good until it got good and hot. Then it would stop running and you could kick your leg off and it would not start. Wait a day then it would start right up 2nd kick. If it was cold out side Ie.. 50 F or less then it would run all day long until you shut it off then it would not restart. I found that replacing the coil behind the flywheel fix it. Seem that it had a broken wire in the coil that only "opened" when the engine got hot and the coil would get hot the wire would grow in length and then the break would happen. I found it by removing the coil and warming the coil with a heat gun and reading the ohm meter when the coil got up to the right temp then to ohm reading would go to 0
I have also had the Condenser do the same thing in the past. Put A Ohm meter on it when it is cold. then Warm it up and watch the Ohm reading it should not change. It is always good to mount the Condenser up by the HD coil helps the Condenser stay cool.
Sorry if I have used the wrong words here But I'm a dam YANK



brownie
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Re: Cota 247 Running Lean and Overheating

Postby brownie » Thu Aug 26, 2010 5:08 pm

G'day again ,
Now I might be shot down in flames here as electrics isn't really something I know a great deal about but any way this how I'd test it.
now I think you have your condensor mounted under the tank so the wire coming from the points undo before the condensor and HT coil and measure the the ohms,take the spark plug out and turn a couple of revolutions to see when the points are open and shut when they are shut should read 0 or close to it when they are open should read up to .5- 2.5 ohms?[any experts] any more there is probably to much resistance.
a joiner in the wire in a easily accessible place so you could test it before a ride, then when it stops or plays up when warmed up would be good just carry the meter and a spark plug spanner on your next ride to see if the ohms have increased hopefully they will have so its just off with coil and get it rewound.
oh red lead to the wire, black to a good grounding point although I don't think it matters much which way around they are as it's only measuring resistance.
Hopefully this works if its not going to work someone might chip in with a more knowledgeable way of doing it.
Cheers Ross



keychange

Re: Cota 247 Running Lean and Overheating

Postby keychange » Fri Aug 27, 2010 6:11 pm

But wouldn't a faulty coil - low or high cause a weak spark - there is no sign of that - spark looks normal and it still won't start until it cools down



TriCub
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Re: Cota 247 Running Lean and Overheating

Postby TriCub » Sat Aug 28, 2010 10:07 am

It's quite common that under the load of compression the spark will not be able to jump the gap to keep the motor running.
When the plug is removed and the motor kicked over there is no pressure and you may see a spark but inside the motor you may have nothing.
Check for spark using a timing light with the plug in the motor, if it doesn't flash that is your problem.
If it is a week spark you can try running a very small plug gap, say .2mm this will reduce the voltage required to make a spark.



brownie
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Re: Cota 247 Running Lean and Overheating

Postby brownie » Tue Aug 31, 2010 5:21 am

Tried the ohmmeter on my 2 Bullies the readings were 0.1ohm points shut ,1.5ohms points open, both the same.
Only tried them cold but should read the same when warmed up unless there is a problem.



keychange

Re: Cota 247 Running Lean and Overheating

Postby keychange » Tue Sep 07, 2010 8:59 pm

Gave the mikuni back to Brownie - thanks Ross - ( bought one eBay day before $30 delivered) then on Sunday I refitted Amal ( forgot that I had previously raised float to flood levels - fuel weeping) and set spark gap to 0.35mm previously 0.55mm - started first kick - then phone rang - son 3 happy father's day...... back to bike started 5th kick ...phone rang son 2 - father's day..... back to bike started 5th kick and I rode it around my hill which is pretty decent hill for 20 minutes. No sign of stalling - engine idle way too high ( float level also way too high) eventually pulled up and killed engine, spark plug still looks a bit lean - which with a high float level still doesn't make sense.

I am still not convinced the problem is coil - but I will do full test this weekend. If it was coil then it should have faltered when hot and it was hot.

BTW- Son 1 eventually rang at reasonable time :)



TriCub
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Re: Cota 247 Running Lean and Overheating

Postby TriCub » Tue Sep 07, 2010 10:49 pm

The reduction in plug gap may have been enough to maintain the spark. The stator coil is were I'd be looking, but you need to know if it is a loss of spark that causes it to stop when hot. In the Amal what size is the pilot jet and were have you got the idle mixture screw. Try turning it in to richen the mixture when it's hot this may bring your idle under control.




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