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Sam GiftSun Mar-13-05 06:05 PM

  
"loss of power after 10 minutes"


  

          

Since getting the newly reconditioned magneto up and running I took the old girl for a run on the weekend and find that after approx 10 - 15 minutes she coughs splutters, as if dropping a plug and loses power. If I let her sit for a few minutes she fires first kick and goes for another 10 - 15 minutes before the same thing again....Any ideas from the outside world...Could it be a plug lead? ?
The mag is fully reconditioned and she fires first time.

Any helpers please

  

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geo46erSun Mar-13-05 11:53 PM
Member since Mar 18th 2009
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#1. "RE: loss of power after 10 minutes"
In response to Reply # 0


  

          

Hi Sam,
Sounds like the classic plugged gas cap vent to me.
However, if you have already eliminated that possibilty, then
I would begin to suspect some electrical component getting warm like the condensor???
justa thought,
G.B.

G.B.

  

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BrithitMon Mar-14-05 11:47 AM
Member since Mar 18th 2009
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#2. "RE: loss of power after 10 minutes"
In response to Reply # 0


  

          

Usually, if the mag fires it one kick when hot, it is not the problem. Sounds like the gas cap vent, like the previous post said. Look at flow from the petcocks as well. If they are the new re-pop ones with rubber seals, they can swell on you, and severely restrict flow, and cause some similar problems. Would depend on the engine speed. If you have a low flow, you are getting a little gas, and it might be enough to plug around the 'hood. They just can't keep up with more than that. You'll think fuel is flowing, and it is, but this situation can cause conditions you think is the gas cap vent.

Don W.

  

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Sam GiftMon Mar-14-05 07:21 PM

  
#3. "RE: loss of power after 10 minutes"
In response to Reply # 2


  

          

Thanks for the replies guys........will show my ignorance and ask can you explain the gas cap vent problem in more detail, am not familiar with the terminology. The fuel petcocks are repo versions so will check them out. It did seem to do it at speed but given I wasnt abou tto push the thing too far home I didnt pursue the open road much further. Let me kno the gas cap vent and I will check it out.....thanks again people

  

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geo46erMon Mar-14-05 10:17 PM
Member since Mar 18th 2009
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#4. "RE: loss of power after 10 minutes"
In response to Reply # 3


  

          

Hi again Sam,
The gas tank has to be vented somehow (IE air must get in to displace the fuel going out). Its the old put your thumb over the straw and pick up the milk trick. Many modern bikes have remote vent tubes from the bottom, but, most older bikes have vented caps. Typically there is a small hole in the cap to let air in, its usually baffled so sloshing gas does not come squirting out.
Its possible that rust or dirt has plugged or restricted the hole. If completely plugged gas will run from the tank until the vacuum building above the gas becomes strong enough to completely stop the flow of gas from the tank. A partially plugged vent is harder to diagnose, typically causing fuel starvation only at high engine load situations.
You could test it by driving with the cap open (be careful) to see if the problem happens again.
justa thought,
G.B.

PS. I've seen tank bags mounted over gas caps cause the same problem

G.B.

  

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Sam GiftTue Mar-15-05 06:14 PM

  
#5. "RE: loss of power after 10 minutes"
In response to Reply # 4


  

          

Thanks GB.....was having a bad day yesterday and overnight spent some thought and clicked with what you were saying...I will check it out and see how it looks....other than the suggestions you guys came up with I don't know what else it may be......a process of elimination it would appear

thanks for the help

Sam

  

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MarcSat Apr-02-05 07:59 PM

  
#6. "RE: loss of power after 10 minutes"
In response to Reply # 5


  

          

I hope you have found that your problem was a vent/fuel problem. If not it unfortunately sounds like a classic bad condenser in the magneto problem. When the condenser is bad the bike will start fine and run ok until hot. Then it starts to misfire and when it dies you can't start it for ten or twenty minutes until it cools down. I have had a magneto rebuilt because it had a bad condenser and then had the same problem all over again because the condenser used in the rebuild was no good. One possibility is that your magneto was rebuilt with the best of intentions with a nos Lucas condenser. I see them for sale all of the time. Unfortunately they're all faulty from old age by now. With all respect to the vent theories, I subscribe to the rule that if you think it's fuel it's almost always ignition. Regards, Marc

  

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andersonSun Apr-03-05 07:18 PM

  
#7. "RE: loss of power after 10 minutes"
In response to Reply # 6


  

          

Agree with Marc 100 %.

I really hope its fuel but it sounds a lot like mag.

John

  

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SamWed Apr-06-05 04:53 AM

  
#8. "RE: loss of power after 10 minutes"
In response to Reply # 7


  

          

Gee thanks guys, you are really filling me with confidence about the blocked tank cap vent. The mag initially had a dodgy condenser and it had all the attributes you mention, hard to restart etc when hot. Since the mag rebuild, and I have only been for 2 rides due to lack of time, the bike doesnt cut out totally and if it does stop, it restarts very easily without waiting for any great length of time. I am really hoping it isn't the mag again. Was thinking maybe a dodgy lead that was suss under heat and load, or the tank cap. Guess I will find out this weekend when i head out to test it out some more....wish me luck. Thanks for the feedback, will keep you updated as we go

cheers

Sam

  

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SlavetoMechNOTThu Jun-23-05 11:37 PM

  
#9. "RE: loss of power after 10 minutes"
In response to Reply # 8


  

          

Did you have that jack ass in Dover Ohio rebuild your mag? Because I had the same thing happen to me.
Look... Just because someone says they fixed your mag doesn't mean they actually did. Trust me... I was so freakin' mad when I found out that the jackass didn't really do a good job... It's not your gas cap.... Everyone loves to say that because it' s so bizarre... Your mag is overheating because it wasn't repaired correctly. Just to rule out other possibilities... check and make sure that the spark plug leads are not corroded... look everywhere especially inside the cap.
Cheers

  

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