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Cutting Out when Hot

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Hi All

Hope you can help. I have brought a 1969 500cc Dommie, I took it out last week and it ran fine for 20 minutes, then cut out. It was very hard to restart. Before I start doing anything I did find the battery was 3 single cell torch like batteries they looked very old!!!, I will have to fit a new battery. 

Thanks 

Hope you could point me in the right direction 

Cheers

Steve

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Steven,

Is that the correct year for your 500 Dommie, I thought they finished the 500 models in the mid 1960's?

If it is a magneto then you'll have to test if there is a spark when it cuts out, if not then I would suspect the magneto needs overhauling.

Philip

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Is the battery a Cyclon cell type? They are costly and allegedly have a very long life. Google for more information. And test with a cheap meter before throwing it away. How wel is it charging?

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Unfortunately, there are many possible causes of the symptoms you describe.  When the engine cuts out, is it suffering from a loss of compression, and overheating?  Does it start easily when cold?  If so, it is possible that the wrong pushrods have been fitted.  Mine were expanding, when hot, preventing the valves closing fully.   A temporary solution is to increase valve clearance, when cold (try 6 thou. inlet & 8 exhaust).  The motor may rattle a little, when cold, but quieten at working temperature.   Weak mixture, and, or, retarded ignition timing, will also cause overheating. 

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If your bike is a '69 500cc it must be a mix of parts because no 500cc domis were made that year. Maybe it is a Mercury frame, which could have a '69 frame #, with an earlier 500cc motor. Anyway the most likely cause of your problem is ignition. Can't diagnose without first knowing if the bike has magneto or coil and points. If it has a magneto the battery is not relevant to the ignition system. Your symptoms sound like a magneto with a bad condenser, but obviously this does not apply if you have a coil and points 

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Hello the  Last 500cc Dominator,s  ever made were End of March 1966  and all these were model 88ss  and all had Lucas K2FC magnetos    if you have a magneto fitted your condenser is on its way out , or there is a blockage in the fuel line      yours  anna j  

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hi all,

i am about to pull apart my dominators laydown gearbox (more neutrals than gears) . The gearbox is on the bench and ready. Any pointers gratefully received

david

Anna, when you actually ride your Dominator, instead of talking about it, you may find your comment somewhat simplistic.  Very few, if any, of these machines (the best in their day) are still in their original specification.  Problems arise now (partly due to various owners "improvements")that were unheard of when they were built.  This, from someone who was actually riding on, in the 50´s.

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What ignition is this bike running, magneto, coil & points or electronic ignition.

I have had 2 issues with bikes running and then cutting out only to then restart.

1. An over heating coil which allowed 100 yds of power before needing 10 mins rest.

2. A Boyer that overheated with a coil with the primary ohms just barely under the spec, again 15 mins cooling got 20 mins running.

1 Was fixed with new coil

2 Was fixed with a coil with 0.3 more primary ohms

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...no one has mentioned blocked breather on the fuel cap?

 

 Only me suffered this?

 

Jon

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my mate fitted a tank bag on his triumph.....he had the same symptoms, it took us ages to find the problem!

I had the same problem on a '62 Atlas that had the original Mag in it. When it got hot it ran like crap then cut out and had no spark- when it cooled down it would start again. Then repeat the problem. It was a slow way to go......

 It was the Mag- I believe the condenser was shorting out. Sent it to to Doug Wood in Boyerstown Pennsylvania and he did a rebuild job- never had the problem again. His rebuilds are known to be spectacularly reliable- and he is fair and fast.  I have never heard anyone on the side of the puddle complain about his service. 

Tristan

 

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The most likely thing if its coil ignition is a flat battery  that is not getting a charge,it will recover enough after time to start the bike but then stop.If its a mag then there is the usual condenser issue.An old 6v coil can fail like this. Not enough information to really help.  Could this be a 1959 88?.A simple (and no cost) way to check is to charge the battery overnight with a 1/2 amp rate. If the bike then keeps running you have the answer. No charge.

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Diagnostics at a distance and with no usefull information  is a hit/miss frustrating  experience. You need a bit of a thick skin as you can make yourself look stupid  or clueless  .  Just once in a while you can have a spectacular success . Around 1965 a mate rang to say he had bought an old scooter that has stopped on the way home. My only comment was that if there was a button on the bars he should rip the wire out. He soon arrived at my home and from that moment believed I have mystical powers . Nice to have mates that look up to you ,so I have kept up the illusion!!. Might be fun to hear of more spectacular/unlikely fixes?.

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Strangely just had this problem with Lucas SR1 magneto. Easy start when cold but as soon as hot cut out at about 2-3 miles out from base and refused to start. 45 mins later when cooled down away to go and would get me home. Changed condenser still same issue and another 45 minute wait. Tested magneto and needed rewinding. Bike is 1957 350cc RE Bullet. Mag is 53 years old and had bike with big brother 59 Dommie for 13 years with out issue on starting so mag very reliable until recently. Debated whether to install electronic as kit available. Given this experience of magneto reliability and possible additional pull on alternator (also 53 years old) to keep battery fully charged (bike is now 12v) thought would go down refurbishment route. Trust this helps in some small way.Hugh

Since the original post was made over six months ago, and so much conflicting advice given.  There seems little point in further comment.  Either the problem has been solved, or the replies have resulted in total confusion! 

 


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