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Post by fatfastroger on Sept 13, 2012 18:18:05 GMT 1
Hi All
I have a 1983 31K PV which has a very frustrating problem (aren't they all ?)
It is tricky to start and runs on the left pot when cold, then the right chimes in and it runs great - plenty of power and no misfires/rough spots all the way up to max revs.
The problem shows up after a run when I have been revving it high through the gears and making progress officer ;D after a few hundred yards when I slow down it seems to run on one cylinder again, usually the left runs ok, and sometimes cuts out.
It will start up without any drama and run ok again, till I repeat the above. If I ride it more gently then all is ok.
I have so far
Stripped the carbs and ultrasonically cleaned them and emulsion tubes. Twice.
Ran it with fuel tap on prime
Replaced plugs/coil/stator/CDI/rotor (from later bike -52y CDI)
Any ideas welcomed please - as I'm starting to fall out of love with this one !
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Post by midlifecrisisrd on Sept 13, 2012 19:04:39 GMT 1
Check the fuel cap is venting ok and not causing a vacuum in the tank.
Steve
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Post by fatfastroger on Sept 13, 2012 19:20:35 GMT 1
Cheers - I did that and it made no difference.
Also I now have a new rust free tank with a good cap
Replaced the float valves from Norbo (Thanks)
Forgot to say that it happened twice on the same hill, as I turned round and tried it again and it repeated - seems to better/ok on the flat but that might be a red herring !
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Post by steve h on Sept 13, 2012 19:53:32 GMT 1
I had a 400f with very similar prob. It only started at high speed (115+) it was fuel starvation. But the cutting out? Switch plug leads L to R and vice versa, see if it cuts out on the other side. Is the replacement coil OK? second hand? off a running bike? My 400 was pretty quick & it felt like you hit a brick wall of spluter! (Is it a single coil on a ypvs?)
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Post by fatfastroger on Sept 13, 2012 21:38:56 GMT 1
Ok my next job is to check float heights - cheers Mark
And I did swap the leads round with no change, the old coil and CDI gave a poor orange spark.
I've not had the head off and as the bike has never run properly since I got it in April, could it be a piston/ring problem? The PV work ok and both valves move together and a finger up the ex port confirms they are the right way round.
At least nobody has suggested a twisted crank !!!
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Post by midlifecrisisrd on Sept 13, 2012 21:47:48 GMT 1
Ok my next job is to check float heights - cheers Mark And I did swap the leads round with no change, the old coil and CDI gave a poor orange spark. I've not had the head off and as the bike has never run properly since I got it in April, could it be a piston/ring problem? The PV work ok and both valves move together and a finger up the ex port confirms they are the right way round. At least nobody has suggested a twisted crank !!! now that you mention it ;D float heights for a start then a compression test may be an idea. other than that you are looking for an air leak when hot which could be crank seal. steve |
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Post by fatfastroger on Sept 13, 2012 21:56:30 GMT 1
Steve i had that thought too, but it is the right pot that plays up. Thought the LH seal was more likely to fail. As the RH one is in the oily bits! Just need to get this running 100% as I'm stripping it for a frame and bodywork repaint this winter.
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Post by fatfastroger on Sept 13, 2012 21:58:29 GMT 1
And yes SteveH it's a single coil and all the electrics were from a running bike I was told.
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Post by midlifecrisisrd on Sept 13, 2012 22:03:32 GMT 1
Steve i had that thought too, but it is the right pot that plays up. Thought the LH seal was more likely to fail. As the RH one is in the oily bits! Just need to get this running 100% as I'm stripping it for a frame and bodywork repaint this winter. you would think that about the seal but i stripped what i believed to be a good bottom end that i had used but stripped to sell the cases and found the right hand bearing was shagged even though the lh and centres were perfect. i have no doubt the play would eventually shag the seal. steve |
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Post by fatfastroger on Sept 14, 2012 16:26:35 GMT 1
Looks like an engine strip might be on the cards along with the repaint
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