Author Topic: Lack of power MarkV  (Read 1112 times)

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Offline Pallijen15

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Lack of power MarkV
« on: 30 Aug 2018 at 09:05 »
Hi all, just wanted to share some other issues so that you more knowledgeable folk can advise if I'm on the right track. When I returned from a 15 mile run last Monday, putting my hand over the bellmouth of the left carb the machine continued to run on one cylinder. Putting my hand over the right carb, the engine stopped. Put my finger up the left exhaust pipe got wet black oil on my finger. Right side just black soot. I think the lack of power is that the right cylinder is doing all the work. I've just sent off for a compression tester to test this. The previous owner did say that he had had a problem here with gummy rings but it was sorted. Will be looking at it again on Sunday when I'm off. Thanks for advice on previous post also. Paul

Offline eddie

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Re: Lack of power MarkV
« Reply #1 on: 30 Aug 2018 at 11:26 »
         Make sure your carbs are truly a pair - same size jets in both, and same cutaways on the slides (don't rely on the number on the slides - owners often tinker with the cutaway to get better running). Take the slides out, sit them on their bases on the jaws of a vice and check that both cutaways are the same height (exactly). If all is well, re-assemble the carbs and carefully check that the throttle cables are correctly adjusted so that both slides lift the same amount. Incorrect cable adjustment often causes the lighter running cylinder to draw oil past the rings and then not fire hard enough to burn it - resulting in an oily exhaust on that side.
    Also, check out the plug leads. Old British bikes with Lucas magnetos run better with unsuppressed plug caps and wire leads (don't be talked into using modern carbon string leads). While you are at it, also check the HT pickups - remove them and look for oil around the carbon brush and on the slip ring. The more work you expect the engine to do, the stronger the spark needs to be - under full power, the spark may be finding another route through the oil and carbon dust to earth. Continuous tracking may leave a burnt path  down the surface of the pickup - in which case, sand back the surface to clean material. This should effect a temporary repair, but be prepared to buy a new pickup for good reliability.


Offline Hampshirebiker

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Re: Lack of power MarkV
« Reply #2 on: 30 Aug 2018 at 13:37 »
If you're buying pick ups on line make sure they and the springs are long enough. Plenty of short ones out there; as I found out.