02GF74
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 posted on 27/10/07 at 07:33 PM |
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backfiring - after adjusting pump lever
was getting hesitation on rapdily pressing down accelerator (1300 xflow, twin dellorto 40's)
so took the carbs off and adjusted the lever so it is in touch with the pump mechanism, as per manual - so once throttle starts moving so does the
pump.
seems a lot better but now getting back firing on the over run., mostinly in3rd, 2nd and 1st gear (worst in 1st).
had to fit new o-rings since the old ones had swollen.
I think this is either something up with the lever mechanism or an air leak.
I did the nuts up - got thackery washers - but not as far as before due to new o-rings and carb. bodies seem to be firm like before. even gave the
insulator a squirt of eazy start and no change in rpm so fairly confident there is no air leak.
exhaust side not touched.
also when come to a stop, the revs sit at around 1,500+ then after a couple of seconds drop to to set idle speed of about 800.
so what can it be causing this?
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MikeRJ
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| posted on 27/10/07 at 07:36 PM |
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Pump only operates when you open throttle, so unlikely to be a problem on the overrun. Popping on overrun is usualy a sign of a weak mixture (e.g.
air leak), or leak in the exhaust.
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02GF74
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| posted on 27/10/07 at 08:22 PM |
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yeah I hear you, so i need to revisit the nuts.
I altered the tension in the spring on the pump lever using washers to get it to the right (?) position so the increased tension my be affecting
throttle closing - that could explain the highish idle andthen slowing down but does not account for the back fire.
woried about over tightening the nuts...
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02GF74
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| posted on 28/10/07 at 02:28 PM |
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been thinking about this - so what is actually happening to cause the back fire?
On the overrun, throttles are closed off and high rpm means there has to be a big vacuum; an air leak between carb and manifold means air is coming in
to weaken the mmixture - this mixture is too weak to be ignited by the spark so unburnt guel reaches the very hot eaxhasut where it explodes?
Is that right or some other reasoon?
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Macbeast
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| posted on 28/10/07 at 03:54 PM |
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Just to confuse the issue 
Have you thought about ignition timing ? You might get these symptoms with sticky advance/retard mechanism ( f you have mechanical system )
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02GF74
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| posted on 29/10/07 at 08:50 AM |
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I did consider it for about 30 femto seconds. Why would ignition have changed all by itself?
It was running fine (well, about from the heistation under hard acceleration) and all I did was remove the carbs to fiddle with the accelerator pump
rod.
Everything fitted back like it was although some doubt if the carb nuts are done up tight so that there may be air getting past the o-rings,
can't see it myself but can't work out what else it can be.
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