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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Nip up Comet
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<blockquote data-quote="Martyn Goodwin" data-source="post: 111968" data-attributes="member: 2433"><p>two thoughts based on my own hard learned experience.</p><p></p><p>Valve guides: "the last owner who informed me he had indeed fitted the new valve and guide but had not investigated further " I would be checking to see of once fitted that the upper and lower valve guides were line reamed to ensure alignment, if they are NOT in line the valve stem at best will wear excessively on one side allowing oil to run into the combustion chamber - or worse, the stress will eventually cause the valve stem to break, the valve head falls and Bingo massive repairs!</p><p></p><p>Mixture: Nipping up is caused by overheating and as our air cooled motors rely to a reasonable extent on the cool fuel being sucked into the motor to assist with cooling (strange but true) and if the mixture is lean then nip up is possible. Check the spark plug - the outer edges of it should be sooty black and the centre electrode, near its tip should be a tan colour. If the centre electrode is white you have a lean problem that needs to be resolved- in this case you should RAISE the needle in the carb by one notch (lets more fuel in) - if the clip is already in the bottom notch , then you need to increase the size of the needle jet by 2 steps ie if you have a 106 installed, go to a 108. </p><p></p><p>You should also check the fuel level in the float bowl for that will also impact on lean running - instructions are in last months OVR.</p><p></p><p>Phil Irving is reputed to have said more damage is done by heavy oil than light. I use 20W-40 multi in my comet.</p></blockquote><p></p>
[QUOTE="Martyn Goodwin, post: 111968, member: 2433"] two thoughts based on my own hard learned experience. Valve guides: "the last owner who informed me he had indeed fitted the new valve and guide but had not investigated further " I would be checking to see of once fitted that the upper and lower valve guides were line reamed to ensure alignment, if they are NOT in line the valve stem at best will wear excessively on one side allowing oil to run into the combustion chamber - or worse, the stress will eventually cause the valve stem to break, the valve head falls and Bingo massive repairs! Mixture: Nipping up is caused by overheating and as our air cooled motors rely to a reasonable extent on the cool fuel being sucked into the motor to assist with cooling (strange but true) and if the mixture is lean then nip up is possible. Check the spark plug - the outer edges of it should be sooty black and the centre electrode, near its tip should be a tan colour. If the centre electrode is white you have a lean problem that needs to be resolved- in this case you should RAISE the needle in the carb by one notch (lets more fuel in) - if the clip is already in the bottom notch , then you need to increase the size of the needle jet by 2 steps ie if you have a 106 installed, go to a 108. You should also check the fuel level in the float bowl for that will also impact on lean running - instructions are in last months OVR. Phil Irving is reputed to have said more damage is done by heavy oil than light. I use 20W-40 multi in my comet. [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
Nip up Comet
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