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Post by paulpg36 on Aug 9, 2021 20:39:53 GMT
My engine had been running fine but I noticed that one barrel was far cooler than the other. The exhaust pipe on the cooler side was not as hot as the other but gasses where coming out of both exhausts and felt about the same.
Maybe rather rashly, I decided to pull the HT lead off the spark plug to see what would happen. The engine stopped and when I replaced the lead I couldn't restart it despite numerous attempts. The engine turns over fine and I get a good spark on both sides and fuel is coming through the carbs.
Could I have damaged something by pulling off the lead? Any ideas on why it won't start and why one cylinder is less hot than the other?
Paul
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Post by Dennismenace on Aug 10, 2021 18:02:21 GMT
The plug caps can be replaced but the HT lead is fixed into the coil. I would unscrew the plug cap and cut off small amount of the HT cable, say about 10mm, and re-attach the cap. If you are brave(!) you could put the HT lead, without a cap, next to the cylinder head and see if you can see a spark when you turn the engine over. That way, you can see if the HT lead is OK. If the lead is good but you get no spark with the cap back on replace the cap. I am a whimp and have had too many shocks from HT leads so I use rubber gloves or insulated pliers to hold the HT lead - Sam Lovegrove just uses his fingers! Must be the camomile tea.
Dennis
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Post by paulpg36 on Aug 11, 2021 6:42:49 GMT
The plug caps can be replaced but the HT lead is fixed into the coil. I would unscrew the plug cap and cut off small amount of the HT cable, say about 10mm, and re-attach the cap. If you are brave(!) you could put the HT lead, without a cap, next to the cylinder head and see if you can see a spark when you turn the engine over. That way, you can see if the HT lead is OK. If the lead is good but you get no spark with the cap back on replace the cap. I am a whimp and have had too many shocks from HT leads so I use rubber gloves or insulated pliers to hold the HT lead - Sam Lovegrove just uses his fingers! Must be the camomile tea. Dennis Thanks, Dennis. I am getting a spark from each plug although don't have a clue if it is a good one. Never tried what you describe and I think I would be in your camp! I suppose it must be a coincidence that it won't start after what I did and need to look at other factors. I was just worried in case I had damaged something although logically can't see how I could have especially as I am still getting sparks from each plug. Paul |
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Post by Dennismenace on Aug 12, 2021 13:53:38 GMT
Yes if there are sparks at both plugs it should be good to go. Are the plugs wet after turning over the engine with the ignition off? If not it could be a fuel issue. I had a bad coil that gave sparks with the plugs out but did not work under load i.e. with the plugs back in the engine. Might be worth swapping the coil if you have a spare or can borrow one. There are also reports on this forum about fake NGK plugs that work badly if at all.
Dennis
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Post by paulpg36 on Aug 12, 2021 19:51:08 GMT
Thanks, Dennis.
Got it going and I think the main problem was lack of fuel although after opening the drain screws on the carbs, petrol came out of the overflow tubes but maybe just not enough fuel in the tank even on reserve! However, one barrel is far hotter than the other although gasses from the exhausts feel about the same. Any ideas why 1 side is far hotter than the other? Paul.
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Post by Dennismenace on Aug 13, 2021 18:29:11 GMT
I don't know why one barrel is hotter than the other but my guess would be that the carbs are not balanced.
I bought a cheap set of vacuum gauges for about £30 off ebay and they were good enough to show when the carbs were both pulling the same vacuum. Alternatively, you could get the carbs balanced at a local garage. It should not be too expensive for what is a quick procedure. I have several bikes and the gauges have come in useful over the years. Don't worry about the absolute value of the vacuum just make sure it is the same across both carbs by adjusting the mixture screw on each carb. Balancing the carbs improved the performance of my NC400 measurably.
Dennis
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willy3pigs
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Post by willy3pigs on Aug 13, 2021 19:23:28 GMT
Thanks, Dennis. Got it going and I think the main problem was lack of fuel although after opening the drain screws on the carbs, petrol came out of the overflow tubes but maybe just not enough fuel in the tank even on reserve! However, one barrel is far hotter than the other although gasses from the exhausts feel about the same. Any ideas why 1 side is far hotter than the other? Paul. An air leak at the manifold can cause one side to run hotter, I've had that problem in the past.. |
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Post by Dennismenace on Aug 15, 2021 18:33:17 GMT
Good point and the manifold rubbers go brittle and perish and crack with age.
I have heard that you can check for leaks by spraying WD40 around the manifold and listening for an increase in engine revs though I have not tried it myself.
Dennis
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willy3pigs
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Post by willy3pigs on Aug 15, 2021 20:04:46 GMT
I use flammable carb cleaner for checking for that..
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