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Hi all iv just replaced the battery as the old one was dead I did have the battery of for 3 weeks and bike was left for 5-7 months.
so fit the new battery and the bike cranked for a while the splutters in to life only for a short time the it sounded as if one of the cylinders had stopped firing the engine light came on and the bike cut out. So I checked the Leeds all look okay with a spare spark plug put that in the leads to check for spark the rear cylinder doesn’t seem to spark when it should if at all I did get some codes as I have a dino jet television which I’ll post up later
 

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"Loose Nut" from Houston, Texas
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A battery sitting for months hooked up will drain a battery to a point of not having enough voltage to start the bike. I would suggest to have battery load tested.
 

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2016 Harley-Davidson Street 750 in Sunglo Velocity Red
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I'm not sure that I'm reading the first paragraph correctly. Sounds like @750Warren got a new battery towards the end of the 2020 riding season, rode with it for 3 weeks, and then put the bike in winter storage for 5-7 months. This spring the bike starts, runs rough, and dies. It sounds like he pulled each of the spark plug wires and put them onto a spare plug to check for functionality, so the coil appears to be good.

@750Warren did get some diagnostic codes which he said he will post later. That should tell us which cylinder is having the problem and halve the diagnostic work to be done.

I think I would start by making certain the battery is fully charged and the gas in the tank is good.

If it isn't firing on one cylinder I would guess that it's either a plugged fuel injector or fouled spark plug. I would diagnose as follows:
  1. Pull each spark plug and check its condition. Posting a picture here would be good as well as searching for an online chart to diagnose engine problems by spark plug condition.
  2. Repeat the test that you did with the spare plug to make sure the actual plugs are undamaged and are sparking.
  3. Clean each plug and check the gap while each plug is out.
  4. While the plugs are out, put a thumb over the spark plug hole and crank the motor. If air pressure is more than you can your thumb can hold back that cylinder should have plenty of compression for the engine to work.
 
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