Looking at this it sounds
1. like and Air leak on the intake
2. a plug cap or two gone high resistance
3. Fake NGK Spark plugs
For the air leak, check the Vacuum take off caps, the intake manifolds are seated correctly and the rubbers from the air filter are seated correctly
Thankfully the plug cap can be dismantled, they can corrode internally and the 10kohm resistor which is a carbon resistor can go high resistance. Unscrew the the plug holder in the cap and you should have the screw section the resistor and a spring. The Base the spring sits on inside the cap needs to be cleaned, I usually clean it with a long very thin sharpened screwdriver as this is the easiest option. The spring may also be corroded and needs cleaning with wire wool or something. Finally I replace the resistors with those from faulty NGK plug caps as these are wire wound and stainless ends. Thses are only 5kohm but it is not a proble as they are only to prevent interference Yes NGK plugs also suffer from internal tarnishing which can send the resistance in the high megohm range and screw up the spark. I have come across plenty of them, the latest was last Saturday on a 2002 Triumph Bonneville 800, broke it open in front of the owner to prove it. At least the NGK caps are a lot cheaper than OEM even if you need to break open a new one for the resistor. when finished cleanin off all the corrosion put them back together.
Fake NGK plugs can be difficult to detect but close inspection will show poor printing, engraving and sealing washers. Only way to avoid them is to buy from a reputable source. Very risky buying ones at knock down prices
1. like and Air leak on the intake
2. a plug cap or two gone high resistance
3. Fake NGK Spark plugs
For the air leak, check the Vacuum take off caps, the intake manifolds are seated correctly and the rubbers from the air filter are seated correctly
Thankfully the plug cap can be dismantled, they can corrode internally and the 10kohm resistor which is a carbon resistor can go high resistance. Unscrew the the plug holder in the cap and you should have the screw section the resistor and a spring. The Base the spring sits on inside the cap needs to be cleaned, I usually clean it with a long very thin sharpened screwdriver as this is the easiest option. The spring may also be corroded and needs cleaning with wire wool or something. Finally I replace the resistors with those from faulty NGK plug caps as these are wire wound and stainless ends. Thses are only 5kohm but it is not a proble as they are only to prevent interference Yes NGK plugs also suffer from internal tarnishing which can send the resistance in the high megohm range and screw up the spark. I have come across plenty of them, the latest was last Saturday on a 2002 Triumph Bonneville 800, broke it open in front of the owner to prove it. At least the NGK caps are a lot cheaper than OEM even if you need to break open a new one for the resistor. when finished cleanin off all the corrosion put them back together.
Fake NGK plugs can be difficult to detect but close inspection will show poor printing, engraving and sealing washers. Only way to avoid them is to buy from a reputable source. Very risky buying ones at knock down prices