Resistor plug cap with resistor spark plugs????

[magpienja]

Hi hope you guys dont mind me using your forum but here goes, I am the owner of a microlight with a rotax 503 twin spark plug engine, of late its been loosing about 500rpm on full power after about 2mins of running at max power, checking the engine over today I noticed it has resistor spark plugs and also its fitted with resistor spark plug caps 5K ohm, could any of you guys advise if this is correct, I would have thought one or the other should have resistors in the them, me thinking it may weaken the spark them both being the resistor type, I should add I have only owned this aircraft a few months.

Regards Nick.

[Fargoo]

If you're using NGK's for example
NGK BR 8ES are resistor plugs - no cap needed.
NGK BP 8ES are longer electrodes for inverted positions to prevent fouling.
NGK B 8ES - standard plug no resistor

If you have resistor plugs you shouldn't have a cap - double resistance/weaker spark.

Could just be a mix up last time the plugs were changed (part numbers similar) or there could be a genuine reason for this set up. I'd suggest getting in touch with whoever serviced it last and find out.

Fargoo.

[magpienja]

Many thanks fargoo I will get myself a set of B8ES which are in the engine handbook along with BR8ES.

Regards Nick.