Forum

[Presto]

An iridium plug will only foul on a slow revving engine if it is of the wrong heat range. The fact that it is an iridium plug will not make it foul more easily, in fact it will have the opposite effect – provided it is the correct heat range.



The main advantage of an iridium plug is that its smaller electrodes require less current than a standard plug to operate effectively. This should – and often does – make starting easier.



Iridium spark plugs are resistor type plugs (‘R’ in the plug number denoting resistor). The resistor is a 5k ohm ceramic element, used to suppress ignition ‘noise’. Resistor plugs reduce electromagnetic interference and are recommended for use with on-board electronics – e.g. electronic ignition systems. The use of a non-resistor plug can, in certain applications, produce an erratic idle, high-rpm misfire, engine run-on, power drop-off at certain rpm levels and abnormal combustion.



The use of resistor type caps with resistor type plugs is not recommended. The combination of two resistors (one integral to the plug and one in the plug-cap) may reduce spark efficiency, especially in older systems, and thus significantly affect fuel efficiency. It is claimed that the combination of two resistors may reduce fuel efficiency by as much as 10%. However, the use of a resistor cap with a resistor plug on engines that use electronic engine control may not lead to these problems, as the plug cap may reduce unwanted electronic noise that could interfere with electronically regulated engines.

[albert]

Have gone with John L and got the ngk BP6ES as the cap is ngk resistor type but still wonder why the continental 535 has the bosch wqr8dc resistor plug plus ngk resistor cap fitted as standard seems against the one only resistor rule.Any comments ??

[zonggong]

There is a small difference between the BR6ES and the BPR6Es and that is with the version with the P the electrode projects past the base of the plug by a few mm. When I was looking around for a replacement plug for my 2015 B5 I was hesitant to use this but fun that it worked OK (and wasn't hit by the piston) I've tried the iridium plugs (they all have the small projection) as well and the standard BR6ES and have settled on this as it seems to work OK. I am also using the NGK cap with the built in 5Kohm resistor. I recall reading somewhere that both the plug and cap resistances are required in REs with electronic engine management to reduce interference.

[Leon Novello]

Bear in mind that there are also resistor high- tension leads, so it is possible to have THREE resistors. Check your leads.

[albert]

Leon thanks for that one, just been out and checked and no markings on the cable so seems a standard cable with no resistence ,but I suppose RE has still a reason for doubling up with a resistor marked plug and resistor cap which is normally not recommended ??

[Rattlebattle]

Zonggong, the issue here is whether to use the BPR6ES or the BP6ES. In either case the plug should be the projection type i.e. have a P in the reference. As for iridium plugs, I found that mine clogged up. It was the grade specified by our host i.e. Heat range 6. I have a feeling that for some of these UCE bikes a grade 5 might be a better bet if the standard plugs foul more often than normal. I have a BPR5ES to try when the weather improves. Whatever, I don't believe the additional cost of an iridium plug is warranted in these engines.

[zonggong]

On my 2015 B5, which I believe is running rich, I have run a BR5ES, which seemed to work well with a nice clean electrode, compared to the sooty one I had with the OEM 'Bosch' plug. I have changed back to the BR6ES during the hotter season here in Australia. Perhaps there is no established reason for this, but I once torched a piston in GT Cortina and I am a bit wary.

[Rattlebattle]

I know what you mean. Years ago I had a Suzuki Hustler. In the handbook it specified 2 grades of plug according to town or thrashing use. I was racing a Triumph Spitfire one day when the engine felt like it was running out of fuel. Back home I found a neat little hole in one piston crown - I'd forgotten I'd got the town plugs in. I may well try the 5 grade; mine ran rich with the EFI on. It's better with the carb but I still think it's worth a try, bearing in mind neither the 5 or 6 NGK is directly equivalent to the Bosch clone. In similar vein I'm considering using 10/40 weight engine oil of the same spec as Motul. Having left the bike unused for a few weeks when I came to kick it over (ignition off) and free the clutch I took ages to do the latter. The supplying dealer put 10/40 in it anyway. Mine runs very cool and as the temperature doesn't get too high here I think it might be better on 10/40. It is the only bike I've owned for which only one oil weight is specified irrespective of ambient temperature. Strange.

[Scalyback]

Kevin runs on Lodge HLN, no resistors. Runs a bloody treat!



Tornado, my bullet had one of those 8IEX whatever plugs and also runs a treat.

[Presto]

In the light of battlerattle's choice to switch from one grade of oil to another, I'd be interested to know what is the difference in viscosity at a 'moderate' ambient UK temperature (say 8-15 c) between a 10/40 and a 15/50 multigrade - maybe zonggong can help?