Trident spark plugs

[daveforty]

I recently changed the spark plugs on my Trident, as part of routine servicing. The dealer supplied NGK DPR8-EA plugs, the same as was already in the engine. 500m after servicing it began running badly - misfiring under load, bad pick up off idle etc. I had a look around various things and noticed that the Riders Handbook supplied with the bike specifies DPR9-EA plugs, so I bought three of those, installed them and the engine is now running nicely. (Also had a go at the HT coils connections etc). I subsequently noticed that the factory workshop manual specifies DPR8-EA plugs. The bike has done lots of miles on the DPR8-EA plugs, so I am sure they are perfectly suitable, and maybe one of the new ones I fitted was a dud. But why the inconsistency between the two factory publications, and what is the practical difference between the two grades of spark plug?

[Lone-Rider]

Dave: I think you just got a dud ! The number denotes the heat range. One number is not going to make it run badly except in extreme conditions. While it is good to use the proper heat range plug, I have many times run one heat range hot or cold because that was all I could get at the time. I've done this in all kinds of engines with no noticable problems. Just not the best way if you have the right ones to put in.

The reason for the inconsistency is that they changed the spec. I don't remember what year they changed it or whether it went from 8 to 9 or vice-versa, but they did change it.

As for starting to run poorly 500 miles later, my bet is that it was coil-related & not actually a direct result of the plug swap.

Cheers,
-Kit

[Lone-Rider]

If the problem returns, I'll agree with Kit. I guess some guys have had problems with these coils. For some reason, I haven't.

Go figure. Seems like one of my coils goes on vacation every time we get real soaker of a storm, but you never see a problem in the desert? :razz:

Seriously, water & corrosion seem to cause the coil problems. I'm still using the coils that came with my bike; they seem to start working again once the dry out &/or heat up.

Cheers,
-Kit

[daveforty]

Thanks for the replies.

I did wonder about coil grief, having read through the coil discussions on this forum, and the Trophy forum. ISTR there are two manufacturers coils used and that the PVL coils, which I have on my bike, are the better coils.

I am a little suspicious of the HT cables though, they look like the conductive plastic strand type (rather than old fashioned copper cores), so I might invest in a new set - they are detachable from the HT coil. Over the years I have had to replace this type of HT lead on various cars 'cos they have caused poor running.

The Riders Handbook supplied with the ('96) bike is dated 1995 and specifies the DPR9, my factory manual is dated 1999 and specifies the DPR8 - so as Kit suggests, the specification was changed from the -9 to the -8, and it was between 1995 and 1999. I would be interested to know why.

It is currently running nicely, so I'll do some more miles on the -9 plugs and then remove one to check it's colour. I think that most likely one of the new -8 plugs I fitted is dodgy.

[Lone-Rider]

I'm running 8's in mine this year with a rather "fat" mixture with no problems. Kit does touch on something though. Living in a desert, I am shielded for some of these problems. Our typical humidity is 35% in the winter and 20% sometimes less in the summer. Keeps everything nice and dry.

[zippythehog]

Hi All,
I was wondering, do you all still have the bit of foam rubber that goes around the throttle, choke cables, and plug leads? It sits on top of the camcover beneath the fuel tank. I was thinking that this might prevent water from getting to the coils.

Zip

Zip: I do have those rubber pieces of which you speak, but they're a bit distorted from heat/age. Replacing them might not be a bad idea; I guess I'll add it to the list of stuff to do when the weather warms up. (Of course, that list already has front brakes, rotors, MC, fender, tank, petcock, locks, left peg hangers, exhaust... Maybe I should just build a second bike...)

Cheers,
-Kit

[daveforty]

This has just appeared on the BBC News website, and may explain my problem. I had filled my bike at the local Tesco not long before the bad running started, and dodgy fuel was one thing I wondered about - but it just seemed too far fetched. After 100m of bad running I filled it with Esso Super Unleaded (99 Octane) which improved the running a little but didnt clear it. Maybe I just needed another tankful to flush it through and the whole spark plug thing has been in vain. UK riders beware!!!!

BBC News