Yamaha TRX850 Enthusiasts Forum

My otherwise very reliable bike was misfiring under very wet conditions. It has been discussed on here before. So I expect the coils and/or the wiring to the plugs to be faulty.
But I am not that smart with ignition stuff. What do I do, replace the coils? Wiring? Both? Spray with vaseline?

Get some copper core lead and replace the leads. They unscrew from the coils and the plug caps.
Don't waste your time or money replacing with anything else. I used some extra silicone rubber hosing over the outside of the 7mm lead to help insulate the lead.

Just to make sure that I translated it correctly: with copper core lead you mean the wiring from the coil to the spark plug, right?
(I don't get why you call these lead instead of wiring or something like that )

cobbadiggabuddyblooo wrote:Get some copper core lead and replace the leads. They unscrew from the coils and the plug caps.
Don't waste your time or money replacing with anything else. I used some extra silicone rubber hosing over the outside of the 7mm lead to help insulate the lead.

I get what you mean, I have some coils with wiring - or leads - as a spare, but it's no use as they are exactly the same age.
I will go to a car parts shop.
Thanks for the advice, much appreciated.

Before you start ripping in to it, find out where the issue is. Take the bike for a run to get it warm and take a atomiser bottle of water with you, stop and spray water onto the coils one at a time and then ride, no change, spray water on the plug leads and keep going till you find the issue, once found replace/repair..water can creep around the engine/tank and wet the wiring under the seat.

Also get a can of "start ya bastard" or any of the ether based starter fluids, with the engine running spray a little around the intake rubbers, if no change then they are fine, then repeat around the airbox etc, water can cause strange issues in many places.

If you choose to replace the plug lead.....
Try a motorcycle shop that deals in old British bikes or classic European motorcycles.
Good chance they may have the solid copper or metal core plug leads.
Motor auto shops have modern hi resistance carbon type leads.
You can choose to remove the 10K resistor from the plug cap too and replace with a solid piece of metal. Look inside the plug cap and you will see how you can unscrew the brass retainer.
The 5K resistor in the spark plug stops any unwanted RF interfering with the ignition.
Have a look on your spare coil Robert...

Rod.s wrote:Before you start ripping in to it, find out where the issue is. Take the bike for a run to get it warm and take a atomiser bottle of water with you, stop and spray water onto the coils one at a time and then ride, no change, spray water on the plug leads and keep going till you find the issue, once found replace/repair..water can creep around the engine/tank and wet the wiring under the seat.

Also get a can of "start ya bastard" or any of the ether based starter fluids, with the engine running spray a little around the intake rubbers, if no change then they are fine, then repeat around the airbox etc, water can cause strange issues in many places.

Didn't know they had cans of it, I always just yell at my bike.
Thanks for the tips.

cobbadiggabuddyblooo wrote:If you choose to replace the plug lead.....
Try a motorcycle shop that deals in old British bikes or classic European motorcycles.
Good chance they may have the solid copper or metal core plug leads.
Motor auto shops have modern hi resistance carbon type leads.

Thanks, I will double check the type of lead I'm getting.

You can choose to remove the 10K resistor from the plug cap too and replace with a solid piece of metal. Look inside the plug cap and you will see how you can unscrew the brass retainer.
The 5K resistor in the spark plug stops any unwanted RF interfering with the ignition.
Have a look on your spare coil Robert...

This is the part I meant: have read about it on this forum but I don't fully understand the topic. So originally it is kinda double; resistors in spark plug itself and in the plug, where you only need one? Removing one of the resistors does no harm and gives a stronger spark?
If so, it's especially of interest for my track bike.

Found the Dyna coils you guys keep talking about, but whew - those are expensive.
The webshop also had just leads with plugs, also from Dyna. So I orderd those, a kit of four plugs with enough length of lead to do all my bikes.
But I don't really like the plug caps that came with it, so I used the original caps with the new lead.




Well, I've never taken a spark plug apart, but here we go. So the red thingy should be the resistor?



Looks like it is. Then I found these pieces of solid metal:



Now put everything together, old coils and plug caps, with new leads. The resistor and the spring were a bit dirty, so that also could explain the (sometimes) faulty behavior. Also put some instant gasket on the connection of the lead to the coil. Hope it helps. Now wait for some rain to try how things go.

It'll certainly help - I had a persistent misfire in the wet on a very wet trackday - I replaced the leads (/wires) with new copper core (zero resistance lead) and the misfire was instantly removed

The coils still give the same output to the plug but with the resistor removed it's a shorter duration but a bigger dump.
Bit like tipping a 2 litre bucket of water upside down and emptying the volume in 1 large dump compared to just tipping the 2 litre bucket to allow the water to pour out over a longer duration.
As mentioned the volitivity of poor quality fuel needs a slightly longer duration of spark to help initiate the burn so the resistor is there for reliability if the bike sold or ridden in countries where fuel quality can be suspect.

Thanks for clearing that up Cobba.

Very wet ride today and no misfire.

Glad to hear it sorted your problems Robert.
Changing leads seems to be something everyone should be thinking about putting on their to do list as most would be around 20 yrs old and this issue has been raised on the forum a few times now over the last couple of years with misfiring in the wet and rectified by changing leads.