Partzilla had Br8s listed so I bought a bunch, but they send me BR8ES

my concern is that the "R" will weaken spark and therefore performance, do I need to make a fuss?

Did you mean B8ES vs BR8ES?

Anyway, not sure what bike this is but correct plug for DT360 is a B9ES.

Hi Mark,
Sorry for being unclear, day job getting in the way!
I thought - incorrectly - that the correct plug for DT360 was B8ES, which is what Partzilla shows. However, they shipped me BR8ES which is the resister version. So good to know that correct plug is B9ES, which is one level cooler so this is what I will use. But in general, is using a plug with the resistor reduce spark output? If you have a chance I would be grateful if you could take a peek at my "life after meltdown" posts about Kickstarter preload, etc.
Many thanks
Martin

Hey Mark, I never thought I would be questioning you but in the Tech section under Spark Plug Table it shows B8ES ??????

NGK has discontinued the B8ES and claims the BR8ES with the resistor is an acceptable replacement. I started a discussion on this on the Yamaha Vintage FB page and it didn't quite get as bad as an oil thread but there were differences of opinion.

I tried the BR8ES in my CT1 and my DT175 and did not notice any difference. I think there's some merit to installing a new resistor free spark plug cap which is available for a few dollars on Amazon or from NGK.

Here's something I posted a while back...

As a project in college, I built and tested a few ignition systems for a single cylinder two stroke.... it was cool to have the test equipment, including a dyno.

Until the spark jumps the gap, the resistor does nothing compared to the "resistance" of the air gap the spark needs to jump. Once the current start to flow, the resistor starts working and "slows down" the flow of electricity making the spark duration longer.... but the resistor does weaken the spark a little...

In a system designed for a certain resistor, removing it will slightly increase the spark energy BUT the spark duration is shorter which can cause misfires.

Adding too much resistance is probably worse... can weaken the spark energy too much and any extra spark duration gained is not helpful... this commonly happens when someone runs a resistor cap and a resistor plug because that's what the shop sold them. Misfires and more easily fouled plugs can be the result.

My advice is to stick to the resistance recommended by the engineers... usually 5k ohms for a Yamaha. OR run a non-resistor cap and a resistor plug. (Not both)

Cheaper option is to use the resistor cap and non-resistor plug... which is how most models came.

Yamaha says B9ES for DT360. B8ES is for DT250. Check the service and owner's manuals.

Hi Martin,

I've seen that thread and I really am not qualified to comment... it's been too many years. MDScott is who I would ask.

MarkT - the two resistors in series is a very interesting way of looking at things, thanks for sharing it. Is the stock spark plug cap on my DT360 equipped with a resistor? If so, then I may use the "R" plugs, but with a non-resistor cap....nobody can hear a radio when this bike is in the area anyhow so what's a little static, right?