Vintage Dirt Bike Q & A

2 part question

1. can i run a BR8EG plug instead of the 9's the honda guy told me it would give a hotter spark. he said that you could move up or down one.. what are you using

2. what premix oil are you using.. i find i am fouling alot of plugs


i have a 76 cr125 and cr250

thanks guys

I'm running the same ignition as your CR125 in two of my bikes, and NGK BP7ES plugs work well in both of them. I was running BPR7EIX plugs before, but one bike wouldn't idle reliably with the resistor plug. Maybe you'd want to start with BP8ES plugs in your bikes.

The projected-nose ('P') plugs gave slightly better throttle response and low end in my bikes; I won't use anything else nowadays. If a resistor plug works for you, that's great, but in these old CDI's I was getting a faint yellow-looking spark. Inserting a 4,500 ohm resistor in the ignition path may give better radio reception and more reliable on-board computer operation, but it sure didn't improve performance in my bikes. Unfortunately, not too many non-resistor plug types are available today.

Here's some NGK plug code info:

B = Thread size 14 mm, P = projected nose, R = resistor, 7 = heat range, E = 19mm reach, S = copper core, I = Iridium, X = series gap, V = precious metal tip

I haven't fouled a plug since I stopped using leaded race gas, for what that's worth. I've used Bel-Ray oil since the early 70's, and today I use H1R ay 36:1. There are plenty of other good oils out there, though.

Ray

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'74 CR125M (175cc), '75 MR175, '82 RM250Z, '08 YZ250F, '14 Zero FX electric, '14 Zero MX electric, '18 Alta MXR electric

if your bikes didn´t run well with 9´s plugs something is wrong.
check your carb, airfilter or other things.

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80 CR250Ra
80 CR250Ra
78 CR250R
80 CR80
82 Bultaco Sherpa 340
78 Bultaco Pursang 250 MK12
76 Bultaco Frontera 370 MK10
76 Bultaco Alpina 250
73 Bultaco Lobito 125 MK6
76 Suzuki RM125A
90 Kawasaki KX250

32:1 mix is good for all these bikes. I run mine 28:1 summer and 32:1 winter.

An 8 plug is acceptable, but if you are fouling 9s then you do have a problem. A lot of times, the needle jet and jet needles get worn on these old Keihin carbs. All the jetting in the world won't fix it and good luck finding the right replacement parts.

So, if your jetting is right, your air filter is clean, your carb is clean and you're still experiencing fouling, I'd look at one of two things: leaking right hand crank seal or finding a new jet needle and needle jet for your carb (or give up like a lot of us and just buy a 36 mm Mikuni carb). If you aren't losing transmission oil, it probably isn't a crank seal, but the loss can be so minimal you might not notice. A leak-down test will check the integrity of the seals.