Hitchcocks Forum

Having just fitted the Amal carb and exhaust upgrade for my Electra 05 i was wondering if it requires a different spark plug, the bike was fitted when i bought it with a NGK BR8ES running on standard carb and exhaust, this plug now runs sooty on new setup, i had a NGK8ES to hand and this ran a lot cleaner , the plug cap looks like one of the hosts metal ones with resistor

I would say your new carb needs tuning. Fitting an Amal is not, IMO an upgrade, there's nothing wrong with the Mikarb.

Hi Peter, slight error in post, the original plug that is now sooty on the Amal is a BR8ES, the plug that is running cleaner is a B9ES, the original carb is the CV not the Mikarb, thanks, Jez

Of course, Electra = CV carb. (note to self - engage brain)
Anyway, still a better carb IMO than an Amal (except to look at)

Reason i changed the carb is i wanted to get rid of the restricted performance of the exhaust/air filter system which meany changing the carb as it ran very lean when i tried it with the CV, which isn't tunable other than changing the main jet?

The BR8ES is the correct plug for the unrestricted set-up. If you have removed air box, plugged PAV etc, put on the 32mm Amal and an open pipe with small baffle, it should be right. Remove the air filter and replace with bellmouth (they come with gauze now) as that aids breathing further. Ensure needle is in middle notch. Keep small baffle in exhaust or you will be touching on megaphonitis - ie not enough back pressure when opening throttle, leading to slight lag in response and probably too loud. The baffle prevents too much popping. Read the AMal Mk1 concentric notes to ensure the fine tuning is as per instructions, but be prepared to tweak as you adjust it to start and tickover at lights when hot. I had a sooty plug and all above was correct - the spring in the carb was sticking and the choke was being kept on - it still ran perfectly but it was rich. Once sorted all was good and the colour of the plug is bang on. It was a pal that had rerouted the throttle cable and made the easy mistake when doing the reassembly of carb top end.

A resistor plug and a resistor plug cap is not a good idea, which is why it ran better on a BP8ES. Bin the BR8 or keep it for something else. Also be aware of the huge number of snide NGK plugs for sale and use a reliable dealer. Incidentally, I changed the NGK for a Champion in my bike 3 years ago and have not looked at it since.

I did suspect that it ran better with the non resistor plug as it would have a better spark as there is already a resistor in the cap, one thing i noticed before i put the air filter on and checked the movement of the needle/slide was that as i opened the throttle the needle as it came up didn't come up centrally but tilted slightly as if rubbing on one side of the needle jet, it ran fine but thought maybe the throttle spring maybe not sat central on top of the throttle valve/needle clip?

Just tried starting bike and checking tickover with 3 different plugs, BR9ES, BR8ES and a B9ES.
The bike started easier and ticked over far better with the B9ES, i think having a resistor in both cap and plug is suppressing the spark?

You should not have both a resistor cap and a resistor plug. Also, good starting and tickover doesn't indicate the correct grade of plug, only that the plug itself is not fouled.