Hitchcocks Forum

Bullet 350 with Amal concenric mark 1. I have just re-jetted the carb from a 180 main jet to a 200 to richen things up a bit. I also replaced the standard B7HS plug with the iridium B7HIX to see what difference it might make to starting.

Whilst the B7HS was a nice "coffee" colour after a run out, the iridium plug appeared almost exactly the same colour after a run out, as it did when I first fitted it! i.e. the white inner is still white.

Any chance it might still be running lean, or do iridium plugs tend to run "hotter" anyway?
Any comments appreciated. As usual, I'm concerned about valve burn-out if it's running too lean.

I replaced the standard plug with it's Iridium equivalent on my Electra X. The old plug was burning a nice coffee colour all over but the Iridium version, for some reason, has a coffee colour central insulator but a whiteish outer electrode, so the mixture evidence is a bit conflicting. If you have changed jet sizes it may be worth changing the plug back to the original and see how that burns and take that as your reference.

I find Iridium plugs don't show colour well.

Thanks for your replies, Frank & Pete!
As per your suggestion, I replaced the iridium plug with the standard version and sure enough, the standard plug is looking normal (??) ie a nice coffee colour.


Can I assume then, that the mix is about right and I can re-fit the iridium plug?

Yep, sounds right to me.

Hi TIM}-------- going back to your original question>>>>>> Did it make any difference to the starting ??

Tim, why on earth have you wasted your money fitting an Iridium plug? They are of little or no value to an engine and simply not worth the cost.

Mike , Alan - To answer both your questions, I would say I've had a slight improvement in starting.
Have I wasted my money??? I suppose its a bit subjective at this stage, because I haven't had chance to check if there's been an impovement or indeed a worsening in fuel consumption etc.

Without wishing to sound blunt, the bike's my hobby and I'm not going to lose any sleep over spending £9.00 on a spark plug!! I suppose one thing we can all agree on, is that the appeal of our chosen marque is partly due to the fact we can do minor mods/enhancements etc., without having to re-mortgage our homes! Thanks again for your input.

Since changing the plug to an Iridium version my bike certainly starts immediately ,idles better, runs smoother and returns 100mpg on a good run. At the same time I also changed the oil and filter, replaced the air filter element, adjusted the valves, replaced the chain and altered the gearing. I'm sure though that at 3-4 times the price of a normal plug it must be that that's made all the difference!!

I found that when I fitted an iridium plug the idling speed increased noticeably and had to be reset. Of course it is quite possible that the old plug I replaced was knackered anyway and therefore any type of new plug would have had the same effect so this really proves nothing!

I figure that only having one cylinder to rely upon it is best to use the best ignition components that I can - although I have to be honest and say that I might think differently if I had to fund iridium plugs for 4 or 6 cylinders!