Plug specification for '49 G80 with no compressio

Samuel · Post by **Samuel** » Fri Feb 17, 2006 11:11 am

I am trying to get the optimum plug for my current setup. I am now using NGK B6HS but would be interested in trying the Platinum or Iridium equivalents to improve starting.
I have a rebuilt Magneto, new standard size Hepolite piston, rings, exhaust valve and all bearings and no compression plate so engine likely to run a bit hotter than normal.
I am currently running with a concentric from a Triumph Trident (which works surprisingly well !) but intend to revert to the Amal '89 with an original style pancake air filter.

bjork · Post by **bjork** » Sun Feb 19, 2006 8:00 pm

The B6 grade is fine, I have used one in my G80 for ages and ages. When I first got the bike it went like stink. I later found that the compression plate had been removed and a similar amount skimmed off the head! This gave a slight piston/head interface argument.

Michael · Post by **Michael** » Mon Feb 27, 2006 7:53 am

I tried which sparking plug is the best.

I started with B6 like recommended, changed to B7 and now I use B8.
I removed the plug a lot of times to check the colour.
B6 was too "white", that means too hot, B8 is light brown, that´s fine.

I suggest to buy a range of plugs and test it by your own, because the carburator and engine setup is different from bike to bike.

The recommodation is always a compromise for all drivers. One should adapt the spark to the personal driving style (racing / cruising / country roads / city limit).

Best wishes Michael

TommoT · Post by **TommoT** » Mon Feb 27, 2006 11:20 am

Michael,
just beware that you don't cure a problem by introducing another. The B8 sounds like a very cold plug to use on a G80, maybe you you have a carburation problem, that you're now curing by using a cold plug? Most people I have asked use either the B6 or B7, but ofcourse there could be other factors dictating the use of a cold plug...

Merlin · Post by **Merlin** » Mon Feb 27, 2006 3:45 pm

Being a chemist could someone please explain the difference between a hot/cold plug

itma · Post by **itma** » Mon Feb 27, 2006 4:09 pm

you burn your hand on a hot one

Biscuit · Post by **Biscuit** » Mon Feb 27, 2006 4:39 pm

The difference revolves around the amount of insulator around the central electrode, and hence the gap between the body and the insulator. BUT I can never remember which is which!!

bjork · Post by **bjork** » Mon Feb 27, 2006 8:34 pm

'Cold' plugs are those that run cooler because they disipate heat into the cylinder head more quickly, hence they run at a lower temperature.
Hot plugs are those that transfer the heat less quickly, and so run at a higher temperature.
If you compare two plugs from opposite ends of the heat range, you will see that one has a lot more material surrounding the centre electrode. (Simplistic explanation-material differences play a part too)
With NGK, the lower numbers are hotter, with Champion it's the reverse. A hotter plug is often used in an engine that burns less cleanly, as it copes with all the unburnt rubbish knocking around the cylinder. Useful with oiled up two strokes. A cold plug lasts better and is safer in an engine that works hard. A hot plug in an engine that works hard starts to melt things. And make 'funny' noises. If you want to know more, take a look at the plug firms websites, there's loads of useful info, including why those Iridium plugs are so good.

Merlin · Post by **Merlin** » Mon Feb 27, 2006 9:17 pm

Thank you people I understand now
Regards
Stuart

Michael · Post by **Michael** » Mon Mar 06, 2006 4:02 pm

@ TommoT

I know that my choice is unusual. I checked it by the coulour of the plug after a lot of tries.

Ok, I should have used a 276 Amal to be original, I found a brandnew monobloc carb for a price I was not able to say no. So I fixed it. Of couse I adapted the jets.

I checked the carb adjustment with my colour tune sparking plug.
Starting and idling is excellent.

After reboring the cylinder, use of new piston incl. rings I got a compression rate 8.5 : 1.

This was not the aim of the procedure but that is the fact now. So I checked everthing and realized that B 8 is the correct plug for my bike.

The hint I tried to give was checking and trying is better than stick to the rules.

Michael