Spark Plugs

[cus]

G'day All,
I'm sure this topic has surfaced many times, I've recently fitted a new 389 carby
& bike is now running a tad rich. I was previously running a fairly worn out 276
with B7ES plugs, & they were keeping a good colour. When I first fitted the 389
I had the 420 main, it wouldn't run on the 7's so I fitted B6ES, seems to run fine
but plugs are now black again, (using 98% oct. fuel). So I knocked the main down
to a 250  a bit of an improvement, (also needle on 1 ).
Was thinking about fitting irridiums BR6EIX, has any one tried these, they seem
a bit hard to get, will have to order them, thought I'd just check what you guys
were using etc.

regards, Cus

[Triton Thrasher]

I hope you meant the richness was at full throttle.  Otherwise the main jet is not the thing to change.

420 to 250 is a very big drop.

[cus]

Yeah, I realise the main jet controls flow at 3/4 to full,
I've been checking after cutting eng. before idle. In the
specs for a '61 S/R with 389, it has 2 listings for main jet,
one at 420 & one at 290, I had a 250 sitting there so
thought I'd give that a shot.

Cus

[tombeau]

Have a look at Hitchcock's pages on monoblocs- very good:

http://www.hitchcocksmotorcycles.com/amal/mono_ht_7.html

Carburetion :frustrating, time consuming and expensive to get right...anyone want to buy a no3 slide? brand new, only done 5 miles

[cus]

After a fair bit of tuning, I've finally soughted it for now, ended up with 380 main & wound out the pilot/air a bit,
still running the B6ES's, bike has nice tick over & plugs after a good run are a good colour, thanks for the feedback.

Cus