Spark plugs

[Green1]

Who would have thought changing just the two outer plugs on the Guzzi would push my fuel economy up from 42mpg to 53+mpg
The old ones were only in there for 6000miles and looked perfectly fine to the naked eye
Just goes to show they don't just print it in the book for nothing 

[K2-K6]

Are they twin plug heads on that engine then?

[Green1]

Yep quit high tec for an old plodder.The inner plugs are platinum NGK PMR8B and the outter are ordinary copper NGK BPR6ES

[K2-K6]

I guess if they run it lean to get good economy then it could struggle to light up that mixture across a big bore like that. Interesting they run a different heat range from the main plug in the same chamber though. Suppose the bpr6es are effectively running over temp which could account for the shorter life expectancy.

I run those, BPR6ES in an old 3.9V8 rover and they do 24000 mls

[Green1]

I think it runs lean to get it through the emissions rather than economy interestingly if I thrash it I get 60mpg
The platinum plugs are inside the V so have to put up with a crazy amount of heat but interestingly you only change them every 12500miles

[MarkCR750]

Do you think changing just the 2 outer plugs on my CB would have the same effect Mick?

[Green1]

I shouldn't think changing just the two on the CB will have much of an affect.
But saying that I didn't think it would affect the Guzzi as much as it has.
Out of curiosity when does Honda say change them?

[MarkCR750]

I shouldn't think changing just the two on the CB will have much of an affect.
But saying that I didn't think it would affect the Guzzi as much as it has.
Out of curiosity when does Honda say change them?

Just to be clear Mick I wasn't being serious 😄, not sure what the service interval is on the CB, I get mine for about £3 each so change them about every 18 months which is way to often considering the mileage but they are cheap so why not.
PS how do you know your MPG has it got a computer?

[Bryanj]

The servicing schedule should be in the bike handbook including when to clean or change, Suzuki used to say swop the plugs on the same coil over to even out spark wear

[K2-K6]

Manual for the 750 says inspect at 3100mls and replace 7200mls.

I thought you were being a bit tongue in cheek there mark.

You're probably right mick, that the secondary plugs on the Guzzi are to clean up the emissions, and probably at low rpm.

The V8 I run is most economical right on the torque peak at 2900rpm (I guess it's the efficient burn that gives max torque)  I thought that wind resistance at 85mph would out weigh any engine efficiency but the fuel range is just more at that speed. Similar cylinder capacity to the Guzzi as well at near on 500cc per pot.

[Green1]

Good to know you wasn't serious.I must admit I wasn't to sure as people do ask strange things at times.
Yes there is a computer on the Guzzi I did calculate fuel costs when I first got the bike and it seems accurate.

[Erling]

About changing the outer plugs of a CB750.
When mine was new I ran 9er plugs in cyl. 2 and 3 to 8 in 1 and 4!
Just to get same colour on them.
We had no speed limits here in Danmark the first 4 years on the 750.
Was used to check plug colours from my mini cooper with 2 SU carburettors.
They are extreme easy to adjust.
Erling.

[MarkCR750]

Good to know you wasn't serious.I must admit I wasn't to sure as people do ask strange things at times.
Yes there is a computer on the Guzzi I did calculate fuel costs when I first got the bike and it seems accurate.

Ha, yes but thanks for having the good manners for giving it the benefit of the doubt in your reply, today I did the top up, record mileage, top up again, note amount of fuel used, work consumption out thing on the Ducati, 53 mpg!, amazing same as your Guzzi, must be an Italian thing.

[Green1]

The good MPG is so you can save your pennies for bus fair when spare parts are on order.
Dam now I'm doing it 
I think its starting to get to me as I have had Aprilia parts on order for almost 4 months 

[MarkCR750]

Ha, knocking Italian bikes gives people a lot of pleasure so that's fine with me, goes with the territory, at one of my regular biking coffee stops I had 3 "fellow" bikers have a good natured go on Saturday, I let them have their fun then asked if they'd ever owned one?"no" ever ridden one? "no", then a motorist walked past pointed at my bike and said "that's stunning mate", nuff said 😄