Down-jetting for fuel economy

[scarfacehugo]

[QUOTE=Lord Stig;406600]... I get over 60 mpg on 15/46 final reduction, and even with the differing jets and TPS of the later RD07a I wouldn't have thought there would be a difference that great.[QUOTE]

And yours is a RD07A...?

[trophydave]

[QUOTE=scarfacehugo;406727And yours is a RD07A...?[/QUOTE]

Mine is.I have only had it a couple of weeks,the first tankful gave 48mpg.It's on 16/45 gearing and is fitted with a Remus can with a baffle in it.
I would hope for a bit more on a long run.

[Lord Stig]

It is indeed - 2001 in fact, with almost 95,000 mile on it. Even with that the thing is blisteringly quick up to the red line (shame that's a shade over 100, but at least I can reach it even against a heavy Scottish headwind, which the standard gearing would struggle to do, let alone raised gearing). Obviously "blisteringly" is relative...

I've been hareing around the last week (again relative - no faster that 90 mph) but today I filled to the brim with 16 litres and did 198. That's still approximately 55 mpg. Some others on the thread I started (see here) are doing far better with higher gearing (up to 70 mpg if I recall). Something is wrong with yours, but what?

[antti]

About down jetting,

I did check my plugs and they indicate that my bike is running rich, jetting is original 118/120. So I ordered smaller mains, pair of 115`s and pair of 112,5`s.

I think that someone has told that his Twin is going fine with even 107 mains, is that only BS?

I started to think that is it even worth for to try those 112,5`s??
Maybe I`ll try 112,5 front and 115 rear.

[jasonbc]

I dont know how far down you plan on going in Africa, and if you've been there before then I'm sure you know all this, but once you get South of Western Sahara, into Mauritania and on into Mali, Senegal etc, bear in mind you will be running on crap low octane fuel.

I've been down there a few times on different bikes and have always used the standard setup without problems, but last year one of our group on a Yam had added an aftermarket can, and also dynojet filter and re-jetted to suit. It ran fine until we reached Mauritania but from the first fill up would not run for more than 30 seconds on the low octane fuel available. Once it was back in Western Sahara (or Moroccan Sahara as the Moroccans call it) on 93 octane or above it was fine again.

The lowest I know I've used in an AT was 85 octane and it ran fine on stock exhaust, filter and jetting.

Did you do the trip with louise Hillier and gary Prisk??

[antti]

About down jetting,

I did check my plugs and they indicate that my bike is running rich, jetting is original 118/120. So I ordered smaller mains, pair of 115`s and pair of 112,5`s.

I think that someone has told that his Twin is going fine with even 107 mains, is that only BS?

I started to think that is it even worth for to try those 112,5`s??
Maybe I`ll try 112,5 front and 115 rear.

I have now driven about 4500 km with 112,5 main in front and 115 rear.
I think it works generaly better and consumption dropped over half a litre for 100 km.

[antti]

Is it really an option to go even smaller mains?

I did check plug from front and it was dark, almost black.
Carbs are in balance, choke is defenetly working.
Airfilter has been taken care.
Plugs have been in use for about 4500 km.

It seems that bike goes to dyno next winter.