Down-jetting for fuel economy

[magwa]

Thanks for all your replys, guys!

Yes, I have in mind that the petrol down there is quite poor, but I only wrote "Africa" to impress you guys , I'm just going to Morocco.

I would love if my bike did 50mpg and that's exactly my goal. It doesnt and I bet Magwa's bike is a RD07A with 115 main jets, right?

My bike is doing 39/40 mpg with a 16/42 final drive!! Do you get my point?

Thank you for your input and keep it comming!!

PS- Did anyone ever thought about or use octane booster in those conditions?
Hugo

Err No idea but its more to do with my riding style than the carb set up.
less revs more MPG

As for petrol in morocco i have a mate thats been there done that and petrol was avilible everywhere and they never had a problem

Morocco on Airheads - ::. UKGSer.com .:: take a look at this post of the GS site

Now they really went into the wilds
so don't worry about MPG just enjoy

[atgreg]

either slide or CV carbs still basically work the same, Ive spent a lot of time fine tuneing my jetting & I can tell you that for part throttle cruising the pilot jet makes more difference than the mainjet.

After lots of experimentation & dyno time Ive ended up with 1 size larger mains & 1 size smaller pilots & get better fuel economy than standard

Sorry to disagree with you on this one, mate.

When at cruise speeds the engine revs at medium rpm such as 4000 to 6000 in most cases and despite the fact that you are only using 1/4 of the throttle travel, the diaphragms are independent from the throttle will be open according to the engine need of air flow. Therefore, the mainjet will be letting most fuel into the engine.

I think you're mistaking CV carbs with flatslides where the needle moves according to your wrist.

right???

[scarfacehugo]

either slide or CV carbs still basically work the same, Ive spent a lot of time fine tuneing my jetting & I can tell you that for part throttle cruising the pilot jet makes more difference than the mainjet.

After lots of experimentation & dyno time Ive ended up with 1 size larger mains & 1 size smaller pilots & get better fuel economy than standard

huuumm... I see. I'm not going to argue with experience.
I'll try to get a dyno and see what I can do.
Thank's for that, mate!

[Chris.R.]

Hi atgreg, what setup do u have (K+N, open can, jets, position of needles, etc) as am interested in your chaning the pilot jet?

I have a RD07a ('93) with 117tkm, open can, 120/122 jets and also want to save petrol...

[atgreg]

oh boy, here we go, my bikes had many incarnations over the years, at the moment it's a lazer muffler, ceramic coated headers, ground out the weld that sticks into the headers, unifilter custom made dual stage filter + extra holes in the airbox, lightly cleaned up ports. In the past its had a standard muffler, modified standard muffler, 1mm OS high comp pistons, dynojet kit, K&N filter & various other stuff.

You can see more about my beast here
AT fork conversion finally started

My jetting at the moment is 1 size larger mains, 1 size smaller pilots & standard needles, cant remember the No's but I can find out if you like. the standard needles are not adjustable unless you put shims under them which means you can only go richer. Dynojet needles are adjustable but I hate em, they are very rough & wear out the emulsion tubes in the carbs quickly so the bike runs rich. To get my bike perfect I'd really like to go a tad leaner on the needles but with standard it's impossible, if i get really keen I may get some custom needles machined up. I could also go back to standard mains & it would make a bit more HP as its a tad rich on the mains but I like to play it a bit safe for full throttle.

Every bike is different as to what jetting it likes even with the same setup, each time my bike has changed Ive put it on the dyno & gas analyser to set up the jetting.

All carbs work the same, pilots give most effect to 1/4 throttle, needles 1/4 - 3/4 & mains 3/4 + but its not that simple as they all interplay at different stages.

Ive found that once the mains & needles are set up correctly going a bit leaner on the pilots helps part throttle cruising economy, Im talking 100-110kmh cruising as it's mostly small throttle openings, of course a higher cruising speed , headwind or being 2 up means your useing more throttle so not on the pilot as much.

I get 17km/l on a cruise, bog stock I used to get 15km/l. At high speed or in deep sand ive had it down to 9km/l.

well ive blthered on enough for now !!

Hi atgreg, what setup do u have (K+N, open can, jets, position of needles, etc) as am interested in your chaning the pilot jet?

I have a RD07a ('93) with 117tkm, open can, 120/122 jets and also want to save petrol...

[scarfacehugo]

Right, back on to the subject...

Had my bike Dyno'd today and it shows an amazing 48.8BHP at 7250rpm

With the stock 40 pilot jets, needles sligtlhy raised and 115 (changed from 118/120) main jets in both carbs, the graphic shows I can get one size down pilot jet and maybe lower the needle a bit, then go back and redyno it.

This is with stock can and air filter.

[atgreg]

excellent, it will be good to see the results

Right, back on to the subject...

Had my bike Dyno'd today and it shows an amazing 48.8BHP at 7250rpm

With the stock 40 pilot jets, needles sligtlhy raised and 115 (changed from 118/120) main jets in both carbs, the graphic shows I can get one size down pilot jet and maybe lower the needle a bit, then go back and redyno it.

This is with stock can and air filter.

[kennymact]

Just bought some sort of carb kit from e bay called 6 sigma engineering that says will improve the fuel consumption and power so will let you know whats in it and if it works.....

[scarfacehugo]

Does anyone know where I can get jet reamers and gauges?

I've been loking everywhere but I can only find them in the US.

[Lord Stig]

My bike is doing 39/40 mpg with a 16/42 final drive!! Do you get my point?

Hmm, that's bad, especially for higher gearing! You might have seen elsewhere that 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. Of course, I do have the chokes blanked off...

As the power looks poor it will be interesting to see how you get on with the mods.

I don't believe anyone can raise the gearing without there being a difference in the way the bike accelerates, no matter whether it's noticed or not. ATs just aren't that tourque-laden. I'm going back to the standard set up when I change my chain and cogs, and I know the kick that I have with that small front cog won't be there. Still, maybe I'll ride more sensibly without it....

And maybe not!