Down-jetting for fuel economy

[scarfacehugo]

Hello again chaps!!

I'm getting my bike ready for a trip next Spring to Africa and decided to tune the carbs using the smallest main jets possible for a good clean spark plug colour and the most miles out of a full tank. I use stock air filter and exhaust.

Mine is a 95 model (RD07) and comes with 118/120 main jets. I know that in the 97 (RD07A) onwards model, Honda decided to use 115 jets in both carbs and I also know that they burn less fuel. My bike does 250kms/+-155 miles untill it reaches reserve and probably 300kms/+-195miles with a full tank and fully loaded. Since I cant afford a bigger tank, I decided to do it the other way around.

I have now 110 main jets, didnt check the plugs colour but by the way it pulls, it's not getting enough petrol. I'm now waiting for 115 main jets from WEMOTO and try them soon.

I would like to know your opinion and if anyone's tried this before.

[atgreg]

mains wont have much effect on cruising economy, the mains really fully take over from 3/4 throttle, for part throttle cuising the needle & pilot jet have more effect.

If the AT had adjustable needles you could go down one notch but as they dont, try going down 1 size in piltot jet, Ive done that on my RD04 & worked OK

Hello again chaps!!

I'm getting my bike ready for a trip next Spring to Africa and decided to tune the carbs using the smallest main jets possible for a good clean spark plug colour and the most miles out of a full tank. I use stock air filter and exhaust.

Mine is a 95 model (RD07) and comes with 118/120 main jets. I know that in the 97 (RD07A) onwards model, Honda decided to use 115 jets in both carbs and I also know that they burn less fuel. My bike does 250kms/+-155 miles untill it reaches reserve and probably 300kms/+-195miles with a full tank and fully loaded. Since I cant afford a bigger tank, I decided to do it the other way around.

I have now 110 main jets, didnt check the plugs colour but by the way it pulls, it's not getting enough petrol. I'm now waiting for 115 main jets from WEMOTO and try them soon.

I would like to know your opinion and if anyone's tried this before.

[scarfacehugo]

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???

[Sully22252]

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.

[magwa]

Honda go to great lengths to give a set of jets to match most conditions
if you 'mess' with air filters/ plugs/silencers you may also get a beneifit with altering jet sizes.
BUT
if you make it too 'weak' with poor 85 octane petrol in a hot environent you will prob overheat the engine and have a bit of a melt down of the terminal variety!
Beware what you mess with I got over 50mpg on my last AT in standard tune ( plus remus pipe) and see no reason to get any more out of the current one

better to stay standard and know you will finish the trip than mess and melt something vital fuel is cheap versus a big blow up of an engine for a few mpg

Take care

Magwa

[StumpyFingers]

If you want to improve MPG, I would suggest changing the sprockets.
An extra front tooth and one less on the back will improve the MPG but reduce the low down pulling power.

[scarfacehugo]

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

[Farmboy]

Went there earlier in the year mate and there are Fuel stations everywhere.

The fuel is spot on and not low octane unless you get near the Mauritanian border.

The only time I had problems was when i ran out in a 1 donkey town in the Desert, I used 2 wine bottles of an unknown fuel from a old bloke at the side of a mud hut.

Rode a further 100kms to the next fuel stop with the throttel pinned at 80km per hour

Never had any issues at all, I would leave well alone, and just keep an eye on your air filter if you head into the Desert as mine got full of orange sandy dust.

Chris

[scarfacehugo]

Went there earlier in the year mate and there are Fuel stations everywhere.

The fuel is spot on and not low octane unless you get near the Mauritanian border.

The only time I had problems was when i ran out in a 1 donkey town in the Desert, I used 2 wine bottles of an unknown fuel from a old bloke at the side of a mud hut.

Rode a further 100kms to the next fuel stop with the throttel pinned at 80km per hour

Never had any issues at all, I would leave well alone, and just keep an eye on your air filter if you head into the Desert as mine got full of orange sandy dust.

Chris

Hi there! I've seen your footage of that trip, looks like you had a great time.
I sure have loads of questions I would like to ask you, but this is the wrong place and probably the wrong time.
Did you take any extra fuel cans?
Cheers for your opinion!

[Farmboy]

I had the same concerns worrying about 250 miles tank ranges after looking at some of the Desert crossings and factoring in the what if scenarios.

In the End i went on the standard 24L tank with no extra petrol cans etc..

I did run out once but luckily I made it through like I said earlier. If you avoid the Long Desert sections you will have no problems whatsoever.

There was a petrol strike on when I was there so it didnt help matters even then there was always a way of getting some

Happy to help with any questions you might have to avoid making the same mistakes I did !!

Although thats half the fun