Needle or Atomiser ?
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Adam_Winstone
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Yep. You'll need to excuse some of the auto corrections and errors of my own fat fingers!
http://www.totoolsupplies.co.uk/uk2ecom ... _-_2_65mm/
looks like the job , and a couple of mates work at Precision engineering firms.
looks like the job , and a couple of mates work at Precision engineering firms.
win or lose have a booze
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Adam_Winstone
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Looks good 
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olliewtf
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This has always puzzled me... im on my leanest setting with a x7 and 264 combo, and would like to try something leaner just out of interest, but I dont understand how the combinations of the two affect each other. I gather that the atomiser controls the amount of fuel available as the needle is lifted, and the needle taper controls that controlled amount through the motion of the throttle opening...
so if i wanted to lean off my mid range, would I go for a leaner atomiser, needle, both, or is it simply a case of trial and error? I think im confused mainly because many say that there are combinations that work and some that dont!
so if i wanted to lean off my mid range, would I go for a leaner atomiser, needle, both, or is it simply a case of trial and error? I think im confused mainly because many say that there are combinations that work and some that dont!
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paulnobodyimportant
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Feedback Update.
Only got round to re-jetting my carb as I mentioned on page 1. Anyway, once I stripped down my carb, I found that I had in fact the X13 needle on the top clip position into an AV266 atomiser (needle jet.)
Then I found this snippet from Mark Broadhurst
“A basic guide is if you get to your top clip position, you may require a smaller atomiser (needle jet). And, if you get to the bottom clip, then a larger atomiser is required.”
So last night, put in the leaner AV264 atomiser and the X13 clip on second from the top. Then went for a run in the drizzle to find that it was running rich from approx. ¼ to ½. Changed the clip to top position and came to work on it this morning (3 fast miles) and it runs a treat. Just checked spark plug colour and it’s the right brown, but will need to do plug chops to check at different throttle positions.
But to conclude, it does look like you change the atomiser first, or it did in my case.
For more info on tuning a carb, from MB, then have a look at the link below, it’s all good information.
http://www.mbdevelopments.co.uk/archive/mag42.html
Only got round to re-jetting my carb as I mentioned on page 1. Anyway, once I stripped down my carb, I found that I had in fact the X13 needle on the top clip position into an AV266 atomiser (needle jet.)
Then I found this snippet from Mark Broadhurst
“A basic guide is if you get to your top clip position, you may require a smaller atomiser (needle jet). And, if you get to the bottom clip, then a larger atomiser is required.”
So last night, put in the leaner AV264 atomiser and the X13 clip on second from the top. Then went for a run in the drizzle to find that it was running rich from approx. ¼ to ½. Changed the clip to top position and came to work on it this morning (3 fast miles) and it runs a treat. Just checked spark plug colour and it’s the right brown, but will need to do plug chops to check at different throttle positions.
But to conclude, it does look like you change the atomiser first, or it did in my case.
For more info on tuning a carb, from MB, then have a look at the link below, it’s all good information.
http://www.mbdevelopments.co.uk/archive/mag42.html
With Dellorto PHBH carbs I chased my tail a bit when first trying to set them up and then with much advice from tuners etc here are my thoughts....
For a start, do not use an AV264 on a 225 kit. If you use full throttle to get speed up and then roll off and cruise between quarter and half on a long journey your engine will get too hot! Get a gauge when setting up (EGT or CHT or both) and see the difference in heat when cruising at these throttle positions with a small atomiser....as a couple of miles clock up the heat will scare you!
Just my opinion!
With a round slide carb you are going to struggle to get rid of splutter at lower throttle openings when out of the power band. You should jet for your scoot (a kitted scoot) when in the power band or on the pipe (whichever term you choose).
The reason you get more splutter at low openings on a round slide is the way the air flows through the venturi (round slide causes eddy currents in the venturi at low openings which reduces the vacuum. A good vacuum is required to pull sufficient fuel through fast enough and therefore you have to over jet to compensate this).
A flat slide is much better and will run cleaner at lower openings and revs (air flows through the venturi faster creating a better vacuum at low revs to supply fuel). In my personal opinion the dellorto flat slides are best as they are more adjustable than the jap carbs.
So in short you will always get splutters at low revs with a round slide carb on a kitted scoot because if you try to jet out the richness at low revs (out of the power band) you will restrict the fuel it needs in the power band.
I would use an av266 as a minimum personally on a 225 as the size of the atomiser is crucial at quarter throttle. You know when there is no wind and your TS1 or Monza is running lovely....cruising along at 60 at quarter throttle or over....well that's when you are going to need to make sure your atomiser is big enough to supply the fuel the engine is demanding.
You can make it better by fitting a powerjet but a flat slide with a correctly fitted power jet is the best option in my opinion.
For a start, do not use an AV264 on a 225 kit. If you use full throttle to get speed up and then roll off and cruise between quarter and half on a long journey your engine will get too hot! Get a gauge when setting up (EGT or CHT or both) and see the difference in heat when cruising at these throttle positions with a small atomiser....as a couple of miles clock up the heat will scare you!
Just my opinion!
With a round slide carb you are going to struggle to get rid of splutter at lower throttle openings when out of the power band. You should jet for your scoot (a kitted scoot) when in the power band or on the pipe (whichever term you choose).
The reason you get more splutter at low openings on a round slide is the way the air flows through the venturi (round slide causes eddy currents in the venturi at low openings which reduces the vacuum. A good vacuum is required to pull sufficient fuel through fast enough and therefore you have to over jet to compensate this).
A flat slide is much better and will run cleaner at lower openings and revs (air flows through the venturi faster creating a better vacuum at low revs to supply fuel). In my personal opinion the dellorto flat slides are best as they are more adjustable than the jap carbs.
So in short you will always get splutters at low revs with a round slide carb on a kitted scoot because if you try to jet out the richness at low revs (out of the power band) you will restrict the fuel it needs in the power band.
I would use an av266 as a minimum personally on a 225 as the size of the atomiser is crucial at quarter throttle. You know when there is no wind and your TS1 or Monza is running lovely....cruising along at 60 at quarter throttle or over....well that's when you are going to need to make sure your atomiser is big enough to supply the fuel the engine is demanding.
You can make it better by fitting a powerjet but a flat slide with a correctly fitted power jet is the best option in my opinion.
would be handy if someone could put a chart up on here showing weekest to richest atomizers ,as in as are weeker than av so would it work that say av264 be weeker than as266 or richer
cheers john
cheers john
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paulnobodyimportant
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Nelson
I think you may be correct about the AV264 and I did suspect that it may be on the lean side. Did a few plug chops last night and it was on the lean side at 1/4 throttle, enough to worry me if I was on a long run. As I mentioned earlier, the original set up was AV266 and X13. So think I will go back to AV266 and try the X7 needle. PS, this carb has a power jet, so got that bit right.
I suppose that's why a Mikuni TMX is a lot better with a flat side??
I think you may be correct about the AV264 and I did suspect that it may be on the lean side. Did a few plug chops last night and it was on the lean side at 1/4 throttle, enough to worry me if I was on a long run. As I mentioned earlier, the original set up was AV266 and X13. So think I will go back to AV266 and try the X7 needle. PS, this carb has a power jet, so got that bit right.
I suppose that's why a Mikuni TMX is a lot better with a flat side??
If I was going flat slide I would go with a Dellorto (the VHSH 30mm) being my preferred choice.
The difference between the popular Mikuni and Kehein to Dellorto flat slides is that Mikuni and Kehein (PWK copies etc) have the atomiser fixed where as on a Dellorto you can choose your atomiser size.
This does make Dellorto harder to set up but you have more adjustment in that quarter throttle range.
The optimum choice for me would be a Dellorto flatslide with power jet but set up by a compotent dyno operator.
The difference between the popular Mikuni and Kehein to Dellorto flat slides is that Mikuni and Kehein (PWK copies etc) have the atomiser fixed where as on a Dellorto you can choose your atomiser size.
This does make Dellorto harder to set up but you have more adjustment in that quarter throttle range.
The optimum choice for me would be a Dellorto flatslide with power jet but set up by a compotent dyno operator.
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Adam_Winstone
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... this supports what I was saying about regularly finding that the AV264 is a tad too weak and the AV266 a bit too rich, and why it is such a shame that Dellorto have said that they will no longer produce/supply their old AV265, even though they still make atomisers with 2.65mm diameters in other rangespaulnobodyimportant wrote:Nelson
I think you may be correct about the AV264 and I did suspect that it may be on the lean side. Did a few plug chops last night and it was on the lean side at 1/4 throttle, enough to worry me if I was on a long run. As I mentioned earlier, the original set up was AV266 and X13. So think I will go back to AV266 and try the X7 needle. PS, this carb has a power jet, so got that bit right.
I suppose that's why a Mikuni TMX is a lot better with a flat side??
Put into the mix auto advance/retard ignitions, which normally need carburation to be richer at low throttle openings, and they is the need for an AV267 too, when a 266 is weak and a 268 rich.
People are regularly hand modifying needles to try to fill this shortfall in atomisers, however, providing an accurate range of atomisers would help out lots of people (those that are bothered about getting their carburation right, rather than just making do).
Adam