Jetex 22 - restore my sanity, please

[dansuper]

Sooooooo...

If there is some freakish unidentifiable problem with my motor and I wanted to richen up the atomiser - what would I do? Are the drilled atomisers that Allstyles do drilled for leaness or richness? Ie, which holes are drilled?

[bristolmod]

You need to be using the 200cc atomiser and slide (slide is flat on the engine side - the 150 has an indentation). Drilling the atomiser is b@11@x and got started with clowns using a 150 atomiser when they should have used a 200. This also resulted in the use of 135 main jets and other such silliness.

Use a 200cc atomiser/slide and fit a 123 main for safety. The airscrew adjustment can be more than 3/4 turns out but if it needs more than 2.5 turns you should fit a slightly bigger pilot jet.

so why then do CamLam mentioned "drilled" atomisers in the list you linked us to on another thread?

[dansuper]

Well, this is interesting:

http://forums.fourtitude.com/showthread ... p=70418973

After reading this and a few other things, my understanding of atomisres is now as follows:

1) Essentially, the more holes in the tube, the more air introduced
2) The upper holes introduce air at low rpm/pressure
3) The lower holes introduce air at high rpm/pressure
4) The bottom holes draw fuel into the tube (bigger is 'more'?)
5) The larger the diameter of the tube, the more air introduced

Could be complete b@11@x and I'm semi-retarded, so please don't bank on the above as the 'truth.'

[nelson pk]

Drilling the atomiser on a "jetex" carb is not bollox! If you find your having to go high on your main jet and your still getting lean readings in the mid and wot range its not rocket science to realise that you need a bigger atomiser (as long as you have no air leaks etc). Problem is that you only have 4 atomisers to choose from and these were made for specific applications and certainly not TUNED machines!
If a bigger atomiser is not available what do you do then? Just use the biggest available then cross your fingers until your engine goes pop?
Another example of this is on the Vespa T5 carb where there is only one idle jet available because the carb was made for one specific application only. Again if you need a bigger idle jet because you have tuned it and you insist on using a standard carb the only option is to drill that idle jet slightly. I've heard of tuners doing this as well.

To answer your question you drill the main hole from the bottom that runs the full length of the atomiser. dont worry about the ones on the side of the atomiser.
Hope you find a solution.

[Donnie]

if it's still doing it after all this then I would honestly be looking elsewhere to find out if there's air getting in somewhere else mate.

I'd be starting with ensuring all gaskets are ok / tight and I don't know how long ago you built the top end up, but being a casa I assume it was retorqued at about 100 miles?

[nelson pk]

Well, this is interesting:

http://forums.fourtitude.com/showthread ... p=70418973

After reading this and a few other things, my understanding of atomisres is now as follows:

1) Essentially, the more holes in the tube, the more air introduced
2) The upper holes introduce air at low rpm/pressure
3) The lower holes introduce air at high rpm/pressure
4) The bottom holes draw fuel into the tube (bigger is 'more'?)
5) The larger the diameter of the tube, the more air introduced

Could be complete b@11@x and I'm semi-retarded, so please don't bank on the above as the 'truth.'

Emulsion tubes are used on four strokes instead of atomisers. Now i guess you can call the atomiser in the jetex an emulsion tube because of the holes on the side to do with letting air mix in but its the "jet" hole where the fuel runs up that you want to be enlarging.

[dansuper]

Thanks!

But I could have sworn that others have posted that increasing the tube diameter makes it leaner? Something about changing the pressure? Seems that there is heaps of conflicting info about this - aaaaargh! Ie, the -5 atomiser is leaner than the -2, but it has a larger diameter tube. Is suppose it is all a combination of each hole's size and location relative to the tube diameter.

Maybe I'll wrap a sock around the filter and put a leaner pilot in it...

I will retorque the head nuts, too. It's about 100 miles since reassembly. I don't think they're loose, as it was also doing this prior to removing the head and it was on tight at the time.

Cheers.

[Special X]

Drilling is only needed if you're running an innapropriately large main jet. You'd be doing this because you've fitted a 150 atomiser. Fitting the correct atomiser would remove the need to do this. It came about because some people said fitting the 150 atomiser improved fuelling in the midrange, they then had to fit 135 and above main jets.

Similar to altering needles with a pillar dril and emery cloth. Real reason to do this is to remove the markings at the top of the needle so you don't know what's fitted.

[Special X]

You need to be using the 200cc atomiser and slide (slide is flat on the engine side - the 150 has an indentation). Drilling the atomiser is b@11@x and got started with clowns using a 150 atomiser when they should have used a 200. This also resulted in the use of 135 main jets and other such silliness.

Use a 200cc atomiser/slide and fit a 123 main for safety. The airscrew adjustment can be more than 3/4 turns out but if it needs more than 2.5 turns you should fit a slightly bigger pilot jet.

so why then do CamLam mentioned "drilled" atomisers in the list you linked us to on another thread?

It's the new fashion, like having to modify the fuel delivery circuit on Dell 32/34 carbs a few years ago which proved to be totally unnecessary I'll chang my stance somewhat and say that if you enlarge the carb venturi to 24mm you may go beyond the capabilities of a std atomser by dropping the pressure past the jets. If you've gone to 26mm you'll be getting air past the slide as it flutters and will have to richen the whole thing up. Tuning a motor (fitting a Casa, Mugello, etc) will put more pressure past the jets which will draw more petrol compensating in part for the tuning.

[nelson pk]

Drilling is only needed if you're running an innapropriately large main jet. You'd be doing this because you've fitted a 150 atomiser. Fitting the correct atomiser would remove the need to do this. It came about because some people said fitting the 150 atomiser improved fuelling in the midrange, they then had to fit 135 and above main jets.

Similar to altering needles with a pillar dril and emery cloth. Real reason to do this is to remove the markings at the top of the needle so you don't know what's fitted.

Your theory is write in the first sentence "drilling is only needed if your running an innapropriately large main jet."
The reason for this weather you are running a 150 OR 200 atomiser it is because the atomiser is too small therefore not letting enough fuel through that the main jet wants to deliver.
So please tell me.......................if you are running a 200 atomiser or a standard "jetex" atomiser and you find that no matter how much you increase the main jet you are still lean from 1/2 throttle up what do you do? Cross your fingers?
A "200" atomiser was built for a standard 200cc machine......not a tuned 185cc, not a tuned 200cc, not even a stage 4 200 (indian) barrel, not a 200cc with an expansion pipe and your telling me that a standard 200 atomiser can cope with fuel delivery with these sort of modifications?
With the greatest respect that sounds like boulderdash to me
I'm sure some bikes will run ok and not need the modification but some will.
I guess that racers who drill out the float needle hole because you cant get one big enough to supply the correct amount of fuel on certain carbs are talking rubbish and you dont need to drill out fuel supplies on the carb to run a supermonza engine conversion either.
They all must have it wrong!