Jetex 22 - restore my sanity, please
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dansuper
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- Main scooter: 1963 LI 185
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So you can therefore modify an atomiser to either enrichen or lean out the mid range, right? I guess the confusion partly arises because of this: drill out the atomising holes for more air or drill out the tube for more fuel. Or both for both!
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Special X
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In the post above yours I mentioned that the incresed volume and pressure air across the jets draw more fuel and adjust the mixture (roughly) to suit the engine. Yes you're right that if the atomiser just won't support the fuel flow needed you'd have to drill the jets, but trying to run a jetex or 22 delly in such an engine is not rational. A 22mm jetex is not going to supply an engine that is built to give high teens upwards horsepower it's unfit for purpose and should not be used on RB's TS's Avantis, group 4 racers etc. If you want more than 11 bhp at the wheels (on a sane dyno) don't use one.
It is, however eminently suitable for a bog std mugello mk1 or 2, Casa, Indian stage 4 , proper stage 4 with a box pipe and doesn't need drilling if the correct atomiser and slide are fitted along with a 50 pilot and 123 main. With a 125 main (the max usable in a jetex) it should support being reamed to 24mm. Arthur Francis was reaming SH22's to 24mm in1969 . . He told me never to try and go bigger than 24mm as the carb would not be stable due to slide flutter.
Group 4 racers do drill delly's for more fuel flow but it was being touted for road use on std TS1's . . . . totally unneccesary! Like the 300 needle jets fitted to PHBH carbs. Martin from chiselspeed once asked me when I was buying one "why do you need to flow 300 when your main jet is only 122?" He could have sold me the jet but he would rather sell you something that did something rather than maximise the possibility of a huge fuel leak.
It is, however eminently suitable for a bog std mugello mk1 or 2, Casa, Indian stage 4 , proper stage 4 with a box pipe and doesn't need drilling if the correct atomiser and slide are fitted along with a 50 pilot and 123 main. With a 125 main (the max usable in a jetex) it should support being reamed to 24mm. Arthur Francis was reaming SH22's to 24mm in1969 . . He told me never to try and go bigger than 24mm as the carb would not be stable due to slide flutter.
Group 4 racers do drill delly's for more fuel flow but it was being touted for road use on std TS1's . . . . totally unneccesary! Like the 300 needle jets fitted to PHBH carbs. Martin from chiselspeed once asked me when I was buying one "why do you need to flow 300 when your main jet is only 122?" He could have sold me the jet but he would rather sell you something that did something rather than maximise the possibility of a huge fuel leak.
I agree that standard carbs will not support other than a mildly tuned engine so we are agreeing there.Special X wrote:In the post above yours I mentioned that the incresed volume and pressure air across the jets draw more fuel and adjust the mixture (roughly) to suit the engine. Yes you're right that if the atomiser just won't support the fuel flow needed you'd have to drill the jets, but trying to run a jetex or 22 delly in such an engine is not rational. A 22mm jetex is not going to supply an engine that is built to give high teens upwards horsepower it's unfit for purpose and should not be used on RB's TS's Avantis, group 4 racers etc. If you want more than 11 bhp at the wheels (on a sane dyno) don't use one.
It is, however eminently suitable for a bog std mugello mk1 or 2, Casa, Indian stage 4 , proper stage 4 with a box pipe and doesn't need drilling if the correct atomiser and slide are fitted along with a 50 pilot and 123 main. With a 125 main (the max usable in a jetex) it should support being reamed to 24mm. Arthur Francis was reaming SH22's to 24mm in1969 . . He told me never to try and go bigger than 24mm as the carb would not be stable due to slide flutter.
Group 4 racers do drill delly's for more fuel flow but it was being touted for road use on std TS1's . . . . totally unneccesary!
In fact i would change the standard carb on a standard lammy to a more modern 24/25mm anyway as i think the standard carbs are pretty crude but it is not a "fashion" where the drilling comes from.
Some have found that a simple change of pipe on an indian stage 4 barrel to say a clubman have had the atomiser issue.
For example...... a friend of mine had problems with his stage four 200 + clubman running a brand new jetex for a 200cc (he had the fast flow tap and fuel flow to the carb was checked). Bike wouldn't go over 55mph and had lean running symptoms no matter what main jet you put in.
The atomiser was drilled to 2.0mm and hey presto, it ran like a dream.
If he had run original delly jets he may have faired slightly better but this is a well known issue and should not be ruled out as a solution.
"why do you need to flow 300 when your main jet is only 122?" He could have sold me the jet but he would rather sell you something that did something rather than maximise the possibility of a huge fuel leak.
I'm sorry but thats just tosh about the 300 float inlet. Probably correct on a mildly tuned bike but on a TS1 or a Monza. DO NOT RISK IT!
Lets look at your example......
You are running a 122 main ok. Its the SPEED that the engine is sucking your fuel through that 122 main that is far quicker than the gravity feed to your float bowl when you are at high revs.
Your fuel has to be a constant level in your float bowl for your jetting to work correctly and not lean out.
If you were running a fuel pump you would be able to use a lot smaller float inlet safely and you could well flood the engine if too big was used but on a gravity feed.....generally bigger is safer and will generally not cause any sort of flooding as its your floats that control where the fuel flow is shut off.
I'm sorry but thats just tosh about the 300 float inlet. Probably correct on a mildly tuned bike but on a TS1 or a Monza. DO NOT RISK IT!
Lets look at your example......
You are running a 122 main ok. Its the SPEED that the engine is sucking your fuel through that 122 main that is far quicker than the gravity feed to your float bowl when you are at high revs.
Your fuel has to be a constant level in your float bowl for your jetting to work correctly and not lean out.
If you were running a fuel pump you would be able to use a lot smaller float inlet safely and you could well flood the engine if too big was used but on a gravity feed.....generally bigger is safer and will generally not cause any sort of flooding as its your floats that control where the fuel flow is shut off.