22mm Jetex

[sunrisemac]

Out of curiosity has anyone had a play at changing the inlet of of a 22mm Jetex, I've got one to which I have made and added a bit of a bellmouth and opened up to 24mm to match up with the inlet manifold that came with my 'box of bits GP150' that I inherited from my son a few years ago, I shall be giving it a kick over tomorrow to see what happens.

I currently run a Dellorto SH2/22 which has been working well for 6500 miles.

[johnnyXS]

great idea for a cheap carb like the jetex.
I'd be very interested in how it goes and what jetting you end up with.

I have a couple of spare 22mm jetex I might try that myself .
it would probably pay to buy a 2mm precision drill and drill out a 5889-2 Atomiser to improve overall flow rate.
I think Pitstop sell a box of 12x different 5mm main jets cheap in various ranges which would give you plenty of tuning options

[sunrisemac]

It started with a few kicks but I couldn't keep it running for long so whilst changing the pilot jet I found a bit of water in float bowl. Drained the tank and cleaned the carb, put in 45 pilot and 123 main for starters with 5899-4 atomiser and a 7895-1 slide that I had in my box of bits. Carb is bored out to 24mm with the bellmouth extension adding about 16mm to the front of the carb.
Refilled with fresh fuel and had another go, it now ticks over nicely and responsive to throttle, tried a quick run up the road but rain got the better of me so will maybe try tomorrow and do some plug cuts at different throttle positions to see what I might need do to the air holes etc. on the emulsion tube and if I need a smaller main jet.

So far so good, here's a pic of the carb.

[johnnyXS]

great writeup
can't wait to try the same myself although I'll probably try to get it to work with a Ramair foam filter . Theres just too much sand and grit on the roads around here .
Just got to wait for the snow to stop

[sunrisemac]

I've got it running through drilled standard airbox and fast flow filter, I just took it off for the pic.

[sunrisemac]

bit of an update

Had a 10 mile run tonight, quite surprised how well it pulls for a 150.
Engine starts 2nd kick, with choke the engine runs faster than before, no bad thing as it was always a bit slow, takes a bit longer to settle down off choke.
Once warm, up to half throttle it picks up a treat, I think its a bit rich after that so might open up the middle and bottom holes a wee bit in the emulsion tube to let more air into the mix, not tried it with WOT and done plug cut yet but the plug looks good up to 3/4 throttle.

[Warkton Tornado No.1]

Post by sunrisemac » Wed Nov 23, 2016 11:35 pm

bit of an update

Had a 10 mile run tonight, quite surprised how well it pulls for a 150.
Engine starts 2nd kick, with choke the engine runs faster than before, no bad thing as it was always a bit slow, takes a bit longer to settle down off choke.
Once warm, up to half throttle it picks up a treat, I think its a bit rich after that so might open up the middle and bottom holes a wee bit in the emulsion tube to let more air into the mix, not tried it with WOT and done plug cut yet but the plug looks good up to 3/4 throttle.

What are you calling the emulsion tube? I tend to think of the emulsion tube as the component that is used to en-richen the carburettor to encourage starting from cold, often called the starter or choke jet.

You can’t mean that though if you want to clean up the mixture beyond starting.

Sorry if I’ve misunderstood...

[johnnyXS]

before you start opening up the atomiser , try fitting a 5899-2 Atomiser . The atomiser you have fitted has a 2mm bore which is probably too rich for a 150cc The correct Atomiser 5899-2 has a 1.75mm bore and should improve things from 1/2 to WOT.
You'll probably need to adjust the main jet size though .

An easy test to see if your mixture is too rich at WOT is to run the scoot up a steep hill at maximum throttle then apply a little choke and see what happens.The engine should immediately bog if your mixture is too rich . If it stays about the same then your WOT mixture should be about right in which case you might need to look at your timing .

Your choke applies a completely independant fuel supply direct to the engine and does not alter your normal running mixture so its a good test.

[johnnyXS]

[

What are you calling the emulsion tube? I tend to think of the emulsion tube as the component that is used to en-richen the carburettor to encourage starting from cold, often called the starter or choke jet.

You can’t mean that though if you want to clean up the mixture beyond starting.

Sorry if I’ve misunderstood...

they are the same thing Emulsion tube is typically an American description for what we Brits call an Atomiser.

[Warkton Tornado No.1]

Post by johnnyXS » Thu Nov 24, 2016 12:19 am

Warkton Tornado No.1 wrote:
[

What are you calling the emulsion tube? I tend to think of the emulsion tube as the component that is used to en-richen the carburettor to encourage starting from cold, often called the starter or choke jet.

You can’t mean that though if you want to clean up the mixture beyond starting.

Sorry if I’ve misunderstood...


they are the same thing Emulsion tube is typically an American description for what we Brits call an Atomiser.

Not according to:

http://www.ilambretta.co.uk/carb.html

SH type.JPG

& if you look @ Dell'Orto diagram for their general instructions:

Dell'Orto Emulsion Tube.JPG

That's the reason I asked sunrisemac the question to get his response rather than more suppositions.

[EddieStone]

I like that - I'd be interested in one for my chop.

As for atomisers/emulsion tubes, I would fit a different one rather than drill the one you have - here's a guide I used to jet mine properly:

Atomiser.jpg

[sunrisemac]

Thanks for the comments,
I am in the business of restoring historic GP cars (have a look at the Crosthwaite & Gardiner Facebook page) and I call the bit of the 'atomiser' with the holes in the sides the emulsion tube, i.e. the part of the atomiser that varies the amount of air mixing with the fuel when it is being drawn into the venturi via the main jet and the well that the atomiser sits in.
When we are tuning race engines I have no problem drilling out holes or soldering up and re-drilling to achieve the correct mixture when running on the dyno so I reckon I will be able to use a similar method to get some kind of result and then buy or make a new one to suit.

[johnnyXS]

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[/color]

Not according to:

http://www.ilambretta.co.uk/carb.html



That's the reason I asked sunrisemac the question to get his response rather than more suppositions.[/quote]

You'd make an argument out of the weather WT

I think you should bear in mind that what you have read on the internet in the Delortto guide has been translated from Italian into English .

Possibly the Worlds most experienced and knowledgable person on Carburettors is David Vizard and he uses the two descriptions interchangably.

An emulsion tube or Atomiser or mixer tube mixes air with fuel to create a fuel /air 'emulsion' or vapour which is fuel suspended in air

[Warkton Tornado No.1]

Post by johnnyXS » Thu Nov 24, 2016 1:03 pm

You'd make an argument out of the weather WT

I think you should bear in mind that what you have read on the internet in the Delortto guide has been translated from Italian into English .

I wasn’t arguing with anybody, actually, although you do keep trying to score points.

You’ll be telling me next that the translation of Dell’Orto technical descriptions vary dependent upon whether they are into ‘English’ or ‘American English’

For your information, it’s been a while since I had an SH carburettor apart & I overlooked the fact that the Atomiser has a series of holes in.

However, I still think that my question to sunrisemac was a reasonable one, there being an actual Emulsion Tube in all Dell’Orto carburettors that functions for the purpose of cold starting. Or should that be described as an Atomiser too? What with you being right & Dell’Orto being wrong...

As usual, you’ve:

shoot.JPG

What is unreasonable is your attitude.

Simply to make a point, you adopt an ‘Americanism’ that is not used by Dell’Orto, LCGB or any of the Manuals that I’ve seen.

[johnnyXS]

I wasn’t arguing with anybody, actually, although you do keep trying to score points.

.

I was simply answering the question that you posted

try not to take this thread off topic.... if you possibly can .

[EddieStone]

Is it Dell'Orto or Dellorto?

[Steve J]

It's all starting to sound a bit like handbags at dawn to me......

[sunrisemac]

sorry I posted in the first place..............

[sunrisemac]

I like that - I'd be interested in one for my chop.

As for atomisers/emulsion tubes, I would fit a different one rather than drill the one you have - here's a guide I used to jet mine properly:

Atomiser.jpg

Thanks for the chart, I have been trying to find that info as reference to help me set up the carb.

[Steve J]

The chart is very useful - as a matter of interest, what was the 5899-3 used on?