SSI Neededle and jet wear

[Bevel bob]

Does anyone know what the measurements are for the needle and jet for a Mach 1, and i dont mean the catalogue references. Pattern parts are about.

[JimF]

Hi Bob,

I have some SSI 29 parts laying about (old and original.) Do you want the measured OD of a needle? How do I measure the jet?

Jim

[Bevel bob]

Hi jim, I think there is a file on needle dimensions on the net but no information on jet diameters, I measured my main jet useing a tapered needle which i measured with a mike , a 107 main jet measures 1.07 mm, the needle jet is the one that wears and a tiny increase in size makes a big difference in mixture in the most used part of the range.But what should it measure??. 2.65 mm? .

[JimF]

I think I see what you are driving at as far as wear goes. But if I do understand then my measuring what I have serves no purpose since anything I have is used and worn.

Do you need somebody that has NOS parts to answer this question?

How accurate a reproduction is this guy likely to make when it comes to the minutia of fabricating and drilling a new jet?

http://francescobazzani.com/

Or are his parts what you refer to as 'pattern parts?'

Is the best thing to do just to try and make adjustments to the carb such as using different needles and jets as the carb ages and wears to compensate for the increasing slop?

[Bevel bob]

In order to check if somethings worn you need accurate data, and limits for acceptable wear. when new orriginal parts are freely availiable its easy to sort out.I think much of whats around is pattern or poor standard new manufacture.The only way to be sure is to check carefully.

[Jordan]

Amal uses the method of defining their jet sizes by how much fuel they pass per unit of time under a specified pressure head, rather than by diameter.
As this test can be applied to a jet that doesn't necessarily have a round hole, it could be useful for ascertaining if a used jet is worn, by comparing it to a known good one. It gets around the problem of physically measuring the possibly un-round hole.
You can make your own jet size modifications, using jet reamers like these: http://www.dealparts.com/product/43-5715-0.html
If you want a smaller jet size, you can solder the existing hole, then drill a small hole before reaming.

Jordan

[MotoMike]

those reamers look like clock broaches. Never seen these before.

[Jordan]

I made a mistake. The main topic is needle jets, not main jets. I believe Amal actually measure THOSE in decimal inches (for example, "106" means 0.106 inches diameter). Sorry about that.
Amal MAIN jets are measured as to how much fuel they pass.
As regards needle jet wear, it can be compensated for somewhat by dropping the needle (using a higher clip groove), especially if the needle only has one constant taper.

Jordan

[Bevel bob]

I measured my needle jet and its 2.6mm ,as its a 260 thats all right!!, I've increased my main to 110, was 107, and dropped the needle to the last(top) notch, I'm hoping to clean up the mixture as the plug mouth is always sooty when running up to half throttle. I notice the needle has slop up and down in the slide the equivalent of one notch,don't know if this is relevant.What i really would like is an O2 sensor stuffed up the pipe and a voltmeter mounted on the bars to read whats happening at the diferent throttle phases.

[Bevel bob]

Been out today and the carburation is well nigh perfect, dropping the needle to the last notch made all the difference, all the settings are weaker than standard, must be the fuel these days.