Amal 930 Pilot Jet vs bush - Triumph Forum: Triumph Rat Motorcycle Forums
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post #1 of 7 (permalink) Old 10-20-2016, 04:07 PM Thread Starter
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Amal 930 Pilot Jet vs bush

Just starting sorting out the carbs on my recently acquired 1968 T120R. I found that I have one 930 with a pilot Jet bush and the other (right) one with a screw in #25 Pilot Jet.

Any one have an idea if the Pilot Jet Bush and a #25 Pilot jet are the same?

Idle is ok, but not great. the Carb with the #25 pilot jet seems to require a more open air screw setting which would suggest the jets are not the same.

Regards, Steve
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post #2 of 7 (permalink) Old 10-21-2016, 11:07 AM
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To start with it check if a carb with a jet has a bush as well. Perhaps somebody didn't realize jest is unnecessary addition.
If the bush isn't there in the carb body, you have to buy a different 930 with bush installed.
Carbs with jets don't work properly with our engines, checked it myself with my A65.
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post #3 of 7 (permalink) Old 10-21-2016, 12:54 PM
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Is the jet screwed into the threaded hole that is normally hidden inside the float chamber?

Early Concentrics had a jet there. Later carbs got a pressed-in bush behind the air screw and a few other different parts and the screw-in jet was left out.

To add confusion, some owners drill out the bush and fit a jet, to give them a choice of sizes. Some do that for no real reason, other than they think something should be in the threaded hole.

You'll never be happy trying to tune two different carburettors.
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post #4 of 7 (permalink) Old 10-21-2016, 12:55 PM
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The bush is #17, as standard, I think.
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post #5 of 7 (permalink) Old 10-24-2016, 08:32 AM Thread Starter
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thanks, have checked closely and clearly Left Carb has bush and Right has #25 Jet. I also found the documentation from Amal that the previous owner left me, which confirmed this.

I emailed Amal in UK and they responded that a #25 pilot jet was roughly equivalent to the pilot bush.
They also indicated that running carbs with a pilot bush and #25 Pilot jet should be ok and no need to replace one of the carbs.
As I indicated, the idle is ok, but not great.

Personally, It bugs me that they are different. And I have some other worn parts that need replacing. So ... I decided to order a set new 930 Premiere carbs.

Thanks again for you help.

Regards, Steve
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post #6 of 7 (permalink) Old 11-01-2016, 05:48 PM
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Right decision.
And this is not true those carbs would work the same.
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post #7 of 7 (permalink) Old 11-11-2016, 11:01 AM Thread Starter
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New Amal Premiere 930 Installed

After fighting all the issues with having one carb with a pilot bush, the other with a #25 pilot jet that the previous owner left me with, I decided to install new Amal Premiere 930 carbs, with 106 needle jet and 190 Main Jet. I was having trouble with very rich mixtures and poor idle that fouled the plugs quickly with the old miss matched carbs.

Along with the new carbs, I installed new petcocks and fuel lines and fixed all the fuel leaks. I also restored the original air cleaners. I also had to replace the throttle cables because, one of cables was stuck in the carb throttle and had to be cut to remove the old carbs.

One difference between the old 930's and the Premiere is the cable adjusters on the top of the carb. The original 930's did not have an adjuster for the throttle, only a hole for the cable ferrule. So when I ordered new 1968 throttle cables, they were about 1/8 inch too short and did not allow the throttle to seat properly. I had to take about 1/8 inch off the cable housing in various places to get enough exposed cable to allow the throttle to seat.

Because my original issue was a too rich mixture, I tried the needle in the top groove to weaken the mixture. Turns out that this was too lean. Using the air valve to increase the richness of the mixture while running, improved performance. So I moved the needle back to the middle groove, which is the way it came from the factory.

After installation and syncing the carbs They run great! Idle is great. Plug color is on target. Bike starts on first kick. And power and acceleration are much better. They are a little pricey, but it was worth it in my opinion.
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Regards, Steve
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