Pilot Jet for 750 ....17 or 19

olympus

olympus

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Aug 5, 2017
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Hi All
I'm running premier carbs on the 750, with conical air filters &17 pilot jets
To achieve the best idle and low throttle response I'm running the air screws a Gnats cock under one full turn out... and the plugs are a lovely light straw.
But in this really hot (unseasonal) weather we've experienced recently the slow speed performance & idle. IMHO has been affected and I'm wondering if it needs 19 pilot jets
Now i read that the 850 benefits from using 19 pilot jets ... but what about on the 750??
Yours thoughts & comments as always would be appreciated
 
Irrespective of 750 or 850… Premiers or ‘normals’… my understanding is that at less than one turn out, the jet it too small. You need a bigger jet that allows the screw to be 1.5-2 turns out.
 
olympus said:
Hi All
I'm running premier carbs on the 750, with conical air filters &17 pilot jets
To achieve the best idle and low throttle response I'm running the air screws a Gnats cock under one full turn out... and the plugs are a lovely light straw.
But in this really hot (unseasonal) weather we've experienced recently the slow speed performance & idle. IMHO has been affected and I'm wondering if it needs 19 pilot jets
Now i read that the 850 benefits from using 19 pilot jets ... but what about on the 750??
Yours thoughts & comments as always would be appreciated
Click to expand...
Amal continues to insist that #17 is correct for all 750 Commandos and #19 for all 850 Commandos and you absolutely can get the fuel/air mixture correct with those jets. However, you get more of the correct fuel/air mixture, a better idle, and better just coming off idle with #19 so that's what I use/recommend.

Plug readings mean little at idle. You should never run the bike at idle long enough to get a true idle plug reading.
 
Just to confirm, I've ridden these premiers 10,000 miles with #17's on my bone stock 850 at sea level, ham can air filter. About one turn out.
You all say 19's work better? Cure the occasional cough upon tip-in?
I'm in here now, got the jets.
But, I don't want to have to tear the seat, tank and one carb off again to change back. (Busy/lazy, you pick) They're not too blubbery rich, right?
C31B2C6D-D9AE-4D41-A3B6-F2A3F68CFD7B.jpeg
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CE185702-EC61-4C90-9DB8-E22A01187B38.jpeg
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No, when properly setup, you will have the same fuel/air mixture, just a little more of it. your air screws will probably be 1-1/4 turns out or slightly more.
 
were all waiting her with baited breath... and a couple of Tinnies;)
I have also now fitted 19 pilots jets but not yet set up or road tested
 
Interesting the Amal premiers use #17 or #19 pilot jets. In the past when the pressed in idle jets are drilled out, you replace them just above the fuel bowl with screw in #25.
 
ILLF8ED said:
Interesting the Amal premiers use #17 or #19 pilot jets. In the past when the pressed in idle jets are drilled out, you replace them just above the fuel bowl with screw in #25.
Click to expand...
The Premier pilot number is the jet I/D.

https://www.britishmotorcycleparts.co.nz/amal-premier-pilot-jets

"622/502-15-23 AMAL Premier Pilot Jets​


The ID of the standard jet is 0.017” This is the same as the nominal ID of the former pilot bush which was rated at approximately 23cc. The new jets are also available in 15, 19, 21 and 23 sizes which again are measured in thousandths of an inch.

Premier ID Grooves
1 Ring - 622/502-15 (Equivalent to 20 Pilot Jet in pre-Premier carbs.)
2 Rings - 622/502-17 (Equivalent to 25 Pilot Jet in pre-Premier carbs.)
3 Rings - 622/502-19 (Equivalent to 30 Pilot Jet in pre-Premier carbs.)
4 Rings - 622/502-21 (Equivalent to 35 Pilot Jet in pre-Premier carbs.)
5 Rings - 622/502-23 (Equivalent to 40 Pilot Jet in pre-Premier carbs.)"

The screw-in pilot jet number is the flow rate (cc/min).
amalcarb.co.uk

Shop Pilot Jet - 25cc Online | Pilot Jet | AMAL Carburetters

Pilot Jet - 25cc
amalcarb.co.uk amalcarb.co.uk
"All genuine AMAL jets are calibrated to a flow rate. The number e.g. 100 indicates that it will flow 100cc`s of fuel in one minute at a specified head."
 
olympus said:
were all waiting her with baited breath... and a couple of Tinnies;)
I have also now fitted 19 pilots jets but not yet set up or road tested
Click to expand...
...it's all back together, I didn't start it last night, wanted the loctite 518 I put on the carb flanges (outboard of the O-ring) to cure. The hope is to reduce/stop the rocking that wallowed out the nut surfaces/mating flange.
I'll see the missus is willing to ride Commando to https://wallysnh.com/ for chicken wings & IPA tonight
 
Well kids, I concur, it does run better at low rpm, and the occasional tip-in cough is gone. Ended up about 1-5/8 from seated.
Thank you for the reassurance (I respect you kids opinions/findings :cool:
 
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