Idle jet sizes, 12848, 13660, 13660A, 13660B & Z.

[Gavin]

I'm trying to find out the differences in idle jet size throughout this range of carbs.

I have several spares here, 3 of which "look" the same, but one of which has a noticeably longer spigot.

Any advice much appreciated.

[rickf]

I have the original blueprints for these carbs so I will look it up tomorrow morning. Going to bed early to try to recover from a 1300 mile genset recovery.

[Gavin]

Thank you, Rick, much appreciated.

[rickf]

12848, Idle #12 and main #30. 13660, Idle #15 and main #28. 13660A Idle #15 and main #28. 13660 B, Idle #15 and main #30.

Now, with all of that said, I have found #30 main jets in all of the above 13660 series carbs, so you do not know without looking to see what the main jet is. I will tell you this, I built a carb for an A2 that ran the first cross country convoy and I put a #28 jet in it due to the high altitudes they would be at. That carb is still on his vehicle and he has run every convoy since then with the smaller main jet with no issues whatsoever. It is my opinion that due to the design of the exhaust manifold the engine cannot breath well enough to ever utilize the full extent of even a #28 main jet. So the main jet makes no difference unless you have a head like this.

IMG_20201206_131156626.jpg

.

[Gavin]

So they decided to cut the idle jet from 25 to 15 in the 13660B?

[rickf]

Sorry, arthritic fingers. The idle jets went from 12 to 15 with the change to the 13660 series and stayed at 15. I have lost my pin gauges or I would tell you the sizes in thousandths. As far as the different types of tips I think you will find that is just production changes over the years

[Gavin]

Thank you Rick, that's exactly what I needed.

[Horst]

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