Hi all!

So my carb (26IMB) is rebuilt and the Idle jet seems to control the idle by how you move it, though it's not smooth at lower RPM's. Reading the factory manual, only adjustments are supposed to be from mixture screw and idle screw. It never mentions the idle jet as an adjustment. I can get it starting, running, driving idling fine.... it's just idling at 1200 rpms instead of 8-9. I can adjust the mixture and idle screw until I'm blue in the face, but the idle doesn't drop to 8-900. If I turn the idle jet at all, the engine does drop, but then begins to run a bit rough. So I'm looking for possible solutions, any thoughts?


Does the idle jet have to be screwed all the way in to where it doesn't move, or is it adjustable?

I'm not a pro at carburetors by any means. I'm just trying to get it all dialed in, though its not cooperating!

Thanks!

Chase

Assuming that your idle jet screw has the necessary seal on it then the standard procedure is to turn the screw right in then back it off 1.5 turns. Run the engine whilst slowly reducing the throttle screw making any tiny adjustments on the mixture screw To achieve smooth running.

Toshi 975 said:

Assuming that your idle jet screw has the necessary seal on it then the standard procedure is to turn the screw right in then back it off 1.5 turns. Run the engine whilst slowly reducing the throttle screw making any tiny adjustments on the mixture screw To achieve smooth running.

Click to expand...

Good point about the right seal... Rubber o-ring? I have a rebuild kit, and that is what fit the jet the best. I received other input from trusted Fiat people who said Idle Jet all the way in locked down and don’t touch it! So many trains of thoughts!

With respect my friend there may be many ramblings and trains of thought but there is only one correct one. Why would the idle screw have a tapered tip that locates in an orifice if it was not meant for fine adjustment.
Think about it , if you are going to bung up that hole you might as well just stick your chewing gum in there.
Even worse if you do as your trusted people say and over tighten the screw a fraction you may crack the carb body Which would actually cause the symptoms You describe and you would need a new carb.

From the workshop manual (attached)

And from the owner's manual. Trust Toshi on this one.

Toshi 975 said:

With respect my friend there may be many ramblings and trains of thought but there is only one correct one. Why would the idle screw have a tapered tip that locates in an orifice if it was not meant for fine adjustment.
Think about it , if you are going to bung up that hole you might as well just stick your chewing gum in there.
Even worse if you do as your trusted people say and over tighten the screw a fraction you may crack the carb body Which would actually cause the symptoms You describe and you would need a new carb.

Click to expand...

I agree with that, though this is my issue, I think we’re talking about two different parts of the carb. The idle jet is what I’m talking about. I circled it in the post that JumpJet was kind enough to post. This screw isn’t tapered, and is just a jet, but unscrewing it makes a big difference in the idle.

As Winston Churchill once said---"never have 2 countries been so separated by a common language" The idle JET stays tightly in, the idle MIXTURE screw is adjustable---basic setting is, as 'Toshi' has already mentioned, to screw it in fully, but gently, and then back it off about 1-1/2 turns, with the idle SPEED adjusting screw set at a basic adjustment of about 2 turns in.