DCOE idle jet size

[Johnny Boy]

In my 40 DCOE,s I have 59f21 idle jets, it will tick over lovely at as low as 500 rpm.

I have a lean condition on light throttle , on the progression .

it might be the fact that the carbs only have 3 profession holes , and I have a 16 valve engine.

I want to try a slightly richer idle jet.

I don’t know what the f number signifies.

any one know ?

[Miniliteman]

Are you sure it is a 59 idle jet?? The F number denotes a (1 or 2 or 4) certain air hole in the idle jet. Unfortunately there is no system in the F numbers but you should be able to find a list of F numbers online.

Edited June 13, 2022 by Miniliteman

[Johnny Boy]

8 hours ago, Miniliteman said:

Are you sure it is a 59 idle jet?? The F number denotes a (1 or 2 or 4) certain air hole in the idle jet. Unfortunately there is no system in the F numbers but you should be able to find a list of F numbers online.

Definitely idle jets 59F21.

The 40 DCOE's came from an Opel Kadett 1300 SR, I owned in the early 1980's. They were an Irmisher Kit for a Nova Sport.

They had a weird idle jet specified for that application, 59F21 

I'm not sure if the progression lean condition is caused by the 16v engine requiring more progression holes, or a slightly richer idle jet.

I've tried 50, 55, 60 idles, but its quite clear that it idles much smoother with the 59F21.

I know the F number is  the amount of air mix  in the jet, and the 50,55,60 is the fuel hole size, but I don't know whether the higher the F number the more air is let in , or the other way round 

The reason I was asking is I don't know what the F signifies, would a 59F21 be  weaker than a 59F9 ?

[YellowTaxi]

What engine is it?

If I was you I would go back to basics.

Firstly is there enough fuel pressure and flow? check fuel pump and filters etc.

Tune the carbs using mixture screws, remember part throttle opening are regulated by these not just idle.

Are your float height correct? Again critical and often masked by adjustment of mixture screws.

Do you have a good healthy ignition system? remember ignition system is under most load when accelerating due to initial ritch mixture.

Is there any inlet leaks? again often masked with adjustment of idles. 

Eliminate the above then look into re-jetting etc.

 

 

 

[Miniliteman]

1 hour ago, Johnny Boy said:

The reason I was asking is I don't know what the F signifies, would a 59F21 be  weaker than a 59F9 ?

When I tune carbs I have a std set of ideljets: 45, 50, 55, 60, 65. And of each of these sizes an F4, F8, F9, F6 jet (from lean to rich). I can make small steps in idlejet-sizes. But the F21 idlejet has only 1 brother/sister: the F22. That is slightly leaner. If you have a 59F21 then there is no small step towards a richer jet. 59 is the biggest and there is no F-number available that is slightly richer than F21. So you will have to switch over another "set" of idlejets or you could drill the 59's out to 60 but I am not a fan of drilling jets and you cannot go back in size.

[YellowTaxi]

Some good advice above.

 

[Johnny Boy]

1 hour ago, Miniliteman said:

When I tune carbs I have a std set of ideljets: 45, 50, 55, 60, 65. And of each of these sizes an F4, F8, F9, F6 jet (from lean to rich). I can make small steps in idlejet-sizes. But the F21 idlejet has only 1 brother/sister: the F22. That is slightly leaner. If you have a 59F21 then there is no small step towards a richer jet. 59 is the biggest and there is no F-number available that is slightly richer than F21. So you will have to switch over another "set" of idlejets or you could drill the 59's out to 60 but I am not a fan of drilling jets and you cannot go back in size.

Ok, thanks,

I have some 55, and 60, but off the top of my head, not sure of the F number.

so the bigger the F number for a certain size, the richer.

I’ll have a look into that 😀

[Johnny Boy]

1 hour ago, YellowTaxi said:

What engine is it?

If I was you I would go back to basics.

Firstly is there enough fuel pressure and flow? check fuel pump and filters etc.

Tune the carbs using mixture screws, remember part throttle opening are regulated by these not just idle.

Are your float height correct? Again critical and often masked by adjustment of mixture screws.

Do you have a good healthy ignition system? remember ignition system is under most load when accelerating due to initial ritch mixture.

Is there any inlet leaks? again often masked with adjustment of idles. 

Eliminate the above then look into re-jetting etc.

 

 

 

Thanks, I’ll look at that lot😀

[Johnny Boy]

1 hour ago, Miniliteman said:

When I tune carbs I have a std set of ideljets: 45, 50, 55, 60, 65. And of each of these sizes an F4, F8, F9, F6 jet (from lean to rich). I can make small steps in idlejet-sizes. But the F21 idlejet has only 1 brother/sister: the F22. That is slightly leaner. If you have a 59F21 then there is no small step towards a richer jet. 59 is the biggest and there is no F-number available that is slightly richer than F21. So you will have to switch over another "set" of idlejets or you could drill the 59's out to 60 but I am not a fan of drilling jets and you cannot go back in size.

Is the f6 richer than the 4 ,8 ,9 ?

[katana]

26 minutes ago, Johnny Boy said:

so the bigger the F number for a certain size, the richer.

From reading Leon's post,

Quote

And of each of these sizes an F4, F8, F9, F6 jet (from lean to rich). I can make small steps in idle jet-sizes. But the F21 idle jet has only 1 brother/sister: the F22. That is slightly leaner.

There seems to be no correlation in numbers to sizes to rich / lean! Basically it seems to be total guesswork LOL!

[Johnny Boy]

I’ll have to have a look at my F’s when I get in the barn again🙄

[YellowTaxi]

We are talking Idle jets here and not Immulsion tubes?

They also have an 'F' designation number.

[YellowTaxi]

[Johnny Boy]

39 minutes ago, YellowTaxi said:

We are talking Idle jets here and not Immulsion tubes?

They also have an 'F' designation number.

Yes idle jets👍

[Johnny Boy]

58 minutes ago, YellowTaxi said:

Thanks, I’ll study that 👌

[Johnny Boy]

All my  jets are F9.

I tried 45F9, 55F9 and 60 F9, none of which it idles smoothly on.

The only ones it likes are the 59F21, with these in it idles lovely smooth, even down to 500 rpm.

So my conclusion is that its the progression holes, I can't check the original 40 dcoes that are on the car, as they are the old type with a plug over the port.

The 40 dcoe Reedmorals replica Weber's that I have as reserve carbs, have 3 progression holes.

It has been suggested to me that 16v engines like the 5 progression hole.

Anyone else had any experience of 5 over 3 progression holes ?

[Miniliteman]

Progression holes have nothing to do with how it's running on idle. For twin 40's I would start with 50F9 's. And ofcourse adjust the mixture screws to get it running smoothly. Can you post a photo of the old type carbs with the plug over the port?

[Johnny Boy]

17 minutes ago, Miniliteman said:

Progression holes have nothing to do with how it's running on idle. For twin 40's I would start with 50F9 's. And ofcourse adjust the mixture screws to get it running smoothly. Can you post a photo of the old type carbs with the plug over the port?

I'll put up some pics tomorrow.

The 59F21 , best idle at 2 turns out, with a noticeable drop off 1/4 turn either way.

The other jets run lumpy, even with the best mix screw position.

[Johnny Boy]

25 minutes ago, Miniliteman said:

Progression holes have nothing to do with how it's running on idle. For twin 40's I would start with 50F9 's. And ofcourse adjust the mixture screws to get it running smoothly. Can you post a photo of the old type carbs with the plug over the port?

I am aware the progression holes have nothing to do with the idle🙄 😁

[Johnny Boy]

Here’s the fitted old 1980s Webers, with a blanking plug over the progression holes, I don’t know how many these carbs have without removing them, but I suspect it’s 3 holes

[Johnny Boy]

Here’s the Reedmoral replica Weber, brass top removed , and 3 progression holes.

[Johnny Boy]

Here’s a pic of the Reedmoral 40 DCOE 

[Johnny Boy]

Here’s the engine idling like a sewing machine on the 59f21 idle jets

 

 

[Miniliteman]

It does idle very well on the F21's. Never seen or heard of "Reedmoral" DCOE replica's.

[Johnny Boy]

42 minutes ago, Miniliteman said:

It does idle very well on the F21's. Never seen or heard of "Reedmoral" DCOE replica's.

That are made by a big carburettor factory in china, called Lantech.

they are very nicely made, not cheap looking like the “no make” ones.

I bought them as a back up set 😀

Edited June 15, 2022 by Johnny Boy