DCOE 50f8 too lean / 55f8 too rich - what next?

[man_mark_7]

21 minutes ago, Stevenc22 said:

12-13 is perfect for carbs.  If you were shooting for 14.7, that is what modern cars use for emissions and doesn't apply to us. 

Although it would be nice to see 14s while cruising at highway speeds for fuel economy, I'm not too hung up on that. I'm more interested in being in the AFR 13.2 - 14.0 (lambda of .90 - .95) for best power. I drop into the 11s sometimes and also hit 16/17 every now and then.

 

As I have seen mentioned elsewhere on this forum, I'll be happy when I see an 11 or see 15 or higher only on fleeting rare occasions.

[Golfcar]

On 11/15/2020 at 9:15 PM, Stevenola said:

 

I'd say this is just about perfect, as long as WOT is around 12.5, no need to frustrate yourself trying to improve on this.

I agree. 12.5 is very good. Carb engines do not run will like a FI engine at 14.7 Stoich.  

[2002Scoob]

Found out why I gave up on the 50f9 today. That sucker is LEAN LEAN LEAN  55f8 is still fat-fat-fat. Le sigh. Parkin' her for winter here soon anyway. It'll be the Jeff of 2021's problem then. 

[man_mark_7]

4 hours ago, 2002Scoob said:

Found out why I gave up on the 50f9 today. That sucker is LEAN LEAN LEAN  55f8 is still fat-fat-fat. Le sigh. Parkin' her for winter here soon anyway. It'll be the Jeff of 2021's problem then. 

I just tried 55f11 and 50f6 over the past couple days since my 55f8s also seem too rich. Both of them were too lean through and slightly above transition. Went back to 55f8s but more experimentation is needed.

 

Does anyone know if in fact a very rich 50 idle jet like a 50f6 would overlap with a very lean 55 jet like a 55f11?

 

This is my understanding of how the air bleed on the idle jets affects the mix:  F6 (richest), F12, F9, F8, F11, F13, F2, F4, F5, F7, F1, F3 (leanest). That being said, I only find F6, F9, F8, F11 in several places so I assume they are the most commonly used?

[TobyB]

I hope this is right, because it's what I use...

 

The size of the jet controls how much fuel CAN get through,

and the air corrector adds the emulsion air.  In THEORY they

should not overlap, as the jet end affects lower- airflow fuel flow,

and the air corrector end (or side, in this case) controls higher- airflow

AIR-in-fuel flow, or in other words, high airflow 'leanout'.

 

In practice, it's an absolute booger to figure out what's happening dynamically inside the carb.

 

I have read at least one book that says you should disable the main circuits, and tune

the idle and transition separately on the car.  I guess you'd need 0 main and emulsion jets for that...

Then, once you have good logs and 'causality relationships'  i.e. have them figured out,

you can start tuning the mains.  It makes sense.  As I've only raced on the things,

I never bothered.

But I can see how it'd be really helpful to have air-fuel curves that show what the idle and 

transitions do, so you could then subtractively deduce how much the mains overlap the transition 

circuits...

 

As to common usage, I have a serious suspicion that what's available

dictates what gets used, NOT what's needed.  These carbs go onto everything,

and the jetting and correction varies a LOT based on that.  Plus, what it's really

used for. 

So if you are up for it, soldering up and redrilling air correctors may

be in your future.  I can't recommend it for the fuel end, as there's a lot more

going on with taper, surface finish, and precise sizing, but on the air end, it's

not nearly as sophisticated, and the diameters change a lot more...

 

I love it when cars, science, art and fabrication come together.

 

t

 

Edited November 23, 2020 by TobyB

[Lorin]

1 hour ago, TobyB said:

I hope this is right, because it's what I use...

 

The size of the jet controls how much fuel CAN get through,

and the air corrector adds the emulsion air.  In THEORY they

should not overlap, as the jet end affects lower- airflow fuel flow,

and the air corrector end (or side, in this case) controls higher- airflow

AIR-in-fuel flow, or in other words, high airflow 'leanout'.

 

In practice, it's an absolute booger to figure out what's happening dynamically inside the carb.

 

I have read at least one book that says you should disable the main circuits, and tune

the idle and transition separately on the car.  I guess you'd need 0 main and emulsion jets for that...

Then, once you have good logs and 'causality relationships'  i.e. have them figured out,

you can start tuning the mains.  It makes sense.  As I've only raced on the things,

I never bothered.

But I can see how it'd be really helpful to have air-fuel curves that show what the idle and 

transitions do, so you could then subtractively deduce how much the mains overlap the transition 

circuits...

 

As to common usage, I have a serious suspicion that what's available

dictates what gets used, NOT what's needed.  These carbs go onto everything,

and the jetting and correction varies a LOT based on that.  Plus, what it's really

used for. 

So if you are up for it, soldering up and redrilling air correctors may

be in your future.  I can't recommend it for the fuel end, as there's a lot more

going on with taper, surface finish, and precise sizing, but on the air end, it's

not nearly as sophisticated, and the diameters change a lot more...

 

I love it when cars, science, art and fabrication come together.

 

t

 

Well said, Toby. 

[man_mark_7]

23 minutes ago, Lorin said:

So if you are up for it, soldering up and redrilling air correctors may

be in your future.  I can't recommend it for the fuel end, as there's a lot more

going on with taper, surface finish, and precise sizing, but on the air end, it's

not nearly as sophisticated, and the diameters change a lot more...

 

Yeah, I have been avoiding drilling the idle jets for these reasons. I have heard that Weber actually flow tests (or did flow test) the jets to make sure that the combo of jet hole, taper, air bleeds, etc makes a 50 behave like you would expect a 50 to behave, not that it has an exactly 0.50 orifice.

 

I do wish I could find .52 jets somewhere though. I have seen them listed on old Weber literature, but can't currently find them. Short of finding some, I may have to start experimenting with drilling out some .50 jets.

[Chris_B]

You might want to check this out: http://Webstore.com/~DCOE_Tuner

 

This gentleman (Keith Franck) has reengineered the calibrated parts in the idle and main circuits. Of particular interest in your situation with the idle jets is that he has designed an adjustable idle jet so that you can twiddle the airflow to multiple settings in the same jet. See the "W" series idle jet. These solved my idle/transition circuit problems in my 45 DCOEs

[man_mark_7]

3 hours ago, Chris_B said:

You might want to check this out: http://Webstore.com/~DCOE_Tuner

 

This gentleman (Keith Franck) has reengineered the calibrated parts in the idle and main circuits. Of particular interest in your situation with the idle jets is that he has designed an adjustable idle jet so that you can twiddle the airflow to multiple settings in the same jet. See the "W" series idle jet. These solved my idle/transition circuit problems in my 45 DCOEs

Wow - great resource. Much appreciated!

[Chris_B]

He actually has two styles of idle jets- one designed for low manifold vacuum at idle and one for high manifold vacuum. I believe the jets currently shown on the website are for high vacuum (e.g., > 10 Hg). Have you ever measured your vacuum at idle?

[man_mark_7]

16 hours ago, Chris_B said:

He actually has two styles of idle jets- one designed for low manifold vacuum at idle and one for high manifold vacuum. I believe the jets currently shown on the website are for high vacuum (e.g., > 10 Hg). Have you ever measured your vacuum at idle?

Interesting. I can't find anywhere that outlines the Franck jet theory of operation. I did have some traces of manifold vac, but I can't find them right now. I'll take some measurements and see if I can get in touch with him (after reading through the Groups.io stuff).

[Chris_B]

Anything like that would be pretty much constrained to the discussion groups. Used to be a Yahoo group but recently moved to Groups.io.

[2002Scoob]

I joined into that Keith Franck mess for a bit, and didn't get much in the way of clear assistance as to what I should actually try.

 

It's also unfortunately not 'forum' based, instead it's this spammy mess that just inundates your inbox with emails that you're supposed to reply to to make threads or get answers instead of going to an actual website/forum. 

 

I dunno. Whatever he's doing product wise seems pretty rad, but his method of reaching out to people technology wise is in-line with the days you used to have to put your home-phone's receiver on a modem box to connect to the internet. 

 

I dropped out because I couldn't take all the junk that was destroying my inbox. 

 

If anyone figures something out and has insight to recommend I'd draft off ya, but trying to get to the right answers or info was just downright frustrating.  

[Chris_B]

It is available in digest form (one email per day, if there are posts). I can see how receiving each individual message would be less than useful. Also, there have been a small group of people in longstanding discussions. Coming in to the middle of one of those would be difficult, but the threads are available for search.