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

[man_mark_7]

It has been a few weeks since installing dual Italian DCOE 40 / 151s, still fettling them in. Stock engine except for header, electric fuel pump (2.75ish psi), 123ignition.

 

Here are my current specs: 

My issues are that with a 55f8 idle jet I'm too rich everywhere, idling about mid 12s and very low 13s for almost every other load condition. When I swap to a 50f8 then the car is way too lean through the transition ports shooting up into the 18s if I try to transition through them slowly. This being said with the 50f8s the car still idles on the rich side (low 12s).

 

I have some 55f11 idle jets on order, but I'm not really sure how much of a difference to expect and it probably wont help get my idle mix out of the 12s.

 

My throttle plates are "perfectly" aligned as best as I can tell. All 4 just start to expose the first transition hole as I begin to move the throttle so I think the throttle plate positions are OK at idle? 

 

What would you try next?

[uai]

I'd leave it as it is as long as the car is responsive and doesn't stutter. I think feeling is what counts on idle circuit not A/F and to me everything between 11 and 14 is ok on idle circuit.

When it comes to WOT and RPM then A/F gets important.

But you could check 50 F9, F12 and F6 in that order.

[TobyB]

Agreed- for carbs, 'mid 12's' is actually pretty good!

 

As long as the transitions to the mains happens smoothly,

you're in good shape.  DO try the larger air corrector idle,

but I bet it'll give you a lean spot getting into the mains.

But you never know- it might lean out light cruise just how you'd like it.

 

t

I love carbs.  I love points.

I DRIVE cars with neither, most of the time.

 

[man_mark_7]

2 hours ago, uai said:

I'd leave it as it is as long as the car is responsive and doesn't stutter. I think feeling is what counts on idle circuit not A/F and to me everything between 11 and 14 is ok on idle circuit.

When it comes to WOT and RPM then A/F gets important.

But you could check 50 F9, F12 and F6 in that order.

Thanks for the advice! I was just worried that idling at mid 12s would start to gum up the plugs. I suppose I can run it for a while then pull the plugs to see how they are looking.

 

Regarding the 50 F9, F12, F6 - Sounds like a good idea. I was trying to go leaner on the 55f8, but I could also try richer on the 50f8. I just don't know which is the better avenue. I do have 50f6's on order too so if these are too rich I will try the 50F9 and 50F12.

 

[uai]

You can get a 0.75 and a 0.80 Drill (if you get metric drills) and just drill the air hole in the f6 Jets.

i also went that way when f6 was too rich and f12 was too lean.

just get regular drills no extra sharp tungsten stuff, they are not good when drilling by hand.

Edited November 15, 2020 by uai

[2002Scoob]

 

I need to get back in the fiddling game...

 

I fired up Brunhilde for a drive today for the first time in prolly 4-5 months. 

She runs a TREAT. Don't be afraid of ordering a handful of jets, or even a kit from Ebay that has a variety in the range you're looking for, and spending a weekend swapping things in and out in a systematic way.

 

Today I put in brand new brass floats I got a while ago from a carb shop here in Germany that had screwed up an order of mine, and failed to get back to me for something like 6 months....While the original floats always weighed exact, they were visually different and one had a small BB sized dent on the top, and that bothered me. Set my heights (7.5) Set my drops (10.5), and after a warm-up, set idle to 13-ish.

 

If ya ignore the wideband, it runs great. But they're still not where I know they could or should be, and maybe you're battling some of the same. I've still got visions of my first setup tuned by my Bavarian Guru that was 13.5 in ALL the right places. ?  I've been unable to achieve such nirvana on my own since.

 

As Toby says, idling in the 12's, preferably mid to high 12's is A-OK. I wouldn't worry about it fouling plugs too much. Just make sure you're wringing it out now-and-again and your AFR's elsewhere aren't too rich. 

 

I need to check what I put in Idle-Jet wise so long ago, as it still feels too rich when at light cruise in the transitions... 10's -11's more of the time than I'd like to see. But at least that dreaded lean-spot is gone.

 

It's like the carbs do exactly the opposite of what I'd like, and think they should.... They're often rich on light throttle cruise (10.5-11.5), and lean-up  when I get on it... When what I'd prefer is to be lean on light throttle cruise (13.5-15) and fatten up when you get on it (12-13.5).

 

Gunna see what's in there tomorrow, maybe it'll help you (and me?) Not many driving days left, pretty much planning to winter the car any day now...That '4th hole' drilling jig for the transitions that someone posted up a while ago seems interesting... But that's stuff I'd leave for an expert to diagnose and implement. 

 

-J

Edited November 15, 2020 by 2002Scoob

[man_mark_7]

1 hour ago, 2002Scoob said:

 

I need to get back in the fiddling game...

 

I fired up Brunhilde for a drive today for the first time in prolly 4-5 months. 

She runs a TREAT. Don't be afraid of ordering a handful of jets, or even a kit from Ebay that has a variety in the range you're looking for, and spending a weekend swapping things in and out in a systematic way.

 

Today I put in brand new brass floats I got a while ago from a carb shop here in Germany that had screwed up an order of mine, and failed to get back to me for something like 6 months....While the original floats always weighed exact, they were visually different and one had a small BB sized dent on the top, and that bothered me. Set my heights (7.5) Set my drops (10.5), and after a warm-up, set idle to 13-ish.

 

If ya ignore the wideband, it runs great. But they're still not where I know they could or should be, and maybe you're battling some of the same. I've still got visions of my first setup tuned by my Bavarian Guru that was 13.5 in ALL the right places. ?  I've been unable to achieve such nirvana on my own since.

 

As Toby says, idling in the 12's, preferably mid to high 12's is A-OK. I wouldn't worry about it fouling plugs too much. Just make sure you're wringing it out now-and-again and your AFR's elsewhere aren't too rich. 

 

I need to check what I put in Idle-Jet wise so long ago, as it still feels too rich when at light cruise in the transitions... 10's -11's more of the time than I'd like to see. But at least that dreaded lean-spot is gone.

 

It's like the carbs do exactly the opposite of what I'd like, and think they should.... They're often rich on light throttle cruise (10.5-11.5), and lean-up  when I get on it... When what I'd prefer is to be lean on light throttle cruise (13.5-15) and fatten up when you get on it (12-13.5).

 

Gunna see what's in there tomorrow, maybe it'll help you (and me?) Not many driving days left, pretty much planning to winter the car any day now...That '4th hole' drilling jig for the transitions that someone posted up a while ago seems interesting... But that's stuff I'd leave for an expert to diagnose and implement. 

 

-J

Thanks - I think I'm seeing pretty much the same as you when I run the 55f8 idle jets. I drop to the 10s sometimes when I get on it gently, then goes lean then starts getting richer and richer as RPM goes up. I still need to drop down a size or so on my Main jet I think since I'm going rich at higher RPM. I don't know how visible this graph will be, but it shows one WOT run up to about 5k RPM.

 

Thanks for any advice.

 

[Stevenola]

10 hours ago, man_mark_7 said:

My issues are that with a 55f8 idle jet I'm too rich everywhere, idling about mid 12s and very low 13s for almost every other load condition.

 

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.

[Chris_B]

Try some 50f9s. that is the next logical step down. With all due respect to other posters, do not drill out your jets. 

[uai]

10 hours ago, man_mark_7 said:

 I still need to drop down a size or so on my Main jet I think since I'm going rich at higher RPM.

A larger Air corrector Jet would be better than a smaller main Jet from what I can see. But I think it's pretty good the way it is.

Edited November 16, 2020 by uai

[2002Scoob]

29 minutes ago, uai said:

A larger Air corrector Jet would be better than a smaller main Jet from what I can see

 

This^ 

 

Your air correctors affect the richness of the main-jet at as your RPM's climb. So if you see a rich taper, go larger. Lean taper, go smaller.

 

ALTHOUGH.....

 

I just saw you're running 32's... Which is what I was running when I got Brunhilde Pro-tuned. Here's that post, and it's jetting. 

 

 

Idle- 50F9

Main-115

Air Corrector-210

Emulsion Tube-F16

 

That was the best my car ever ran with 32's, and that was with a bone-stock bottom end and 292 Schrick. Ya tried something similar, yet? 

 

 

[uai]

4 hours ago, Chris_B said:

Try some 50f9s. that is the next logical step down. With all due respect to other posters, do not drill out your jets. 

And what do you do when f6 is too rich and f12 is too lean?

[2002Scoob]

41 minutes ago, uai said:

And what do you do when f6 is too rich and f12 is too lean?

Go fuel injected? (or electric?)

 

I joke, but only 49% joke

Edited November 16, 2020 by 2002Scoob

[TobyB]

Quote

Thanks - I think I'm seeing pretty much the same as you when I run the 55f8 idle jets. I drop to the 10s sometimes when I get on it gently, then goes lean then starts getting richer and richer as RPM goes up. I still need to drop down a size or so on my Main jet I think since I'm going rich at higher RPM. I don't know how visible this graph will be, but it shows one WOT run up to about 5k RPM.

 

Hey, thanks for posting that- it's very useful with the TPS.

 

Mains first, because they're easy:  your main jet may be a bit too big.  You can try the next step up, and see.

When you do, your air corrector may then be too big, and need to go smaller, to get the smaller jet to pull more fuel

at higher flow rates.  One step smaller may just be TOO small, tho.  I wish they went in 2/3 steps, like Mikuni.

If a smaller main makes you go too lean (above 13) then yes, a bigger air corrector will help with your over- rich

condition.

The question is- is the grey box all main jet, or is the transition helping?

If it's all main, then it's about right, and the brown box is all air corrector.

But the sharp knee makes me think there's transition jet effect in there.

It's hard to tell because the throttle was still opening.

 

You will make a noticeable amount of power from getting your 3k and up mixture leaner.

 

Now, on to the hard part- you're going pretty lean on the transition (idles), early on.

That will certainly be affected by how the throttle was opening, but that's going to hurt

power.  (red box)  And it may detonate, since it seems to go leaner as the throttle opens.

This is one place where more pump jet might help, as it's a transient effect that seems to

happen as you open the throttle.  

One thing that's odd to me- you're good with the throttle closed but revs up (green box)

which is great- except that all my carbs are usually pretty lean there, since the engine's

spinning fast and drawing a huge vacuum.  Maybe I have idle air leaks...

 

You could try a LARGER transition jet....

But here's where the tuning limitations of carbs kick in-

you need that transition jet for driving around on.  So log a bunch

of 'grocery store' type trips, whatever that is for you and the car

(if it's relatively spirited drives on winding roads, that's just fine.

But lateral acceleration affects fuel ratio, so be careful there...)

See if you can find any consistent trends, and try tuning for those.

Then check against a hard pull (from almost idle in 3rd, or below 2k in 4th)

and see what's happening.

 

Keep posting the traces- from those, we can offer meaningful guidance.

 

And yes, this is totally a 'try a different jet and see what it does'

type thing.

 

t

ps, you won't foul your plugs enough to matter at 12:1...  

 

Edited November 16, 2020 by TobyB

[man_mark_7]

14 hours ago, 2002Scoob said:

 

This^ 

 

Your air correctors affect the richness of the main-jet at as your RPM's climb. So if you see a rich taper, go larger. Lean taper, go smaller.

 

ALTHOUGH.....

 

I just saw you're running 32's... Which is what I was running when I got Brunhilde Pro-tuned. Here's that post, and it's jetting. 

 

 

Idle- 50F9

Main-115

Air Corrector-210

Emulsion Tube-F16

 

That was the best my car ever ran with 32's, and that was with a bone-stock bottom end and 292 Schrick. Ya tried something similar, yet? 

 

 

I can't believe I didn't find your write up when I was originally searching the archives. Thanks for pointing it out! I think after playing with the idle jets that I will try a 115 main to lean out my higher RPMs a bit. I am surprised that you were running a 115 main with a 210 air corrector. I have been lead to expect that the air corrector will be about 50 larger than the main. That being said - if it works, it works!