40 DCOE Jetting

[drola]

I just installed a korman autoworks stage 2 in my 1973 '02. I'm having a hard time with the transition from idle to part/full throttle. the idle is nice and smooth but when i accelerate under load it bogs down and sputters like it's running on 3 cylinders. below is a sheet with the specs of the motor. it has a 72-73 tii 008 distributor. so like i mentioned, the idle is perfect. once it gets above 3500 rpm's it kicks in and runs strong. it's just that transition spot that is driving me nuts.

so, in order not to get into all the tuning procedures etc here, my question is about the jetting of the carbs. I'm at sea level and my question is if the jetting i have is adequate for that motor at sea level or if it was jetted for another elevation. i bought the engine out of philly and it is in practically new condition albeit having been built 25+ years ago. it was just never driven.

i will go over all the tuning/setting/adjusting/troubleshooting this week but wanted to know if i'm starting with a good baseline for the jetting.

any suggestions are appreciated

 

Korman Engine Page 1.pdf

[majdomo]

Hard to say, but I’d wager the shop knew what it was doing when matching jets to the build. Here’s a jetting table, though, for reference. http://www.gracieland.org/cars/techtalk/weboem.html. Easiest to match your main chokes to the table, and then check your jetting against the chart. For what it’s worth, I’m a little up in elevation, 2250 ft, but took it all the way up to 8000 ft yesterday without any issues. My jetting, which was set for sea level:

- Air Correction- 180

- Emulsion - F16

- Main - 115

- Accelerator (pump) jet - 40

- Idle - 50F9

- Main choke - 32mm

- Aux Venturi - 4.5mm

 

YMMV, but my bogging between circuits was related to floats that were misadjusted (by me, no less...) to shut off the fuel flow earlier and lower the level in the bowl. Once I adjusted them back, the bogging was gone. If you haven’t already, worth pulling the lid off the carbs and checking the floats. If they’re brass, see if they maybe have some fluid in them (one of mine did and was probably as old as yours, maybe older). Doesn’t cost you anything but time  Also, a good cleaning never hurt, either. Good luck!

 

[NickVyse]

90 percent of carb problems are ignition related, or however the saying goes. I repeat this often but recently got caught out myself to the point of removing my 40s, sonically cleaning and rebuilding. Exact same misfire at low revs, coincidentally on the transition. Idled fine, went like stink up top.

 

Forced the misfire by driving for a couple of kms left foot braking in the rev zone effected. Shut the engine straight off and looked at the plugs to atleast ascertain which cylinder was to blame. With a constant misfire for this long the black trace of a short from a hairline crack in one of the plug connectors was clear to see, but hadn't been when inspecting before.

 

1 minute swap with a few euro part and she was back to rude health. You're never too old to be an idiot!

 

[drola]

8 hours ago, majdomo said:

Hard to say, but I’d wager the shop knew what it was doing when matching jets to the build. Here’s a jetting table, though, for reference. http://www.gracieland.org/cars/techtalk/weboem.html. Easiest to match your main chokes to the table, and then check your jetting against the chart. For what it’s worth, I’m a little up in elevation, 2250 ft, but took it all the way up to 8000 ft yesterday without any issues. My jetting, which was set for sea level:

- Air Correction- 180

- Emulsion - F16

- Main - 115

- Accelerator (pump) jet - 40

- Idle - 50F9

- Main choke - 32mm

- Aux Venturi - 4.5mm

 

YMMV, but my bogging between circuits was related to floats that were misadjusted (by me, no less...) to shut off the fuel flow earlier and lower the level in the bowl. Once I adjusted them back, the bogging was gone. If you haven’t already, worth pulling the lid off the carbs and checking the floats. If they’re brass, see if they maybe have some fluid in them (one of mine did and was probably as old as yours, maybe older). Doesn’t cost you anything but time  Also, a good cleaning never hurt, either. Good luck!

 

yes, i planned on checking float levels as one of my troubleshooting steps. also need to check the butterflies in relation to the progression holes. also the clod start system. lots of things to check. thanks for the chart. i'll use it to compare. i also cleaned the carbs before installing the motor so that's one step done

 

Edited July 6, 2020 by drola

[rcf925]

I cured same problem by changing idle air jet from 50 to 60

[jireland2002]

Try a larger idle jet.

[drola]

14 minutes ago, jireland2002 said:

Try a larger idle jet.

by larger would i go with a 60F8, 50F9, 55F8?

I'm not clear on how the idle jets are sized and what the 50,55,60 means in relation to the F8, F9..

[rcf925]

My emulsion tube is F9, Don't change yours yet, Just the idle air jet that pushes into bottom of idle jet holder, Takes like 5 minutes to change all four. If you have a 50, Start with increase to 55, If that doesn't help go to 60. If none of that helps just go back to what you had and look elsewhere. Jets are marked on them what they are 50,60 etc

Edited July 7, 2020 by rcf925

[TobyB]

Read Nick's post and check your ignition over.  The 'running on 3 cylinders' part especially makes me think he's onto something.

 

When the ignition's 100%,

Your jetting looks fine.  Jetting problems don't

usually cause a full- on bogging when you're in the right range-

and the 'right range' is pretty wide.

 

Check that your linkage is keeping you in sync in the transition from idles to

transition holes.  Google Synchrometer- it works, for $50.

 

If it's idling on all 4, then the transition jets are flowing fuel.

You can pull the covers off the progression drillings and confirm that

they're not plugged, because THAT would certainly cause a big splutt....

 

t

https://www.lainefamily.com/images/WeberTuningManual.pdf

[majdomo]

16 minutes ago, TobyB said:

 

https://www.lainefamily.com/images/WeberTuningManual.pdf

I was looking for this link too. This helped me out a bunch.

[drola]

52 minutes ago, TobyB said:

Read Nick's post and check your ignition over.  The 'running on 3 cylinders' part especially makes me think he's onto something.

 

When the ignition's 100%,

Your jetting looks fine.  Jetting problems don't

usually cause a full- on bogging when you're in the right range-

and the 'right range' is pretty wide.

 

Check that your linkage is keeping you in sync in the transition from idles to

transition holes.  Google Synchrometer- it works, for $50.

 

If it's idling on all 4, then the transition jets are flowing fuel.

You can pull the covers off the progression drillings and confirm that

they're not plugged, because THAT would certainly cause a big splutt....

 

t

https://www.lainefamily.com/images/WeberTuningManual.pdf

i'll check plug wires. they are not very old but worth a look.

i need to check the sync. at idle i had them pretty close but need to check at higher rpm's

earlier today i checked the progression holes and they looked fine. i also compared the butterflies/progression holes and if there is any difference it's negligible

but i'll double check everything again

i set the timing as per the sheet from the engine builder. 25 deg at 1500 rpm's. i need to check the advance at different rpm's to see how the distributor is working

[2002Scoob]

17 hours ago, rcf925 said:

I cured same problem by changing idle air jet from 50 to 60

Ya keep saying this on allot of DCOE posts, but 50 or 60 WHAT.

 

F2, f6, F8, F9, F3?

 

Pull those puppies out and let us know what ya actually got!  I'm honestly very curious.

 

16 hours ago, drola said:

by larger would i go with a 60F8, 50F9, 55F8?

I'm not clear on how the idle jets are sized and what the 50,55,60 means in relation to the F8, F9..

 

If you're 100% confident it's not an ignition issue, move on to your jetting. 

 

The first number references the size of the hole which the idle/progression circuit is pulling fuel, and the F# is the amount of air correction provided into that fuel, to create your mixture. And those F#'s are not sequential, they go as follows from lean to rich, as follows, with the most common sizes in bold. 

 

 

If your feelin' what I'm feelin... when it comes to that lean stumble in the progressions to reach the mains, it's likely down to a combo of issues with your float level, carb sync, and idle jet. and I'd suggest trouble shooting them in that order.

 

Get your float heights dialed, get it running, set your sync, and check it in a few positions in the progressions too. Confirm and re-check after you tighten things down, and again after a few heat-cycles because things do settle into place, or a good sync can be thrown outa' sync when you batten down the hatches.

 

I've had most success with a 55f8. It's still rich in places that doesn't make me happy, but she scoots the boots with it and is the leanest jet I've found that has the least issues with stumbling in the progressions before getting to the mains.  

 

50f6 works well for me too, and is very similar to the 55f8. (at least my jets are... I recently learned that 'calibrated' Weber jets aren't really THAT calibrated just a few are checked outa a VERY large batch) Still ain't perfect, thou. But ADD has kicked in and I got tired of throwing wads of cash at jets for the time being...so it'll stay there for now as I'm not really driving the car. 

 

And, of curious note... a 55f2 is WILDLY lean compared to a 55f8, even if it's somehow considered a logical lean step  from the f8... Regarding 'calibrated' parts... turns out 3 of the 4 55f2's I got from a reputable supplier, the F holes were improperly drilled, and were actually richer than they shoulda been, but very inconsistent cylinder to cylinder.... When i finally got 4 good ones, it would barely run it was so lean. 

 

I've tried 60F8 and F9's, and they're pig-piggy rich... but I haven't gone to the complete end of the lean spectrum so maybe that's where @rcf925 is playing?

 

Watch this guys video... It's super good for understanding function and theory. He's going for 36mm chokes, and it's a Pinto 2.0, so it's not straight applicable to our 2l, but great learning for setup and theory!!!

 

 

[NickVyse]

It's a small price to buy a new set of plugs, leads, cap and rotor arm (and always good to have a spare set anyway) - this car was set-up and dynoed and run in by Kormann, so I think you can be quite confident the jetting is pretty good. What you desribed in your OP doesn't sound like a mild stumble on transition, but a loss of spark.

[rcf925]

  23 hours ago, rcf925 said:

I cured same problem by changing idle air jet from 50 to 60

Ya keep saying this on allot of DCOE posts, but 50 or 60 WHAT.

 

Sorry for confusion, My setup is F9, 160 air corrector jet, 60 Idle jet, 130 main, 34mm choke

[2002Scoob]

2 hours ago, rcf925 said:

  23 hours ago, rcf925 said:

I cured same problem by changing idle air jet from 50 to 60

Ya keep saying this on allot of DCOE posts, but 50 or 60 WHAT.

 

Sorry for confusion, My setup is F9, 160 air corrector jet, 60 Idle jet, 130 main, 34mm choke

 

 

Ah ok. then you're 60f9 idle jet (these two factors identify a single jet... F9 is the air correction hole drilled in the side of the 60 jet itself), 130 main, 160 air, and 34 chokes.

 

Don't wanna derail the OP's post, but that sounds like a crazy rich setup, but of course every motor is different. Did ya ever get a wideband? A 60F9 in my car wouldn't even register a number on my wideband when on the progressions, which stops at 10:1. If I were to combine that with a 130/160 , you for sure aren't going to be getting a lean stumble, because I  think that would also make for an extremely rich midrange/top end. 

 

According to my not-so-great memory of  my recent tuning (I'd have to go back, it's been a little while), I found a 130/180 main/air and a 55f8 idle jet with 34 chokes nets me a max 10.5-11.5:1 at WOT, which is quite rich. 125/170 is closer to 12.5, and a 175 gets me closer to 12.8-13 at WOT. 

 

But the OP's motor is running more cam than me-292 vs 304, and i'm sure there's enough other differences in there as well.

 

Of note though, if you look at that dyno note sheet it says that the motor wasn't brought to WOT or lugged (I assume meaning, applied load). It says it's just run-in on the dyno, which doesn't necessarily mean the jetting was really dialed in on the dyno either, so maybe there's room for improvement?

 

If ya don't end up getting it fully sorted yourself, don't rule out taking it to a guru who knows DCOE's either. If ya like the act of driving more than the hobby of fiddling and throwing away money on jets, it's a good option

 

But do eliminate all other potential variables before assuming your jetting is the problem!

Edited July 7, 2020 by 2002Scoob