DCOE Tuning Help

[Stevenola]

I agree that your mains look small, I would drill those 120's out 5 at a time until your lean hole improves, my guess would be 135 or so, then adjust air correctors accordingly if it is too rich in the upper rpms.  I think the reason you are only 1.5 turns out is because your idle jets are quite large, so consider a 55 or so, you will likely need to open the mixture screw to compensate for the smaller jet, further improving the lean hole off idle and compensating for the richer mains.

[TobyB]

Quote

 I would drill those 120's out 5 at a time until your lean hole improves, 

 

...only if you have a set of jet drills, as reaming a jet oversize is removing a TINY bit of metal.

And then the inlet and outlet tapers need to be restored, as a DCOE 'number' is a flow rating,

not a size measure, exactly.

 

The ONLY time I've ever contemplated drilling was when I needed a set of 127.5 mains.  

And the more I measured, the less I was confident that I'd get 4 balanced jets...

 

t

 

[TobyB]

Oh, and DON'T change the main air correctors to fix this- you're not using them yet.  They don't kick in until

flow is significant, and you're not flowing enough at 3k to be using them.

 

AND they make things LEANER as you go bigger. 

 

So if you're starting to go rich at 5500, you'd go up by 15 on the airs.

If you're going lean, go down 15.  Or so.  I usually just use what I have, then

look at the trace to see what effect the air had.  It's less than fuel, and the emulsions modify it.

 

fwiw,

 

t

again

[Stevenc22]

This is all good info. Who knew that when i set out to lean out the engine i would end up with significantly fatter main jet.

 

I have some fatter mains ordered and will report back.

 

These DCOE's really are pretty crazy to tune. 

 

 

[2002Scoob]

On 9/9/2020 at 6:29 PM, Stevenc22 said:

These DCOE's really are pretty crazy to tune. 

 

Yup.

 

I bought a little run-about electric car here in Germany, and Brunhilde has only moved once since. (also the reason I haven't been posting or on the forums much...)

 

I thought I had things pretty good from my most recent bouts of experimentation, but when I did drive it last, that damn 'hole' is still very much a thing, and it's just what you're experiencing.  

 

You're welcome to digg up my last thread and try some of my experiments... It's only been a few months but I can't even remember where I left off. 

 

There's something about 34 chokes in 40DCOE's that is a PITA to tune reasonably lean, reliable, and consistent with 34's and F16's. It opens up all sorts of issues I never had with the 32's, cept they didn't have much power up the RPM range. It's tempting to just go back to 'em and live with that my 02 will never really be a screamer. 

 

Till it's electric. 

 

Edit-

Here ya go, that was my last effort-

 

 

Edited September 12, 2020 by 2002Scoob

[uai]

2 hours ago, 2002Scoob said:

, but when I did drive it last, that damn 'hole' is still very much a thing, and it's just what you're experiencing. 

Perhaps that hole is not carb related.
Here same engine only different exhaust header/downpipe (blue vs. magenta) and jetted to fit the exhaust one goes up the one goes down. Will drive two other headers to the dyno in the next weeks. And although the Magenta has lesser torque driveability in day to day traffic is better because that hole is bit further up the rpms.

Edited September 12, 2020 by uai

[2002Scoob]

17 hours ago, uai said:

Perhaps that hole is not carb related.

 

I wish.

 

That, dear sir, is a dip. If that were a hole, then what I have would be the Verdon Gorge

 

How Steven Describes it, and displays in his vid is pretty well aligned with the issues I've had getting.

 

We also have very similar motors. 'built' 9.5:1 compression, and @Stevenc22, don't you also have a 292?'

 

On 9/8/2020 at 2:39 AM, Stevenc22 said:

The car used to run pretty good but was super rich all over (10:1)

 

Uh huh. Sounds bout right!

 

On 9/8/2020 at 2:39 AM, Stevenc22 said:

Now if im cruising along and i give the car anything more than 30% throttle, the car immediately goes lean (19:1) and the car doesn't accelerate. Its almost impossible for me to get onto the main jets now the lean hole is so big. Any decent throttle, the car goes lean and stumbles.

 

Yup. I feelz, your feelz.

 

[Stevenc22]

Scoob, got some more jets yesterday so the testing will continue. I'm running a stock cam. 

 

I'm running a 123 with a good curve however I do wish we could hook up a vacuum signal to allow the 123 the better react to throttle input.

[Hans]

7 hours ago, 2002Scoob said:

 

 

That, dear sir, is a dip. If that were a hole, then what I have would be the Verdon Gorge

 

 

 

No Grand Canyon, but impressive nonetheless.

 

Out of curiosity, OP, what is your max advance?

[Stevenc22]

36 degrees.

 

 

I tried 130 main jets with the F955 idle jet and the lean hole was still there and the car was near undrivable.

 

I went back to rich idle jets, F965 and the 130 mains and the car is better and drivable. So im back to where i started, make everything super rich and the car drives okay.

 

[Hans]

Ok, timing not an issue. A stupid question perhaps but is it possible you have too much carb for the engine with 34s?

[rcf925]

2 hours ago, Hans said:

Ok, timing not an issue. A stupid question perhaps but is it possible you have too much carb for the engine with 34s?

 

 

And stock Cam

[TobyB]

Howabouta 65 transition jet???

 

t

 

[Stevenc22]

17 hours ago, Hans said:

Ok, timing not an issue. A stupid question perhaps but is it possible you have too much carb for the engine with 34s?

 

Dont think so. Top End performance uses 34's on even their mildest 120hp engines.

 

 

[Stevenc22]

9 hours ago, TobyB said:

Howabouta 65 transition jet???

 

t

 

 

Honestly i dont even know where the pump jet is located

 

I am happy to order some 65's to try out.

 

Thanks

Steven