Weber 45DCOE lean transition

[Vali]

Hello Guys,

I have a CBR race engine with 45DCOE 152G (4 progression holes).
My engine runs well but has a rich idle.
Idling is around 0.85 Lambda and with small throttle opening up to around 2500-3000 it goes leaner up to 1.05 Lambda. If I set the mixture screw like it should be set (highest idle running) and want to go up to 2500 it stutters as it gets too lean. That´s why the idle is set very rich (3.25 turns out). Engine and carburetors have done around 400 kilometers.
If I fit a 60F8 or 65F8 then the car bogs and won´t rev to 2000.

Will I get the transition with steady 0.9-0.95 right, if I find the correct idle jet or does it has more to do with the emulsion tube?
The "classic car specialists" in my area in Germany can´t help me.
They only set up idle with their gas tester.
Can´t help me with suggestions whether go go leaner/richer with jets etc.

Engine and carbs are new.

Currently fitted:
45DCOE 152G (4 progression holes)
Emulsion Tube F16
Main Jet 150
Air Corrector Jet 130
Idle Jet 55F8


Anybody from Germany here and can recommend me a carb specialist, ideally with dyno?

[mbell]

Anybody from Germany here and can recommend me a carb specialist, ideally with dyno?

Maybe look for Italian classic car places, they'll have more expereince with webers than you averavge rolling road that tunes modern BMWs and Audi's.

Can´t help me with suggestions whether go go leaner/richer with jets etc.

I'd go back to the original jet size and try an idle jet with more/larger air holes. My understanding is the air hole changes how fuel is delivered between low revs and high revs. More air holes means less fuel at low revs but more at higher revs. So helps with transitions.

After that you can mess with main circuit to get it kicking in sooner:
- Raise fuel levels
- Smaller choke
- Change air jets
- different tubes

Personally I use the setups from Keith,as they more configurable and easier to understand how to adjust them.

[661]

What does Craig suggest?
He likes his engines to run at 0.91-0.92 .
I've just changed my exhaust and choke size so am off to the rolling road in a fortnight.

[Vali]

The italian classic car specialist (with huge collection of Abarths) was very nice and helpful but can set idle only, too.
And does synchronizing just by ear which were very far of being synchronized to my STE and clock synchronizer.


However, I just found the white paper of Keith somewhere here in the Forum and do understand a lot more now.
And the idle with 12.5 AFR or 0.85 Lambda just seems to be spot on.
I understand it´s not like modern engines but now I know it just seems to be normal.

What I still could do is setting up the float height from 27mm to 25mm. I already have no hesitation between 2000-3000 rpm.

@661:
I had a chat with Craig earlier because of a rich mixture at WOT with 0.7 Lambda and lower.
Which is very different to his dynoeing which had 0.88 to 0.92 from 3000 to 8000 rpm but that´s on his dyno with engine only. Maybe he forgot to put the air filter on at dynoeing.
He suggested to me trying a 145 main jet.

I´m learning.
Now I will study the Keith papers carefully and try to understand much more.

[RichardHawkins]

Keith Franck runs two web sites, sidedraft central and vintage technology garage. Keith seems to know more about Webbers than most people, and has done a lot of work designing and making alternative jets, tubes, and repositioning the progression holes. I have been following his work for a few years now, and whilst I don’t understand a lot of what he is doing I do think his work is based on sound evidence.

Hope this helps,

Richard Hawkins

[Andy8421]

Hello Guys,

I have a CBR race engine with 45DCOE 152G (4 progression holes).
My engine runs well but has a rich idle.
Idling is around 0.85 Lambda and with small throttle opening up to around 2500-3000 it goes leaner up to 1.05 Lambda. If I set the mixture screw like it should be set (highest idle running) and want to go up to 2500 it stutters as it gets too lean. That´s why the idle is set very rich (3.25 turns out). Engine and carburetors have done around 400 kilometers.
If I fit a 60F8 or 65F8 then the car bogs and won´t rev to 2000.

Vali,
You mentioned it is a race engine. What cams are you running?
I have a tuned twincam that I race(d) in the HSCC roadsports series. The engine coughs and splutters like an old tractor until it 'comes on the cam' somewhere around 3000rpm. From then on it is different beast entirely.

Light throttle, low rev running is not usually an area that builders / tuners of race engines spend much time trying to optimise.

Andy.

[Vali]

Hi Andy,

camshafts are both CBR450.
Today I have visited someone with my car who had a quick look at it.
He will get it on his old dyno and set it up correct for me.
He also thinks there are only small changes requiered.

We´ll see.