Quick one guys. At a track event and I think i'm running to lean.
What is ideal?
I know we've killed this topic to death! I'm terrible at the search function.
Please help

13.4 A/F
135 main jets on 45 webers

at full throttle it will be rich and then get leaner and leaner towards redline

you want between 12.5 to 12.9ish... at the lean point of redline
so it will likely be more rich at 4k.. or 5k than redline

what rpm were you getting your readings?

dyno pulls start around 3k ish... then give the motor time to clean out and have consistent full throttle to watch the AF ratio under load

running lean at redline is a sure way to hurt the motor

an do you mean 44 webers?

the velocity (affected by choke size) has a lot to do with how well the carbs atomize at tip in.... and thus what jets will work best. Which main venturi size are you.

if you leave the chokes alone you will want bigger mains
if you put large chokes in you can pick up a few hp at redline by giving up midrange. But this is standard operation for a race motor that ideal is going to redline every shift. bigger chokes also require bigger mains

rpm is 5500-6500 with the 13.4
Thats with 135 mains
I don't have a 140 set. I do have a 145 set. Is it that simple?
Thanks Brant. I'd figured you'd speak up.
Shane
40idf sorry really tired.

I would absolutely throw the 145's in.
they are probably the right ones... but if they are too big or you pick up a midrange stumble you can buy something else.

if it does pick up a midrange stumble, you may be able to play with air correction/emulsion tubes or idles to fine tune it out

the biggest jets that dont destroy the midrange are the most power
and the same technique applies to chokes.

this will not make a fun street car... but will inch towards HP for the track.

Shane,
with your displacement and camshaft, you're giving up a lot of potential using 40IDFs without doing substantial mods to the carbs.
Big primary venturis like the 36mm chokes I use don't work too well in 40IDFs unless the top plate is opened up and the secondary vent support ring is trimmed.
44IDFs have a more open inlet to the carb throats and don't need any mods to flow much more air.

In regard to your jet sizes, I wouldn't hesitate to try the 145 mains and also increase the air correction jet size as needed to compensate for any over-rich condition which might occur.
The ideal jets will likely end up around .25mm apart.
For example - 150 mains:175 a/c

I'm sure my random fuel mixture isn't helping.
What fuel would you guys run with 10:5 to 1 compression ratio?
Thx Chris for your help too. My dad "the real mechanic" is not with me or I'd be bothering him.

100 octane unleaded should work.

I agree with everything that's said, particularly Chris's suggestion about the 44s. For that displacement, you're much more in the range of 32-36 mm main chokes (venturis). If you're running 40s, it's very likely that your venturis are 28mm, or at most, 32mm. I think that 36mm are pretty hard to find for a Weber 40.

I have a set of 44s that I'm going to be selling soon once I finish rebuilding them. They're currently setup with 36mm vents and you can swap over all of your jets to them, including the 145 mains. Or I can do it for you if you're interested.

Do the 44s fit on the same manifolds?

Almost certainly. Most of the manifolds around were made to accept up to Weber or Dellorto 48s.

You can also purchase a carb drill set and drill each jet progressively until you hit on the right size. Then order the correct ones.

That works too. Though it won't net you the full potential that the larger carbs will, you can go this route and get the jetting more fine-tuned. I've got a set of jets that were filled and drilled previously, but they're currently somewhere around 1.25. You could open them up to your current size and go from there. That way you wouldn't be drilling an original set of jets.

what displacement is the motor?

Hi,
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Nuther...

2258cc

Thank you, I can't help with your issue, these guys can though.
I am just going to learn whatever setup you land upon.



Rich

Shane. I didn't realize the motor displacement. What size chokes? I'm guessing you have a lot of easy horsepower left in your induction. Bigger mains and chokes.

Thanks for the help and advise everyone. Working on the carbs next week.

So I think I contaminated my O2 sensor. Just ran the car, changed the mains from 125 to 145 with no change on my gauge. So who knows what my true mixture was on my last race weekend.

Same weather?

Yep. It read from 13.9-14.5
The gauge read the same numbers no matter what mains were in there.

what do your plugs tell you.
Also are you sure you are truely on the mains? Becauase of the design of a carb the idles do a lot of the work for a good portion of the RPM and gradually get phased out as the mains start coming in.

To make a plug check you need new clean plugs, zip out on the highway make a real 3rd gear pull to WOT and ride close to the limiter say 5000 RPM. then as you take the off ramp shut the car off and put it in nuetral. coast to the stop and check plug for color.

We don't use meters in karts, just a plug chop or bore light in the cylinder to see what the top of the piston looks like. Pop the header off and look and the exhaust port color.

Yeah, what Joe said. Make sure when you're testing, you run the car at WOT at decently high RPM or you won't even be using the main jets. You should definitely notice a difference going from 125 to 145.

Scott

Update after Sebring...
O2 sensor replaced
A/F was at 11.2-11.4 WOT
98 octane fuel
Need some more tweaking.
Next time.
Thanks for all the advise again everyone.

Now it's a little rich, which isn't too bad and aircooled engines like being a little rich anyway. Might try a step down at 140. But, that also depends on what the AFR was throughout the rest of the main circuit engagement before you hit 3-4k rpms and above.

If the rest of it is good, and you only need to lean out the very uppermost RPMs at WOT, you can try numerically larger main air correction jets, which introduces more air with the mains mixture.

Typically A/C jets are more for fine tuning the very upper end of the range though and you'd start with a smaller main.