My Alfa Romeo 33 rebuild - FIRST TIMER

[Brit01]

No knocks so far - touch wood!

You know when I replaced the upper gear stick gaiter the 'shhhhh' sound disappeared!! Lol
So it was there all along it appears (or not!), but just soundproofed by the upper gaiter.

The Motul 'gearbox' is really nasty grey/black, horrible smelling oil.

I will remove the gaiter again to see if the noise is evident after I changed the box oil this weekend.

I was surprised about the idle rpm though, despite the higher viscosity oil 60, the idle increased by 300 rpm or so concluding there was more friction with the previous mineral oil. Please correct me if I'm wrong or have another explanation.

Regards

Chris

[Brit01]

Just curious about the size of the chokes on my DRLA 40's.

They currently have 32 chokes.

Would there be any benefit increasing the size of these with standard cams?
And what changes would I need to make with the carbs jets etc?

At the moment the mains, 142, work just great.
But always had an issue with the idles up to 3000 rpm.

53's seem a bit hesitant and lean. Recently put 55's in, more power yes but sometimes I get an occasional nosedive due to too much fuel going in under very hard acceleration.

Maybe 34 chokes with the 55 idles?

Guy how familiar are you with DRLA's on a 1.7 boxer?

Or maybe Tom?

Regards

Chris

[Urbancamo]

Chris, I personally would stay in 32 mm chokes if you want to maintain good over-all torque and response. With carburettors it's all about air flow velocity. You don't want to "over"choke your engine, it kills the whole rpm range.

If I've understanded your problem correctly, idle jet circuit seems to last bit too long until main jet circuit starts to operate. What e-tubes you are using by the way? And what is the stock factory jetting for these carbs? (wouldn't find it anywhere, only sidedraft carb info for Alfa Romeo)

Fortunately Dellortos have idle jet sizes by 0.01 mm increments, makes life so much easier.

T

[Brit01]

e-tubes can't recall by memory sorry. Standard for sure I remember.

52 idles are standard for this engine (and 142 mains with 35 pumps) but since changing to K&N I found it always needed more fuel up to 3000 rpm.


Thanks for the choke advice.


What I might try is shortening the main air intake tube slightly as I made it longer than standard to bring in colder air from a different location (instead of next to the hot radiator which was never a sensible choice by Alfa romeo IMHO).

May compensate for the occasional nosedive and balance the intake a little with the richer idle jets

[Urbancamo]

Factory (idle) jettings are usually made pretty lean for economy reasons. They might work reasonable well with completely new and air-tight engine.
But if you're done small modifications or engine is old and worn, sizing up the idles usually helps to cover flats spots and usually provides much better throttle response.
You don't want to drive your dual carbs with too lean A/F ratio, it instantly shows up.

Usually 15:1 A/F ratio is limit for cruise, going up usually makes some hesitation and "lean" feeling (depending heavily on application) Your ignition advance is in big role, lean mixture needs pretty much advance because it burns slowly.
Going 15:1 to 14.2-14.5 ratio in cruise won't hurt the economy but usually greatly improves the feeling.

Hope this helps.

Tommi

[Brit01]

Hi Tommi,

Yes I agree with you there. The boxer never likes to be driven on the lean side/border. I've always tried to keep it on the rich side.
You can tell immediately when it's lean. It does not respond well.

53 idles are too lean, 55's much better but just a touch rich at times under hard acceleration.

I will shorten the cold air intake tube somewhat. This may help the occasional nosedive by allowing a better/faster intake of air in under these conditions.

I may be able to get another 1 degree of advance without any pinging. Set it at ~9 degrees last week and no signs of pinging under the hardest load.

Regards

Chris

[Brit01]

Tommi,

As I have 142 mains (factory set), if I was to try a larger size what increment should I first use?

Maybe 145 or 148?
I have never messed with the mains.

My AFR shows around 14.7 (which I know is leaner than 14.7 because I have a couple of pinholes in the exhaust manifold) while cruising at high speeds on the mains. Alfa got that right but as we discussed we want to lean on the rich side a bit.

I have a spare set that can be enlarged by a local specialist.

Thanks

Chris

[Urbancamo]

Are you sure you're on mains even at higher speeds? I don't think so. Idle jet circuit affects very long time at these production cars. Cruising in 3500 rpm might be still at idles.
It's easiest to see what idle jet size does if you change the idle jet size on some direction and then check for changed A/F ratios and feeling.

Sizing up the main jets 2-3 sizes is good. With Webers change of 5 is sometimes bit too coarse. Again points goes for Dell'Ortos...

[Brit01]

Are you sure you're on mains even at higher speeds? I don't think so. Idle jet circuit affects very long time at these production cars. Cruising in 3500 rpm might be still at idles.

I thought they cut off at around 3000 rpm. But maybe you're right.
But the mains do begin to come in early around 2200-2500 rpm.
Once I had one blocked and it felt like it was running on 3 cylinders above 2000 rpm.

The Dellortos have 5 progression holes for the idles spread out about 1cm in height.

Cruising at 2000 rpm would give me an afr of around 13.5 more or less. 3500 rpm - 14.5/14.7.
Maybe because of cold air forced induction at higher speeds causing it to become leaner?

Sizing up the main jets 2-3 sizes is good

What is the increment of 1 size? 0.05mm?
so 142 up one size would be 147? Or 0.01mm?

[Urbancamo]

That's ok Chris, there is very much variation depending on carbs/engines when the mains start to operate.

One size in jets is 1/100 mm eg. 0.01 mm. 142 = 1.42 mm hole, 145 = 1.45 mm hole etc. Dellorto has these great dense increments, 141, 143, 146, 147, 149 and so on.
Weber has jets only 0.05 mm increments. So with Dellortos you have more to choose and it makes fine tuning bit easier.
When I speak 2-3 sizes up, it means going 142 -> 144/145.

Hope this helps, sometimes these things are bit hard to explain with foreign language, but I'll do my best.

[Brit01]

Thanks sir.

Last night I modified the cold air intake to the original length and position. Perhaps there was just too much restriction down the longer pipe I made.
Friday will be testing day for that.

If not then I will try with enlarging some spare sets of mains I have, as you mentioned a good start would be 144 mains.
A local workshop is a specialist in making their own jets/pumps jets and parts for Weber/Solex and Dellorto carbs.
Luckily this country has some excellent workshops that replicate these parts due to the limited resources we have.
Excellent craftsmanship created over decades of working on old cars.

They made some pump jets and pump diaphragms for me. The diaphragms were of better quality than the Dellorto originals believe it or not. I have a set of originals as spares in my car in case one day they spring a leak which is what happened to me once.

Regards

Chris

[Guy Croft]

"A local workshop is a specialist in making their own jets/pumps jets and parts for Weber/Solex and Dellorto carbs.."

Amazing!! What is their website?!!

G

[Urbancamo]

I'd like know too, but I'm afraid they don't have one...!

[Brit01]

Amazing!! What is their website?!!

I don't think they even have a phone! They work in a tiny space, you would miss the entrance if you blinked. Came across it by accident. No fixed opening hours!

We have about 4 blocks downtown crammed with spare car parts specialists, workshops etc
One workshop for oil pumps, one for rubber bushings etc.

Interesting place indeed.

Chris

[Guy Croft]

Photos with their permission would be nice!

Those days have near gone here in the 'developed' West. If it can't be made_in_Chiner you can't get it..

Bloke walked into my works the other day and remarked, 'didn't know there were still places like this, dying trade innit?'

Ho hum.

G