My Alfa Romeo 33 rebuild - FIRST TIMER

[TomLouwrier]

hi Chris,

Just as I thought. As far as I can see the air corrector is supposed to press down on the emulsion tube and main jet until the whole set bottoms out in the carb body and everything is locked into place. No looseness, no height difference.
Are the bore and threads clean?

regards
Tom

[Brit01]

Just as I thought. As far as I can see the air corrector is supposed to press down on the emulsion tube and main jet until the whole set bottoms out in the carb body and everything is locked into place. No looseness, no height difference.
Are the bore and threads clean?

If you're right Tom then that is good news and one less factor to think about. I didn't they they bottom out below, just thought they hung within the petrol chamber below.

I can see the emulsion tubes bottoming out with the air corrector precisely once screwed in BUT I would like to check where the main jets are pressed into the emulsion tube. If one is slightly deeper set than the other this will alter the emulsion tube height. There is room for error here.

Yes they were clean last time I checked but always worth another clean.
I'll get the Carb cleaner out and clean them.

Thanks

Chris

[TomLouwrier]

hi Chris,

Well, those jets must bottom out and seal against the conical face, otherwise the fuel would be leaking around them, upsetting the metering by the nicely machined hole in the jet.
You can colour the jet's nose with felt tip pen, screw all of it (jet, tube, corrector) in and out again, and see if you get an even impression, just like checking a valve on its seat. If it's not sealing right, there are little tools to clean up the bore bottom, a sort of scraper with the correct size and angle. Looks a bit like a special twist drill. You could make one yourself if you must, you'll only be using it once in a century and the carb body is soft.

regards
Tom

[Brit01]

Tom:

Thanks for the tip and info. Good to know.

Does the idle jet also seal against a conical seat in the same manner?

Regards

Chris

[TomLouwrier]

Chris,

If they too have conical noses, most likely they do. You should be able to see the mark as a shiny ring on them. They can't be 'just hanging in there'; the fuel must be forced to travel through the calibrated hole otherwise there's no point in having them.

Look at your parts and the sectioned view you posted (nice drawing). Understand the construction. (The guy who drew them is telling you what he meant, if you listen.)
I drew up two quick sketches to show the difference. Where it bottoms out, it seals. Threads never bottom out, unless something is wrong. There must be a firm face (conical or flat) that provides the 'stop' and the seal.

Left: sealing on conical nose at tip.
Right: sealing on flat face under head.

jets.png (18.42 KiB) Viewed 8639 times

regards
Tom

[Brit01]

Great clear explanation Tom. Thanks very much for your time.

What I also want to check now is the distance between the conical jet and the main body fitting as where it squeezes into the body there is always a small gap. If they are all the same I'm happy but if there is a difference then the correctors will be at a different height or at the wrong height.
This applies for the idles also.

Not sure if they should all be flush with the main bodies.
Update: Just been searching the net for photos and all I have seen the jets fit flush into the bodies. Maybe this is the issue. Sometimes the simplest solution is the last one you look for. The emulsion tubes if not seated flush into the main jets (even though the jet is seated properly into it's seat in the carb body) will be higher than normal. Would be like having the floats too low, maybe at 8mm instead of 6mm (maybe 2mm's of gap), making it run lean.

[Brit01]

I will remove all the jets this weekend and make sure they all fit flush with each other as I have seen in all of the photos of these. They will be a very tight fit.

I cannot remember at all if they were flush when I first overhauled the carbs about 2 years ago. Maybe so I when I re-assembled with new jets purchased it didn't occur to me this important factor (being a little ignorant when it came to the jetting).

Making these flush will lower the emulsion tube on the mains and also the air corrector on the idles.

May even have to go back to leaner idles if this is the case as I've been trying to compensate for a lean mixture by putting in large jets, instead of simply fitting them correctly in the first place!

[Brit01]

Checked all jets this weekend.
All bottomed out and flush as they should be. I was mistaken in the previous post.

All ok.

Didn't have much time but I'm suspecting it's running rich on the 55's and not lean. Can be a bit misleading sometimes.

If I had the original air intake attached (63mm pipe) to the airbox, it would hesitate under acceleration from light to 3/4 throttle. Only under full throttle it would kick in.

Then I opened the airbox to allow no restriction and the power kicked in much earlier leading me to believe it was starved of air and not lean at all. But under wide throttle it would hesitate a little(going lean).

I will install the smaller idle jets with the 63mm original air intake and see how it behaves.
Maybe going back to factory specs with the original airbox intake is what it needed as it was designed for. If I had open filter boxes on the carbs I'm sure I would need the 55's and larger mains but these suck in hot air from the engine bay.

(another issue occurred coming back during the last 2/3 kms) - a little knocking from the left front wheel hub area when turning the steering wheel either way. Have to remove the wheel and inspect all bolts. Hope it's not the outer drive shaft.

Update: getting some feedback in regards to the clunking noise. Possible strut pan bearing failure! Can I still drive with these clunking a little?

Had a bad migraine most of the weekend so productive work on the car was pretty much impossible.

regards

Chris

[Brit01]

I have a question about the metal damping device connected between the vacuum advance of the distributor and the vacuum port on the carb.

Must it be placed a specific distance between the 2? I mean closer to the carb or closer to the distributor?
Would this have any effect on the performance of the advance curve?

Just curious.

[WhizzMan]

Strut pan bearing?

I doubt the restrictor in a vacuum line would matter much in placement as long as there are sufficient lengths of hose in it.

[TomLouwrier]

I don't think it will influence the vacuum advance enough to notice, or even at all. But, if you are using a restrictor in the line then that should be upstream near the carbs. That way you have more volume in the line behind the restrictor which will help dampen out the pulses.
It's the same situation as when you're using a set of vacuum meters for synchronizing the carbs: they tend to flutter a lot (engine running at idle) unless you put a restrictor (fixed bore or needle valve) in the line. The closer to the meter, the harder it is to steady them.

regards
Tom

[Brit01]

I don't think it will influence the vacuum advance enough to notice, or even at all. But, if you are using a restrictor in the line then that should be upstream near the carbs. That way you have more volume in the line behind the restrictor which will help dampen out the pulses.
It's the same situation as when you're using a set of vacuum meters for synchronizing the carbs: they tend to flutter a lot (engine running at idle) unless you put a restrictor (fixed bore or needle valve) in the line. The closer to the meter, the harder it is to steady them.

Hi Tom,

yes that's what I was thinking as I use vacuum meters and have the damper (small fish tank air tap), and it's recommended to put it near the pulse away from the gauge.

Same principle could be applied to the advance mechanism of the distributor. I know mine is too far away.
I will buy some new piping and place it nearer the carb vacuum port.

[Brit01]

55 idles changed back to original 52's.

A definate improvement!

1st/3rd/4th great smooth acceleration, rallying through the peak hour traffic!
And no popping on the overun!! 3rd/4th was surprisingly impressive - great take off - really wanted you to push it harder and harder. So addictive the Alfa boxer.

in 2nd just a very slight stumble on take off if I push it hard.
Maybe either one carb is opening just before the other, pump jets a tad small or slightly retarded ignition.
I will revise the opening of the carbs in good daylight at the weekend.
If that's ok then one of the other 2 options.

Pretty happy with the outcome in the city traffic driving.

Tomorrow we have a 100km run on the highway so we'll see how it goes under those different conditions.

[Brit01]

Just purchased a VDO oil temp gauge. Used but worth a try for 3.20 pounds!! Lucky auction - normally they get up to 30 pounds or so even second hand ones.

Changed plugs back to B7ES. '6' plugs were too hot for the highway. Ok for the busy town driving though.

Chris

[Brit01]

100 km journey back home last night and carbs still misbehaving under 3000 rpm, light-mid throttle.

Quite frustrating. I'm thinking one of them maybe opening slightly before the other, despite checking them with vacuum meters.

Easter week is coming up so I think I will have some time to play around with them.