My Alfa Romeo 33 rebuild - FIRST TIMER

[Brit01]

Ok good tip Thanks Guy.

I'd have to be quick there though, as the airbox, and 90 degree trumpets need removing to see down the barrels.
Could be that the excess petrol drops back to normal by the time I've taken everything off.
Was thinking the small gasket washer under the needle valve assembly may have dried and cracked while the carbs were off for 2 months. Will check and replace that if needed.

Float level:
5-6mm top
12-13mm bottom

But I'll give it a go.

Also running the car without the airbox is too risky here as we have so much dust (some volcanic dust also from Chile still floating about which is extremely abrasive).

Could a worn/sticking throttle shaft on the carbs cause this issue also when they get hot?

Remember the 4 small breather/vapor pipes on the inlet manifolds I blocked off? Couldn't have anything to do with this could it?

[Brit01]

Thinking about before I did the engine rebuild this Christmas, the carbs worked just great,
Responsive, revved up and down in a snap. Really nice and crisp.

I did not touch the carbs during the rebuild (stored in the boot of my car). So obviously something dried out/cracked, or debris got in somewhere, as Guy mentioned could be slow dripping causing the high idle after hard driving.

I'm eager to see what's inside and clean/check everything out.
Strangely enough I enjoy cleaning the carbs. Great piece of engineering.

Chris

[Guy Croft]

It's not something as simple as carb linkage is it?

Like maybe one carb 'holding open' because the linkage and throttle return spring/s aren't set up quite right?

G

[Brit01]

It's not something as simple as carb linkage is it?

mm.. that's what I was checking so carefully on Sunday, lubricated the springs also, and made sure they opened the same time.
All works perfectly, even gave it a test spin after re-balancing them and acceleration was good and smooth.

But then again on the drive home after about 20 mins of hard driving at 120km/hr on the motorway, stopping at the traffic lights, the idle didn't come down below 1300 rpm, and I could feel the awkward gear changes as the revs weren't dropping quickly between changes.

Once I get a couple of hours free I will remove the top plates with floats and revise everything carefully. Maybe even put the old original needle valves back in that were working fine.
I think the floats were at just below 5mm as they were new and very floaty.
I will change them to 6mm. (5-6 is recommended) and check the drop height also.

Thanks

Chris

update: also I remember the new float needles I put in a year ago or so were slightly different. They had the needle plus and extra pin inside that had about 5mm of vertical movement. The old one was fixed and just held firmly in between the fork spade from the floats.
Not sure the reasoning behind this extra play within the needle. Maybe some debris got stuck inside the shaft of this and is causing an overfilling.

We'll see. All speculation at this point until it is opened.

[Brit01]

What a silly mistake and the last thing I would have thought of checking.

After removing the floats and needles, cleaning and checking everything, re-installing and re-checking I found the reason behind the high idle when hot.

The expansion tank tube that goes around the left carb linkage was flexing enough to touch the throttle linkage by 1/2 mm to prevent it from returning.

This was happening only when the engine got hot under load and was just enough to make the pipe pliable enough to move sideways.

When cold plenty of clearance.

All of that and turned out to be such a simple explanation.

Chris

[WhizzMan]

Good to hear you found the reason and it was such an easy fix.

[Brit01]

Thanks. Yes but wish I had seen the issue before spending hours checking the carbs. Well at least they are all clean (even changed the pump diaphragm on one of them).

Now just got to put the richer jets back in (55 idles I think) and give them a go.

As it was balanced again and not running rich on one side when letting off on the throttle (as the left carb was running much faster than the right before), last night's journey was popping and crackling a bit too much on deceleration.

Also some pinging under heavy loads. Mind you that happens sometimes when I get a bad tank of fuel - filled her up last night).

Idle mixture screws are already 4.5-5 turns out on the 53's.

[Guy Croft]

Pop & bang on over-run is too lean on one or more barrels, they need to be set borderline rich at idle and Colortune is the way to do it.

Pinking - retard the ignition a fraction till it stops.

G

[Brit01]

Pop & bang on over-run is too lean on one or more barrels, they need to be set borderline rich at idle and Colortune is the way to do it.

Yes very true Guy. Thanks.
With the 53 idles (factory 52) I set them to rich borderline at idle yesterday but obviously by the sounds it requires larger ones. (also a little hesitation under acceleration).

Although some Alfa boxer owners tend to stick with the factory recommended 52 idle jets and take the crack/pop sounds on the overrun as a characteristic of this engine! Also to avoid MOT emission test failure. (we don't have these tests in Uruguay)

Pinking - retard the ignition a fraction till it stops.

Yes I will do this. It's a shame the petrol here is so unpredictable in regards to quality. Once I get the BTDC on it's limit to get the most out of the burning rate without pinging, I encounter a bad load of petrol and it starts pinging again.
So I'll need to keep it slightly retarded just to avoid this.

[timinator]

Hi Chris, What rpm are you experiencing the heavy load pinking (in US we say pinging) or does it occur based on throttle angle? In other words, does it always happen at say half throttle at 2500rpm or just half throttle?

[Brit01]

The pinging only occurs under full throttle in 4th or 5th under heavy load. Maybe up a slight incline for example.

If you get pinging at half throttle then the timing is way off and imagine could cause serious damage in no time at all.

I've always played around with the timing between seasons just to get the most out of it.
Our winters will fall down to freezing point some nights but in summer we can have 35-40 degrees C so the carbs always behave differently.


I recently advanced it just a touch, maybe 1/2 - 1 degree as the cooler autumn days started but then the heat came back! Just hit the limit with the bad fuel (fairly warm evening, lot of traffic, overtaking and driving it hard, also which exaggerates the symptoms - was about 30 degrees C).

Thanks

Chris

[Brit01]

As I had the floats and needles out this weekend I would like to know the differences between the spring loaded needles and fixed needles. Maybe some performance benefits?

The old ones I replaced a year ago were fixed and the new ones I put in have that small spring loaded needle.

Thanks

Chris

[timinator]

Still curious as to what rpm the engine is pinging. If it is at a specific rpm or anytime you go full throttle?

We put springs on needles to help with driving off road or on really rough tracks to offset the reaction to the gas in the bowl splashing around.

[Brit01]

I believe at any rpm it will ping but only in 4th and 5th as mentioned under heavy load.
Maybe more evident at mid rpm(3000 rpm) under full throttle.
Traffic was very heavy so I wasn't paying too much attention to the rpm at those moments (my 2 year old was in the back of the car). Eyes were more on the road.

You just need to avoid full throttle when you hear a slight pinging if it occurs before the timing can been adjusted.
I have never had pinging in gears 1/2/3. Normally evident in 5th at full throttle.
This is a common occurrence if timing is too advanced I understand.

[timinator]

The car can ping for several reasons besides bad gas. I was trying to determine if maybe extending the rpm that total advance is in would help. Or if your car was going top end lean due to several reasons. Do you have an advance curve custom for your engine, or is it stock, and do you know what it is? Is your wide band working properly yet?

It is a good idea to do test drives with two people for safety reasons and recording of information. Also that the second person does not require more attention than driving the car. :)