My Alfa Romeo 33 rebuild - FIRST TIMER

[TomLouwrier]

hi Chris,

I'm with Nabih here. A couple of inches won't make or break it.
This pressure loss you're wondering about, it's... well about 6 to 8 'inches of petrol' pressure, which would be 4,8 to 6,4 inches of H2O, taking 0,8 as density for your average oil product. No idea how much that is in psi, you do the math. But it's not much. :-)
And anyway, as the line goes back down to the carb you regain whatever you lost in pumping it up. It's a syphon, right? The pump plays no role in this really, unless it fails to prime your carbs from empty.

regards
Tom

[Brit01]

And anyway, as the line goes back down to the carb you regain whatever you lost in pumping it up. It's a syphon, right? The pump plays no role in this really, unless it fails to prime your carbs from empty

ok thanks guys.

not sure what you mean by a syphon system (syphon I understand but the system no). It runs back into the tank from the right carb.

The pump does NOT prime the carbs after they are empty. That is what's concerning me.
If I start up the car every 3/4 days no problem. But a week and then the pump won't prime just on the starter motor running.

[TomLouwrier]

hi Chris

What I mean with a syphon is the part of the fuel line that goes up first and then down to the carbs. That is a closed line for sure and as long as you can get the first fuel to go over the top, than you're not really losing pressure between pump and carb.
Good you mention the return to the tank, I forgot that. It may be that the fuel in the 'down' part of the line does run past the RH carb back to the tank when it's not running. But I'm still not convinced that that is your problem.
The fact that your pump does not prime the carbs by itself is suspect though. Are the lines clogged? Does it build up enough pressure? Can it suck the fuel from the tank properly?

regards
Tom

[Guy Croft]

Chris - I think your fuel pump is defective...


G

[Brit01]

Thanks Guy.

That's what I was suspecting. After all of the other tweeks I've done on the carbs with the jets etc, and more importantly the non-starting after 5/6days this could well be the issue.

I am trying to source a replacement mechanical pump.

Regards

Chris

[WhizzMan]

I'd say it's a return valve in the pump system then, if your fuel pump isn't priming the carbs, but it will sustain high powered driving once the engine is running and fuel is flowing.

Still, I think it shouldn't empty the bowls of the carbs, since the needle valves are above fuel level. Any reverse flow should be air, leaving fuel in the bowls, right? So the question is now, are the bowls empty when you try to start the car, or do you start them empty and is there no replacement fuel flowing in?

[Brit01]

There is fuel in the bowels when starting.

It will jump into life for a few seconds then die, maybe 2 or 3 times after pumping the jets then I guess the bowels are empty after that and the pump will not fill the carbs up.

If I fill them right up full by hand after this then is sufficient to get the pump going and then it idles nicely.

Going to buy a pump today. Will be a couple of weeks due to shipping here.
(anyone travelling to Uruguay?) lol

[TomLouwrier]

There is fuel in the bowels when starting.

Aha. In that case it's the pump indeed as Guy said (now there's a man who doesn't waste words like we do ;-) ).
Still, while you're waiting for that new pump? How's the lines, especially the feed from the tank to the pump? I've seen engines starve because the lines were clogged up with dirt and rust coming in from the tank.

regards
Tom

[Brit01]

Yep just purchased the pump online.

Once it arrives I will check all the fuel lines before installing.

The rubber pipes are new but the metal pipe that goes under the length of the car I'm not sure.
Best to replace it or can I clean it out somehow? Or maybe replace the whole length for rubber tubing?

Will be about 18 days before I get it though.
I will keep you updated.

Thanks all

Chris

[WhizzMan]

You will have to run a new hard line if some "carb cleaner" in the tank doesn't clean it out and you feel it's too dirty. Don't use rubber hose, that deteriorates way too fast under the car and it's very vulnerable to hard objects cutting it.

Since your car is running just fine on power, I doubt your fuel lines are clogged. There may be a small leak in them, but you would have found that from the smell and leakage by now, I think. Just clean out the tank and the line with some injector/carb cleaner, make sure you have a good and fresh fuel filter in the system and you should be fine I think.

[Brit01]

Thanks for the advice whizzman. Tank removal won't be possible now until next summer.

Once the new pump arrives I will clean out the pipes and make sure all are new with good clips.

I have also purchased a new rad temp sender 88/79. I currently have 90/80 and feel it comes on a little too late in hot weather in traffic.
I was looking for a 88/80 but the 88/79 will do just fine.
2 new temperature senders also, one for the water on the inlet manifold and one for the new oil gauge that should arrive very soon.

Good evening

[WhizzMan]

With much respect for your attention to detail, most of those senders are off, or get off fairly quickly after putting them to use. Two degrees or so won't really make much of a difference on a street engine and I think you will find bigger variance than that on a batch of thermo switches that are labeled the same.

[Brit01]

If you are right whizzman fair enough duly noted.

I don't know when the sensors were last replaced so probably best practice to renew them anyway as I skipped this step when rebuilding my engine.

Regards

[WhizzMan]

I don't know when the sensors were last replaced so probably best practice to renew them anyway as I skipped this step when rebuilding my engine.

That is a very valid reason to replace.

You can, out of curiosity, test the new/old sensor with a good, calibrated thermometer, boiling water and a multimeter. Put the setup in boiling water, set the multimeter to "beep" and let it cool off until the beeping stops. Then look at the thermometer and you'll o at what temperature the sensor switches off. Testing when it goes on should be done by slowly adding boiling water while stirring. Make sure to stir well and add water slowly, or you'll have too much of a difference in temperature between the water and the sensor to be adequate. I myself would be curious to see how much degrees off the markings on the sensors would be, both for the old and the new one. Even if your thermometer is not calibrated very well, you can still tell the difference between individual sensors, just not the absolute value at which they will switch on or off.

[Brit01]

For sure I'd like to know the accuracy of the old one.

I don't have a DMM that beeps but I could set it to a low resistance and see when it reads infinity.

It will read infinity when cold, then heat it up slowly while reading the thermometer, making a note when it switches on and off.