Hello

I recently fitted a dellorto FZD carburettor to my 1970 Giannini look-alike 500L. The engine is 650cc and when I took it for a 20 mile test drive it was amazing. It was scarily fast, I reached an indicated 100 kph and that makes me think that suspension and steering will have to be next. However, as I got nearly back home the engine started to hesitate a little and on inspection of the spark plugs it would appear that the mixture is far too rich. I took the main jet out and checked the size, it is 135 and I have ordered an assortment of smaller jets to see if I can get the balance right.

But this leaves a couple of questions which I hope someone can help with. Firstly, when I fit a smaller jet, do I need to adjust the fuel air mix on the carburettor or is changing the jet sufficient? Secondly, when I removed the main jet fuel came out of the carburettor, on refitting the old jet the car now won't start. Could there be an air-lock, is there any technique for restarting an FZD fitted engine after removal of the main jet?

Thanks for reading this far, I hope someone can help.

Mauro

When you remove the 'main-jet' holder you empty the float bowl. It will take a bit of cranking to refill the float-bowl to the point that the engine will start and run.
What size FZD do you have fitted. I have a number of settings for the FZD. I also have a 652 engine, with a 32/28 FZD fitted and have taken some time to sort out the best jets. Feel free to contact me:[email protected] and I will let you know what I am running. One thing that I always reccomend is that you run a log regarding what jets you have in the carb, when you change them and what you change them to.
Just for the record, down a slight hill, foot to the floor I have seen 136kph (82mph) on my car---a tuned 652 engine Wiill shove it along!

It is normal to have a thermal break spacer between the manifold and the carb to stop the carb getting too hot.

Thank you both for your replies. Yes, I was stunned by how much better the FZD is than the stock weber. Like I say, it was scarily fast. We live on a hill and with the weber I was struggling to get up in second gear while with the FZD it accelerates uphill in third. My FZD is a 32.26 which I understand is quite an unusual size. I'll take your advice on keeping a log and hopefully the FZD will start up before I flatten the battery cranking the engine. At this point, it's probably worth waiting for the new jets to arrive because I will end up draining the carb once again when I fit the new one.

Where about in Italy are you Mauro? You should be able to get plenty of advice where you live as to jetting for the carb. Yes, the 32/26 IS an unusual size. Unless you live in a very dusty area, I would give serious thought to removing that air-intake adaptor---it won't help air-flow, and looks ugly! The normal short trumpet/stack with the integrel gauze is still available
As Dave (Toshi) mentioned, there should be a thermal gasket (they are about 5mm thick) between the inlet manifold and the carb base flange. If you don't have it fitted, you do run the risk of the carb getting too hot.
Welcome to the Forum, we are here to help.

Hello

Fortunately, I do have the thermal spacer fitted.

So, I fitted the 128 jet today and took the car for a 10 mile test-drive. It ran great after I cleaned the soot off the spark plugs from when I had the 135 jet fitted. But to be fair, it ran great on the 135 jet until after 20 miles the spark plugs were so sooty I couldn't restart the engine.

So everything seems fine for now but how can I check that it is really running ok? Do I keep checking the spark plugs to see if they are getting sooty again or is there a smarter way? I'm wondering if it is still running rich because when I accelerate the engine, now after the test drive, there is a bit of black smoke out the exhaust.

Thanks for all comments.

Mauro

Hi Mauro; I would suggest that the black smoke is possibly indicating too big an accelerator-pump jet---you don't really need one much bigger than a '35'. the acceletaror-pump jet is accesible from the outide of the carb---as you look at the carb down the venturi, the large brass screw to the LEFT is the cap for the pump jet. Unscrew the cap and the hoik the jet out Have you been able to check which emulsion jet you have fitted? It should be a 6747-6 (available from ROCKY Srl)--this can also cause a little bit of black smoke, but as it easy to remove and check, go to the accelerator-pump jet first.

Thanks Tom. I don't know if I am brave enough to check the emulsion jet but checking the pump jet sounds like a good plan and should be easy enough, if I can reach it there around the back of the carb. What are your thoughts on how to tell if I have the correct main jet, keep checking the spark plugs for soot?

If you haven't got a 'gas analyser' or plug colour analyser (forgotten the name of the device--you screw it in, in place of the spark plug) than the only other method IS to check plug colour. Remember though, is better to have an air-cooled engine running slightly rich than lean.
The emuslion tube on the carb is also very easy to get at---it is under the small triangular cover on the top of the carb---it is a long jet with little holes down both sides--screws out and can be removed with the engine and carb in-situ.

the hobbler said:

If you haven't got a 'gas analyser' or plug colour analyser (forgotten the name of the device--you screw it in, in place of the spark plug) than the only other method IS to check plug colour. Remember though, is better to have an air-cooled engine running slightly rich than lean.
The emuslion tube on the carb is also very easy to get at---it is under the small triangular cover on the top of the carb---it is a long jet with little holes down both sides--screws out and can be removed with the engine and carb in-situ.

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Colour tune - spark plug with glass insert so colour of fuel burn is visable.
Cheers
Jack

Excellent advice. Thank you all.

Thank you Jack---I knew SOMEBODY would know the answer!

the hobbler said:

Thank you Jack---I knew SOMEBODY would know the answer!

Click to expand...

I just had to beat Jock to it (-: especially as he posted a picture of an immaculate first edition in one of his quizzes.
Best wishes
Jack

I did a test drive of about 20 miles with the 128 main jet but when I checked the spark plugs they were as sooty as before. Today I tried the 125 jet for about 10 miles and with the air filter disconnected. See the photo. I think I am getting close to the right setting. I know these still don't look ideal but it really is a huge improvement. In every case the engine runs great with the FZD until it won't start because of the sooty plugs. Hopefully, the plugs will now stay reasonably clean. It seems like no paper air filter is also helping.

This thread motivated me to order a Gunson Color tune (or colour if you’re of the excess ‘U’ persuasion). A little tricky to find in the US, but I’ll happily loan it out once finished if anyone needs one.

JumpJet said:

This thread motivated me to order a Gunson Color tune (or colour if you’re of the excess ‘U’ persuasion). A little tricky to find in the US, but I’ll happily loan it out once finished if anyone needs one.

Click to expand...

Matt- I will definitely take you up on that once it’s time to get her properly tuned.

Learn something new today, Gunnson colour tune? Didn't know there is such a tool. I think I will order one also since I am having trouble lately tune my carb.

gordinir8 said:

Learn something new today, Gunnson colour tune? Didn't know there is such a tool. I think I will order one also since I am having trouble lately tune my carb.

Click to expand...

https://www.fiatforum.com/500-class...sed-colortune-their-fiat-500-a.html?p=4571089

A little while ago (2015 - where did that time go) I posted a thread on the FZD. A complete strip down of the carby with pictures and literature.


See here - https://www.fiatforum.com/500-classic/423634-dellorto-32-28-fzd.html

Might be helpful.

Cheers,
Chris
Australia

Thanks Bambino. That was very useful.