Hi gang
I’d been having a great run with little blue but I’m stumped now.

Essentially since the refurb work, she is now displaying these odd symptoms.

I took a short video which basically shows on light application of the accelerator the revs actually drop. Then passing that point of acceleration they pick up.

In addition, I have to drive with the choke (or whatever it is) partially out constantly now otherwise the car just cuts off when coming to a stop. It otherwise drives nicely.

I can only think of a few likely causes as I haven’t messed around in the engine bay at all between when it was fine and now
- fuel line: new hose put in, issue there?
- fuel sender: the fuel light flashes occasionally but it’s got about 8 litres of fuel in it
- electrics? The two wires that connect to the fuel sender were removed and fiddled with, plus some paint applied, could it relate to that / connection issue with them?
- tank: I completely emptied and scrubbed out the tank, so I don’t imagine any sediment could have been left

Any thoughts would be amazing. Feeling a bit gutted.

Video here

[ame]https://youtu.be/iM_khK3bpQg[/ame]

Hmm another drive and problem persists with the fuel light coming on and off. At what point is the trigger for the light?

A search of the forum suggests the sender unit starts flicking it around the 5L mark...

But even then, I’m pretty sure it’s not actually related to the fuel level as the behaviour isn’t typical of when I’ve had even less fuel than this.

I've messed with the idle and mixture screws but without any luck. I can't work out if I should assume the valve clearances, carb and distributor are all fine, seeing as they were before and haven't been touched, and just troubleshoot between the fuel tank and carb...

Hmmmm!

Your fuel light flickering on/off----this might be related to the paint, try cleaning the paint off around the earth wire (to the tank sender) and give the wire terminals a good clean (wet 'n dry paper). With regard to the acceleration problem, this could be a 'low speed jet' problem. Commonly called the 'idle jet' (by everybody bar Weber), this effects the running and acceleration at the lower speeds. I would be tempted to remove the 'idle jet', give it a good blast with an airline, and if you can get an airline nozzle to the carb, give the 'idle jet' hole a good blast as well. The problem sounds like a blockage in the passages affected by the idle jet, especially as you are having to run with the 'choke' slightly on, which would indicate a lack of fuel at low speed. If you can't get an airline to the carb (with it still in situ), you will have to take the carb off and clean it out on the bench.
I have run into this problem myself, when my (new) wife and I were driving down to Cornwall for a belated Honeymoon. The lads at work had covered the 500 I owned at that time with the punchings from postage stamp perforations--some got into the fuel tank, and then into the carb. Going UP Cornish hills she wouldn't pull the skin off a rice pudding (I seem to remember cyclists going past us). However, going DOWN the hills when the main jet came into effect, we went past everybody who had passed us on the previous uphill! A quick carb strip and blow-out at our Honeymoon destination sorted the problem out and she ran as sweet as a nut for the rest of the holiday. :bang:

Thanks Tom as always! Perhaps my fuel tank cleaning wasn't as good as I hoped?

I'm trying to decipher the italian on my little dellorto carb note here from you.
From what I can tell, the idle jet is on the inside of the carby, is that your understanding?


I also just had a read of this thread and it sounds like some similar symptoms
My points were fine and she's hardly been driven between the fine and not fine moments, but I'll check them tomorrow if it seems a likely culprit
https://www.fiatforum.com/500-class...ng-engine-peters-out.html?430480=#post4112784

Sadly I do not have an 'exploded' diagram of the FRG28--they are very difficult to find. However, if you have a friendly Renault dealer near you, have a word with them because, the 'Renault 4' was another car that used the FRG. In ALL the technical bumph that I have on 500s, only the Weber carb variants are discussed/detailed. I do think though that the root cause of your problem is muck in the system--if it is, I would also (if you gave one fitted) renew the in-line filter. I would also suggest that if the FRG has a small filter in the top cover (where the fuel comes in), check and clean that.

I think tom has hit it on the head there.. you have pulled and pushed components in the fuel system somewhere you have probably dislodges some muck that has fond it's way through, it may already have been in some where just stuck...
a nice job for your weekend Renovations...
take the carb off.. a strip down good clean and dry..
I tend not to use paper towels any more or cloth but try to let things basically air dry, as lint and fibers can cause as much trouble, these synthetic cloths that block the sewerage systems are good as they have no fibers...
If you have an air line they are are excellent....

Thanks guys, I think you're probably right.

I had a read of this:
http://www.iwt.com.au/private/Dellorto manual.pdf

IT's a great little guide on the carb. Explains the idle jet role in the progression mode from idle to main jet. Which sounds like my problem

Pics on that manual don't seem to match my carb unfortunately! I'll have to have a look around - another step in the 500 learning curve


I've also spotted a service kit, pic attached - is anyone able to identify which component might be the idle jet?!

Sorry this is a bit of a slow process.
I’m worried about pulling the carb off and messing something up so I was hoping the idle jet might be one of the two brass screws circled on the front of my little dellorto frg 28 carb

When I unscrew then it’s basically a thin needle with a point on the end, but no hole anywhere along. I thought the idle jet should have a hole somewhere? Guessing I got the wrong bits but any thoughts on what they could be?
Thanks guys sorry I’m stumbling through this... there’s very little info out there on these carbs!

On the Weber, the 'idle'jet is a 'push-in' jet (it pushes into its holder), I believe that this jet on the Dellorto FRG is the same. look at the "Eurocarb" site. Their Dellorto part number is: 4576----this will show you what you are looking for.:bang:

the hobbler said:

On the Weber, the 'idle'jet is a 'push-in' jet (it pushes into its holder), I believe that this jet on the Dellorto FRG is the same. look at the "Eurocarb" site. Their Dellorto part number is: 4576----this will show you what you are looking for.:bang:

Click to expand...

Thanks for the pointer on this obscure little thing! The FRG seems the least known from my searches. According to that page the part matches the starter jet for my carb, rather than an idle jet.

But fear not! I think I may have fixed her, and many thanks for the persistence of those here.

I was reluctant to pull off the carb, mainly because I want to drive her and don't know how long a carb off and clean job is.

So I unscrewed all the things I could. The two on the front came out looking like the image attached, the short ones. No holes in them.

Then I found a sneaky one on the top, hidden under the breather hose. Pulled it out and it looked more like some kind of jet! But certainly not a push in jet. Scouring the eurocarb page and all the jets / parts, the closest thing I can find to it is an FRD pump jet, but to be honest I'm still unsure what it is.

Took it out and gave it a spray with carb cleaner, and inside the hole it came from with the engine running. Success! Applying the throttle by hand was smooth and glorious, so I took her for a spin. But then the symptoms came back...

This time, I took out the mystery jet and blew hard through it. There was definitely stuff in there because initially the air sort of crackled out. Eventually blew through cleanly, and added a blast of carb cleaner through the top holes and out the end hole.

NOW she runs beautifully. Glorious warm sunny day here so I flipped the top and just kept driving for a while.


To stop this happening again, it's time to fit a fuel filter I think - is this likely to protect the carb from this kind of thing?

If so - I've spotted this one at my local:
http://www.supercheapauto.com.au/Product/Ryco-Fuel-Filter-Z676/337904
for a 6mm fuel hose (need to check exactly which my hose is)
However it is plastic - is there any benefit in an aluminium one such as this:
http://www.supercheapauto.com.au/Product/Ryco-Fuel-Filter-Z578/155728

The only other question is - can it go between fuel pump and carb, rather than before the fuel pump? I have minimal hose length before the pump, but enough to fit a filter in vertically between pump and carb if that would be acceptable?

Thanks again, :worship::worship:
back on the road!:slayer::slayer:

Go for the plastic one and fit between pump and carb

Well done for persisting, and solving, the problem. Prior to buying any filter, just check what size of fuel line you have--it will be either 6mm OR 8mm. Just above where the fuel goes into the carb is a small plate (held in place with what looks like a small bolt). Check under that plate as there is a good chance that there is a small filter in that chamber--make sure that filter is clean.