Technical Hello & help!

[createcartel]

Hi there, this is my first post on the forum but I have been reading & learning from you all for a while now

I bought my Italian wife a 1974 500R for a wedding present a couple of years ago and it's been fairly well behaved up until now. After fitting a brand new IMB 28 carb and a few other service parts, it doesn't want to play nicely any more.

The 500R has the IMB 24 as standard, so I upgraded to a 28 last week. At the same time, I replaced the fuel filter, coil, condenser, rotor arm & dizzy cap, HT leads, plugs, points and plumbed in a brass T for the fuel return with all new hose from the rigid pipe.

I had already fitted a new fuel pump, fuel & air filters in February 2019 and the car has done less than 200 miles since then.

So, I took it out for a drive on Friday evening and all was going well, it was noticeably better with the new carb. However after a while, on a hill, power dropped & I pulled over. At which point the engine spluttered & died.

I checked the tank & noticed the idiot light positive wire wasn't connected and, looking in the tank, there wasn't a lot of petrol. I called my wife & as I had a plastic fuel can, thought I just needed a lift to the petrol station and back.

With some more petrol in the tank, the engine would idle for a bit then die. I had a few tools with me, so took the fuel hose off the filter & blew back down the line. The (plastic, clear) fuel filter had very little fuel in it. The car ran for about 1/2 mile then the same thing happened again.

As my wife was following behind me, we parked the Fiat up & drove home so I could get some more tools & spare hose, etc. After a bit of fettling, it drove home ok then conked out on our driveway.

So... this got me reading a whole bunch of threads on here. Maybe it was due to the engine temperature? Maybe the coil was faulty? Maybe the fuel line was blocked?

I got it started & drove it round the back of the house to my garage (at the bottom of the garden). I took the fuel pump off & it looks clean inside, pretty much like new. It squirted fuel some distance when the pivoting arm was pressed in, so all seems ok there. I blew the lines through with a bicycle pump in both directions, all seemed ok. No sign or smell of any leaks. The rod that operates the pump seems to be moving as it should.

I put it back together & it wasn't drawing any fuel.

I had a new 12v fuel pump from another project car so put that inline just after the tank, which I could see filled the fuel filter, so took that out & started it up fine... until it coughed & died when it ran out of petrol.

So I assumed it must be the pump or the rod, so I took it off again. The bakelite spacer had a hairline crack in it, which easily snapped into two with very little force... so I've ordered another (the correct 500R version).

I'm not really sure what else it could be. Almost everything is brand new. Any thoughts?!

 

[the hobbler]

Welcome to the Forum. Being that the problem has only occured since you ran out of fuel, it would sound like a fuel blockage due to running so very low on fuel. I would be tempted to remove the carb, give it a good clean and check for any debris in the float chamber and any of the jets. Check the little filter at the top of the carb (where the fuel enters the carb).
It is not unusual for the pump to have real difficulty in pulling fuel through after it has run out. I have a tuned 126 enging in my 500 and if the pump has been disconnected for any length of time, and the fuel tank level is low I usually have to pressurise the tank to force fuel through to the pump. Whilst you are checking things, the tank is very easy to remove---might be worthwhile getting the tank cleaned out just in case there are foriegn bodies in it---check the fuel pick-up filter in the tank.

 

[createcartel]

Hey, thanks for the swift reply. Yeah, could be the carb. I didn't really want to pull it off & take it apart as it's brand new & didn't want to disturb the gaskets. Oh well, can't rule it out until I do

I forgot to mention I pulled the pick up out of the tank & that looked fine, too. I was considering a new cap, but it seems to be venting ok, which came up on another thread.

I think I saw a post from you elsewhere saying there's no need for a fuel filter as there are effectively 3 in the system already, which I thought was a good point.

I think I'll pull the carb & check it out & whilst I'm there check the valve clearances.

Should I use the 126 clearances, or the 500? Can't seem to find anything specific to the 500R.

Also, I'd share some photos, but can't due to not having posted 5 times yet

 

[createcartel]

Aha, I found the valve clearance info on another thread. Posting this here so I can find it again

Inlet: 0.20mm
Exhaust: 0.25mm