As regular readers of my troubles will know (oh how I've been looking forward to starting a thread with hose words...) my car will not run under load for more than 20 minutes before cutting out.

As part of the fuel system strip, I found that there is a lack of gaskets by the previous owner/garage. The car would run at idle very nicely and pull well until it cut out. Altering the setting of the idle mixture jet had little effect on running.

Under load and when warm, pressing the accelerator will cause the engine to cut immediately. If I am lucky it will then just about idle but most often cut out and need a long cool down.

The primary and secondary main jets are slightly blocked too.

Anyway, to the main point of this thread: I now see that the main primary jet has been increased numerically from 107 to 110. I assume that related to an increase in the orifice diameter and thus allows more fuel to mix with the same volume of air and so enriches the mixture.

Do the experts on the forum think that the increase has been (lazily) made to counteract the inevitably lean condition that the lack of carb base and intermediate gaskets will have caused, OR is the increase now a usual modification to deal with today's different fuel?

Is it worth going back to the 107? car is standard tune 1500. emissions and fuel econ are more important to me than "sporting performance"...

cheers

RDS

Good to read you are making some progress RDS, 107 to 110 is a small step, I wouldn’t worry about it. It will richen the mixture slightly across the whole Rev range which is no bad thing with modern E5 fuel

Thanks for that NEG; maybe that was why the jet change was done. I will leave the jets as they are, therefore.

I did a preliminary clean of the carb last night after splitting the carb halves:

Intermediate gasket was already torn and numerous open ports and channels (ie not the very small drilling, which I have not yet reviewed) were choked with dirt. New gasket is ready to add to the two gaskets sandwiching the bakelite heat shield; though I might see if the thicker gasket sold by Eurosport will fit, in addition to the tray for a better seating and heat isolation.

Float valve seemed to catch in certain positions but I cannot tell if that is beyond the actual amount of travel in practice in the float chamber. Viton tip seems more or less ok under 20x magnification but I may change it anyway.

All thought welcome.

cheers

RDS

Yes I’d change the float valve anyhow. Make sure both sides of the float are at the same height above the gasket with the float tab just touching the valve, 7mm is what you are aiming for, measure both floats. Make sure the floats have not cracked and let fuel in. Also the max drop of the float assembly should be no more than 15mm measured from the gasket.

The 7mm is quite critical, try to get as close as you can. Blow all channels out with compressed air and the jets, use an eye glass to check the jets are all clear.

Good luck

I will change the float valve NEG and most liley the float itself. I looked at it and the surface seems to be laminating in places and has crevices at the seams, using my x20 eyeglass. However that could be over magnification becasue an immersion test in warm water doe not let air bubbles out.

Re the max float drop, I am glad you mentioned this, because it is not sufficiently clear to me from the Haynes manual: doing it our way, do you mean the critical distance of no more than 15mm is distance between the gasket and the midway point of the top of the float, when the carb (top half) is held horizontally (and not vertically per the Haynes) AND the float is allowed to drop to its free maximum amount, and held against the tang-stop?

If so, my float drop was way more than 15mm.

By way of summary at this stage, we had a combination of
leaking exhaust at the manifold (no gasket)
poorly seating carb (gaskets),
partially blocked jets
blocked passageways
a sticking valve
a float level way out of spec
weak accelerator pump delivery (possibly due to the dirt; I have not checked the diaphragm yet)
an idle mixture that was impossible to get any variation out of
a mis-set choke

I am amazed the car ran at all. I just hope that addressing all of the above will cure the 20 mins/stall/20 mins cool down/start issue.

The dirt in large part seemed to be solidified black crumbly engine oil residue. Doesn't one of the tubes that attaches to the base of the carb take a feed from the crankcase? (I am not talking about the one that goes to the aircleaner).

cheers

RDS

Hi RDS yes measure the drop to the middle of the float with the carb top horizontal. If the drop is too great there is a chance of the float jamming open. Reading that I’m surprised it ran as well!

The black crumbly stuff could be material from old fuel hoses, ethanol does this over time and if there was no in line filter there could be quite a lot of it in there, good luck!

Ok thanks NEG

I will give the set up ago when the heat subsides!

Annoyingly i remove the filter as part of this fault funding process. I will see how things go before reinstalling and cutting new hoses.

Ref running at all, I mentioned the issue to an Italian mechanic a while back and he just said, it will be ok, "é un cavallo di motore", ie a horse of a motor. I think he meant that its rugged. At least, that is what I hope he meant....

Cheers

RDS