Problem with my carb - 1975 Fulvia 1.3s

[BermondseyBoy]

Hello everyone. I have a problem with my ’75 Fulvia 1.3s which I am sure is carburettor related. I wonder if anyone can please suggest what may be going on?

When the car is warmed up and I pull away I put my foot on the accelerator and the car takes off. After a couple of seconds of acceleration, and as I put my food down further, the car slows down suddenly and feels almost like the choke has been pulled out and the engine is flooding. After a further couple of seconds the performance picks up and you fly off. Obviously this is exceedingly unnerving but is also very dangerous if I’m pulling out on a busy road so I’m reluctant to take the car out with any passengers.

Can anyone think what may be causing this?

Many thanks, Nick

[lancialulu]

Any particular revs that the flat spot occurs?

Have you changed the timing chain? If so how accurate did you time the cams....

How clean are the carbs - you say your car has been sitting for 15 years...... have they been opened up and cleaned of crud......

Very hard to diagnose at a distance

[BermondseyBoy]

Hi there, thanks for the tips. Yes the car had been static for 15 years but last year it had a new petrol tank, the carbs were given a good clean out and I did about 400 miles before I put the car away for the winter. I don't recall the particular revs the problem occurred at but I wouldn't have been piling them on so they probably would have been fairly low.

[Richard Fridd]

Perhaps the carburettor slow running/idle circuit is 'gummed up'?

[DavidLaver]

If you are in Bermondsey then I can recommend Sanspeed in Bexleyheath.  Very good at fault finding from first principles, previous bills very reasonable, nice people.  If you had to leave it with them ten mins from Bexleyheath station on the London Bridge line.

http://www.sanspeed.co.uk/Home

http://www.classiccarwebsite.com/sanspeed

I've been for a rolling road tune of an MG - ran much smoother with a little more power.  Took a 1987 Mercedes with a heap of issues which they correctly traced to needing the fuel injection rebuilding, however they took it all apart and cleaned it and recommended a fuel additive to keep it clean which improved things no end until I got the work done by an injection specialist.  My local Mercedes specialist hadn't been brave enough to take the system to bits and hadn't got beyond "take a bit off, put another bit on, hope that improves things".  A friend took his Austin 7 there for ignition and carb setup, and I think a 500 cooper as well.

I also like Classic Cars of Kent who also have a rolling road.  They're down a lane near Uckfield, but having found them they are pleased to see you (not a lot of passing trade!!!) and even have a little museum to amuse.  They'll also be all sorts of interest in the workshop and last time I was there most of Julius Thurgood's stock.  Last time I was there they had Julius's dark blue Flavia Berlina that had sold at a Brooklands auction with an LPG conversion that they'd just recommissioned. Think it had done a circuit of Ireland rally as well.  Wonder what happened to that car...

http://www.cckhistoric.com

[davidwheeler]

Sounds a bit like mine - I put in larger intermediate jets and improved things no end.  Modern petrol is of different viscosity.   There is a thread somewhere on the subject.

[dhla40]

I agree with fitting larger idle jets, on mine I went up .02mm and car feels much better, petrol has changed a lot in 40 years.

Sean

[Richard Fridd]

Where are the different jets available? Is it a case of drilling?

[Jaydub]

Richard, in answer to your query " is it a matter of jet drilling?" NO is the answer. Jets are sized by drilling and then broaching with a calibrated tool and then flow tested to determine the size stamped on them. So a jet drilled 0.75 may flow at 0.70 or 0.80, and will be marked accordingly.

[lancialulu]

Where are the different jets available? Is it a case of drilling?

There are a ready supply of jets for solex (and indeed emulsion tubes) from Italy.

[davidwheeler]

Mine came from the UK.  Try Eurocarb, EBay or Mr Google.

[stanley sweet]

I agree with fitting larger idle jets, on mine I went up .02mm and car feels much better, petrol has changed a lot in 40 years.

Sean

Was this on a 1300? What size did you end up with? (me not knowing the standard size offhand).

[chriswgawne]

"Modern petrol is of different viscosity." resulting in larger idle or main jets being needed today?

Is this really true? If so, all carbs ( all because generally fuel Injection took over around 20/25 years ago) on all cars would need re-jetting.........and I haven't been aware of this being suggested anywhere else in the old car world.

And certainly with Aurelias on Solex or Weber, single or twin I have found no need to alter the original jet sizes which were used back in the day. And the same with Fulvias which we have driven continuously in one form or another from 1971 to date.
Fulvias and Aurelias  in my experience need the correct good quality plugs and points gapped correctly with a decent original fuel pump delivering fuel at the correct pressure/rate. And I always use the original distributor  based ignition system with points although I have tried electronic ignition substitutes with Aurelias. These seem to give smoother slow running under 1000rpm but above that I have found no improvement. This presumably must be because of wear in what is a >60 year old distributor. 

Having said all of that, certainly fuel vaporisation on very hot days here in slow moving or stopped traffic can be an issue with modern fuels where there is no circulation back through the tank to keep the fuel cool.

What has prompted me to write this post is that some of you will remember that in the 90's and early 2000's I used to bring to the UK good quality comprehensive reasonably priced Italian carburettor kits for LMC members using Webers, Solexs and Dellortos  and also for fellow competitors  in Historic Motor racing circles.
I stopped doing it simply because I got fed up with potential LMC customers who appeared to have carburation problems which they felt would best be solved by simply spending money on replacement parts without having already checked the basics. In far too many cases, when quizzed in their first contact with me as to what the symptoms were and what they might have already checked I realised that hardly any of them had bothered to simply give their carbs a good clean and check plugs points and timing etc. So in a large % of cases in a friendly fashion I refused to sell them a kit until they had done all that....and guess what? Most of them didn't phone or email again.

I am all for progress and improvement  but you will all know that Lancia's mechanical design and engineering back in the day was superbly executed. Over the last 48 years of Lancia ownership I have found myself saying from time to time 'if it was good enough for them its certainly good enough for me'.
I have to also admit that this is against the background of admitting to having gone down a lot of car improvement blind alleys in the dim and distant past.
Chris

[davidwheeler]

What ever the reason I found that, as I progressively increased the size of the slow jets, so the low range hesitation improved.

[Jaydub]

Increasing the idle jet size will possibly overcome any hesitation issues as the idle circuit is part of the progression process until the throttle plate is open enough for the main jet circuit to operate.

I agree with Chris in that petrol viscosity hasn`t changed, it`s the fact that in the last 20 to 30 years there has been so many lacquers/varnishes/ additives etc added that it only takes a few microns of these coating jets and especially fuel injector nozzles to cause problems.

 I spent many years in the engine diagnostic business tracing causes of hesitations/ misfires etc.and a large percentage of problems were down to owners and other garages ignoring the basics and blaming carburetors or injection systems and ECU`s. You need the ignition system, distributor, fuel pressure/ flow rate, valve clearances, timing and most importantly compression pressures and vacuum readings all in good order before you even think about carburetor set up and changing jets and such.

Nick your problem could be a possible plug/plug lead breakdown when the ignition demand is high under acceleration. Another good thing to do when laying a car up for any length of time is to add fuel preserver to the tank and run it through the system as the aforementioned varnishes etc will gum up jets and passages, as modern fuel does degrade more readily when stored.