Hesitant on initial throttle application

[andyps]

Now I've got my Fulvia running reasonably well there is one thing that is still frustrating - whenever I initially accelerate, either whilst already moving or when setting off there is a hesitation before the revs pick up. I've tried altering the timing but that didn't really make a difference and generally the carb setting seems reasonable with decent acceleration once past the hesitation.

Any thoughts on what it could be? As far as I know the carbs and engine are standard 1.3 S2, I've rebuilt the carbs and cleaned all the jets etc. in an ultrasonic cleaner so there is nothing blocked. The only thing I didn't change was the float settings as I preferred to leave them alone as I don't fully understand how to set them.

[jus]

Maybe just take the airbox off, and have a look inside each venturi as you operate the throttle lever (engine not running). You should see fuel squirt into each one as the lever operates. I think that's probably the first thing I'd check. Is it better if you run with some choke?

[andyps]

Maybe just take the airbox off, and have a look inside each venturi as you operate the throttle lever (engine not running). You should see fuel squirt into each one as the lever operates. I think that's probably the first thing I'd check. Is it better if you run with some choke?

I'll have a look at that, thanks. It doesn't run well with choke once it has fired up but I've not tried using it when warm - I will do next time I have it running, which might be a couple of days.

[lancialulu]

Fulvias are quite sensitive to valve timing which if not correct will leave a "hole" at  around 2200-2500 (just the revs normally used to pull away from a junction). This is  more noticeable on 1600's.

I doubt float levels will cause this but a quick and dirty way to check is t run the engine so the carbs are full. Take off the little cover on the top with  the domed breather cap and remove one of the middle "jets". With a black 3mm cable tie mark a datum 30mm from the bottom. Stick the cable into the hole where the jet was down to the mark and withdraw. See where the fuel is in the   tie notches and measure to the datum line. The gap should be c19mm+-1mm.

[andyps]

Thanks Tim, the valve timing is as accurate as I can get it on the basis my engine doesn't have the vernier cams. I think it would benefit from a new chain and tensioner which is a job for the winter I think. I'll try the cable tie trick and see how I get on.

[nistri]

How good is your distributor? With the engine off, remove the distributor cap and by hand move up and down the rotor arm to feel for free play. If there is a clear click (max axial play 0.1mm), then the shaft needs re-shimming otherwise you get erratic firing especially at low rev. The shaft needs regular oil lubrication via the purpose made hole in the distributor baseplate, Andrea

[andyps]

Thanks Andrea.

[davidwheeler]

Bigger jets needed for modern petrol.  There is info. in the technical thread I think.

[fay66]

Bigger jets needed for modern petrol.  There is info. in the technical thread I think.

David, I have no problem with my 2c, however I fitted Dellorto 32 DHLB's years ago.
Brian
8227

[Mikenoangelo]

Pardon my ignorance of the Fulvia - what breed of carb does it use? I'd suspect a mixture issue, what you describe sounds like transition from slow running jet to main. Rolling road test might help or if you get really keen invest in an air/fuel ratio gauge which shows what the mixture is at all times. Certainly worked for me on my Augusta but pricey.

Mike

[Richard Fridd]

Solex breed?

[Spider2]

I already started  a different post about possible solex carb problems as I have no power above 5000 rpm although fine up to that point.
I have the carbs off and am ultra sonically cleaning all the jets etc. I note my main jets are 120. What is the consensus amongst solex experts. Are these correct or should they be a bit bigger?  It is a series 1 1.3s The emulsion tube/air jet is stamped either 80 or probably 180 but a bit difficult to read as the tops are a bit mangled. I do have the feeling that the carbs are under fueled at high rpm/high throttle.
I do not need a rebuild kit but need some carb to manifold gaskets. Who supplies theses?
The timing is good so If the carbs are not the problem I will go to valve clearances and valve timing. I am fairly new to Fulvias so what is the fly wheel marking for No. 1 TDC?
Thanks.
Simon

[davidwheeler]

Notin tech. thread but I knew it was somewhere....
I increased my fast idle jets to 60 via 55 with considerable improvement.  I am consideering increasing the main jets as well but currently am doing the bodywork.   I think it well worth your while experimenting, jets are cheap...

 
   
   
" Re: Carburettor tuning
« Reply #16 on: 22 October, 2012, 03:45:35 PM »
   Reply with quoteQuote
Hello David

I have been following the posts about your engine faltering on pick-up with some interest, as I experienced similar symptoms.  Having now seen that you have exhausted alternative suggestions, it is perhaps time to throw in my tuppence worth......

I am convinced that the viscosity and volatility of current petrols is so different to that of 40 years ago that the behavour of the fuel in Solex carbs is different from what the factory developed.  Admittedly both my 1600 Fulvias have altered ports and manifolds from standard, but on both cars I found idle was fine and main-jet running was good, but to get an adequate pick-up, the fast idle jet had to be significantly increased from the standard 50.  On one car I am using size 55 and the other, size 60 (states of engine tune/distributor advance curve/spindle wear etc. are different), but both now give good instantaneous pick-up. I had to do similar alterations on the 1300 engine, too.

Italian Carburetors of Corlo, Ferrara, Italy can supply new Solex jets in most sizes for a very reasonable amount, and offer a good service.  The url is :
http://stores.ebay.com/ALFA1750S-CARBURETORS-PARTS-STORE

They can also supply the diaphragms - which do seem to harden with age / degrade with modern fuels.  With the carbs off to fit the diaphragms, take the opportunity to try and adjust the drop rods to ensure the activation arm moves the same amount for each diaphragm.  Good luck.

Regards - Roddy
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Roddy Young
Dunfermline, Fife "

[andyps]

That is really helpful David, thanks.

I can't see fast idle jets from that eBay seller but will have a search and see if I can find them somewhere.

[lancialulu]

That is really helpful David, thanks.

I can't see fast idle jets from that eBay seller but will have a search and see if I can find them somewhere.

They have what ever you need. Just email them. They do a kit containing 8 jets - 4 of one size 4 of another. Suggest you order +5 and +7.5 to start. However as I said before real hesitation (a “hole”) is likely to be something else underlying.