Many times over the years people have asked me for recommendations for carburettor jetting for modified cars.
Of course I either tell them the jetting I have used (when I had carbs) or give them the standard answer i.e., "All engines are different: take it to a rolling road and set it up".
However it is always nice to have a starting point and this time it's 1300s.
At Evolution Engineering, we had a very good client, sadly no longer with us who was a great Fulvia enthusiast. He lived part of the time in America where years ago, he had bought up a large stock of ex-works Fulvia parts. I recall him saying that he had new 1.3HF crankshafts in their factory wrapping, special 40mm Solex carburettors and so on.. Don’t ask! I have no idea what became of all this wonderful stuff.
Anyway he came up with a most interesting document that I have copied here that lists a variety of carburettor jetting for 1300s in various states of tune. Of course Solex parts are very hard to find. Main jets can be bored to the correct size as twist drills in 0.1mm steps are easily available – this should really be done on a lathe at high speed to ensure accuracy and a good finish inside. Air correction jets are usually reduced in size when engines are developed. The trick with these is to fill them with solder and re-drill.
Here are the specifications; I hope that they are of interest. Sharp-eyed readers will have noticed that apart from the idle jets, the jetting of the 1.3HF is identical to that of the S2 coupes.
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Note:
The early owners’ manuals did not keep up with the production specification. The HF cams, also common to the 1.3 S were never used on any 1.3 engine with 29 mm choke carburettors. Dropping the main jet to 115 as with the 1.2 HF would not provide sufficient fuelling for the 1.3, 1298 cc engine; the jetting and carb. specification is very sensitive.
From the original Solex S.p.a. Technical Bulletin, No. 65-A/June 1967, supplied by the Lancia Competition Department.
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1.2 HF (76 x 77 engine)
Full air cleaner
HF cams
Solex C. 35 PHH (CR. 186)
Choke 29
Main Jet 115
Air Corr Jet 160
Idle jet 42.5
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1.2 HF Corsa (77 x 67 engine, 1247 cc)
No Air Cleaner
HF Cams
Solex C. 35 PHH (HF Corsa, special velocity stacks, C. 23263)
Choke 31
Main Jet 125
Air Corr Jet 145
Idle jet 42.5
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1.3 Rallye Coupe and Sport (77 x 69.7 engine, 1298 cc)
Full Air Cleaner
Standard Cams
Solex C. 35 PHH 2 (CR. 192)
Choke 29
Main Jet 120
Air Corr Jet 190
Idle jet 42.5
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1.3 HF (77 x 69.7 engine, 101 BHP)
Full Air Cleaner
HF Cams
Solex C. 35 PHH 3 (CR. 193)
Choke 31
Main Jet 120
Air Corr Jet 180
Idle Jet 42.5
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1.3 HF Corsa (77 x 69.7 engine, 114 BHP)
No Air Cleaner
HF Cams
Solex 35 PHH 3 (HF Corsa, special velocity stacks C. 23263)
Choke 31
Main Jet 125
Air Corr Jet 145
Idle jet 42.5
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From the original Solex S.p.A. Technical Bulletin No. 71/October 1967, supplied by the Lancia Competition Department
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1.3 HFR Variante 1014 (77 x 69.7 engine, 132 BHP)
No Air Cleaner
HF variante 1014
Solex C. 40 DDHF (Special velocity stacks)
Choke 34
Main Jet 145
Air Corr Jet 155
Idle jet 50
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8 comments:
Paul, lots of interesting information here, how do the Dellorto DHLB 35s compare to these, I realise they were an aftermarket option and not used by the Lancia competition department, were they much better made than the Solex variants? Good blog with interesting photos, keep up the good work! Neil
Thanks Neil.
Undoubtedly the Dell'Ortos were a vastly superior product. The Solexes are really rather cheap and nasty! The Dell'Orto has I believe a superior pick-up circuit and is much better built with I think bearings for the spindles in place of Solex's running them directly in the metal of the body. I do not agree though with using the DHLBs on 1600s; 35mm is too small and tragically Dell'Orto never made them in larger sizes
Interesting stuff about the Solex 40mm for the HFR 1300. 34mm choke. These carbs are undoubtedly impossible to find. My tuned 1216HF is using Dell Ortho 35s at the moment but i wish to experiment with larger carbs. What do you think of the Idea of making smaller 34 venturis to put in the (easily available) solex 42's? This is 2mm larger but the smaller venturi should compensate.
Thanks for the comment William.
I think that 42s might just be a bit big, unless you are happy to keep the engine spinning. After all when Triumph prepared the Spitfire (1147cc) for race use, they used 45mm Webers, so it should be possible. I would think that your chokes should be perhaps 33mm though or even 32mm.
40's were used on about all 1300 Alfas albeit with 32 venturis. The Simca Abarth 2000 used 58(!) chokes to reach over 200Bhp. Poor comparisson but 42 with maybe a 33 venturi might work. Any smaller and the original 35's would flow better.
I doubt that the Simca used 58mm CHOKES - probably 58 mm carbs with 44mm chokes perhaps.
Perhaps 32mm chokes might be better for your car.
An unrestored never raced '68 1300HFSpeciale just sold on Ebay had a accompanying factory letter stating 113Hp at 7000 rpm. Solex 40DDHF (main jet150. idlejet 60.) And 38/70 in and 76/32 ex. cams (measured with 0.4mm valve clearance) 11.3CR. This was the private team factory offering. I wish I was the buyer...
Thanks again William; that's super information. I wonder if those camshafts were original? They are of course VAR 1016 camshafts. 0.40 mm was the normal checking clearance for timing for all the cams. Perhaps the 1016 cam acually pre-dated the 1600? Interesting if it did!
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