Weber 40IDF jetting for 1919TC

[alexfl82]

Hello!!

I have a 1.919cc (84x86,6) with twin weber 40 IDF. Which is the best jetting for this engine?


Alex.

[Guy Croft]

Alex sent me the following info by pm:

Engine is TC Fiat: 1919cc (84x86,6) with twin weber 40 IDF

camshafts: timing 50/80 80/50 310deg., duration 10.6mm lift
valve sizes: 41,6mm inlet 35,8mm exhaust
head state (porting):
exhaust manifold & mufflers: Vimesa 4-1, original mufflers (like a Fiat 124 Spider 2000) pipe 50mm
Compression ratio: 9:1
Fuel pump type: Facet Red top
Which is the best fuel pressure? I have a fuel pressure regulator.
And best spark plugs? I use Champion N7YCC or N6YCC.

It is very difficult to offer jetting when I don't know the engine exactly! I need to make some assumptions:

1. The head is factory standard (you have not mentioned any porting)
2. The cams are good quality billet (not regrinds), you time them at 105 deg (see Virtual Workshop for cam timing info)
3. The mufflers are 'straight-thru' and do not offer any back pressure.

I will compare with the Fiat-Abarth 124 Spider (124CSA) which was an 1800 TC with standard 1800 cams and 124 1800 head, 9.8/1CR, same valves as yours, twin 44IDF, 4-2-1 exhaust, 3 Abarth silencers, gave 128bhp, and other dyno data on my own 1800 engines from the late 80s.

Your compression ratio is a bit low for those long duration cams but they will, if you are lucky, offer some reasonable power over 4000rpm. If assumptions are correct your bigger 1919cc engine (it's a long stroke 1800?) could deliver about 134bhp at 7200.

The 40 IDF Weber jetting would be:

Chokes 34mm
Main jet 140
air corrector 180
pump jet 45
idle 55

As with all jetting a good rolling road session or thorough road test is essential.

Problems to watch out for on your engine:

1. Balance carbs (one barrel must be balanced against another on each carb and the one carb against another).
2. Set idle mixture accurately. If you cannot get a a clean setting, the pump jets are leaking, there is a compression (valve) problem or the the carbs are out of balance. There is often a problem with IDF carbs where the old throttles do not close properly and at idle one or both carbs runs on the progression drillings and it runs too rich/idle mixture does not respond.
3. Make sure the carbs are giving full throttle when you press the accelerator pedal.
4. Set the ignition timing at 10 deg advance at 800 rpm, make sure the advance mechanism works, max advance should be 34-36 deg at 5500.
5. Check that the pump jets work properly and do not drip petrol into the barrels when the engine is running.

The Red Top pump give far too much pressure, it will never be right even with a regulator. Set it to give 3.5psi line pressure at the carbs at idle if you can and hope it does not flood - better to get rid of it and use a Silver Top, with NO regulator.
The Champion road spec plugs 6 grade will be fine, the CR is not high enough to require race plugs or cold 'road' types.

If you get the power I have suggested - or more, great. If not, the compression is low (rings, valves) or there is too much back-pressure in the mufflers, or the cams are no good. More important for GC diagnosis - the max torque should be somewhere between 116lbf ft and 120lbf ft at say, 4800-5000.

I am interested in how this engine cc size achieved. Long stroke crank? Some pictures would add a bit of interest. The car? These threads with nothing but writing can be very dull for other readers.

Anyway I hope this all makes sense and is helpful,

GC

[tmvolumex]

As I recall reading on a site a while back, it has a shorter stroke than the more common 1995cc engines stroke of 90 mm.
From the 124 site Dave wrote:

"10/02/03 I need some help. I am trying to source a 86mm crank that is found from the SEAT cars. I think these cars were made under license and are essentially old Fiat castings and toolings that were purchased from the mother company by several
companies in Europe, Specifically - I think - Spain & Portugal. I have enclosed some pictures of the Crank and if anyone knows where i can find one, could they please contact me."

2003 that was a while back!
Tom McGaffigan

[alexfl82]

I don't know this page, but I have some cranks of this engine in Spain is easy to find. If you can talk with this person tell it.

The 84x86,6 was made by S.E.A.T to save a Luxury taxe that was in that years. Cras with engines over 1920cc must pay this taxe.
The engine is the same as 1995cc, I think only the crank and pistons are different.

This is my engine.

(You have more data by pm Guy)







Alex.

[tmvolumex]

I have forwarded your message to Dave B.
He may be contacting you about a crank.
Tom McGaffigan

[tmvolumex]

Nice looking engine! What is the drive shaft under the carbs for? looks like a drive shaft running off the front of the crank going to the rear of the engine?
Tom McGaffigan

[Uros Piperski]

Extension of the brake pedal, I think. It's connected to the brake booster.

[alexfl82]

Extension of the brake pedal, I think. It's connected to the brake booster.

Yes!!, it's to work OK in the carbs, and to possible install DCOE cabs too.



Alex.

[Guy Croft]

Alex, hi

well done! That information about your remote brake booster and the good photos is priceless, I have never done one, only heard about it and as you say, it's a conversion that permits use of race carbs on left-hand-drive Fiat 124 vehicles. However the info will be lost in this thread because the title is about carbs.

If you are willing to share the details, I'd like you to start a new thread in General Discussion, 'competition cars', called

'Fiat 124 remote brake booster conversion'

and then describe the conversion, if you have time. I can help with language if you need it.

I am certain many will wish to read it.

GC

[alexfl82]

I did the post in the other forum.



What about emulsion tubes Guy?, the data that I sent you second time changes something in the jetting?



Regards from Spain,

Alex.

[Guy Croft]

Emulsion tube either use F9 or F11. My advice is go with the jetting that I have listed above, I worked it out based on your engine spec.

Do some full-load road tests on a long hill in 3rd/4th gear (hold the engine under power for 10 secs and then cut the engine and disengage the clutch - make sure you don't lock up the steering). The do plug checks and adjust up or down on main jets and air correctors by one size at a time to enrich or lean out. Never change both at the same time.

Main jet - controls fuelling on 1/3 throttle to full throttle from about 3000-max rpm. Bigger jet - richer.

Air corrector - mainly controls top-end say 5000-max rpm. Bigger air corrector - leaner.



GC

[alexfl82]

Thanks Guy,

this week I bought 44IDF carbs with this jetting.

Main jet 145
Air corrector 210
Idle 55
Pump jet 45
Emulsion tube F9
Chokes 36mm

What do you think about this setting to my engine,

are 36mm too big for my engine?, I also have 34mm.
what E.T. are better F9 or F11?


---------------------------------------------------------

[Guy Croft]

Alex,

your new 44IDF carbs jetting of:

Main jet 145
Air corrector 210
Idle 55
Pump jet 45
Emulsion tube F9 (ET)
Chokes 36mm

is basically from the 124 CSA 1800 engine, except that car used F11 ET.

Your F9 is a bit richer than F11 and so, as your engine is bigger, I think I would use the F9 and see how she runs. I would change the air corrector to 185, but the rest seems fine. If it is over-rich 3000-7000 rpm on F9 try F11, but don't change the jets at the same time or you'll get totally confused..

GC

[alexfl82]

Hi Guy,


About chokes, 36mm are fine?. What will be the difference with 34mm?



You are the best Guy!!!

Thanks for all,

Alex.

[Guy Croft]

You go up on choke size to increase the power. I'd run with 36mm as per 124CSA.
There is a slight bottom-end torque loss with 36mm compared with 34mm but that is inevitable if you want the top-end power. You can go to 37mm too on 44IDF but it means boring them out and reshaping the venturi to its original form, with the smallest section in the right place so as not to upset the signal in the secondary choke (depression).

GC