Fiat Strada 130TC - Dellorto 45 DHLA Tuning

[130tc]

Hello Guy, all

I am about to take my 130TC in for its 1st tune up after changing the carbs. At the moment car runs fine but stutters when the accelerator is pressed under light throttle, under full throttle stutter is less.

This is the current jetting

Choke 8011.1
Venturi 36
Pump 35
.7850 .1
Idle 50
Main 145
Air 150
Emulsion 7772.6

Any suggestions ?

Also has any one had experience with spark plug indexing on the 8v Twin Cam.

Thanks

Stephen

[Guy Croft]

I assume from the choke size that you are running 45DHLA?

If so the jetting is not far out but I would go up to 45 pump jets and 180 air correctors, I think a 150 air corrector will make the top end too rich.

I'd certainly check that the pump jets are working effectively when the throttle is opened, this can cause that flat spot, if you look down the barrels with engine 'off' and open the throttle each pump jet should spray a nice laminar jet of fuel. If they don't then the pump jet diaphrams should be renewed. Also check the idle mixture settings - one per barrel. I'd strongly advise use of Colortune for setting up (use search facility, I've written before on this, and see links section for Gunson website0.

I know a lot of 130TC owners experience a flat spot even when everything is set up perfectly, I am tempted to suggest that the OE exhaust silencer setup develops too much back-pressure. Either that or there is some fault I cannot ID with the Digiplex. Personally I am getting more and more annoyed with 'black boxes'!

GC

[1969race125]

Regarding the second part of your question, I indexed the plugs in my 8V high-compression race engine, assuming that it would be important given the high piston dome. I later discovered that, after a compression test, the plugs had been replaced with the indexing marks all wrong. The car ran pretty much identical times (and felt like identical power - although I didn't test this) during that time, and again after I lined them all back up. I guess it either doesn't matter too much (in proportion to every other variable) or I'm indexing them to the wrong place in the chamber! It certainly shoudn't affect the stutter you're experiencing.

There's some more advice on plugs in this thread:

viewtopic.php?p=983

Andrew

[Guy Croft]

From my point of view plug indexing is a bit of a 'non-issue'. It's not something I've ever thought of or considered seriously, but I am open to correction.
From my point of view there are so many other more tangible things (and things to worry about) that affect an engine's behaviour and power. Take the variation in port to port air flow eg. I think indexing plugs is going a bit, well, too far...!
No offence intended.

GC

[Abarthnorway - Remi L]

Hi all!

I have the same experience with 45 DHLA Dellortos as Stephen/130 tc regarding light throttle acceleration hesitation. More specifically in RPM area 2700 - 3200.

Engine: 130 tc
GC 3A inlet
Colombo Bariani 272 / 10.3 exhaust
Carefully ported and flowed head/valves etc according to GC book
10.5:1 pistons
Free flow exhaust
Original Airbox

Dellorto DHLA 45 new buildt: Current jetting:
36 chokes
152 mains
45 pump
6 emu tube
9 idle mixture tube
58 idle jets
Pipercross ram pipes


In trying to get rid of the hesitation I have changed the following parts with the following results:
emu tubes: 5/6 No change
mains: 148/150/152/155 even 158 no change
idle jets: 50 to 52 to 55 to 58....
50 idle jets didn't pull clearly from idle and was changed for 52 which works just fine up till approx 2700 then its very very jumpy till 3200, 55 better, and 58 problem solved..... and a new problem arises. On idle and low revs mixture is just too rich and engine gets sour, and consumption goes up on roaduse.... a lot.

Seems like the engine gets too little fuel in the transition between progression and before main circuit kicks in.

Two solutions remain, and I havent had time/parts to try it out yet. Changing the idle mix tube for one with smaller air bleed to richen progression top end, and changing ram pipes to original - I am thinking the wide Pipercross pipes flows the air into the carbs differently than the more straight Dellorto types.

I will be happy for inputs/replies!
And I will keep You posted on my progress - when spring comes.

Best regards

Remi Lovhoiden

This leaves two solutions to try out

[Guy Croft]

Remi, thanks, useful post there.

Are you on Digiplex ignition? I know the standard 130TC does not suffer from this hesitation. I wonder if the Digiplex mapped ignition settings are upset when the engine spec is changed, after all, it is a speed vs vacuum pre-calibrated system.


GC

[Abarthnorway - Remi L]

Hi Guy!

Yes I am running the standard Digiplex ignition, and all connections and functions checked out. I have even changed the box just to check.

The reason I do not regard the "black box" to be part of the problem, is that the problem seems to be related to a lean mixture at the transition phase between progression/main circuit. When changing to richer idle jets, problem goes away - but low rpm suffers from too rich mixture.
Btw the cams are timed 110/110 in/ex. I have also had a tuned Strada Abarth with Solexes - although with different specs - but never had a problem like this.

:idea: I really suspect the wide/open Ram Pipes to be the problem, as the flow into the carbs must be very different to the very straight original pipes. May it cause the main circuit to start slightly later because of big inclined angle, and produce a less clear signal at the choke??

Thats my idea - but so far thats just speculation.

Btw the car runs excellent otherwise, and pulls hard from 2200 all the way to approx 7000 rpm. Thanks for lots of good advice :!:

Best regards
Remi Lovhoiden

[Guy Croft]

Hi Remi, thanks.

Fair comment but I am still not sure why progression should be such a problem on that motor... I have never had it on any other TC.

Incidentally the new line 45 DCOE carbs have more progression drillings.

GC

[vcg]

Hi guys,

This is a really late reply, but very relevant. I run DHLA 45E with an Alquati manifold on my 131 Racing 2.0Lt. Engine specs are 11:1 CR, Kent FT10 282 duration cams, 42-48-55mm 4-2-1 header, 42mm inlet - 38mm outlet valve ported head.

DHLA 45E jetting:

choke: 36
main: 145
iddle: 60
pump: 42
air: 180
emulsion: 7772.5
needle valve: 170
float level: 14.5

The car runs sweet, no flat spots, nice top end. Just one problem: I have always felt that acceleration should be stronger. Any ideas?

Should I try 200 needle valves instead of 170? Should I try 45 pumps instead of 42?

Please advice. Thanks,

[Guy Croft]

Vassilis, hi

no, it's not jetting as such, that jetting, and though you don't need 60 idle jets (I'd be on 50s) the adjustment screw can cope with that.

I need to have lengths of the header, the silencer layout and whether the FT10 cam is regrind or billet.

GC

[vcg]

Hi Guy,

Thanks for the reply, the FT10 is a Kent regrind exchange. The header is 4 42mm-62cm long primaries, 2 48mm-35cm long secondaries and a 55mm tailpipe with single see-through silencer of same inside diameter as the tailpipe.

[Guy Croft]

Your problem is mainly the cams, you will never get decent torque out of regrinds with the 8V TC unit, all you'll get if you're lucky is a bit of extra top end. I found this out the hard way many years ago and when I overlay the cam maps it's easy to see why, the lift integral is very weak.

Here's my advice; get rid of those cams, get some GC 3A, Alquati or C&B StII billet cams, go up to 38mm chokes, 175 air correctors and time the cams at FL 110deg, shorten the secondary pipes to 20.3cm (8"). This will tune it quite nicely with powerband 3-7000 rpm with 16mm rampipes.
I have taken info this from software simulation setups. Those secondary pipes are way too long with the (OK) 24" primary pipes.

GC