Starting driving the Fiat and I have some Qs...

[mosu]

Hi all,

So I started driving the Fiat regularly now and had some questions about the behaviour that I'm seeing. First of all, it's simply amazing to have no roof on the car, to be surrounded by the wind and fresh air. The engine is smooth, shifter is crisp, it bellows authoritatively when the secondary engages and there's a slight popping on the overrun...absolutely engrossing for all the senses...

1) Am I in love with a machine? This is disturbing thought...

2) The car is thirsty - I mean half a tank on the gauge in 130 miles, and there's no 6L V8 under the hood. It's a 1608 motor with a DMSA carb on an 1800 intake. Could it be because of the thermostat that's stuck open that I was asking about in the other thread? There are no sensors or anything that I can think of that can cause a carbed car to guzzle gas like this...

3) Power begins to flatten off badly after about 4500 rpm to redline. If I hammer it, it pulls strongly to about 4000-4500 rpm, then it seems to lose all desire to pick up. I'm better off upshifting. Almost all the ignition components are new: points, cap, rotor, condensers. I adjusted the points gap by feeler gauge to spec, but I can't tell if the dwell angle is ideal. Timing is at ~12 deg BTDC.

Any ideas? Is #3 typical/normal?

Cheers,

Alex

[So Cal Mark]

130 miles for 5 gals of fuel isn't poor mileage, especially if you're hammering it while you drive. From your trouble description, I'd say either the secondary isn't opening or the jet is plugged

[mosu]

I regasketed the carb before the swap and cleaned it, and the secondary was working fine. It does make a very distinct bellowing sound when I approach WOT so I assumed that it was the secondary opening fully. I'll check the jet, maybe it got plugged with some debris. You're referring to the "external" secondary idle jet, or the one inside the float chamber near the air correction tube?

Also, could the ignition components play a role in loss of high rpm power?

[joelbert2k]

Another area to look at is the vacuum advance. I don't have any right now, no port on the carb, and the top end power seems rather limited.

[kilrwail]

#1 is normal. Welcome!
#2 is normal - it's a small tank. 200 miles with a margin for error is normal.
#3 is not

[mosu]

LOL, thanks kilrwail! I've accepted #1 and decided to enjoy it. Man and machine must have a bond and that's good enough for me.

For #3, the power tapering off badly above 4.5K rpm, I checked the jets as per your suggestion Mark, and they're still squeaky clean. What else should I look towards? Engine not being at 90 celsius? Could it be weak spark? Or should I turn my attention to the carb's jetting?

I come from the world of FI where my choices were limited to no vacuum leaks and sensors working. This is a whole new ball game with the wealth of adjustment possibilities.Damned Honda motors that work perfectly even after a nuclear attack spoiled me

[So Cal Mark]

the secondary jet could be too small. The vacuum advance only works at cruise; light throttle/high vacuum. It won't have an effect on top end power. What is the total advance you have? If you're going to run without the vacuum unit attached, add another 5 degrees initial timing. To check the secondary jet you can blow down through the air bleed without doing any carb disassembly

[joelbert2k]

Mark,
I realize that you work on these cars for a living but I have to disagree on the vacuum issue. Since the vacuum advance port is above the throttle plate it is not the same as manifold vacuum. It is actually more the opposite. The more air flowing through the venturi the higher the vacuum is at that port. At full throttle manifold vacuum is low but the high airflow through the carb creates high vacuum at the port/distributor. Just my 2 cents.

Joel

[So Cal Mark]

What makes fuel flow from the main discharge nozzle? A difference in vacuum between the float bowl and the venturi. At idle, the pressure is nearly the same in the venturi and float bowl, hence no flow from the discharge nozzle. If you want to disagree, that's okay with me. It's all free advice, take it or leave it

[mdrburchette]

You fellas are arguing for no reason. The guy says he adjusted the points gap so I feel certain he doesn't have vacuum advance.
What year car do you have? I'm not sure how the dual point system works on the 74 and later distributors to determine if that's a problem, but may be something to look into if you have that setup.
Could someone have installed the timing belt on the wrong teeth? It sounds like a timing issue to me.

[mosu]

You're right, there's no vacuum advance on my setup, just mechanical.

My secondary jets are as follows (mine/DMSA spec on Brad Artigue's site):

Air correction 160/155
Main 135/145
Idle 50/60

The idle and main ones are 10 "points" smaller. However, keep in mind that this is a 1608cc motor, not the 1756cc that the carb was originally jetted for. Mark, do you think that this is the issue?

If it helps in any way, the car is peppier when it's colder outside(15 celsius) than when it warms up (20+ celsius).

[mosu]

Hi all,

Ok, I'm back with more questions after some fiddling with the jets. I basically left the idle jets the same size since the adjustment seemed alright, and I bumped the primary main jet by 10 points and the secondary by 20 to see what happens with some jets that I had lying around. Switch over was done with the engine warm.

I have to say that definitely answered the power problem. Now it pulls nice and evenly almost to the yellow line, and power delivery doesn't seem to have holes in it. However, next morning, on the cold start, it barely chugged along with the choke pulled out. If I go under the hood an hold the choke flaps open without touching the cable position, the idle evens out nicely.

I want to understand this better: when the cable is pulled, it doesn't JUST pull the flaps right? It also opens the throttle slightly? Does this mean that it's running partially off the pig-rich secondary main jet causing it to chug along?

I want to understand the impact of the various jets in the various running conditions...

[racydave]

It sounds like a minor choke adjustment should do the trick. It has already shown you what it wants, a little more air!

[mosu]

More or less...with the choke fully pulled it wants more air, but pulling the choke I'm guessing opens the accelerator plate slightly as well. I don't think there's a way to adjust the choke flaps independent of the shaft that moves them. It's likely that I have to play with the jetting, the airflow is fixed.