Last ride of the season

[KandJinmaine]

It’s been a while since I’ve been on this forum, life stuff like everybody else I guess. Yesterday my wife and I had an opportunity to take our ‘80 out for a drive to a beautiful part of Acadia National Park. It was about 60 degrees and sunny and awesome. After about Halloween the season is over up here in the Hinterlands of Maine! We went to a restaurant, sat out in the sun and had a burger and a local barley pop. Chatted with a couple that were even older than us, it was a nice time. When we went out to the parking lot they were getting into a 1949 Jeepster, in mostly perfect condition. It’s funny how car people are almost always nice, even when you don’t know they are car people.....
Enjoy The Ride!
Jeff

[SteinOnkel]

One of the perks of living in Northern California - ti's the convertible season, always. Just gotta remember to put the car cover on 3 months out of the year.

Although, I was in Maine in December last year and my goodness, we were driving through a forest that had just seen ice rain a few days prior. It was an absolutely unbelievable sight! Beautiful part of the world you live in.

Enjoy the Lobster and be back on the road in April/May

Cheers
Steiny

[Nut124]

Took a good ride in my -78 1800 tonite and plan on doing the same tomorrow. These are the last nice days in the forecast for SW MI. High today was maybe 62F. By the time I got home at 7:30 it was high 50's.

My recently built 1800 runs awesome other than a bit rich off idle. AFR in the 10.5 - 11.5 range at very low speed cruising. Need a bit smaller idle jets. Have .55s now, tried .45s and the lean gap was wide and undriveable. I think 0.50 or drilled .52 would do it.

[18Fiatsandcounting]

You might also check the main and air corrector jets. Between 1000 and 2000 rpm, you're running on the transition (progression) circuit, which will be affected by the idle jet size, but above around 2000 rpm, you should be on the main jet circuit only.

Depending on which cams and carb are installed, the DOHC engines can run rich at low rpm cruising, and back when I had to get my cars smogged, this was always an issue as they checked the emissions at 1500 and 2500 which is not where the Fiat engines were designed to run.

My "solution" has always been to just rev higher!

-Bryan

[Nut124]

Bryan, thanks fore the reply and tips.

I think the main circuit kicks in a bit later. With the smaller .45 idle jets I could cruise up to about 2000-2500rpm but after that it went totally lean and stopped pulling. The main circuit would kick in if I stepped and got over the gap, at about 3500rpm steady cruise.

I think .50 idle jets would do it. I do not expect perfect AFR but I would like to be no lower than 12. Top end I would like about 13.5 or so. I think a bit rich is safer, less likely to detonate.

I have .50 drill bits. Thinking of drilling out the .45s. Nice days for testing may be done though.

[18Fiatsandcounting]

You might also try raising the float level a bit, or decreasing the size of your air corrector jets. Both will cause the main circuit to "turn on" a bit sooner in terms of rpm.

On my two spiders, if I open the throttle by hand wide open from idle, while peering into the carb, I can see a spray of fuel emulsion from the main jet (auxiliary) venturis, even before the engine gets much over 1500 or 2000 rpm. Doesn't take long, of course.

-Bryan

[Nut124]

Bryan, thanks for the tips again. I had actually just checked the float levels and set them a bit higher, 11mm. They were at 12-13.

Interesting about your main circuit starting so early. What carbs?

Juha

[18Fiatsandcounting]

Interesting about your main circuit starting so early. What carbs?

On my '71 spider, the carb is the original 28/36 DHSA2. On my '69 spider which has a 2L block and the original cylinder head/cams/intake manifold, the carb is now a 38 DGAS. Back when the block was the original 1438 cc, the "spray" from the original 26/34 DHSA was similar in behavior to my '71.

I'm no great expert on Webers, but my understanding is that the idle jet(s) meter the fuel at idle, but also to the progression holes up above the throttle plate, and all these are active to varying degrees from idle to around 1500-2000 rpm. After that, and assuming the throttle plate is opened up enough, there should be enough air flow through the auxiliary venturi (that thing that sits in the middle of the main venturi) to cause fuel to be sucked from the main jet circuit through the opening in the auxiliary venturi. Anything that makes the fuel easier to suck from that auxiliary venturi, such as a higher float level or smaller air corrector jets, will cause the main jets to "turn on" at lower rpms.

Under very small throttle openings at higher engine speeds, I guess it's possible the main jets are not active, and you're just running on the idle and progression circuits. However, it's hard to get enough fuel through a 0.50 mm idle jet to develop much power, like you would with the 1.35 mm or so mains. But, at very slight throttle openings, you don't want a lot of power being developed, so all is well in the world.

-Bryan

[Nut124]

Bryan, I think you are correct in your assessment of the cab operation in principle. Both of the carbs you quote are shared plenum carbs. Mine are big 44IDFs. Desire for high flow and top HP sacrifices low speed operation due to lack of velocity in the venturi for the main circuit to have good signal at low speed. These run on the idle/aux circuit longer than shared plenum carbs typically. Yes, the idle jet does supply the aux holes. Main jet has little or no impact on this. Some folks drill additional aux holes in the carb above the factory holes to extend the aux circuit and allow running bigger carbs/chokes yet.

The air corrector size has more impact on top end mixture than it does on start of main circuit. Float (fuel) level and placement of holes in the emulsion tube can affect start of main circuit.

I may try to increase fuel level a bit more but am close to max.

This site has pretty good info on IDFs and carb tuning:

http://www.performanceoriented.com/performance-tuning-2

There are multiple pages to browse.

[18Fiatsandcounting]

Nut, definitely, if you are running 44IDFs, than most of what I just posted above is drivel. My only experiences are with a single dual barrel Weber of the DHSA, DFxV, DGxS, ADxA, etc. variety.

Racing carbs are a totally different matter, and I don't have much experience here.

-Bryan