Jetting

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phaetn
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Your car is a: 1974 Fiat Spider 1800
Location: Ottawa, ON Canada

Jetting

Postby phaetn » Mon Oct 02, 2017 11:05 pm

I had my head machined earlier this summer, with a multi-angle valve cut. I didn’t play at all with jetting, but did add a 14mm spacer under my 32/30 DFEV carb.

Now that the temperature is going down, performance is going up. I know this is because there’s a lot more oxygen by volume in the air charge.

It’s about 55°F (12°C) here this evening and the car is SOOO much more responsive than on hotter summer days. Does that mean I have an overly rich mix during warmer temperatures? The car sure loves to run leaner in the cold air...

Cheers,
phaetn
1974 CS1
32/36 DFEV; CompuTronix ign.
9.8:1 c/r; 40/80 intake cam w/ Isky springs
Vicks' SS header & adj. cam pulleys
A/R's progressive coils, Koni Yellow dampers
205/50-15s on CD-66 style rims
Momo wheel, Corbeau seats w/ 5 pt belt
pics and HD vids

sptcoupe
Posts: 987
Joined: Tue Mar 17, 2009 9:25 pm
Your car is a: 1972 124 Sport Coupe

Re: Jetting

Postby sptcoupe » Wed Oct 04, 2017 7:40 am

Carbs are a compromise throughout their operating range (throttle position) at a given ambient temperature and altitude. They will rarely, if ever, provide the perfect AFR under any circumstances, and if jetted correctly, they will rarely be very wrong, either.

Unless you have definite indicators that it is running rich in warmer weather (black smoke, stumbling, gas odor, badly fouled plugs, etc) just enjoy the power boost you get when the temperature drops and drive on.

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phaetn
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Posts: 575
Joined: Thu Jan 02, 2014 7:42 pm
Your car is a: 1974 Fiat Spider 1800
Location: Ottawa, ON Canada

Re: Jetting

Postby phaetn » Thu Oct 05, 2017 1:32 am

Wiill do, thanks.

I guess the only way to really perfect jetting is to get the car on a dynometer and test with various jets, given that all other variables remain constant. That's not going to happen for me.

I'll just enjoy the autumnal power. :)

Thanks and cheers,
phaetn
1974 CS1
32/36 DFEV; CompuTronix ign.
9.8:1 c/r; 40/80 intake cam w/ Isky springs
Vicks' SS header & adj. cam pulleys
A/R's progressive coils, Koni Yellow dampers
205/50-15s on CD-66 style rims
Momo wheel, Corbeau seats w/ 5 pt belt
pics and HD vids

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michaelj
Posts: 85
Joined: Sun Dec 29, 2013 9:25 am
Your car is a: 1976 Spyder
Location: Mount Dora, Florida

Re: Jetting

Postby michaelj » Thu Oct 05, 2017 7:03 am

I play with jetting a bit in my big block chevy, its not too hard really. I would recommend you get the next size BIGGER jets for winter. Maybe even two sizes bigger. You need more fuel with the denser cold air. Takes me about 5 minutes to change my jets. And i leave them for 5 months, then go back to smaller jets when the weather heats up. Makes a big difference.

I just welded a bung on my Spider and bought an AFR meter so I dont know exactly how far I can push the fiat, but Im sure it will need two diff sizes for best performance year round

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phaetn
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Posts: 575
Joined: Thu Jan 02, 2014 7:42 pm
Your car is a: 1974 Fiat Spider 1800
Location: Ottawa, ON Canada

Re: Jetting

Postby phaetn » Thu Oct 05, 2017 6:38 pm

Good idea! I sense another "project" on the horizon. :)

If anything, given the better performance now with the cooler air, I'd go a bit leaner in the summer. Maybe I've been too rich all along.

I don't feel like doing plug chops at WOT or mid-throttle like I used to do back in my bike days. An AFR sensor sounds like a good plan. How far along the pipe do you install it? Is anywhere after the downtube fine?
Once you install yours make sure to share some pics! :P

Cheers,
phaetn
1974 CS1
32/36 DFEV; CompuTronix ign.
9.8:1 c/r; 40/80 intake cam w/ Isky springs
Vicks' SS header & adj. cam pulleys
A/R's progressive coils, Koni Yellow dampers
205/50-15s on CD-66 style rims
Momo wheel, Corbeau seats w/ 5 pt belt
pics and HD vids


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