Dual Weber IDF's for 1438

[sptcoupe]

THe TB doesn't breathe wll if you use airhorns, as there is not enough room over the horns for the air column to build. You need about the same space over the the tops of the horns as the carb bore - or 40mm. If you use it, take the horns off for better results. That said, I have always liked the TB because it quiets down the roar of the carbs and makes the car easier to live with on a daily basis. The lunch box filters work fine, but are noisy. The best performance comes from a box that takes cold air in from in front of the radiator or the wheel well.

[Redline]

Thanks for the info. I just wish I didn't need five joints in my fingers to get the oil dipstick under the TB...

[normark]

Guess it's both pros and cons with the TB. It's nice with some sound, but you can get tired in the end. Otherwise, all other air cleaners certainly look better!

[fiat218]

hmm so the duals will work good on a 1438 huh

[normark]

Alright, let's put this old thread back to life again

I've actually stumbled upon a pair of dual IDF's with the waffle manifold. I'm thinking of installing them this summer and want to be as prepared as possible.

Anyone knows what jet sizes I should go for? I guess the carbs came from a 1608, and mine's a stock 1438 (except the 1608 head). All advice will be helpful!

[So Cal Mark]

first you need to determine what size chokes are in the carbs

[sptcoupe]

Your carbs likely have F11 emulsion tubes. With F11 emulsion tubes, to find the range for the main jets, multiply the choke size (usually 32s) by 4.1 and 4.3. To get the idles jets, multiply by 1.6 and 1.7. For the air correctors, add 50 - 60 to the main jet size.

Rounding off - so if you have F11 emulsion tubes and 32 chokes, your main jet range is 32 X 4.1 = 131; to 32 X 4.3 = 137.

Your idles jet range is 32 X 1.6 = 51; to 32 X 54.

Your air correctors will be in a range of 180 to about 190.

Use 200 needles, 55 blow backs and 55 pump jets and you will be ready to start dialing them in without damaging your engine with a too or too rich set up.

Since the jets are only readily available in size incremnets of 5, the ranges above would be mains: 130 to 135 (they do sell 137s); your idles would be 50 to 55 (they do sell 52s); your airs would be as stated.

Depending on what other mods you have made to increase the breathing ability of the engine (cams/header/porting/valves), you would start the jetting toward the richer end of the range the more mods you have made. For a dead stock engine, you would start at the leaner end. If you move in increments of 5 on the mains and idles, that is considered "one step". So going from 125s to 130 mains is one step richer. 50 to 55 is one step richer on the idles. For the air correctors, one step is 20 (some say 15). So going from 185 airs to 190 airs is NOT a full step. A full step would be 185s to 205. Keep that in mind when you are dialing it in. If you move one step richer or leaner on, say, the mains, you will have to about 15 to 20 on the airs to maintain the same relative mixture strentgh.

I often egt calls/emails form guys that they moved, say, from 125s to 130 mains and love the bottom and middle range performance, but were now rich at WOT, even though they went from 190s to 195s on the airs. Once they went from190 to 210s, they were fine. This is a common error made when dialing in the carbs.

1438s with dual 40 IDFs from the factory came with F11s, 125 mains, 55 idles 195 airs, 55 pumps, 55 bleed backs and 175 needles. I had one in Spain in 1972, and it was on the lean side (all the IDF factory cars, both 1438 and 1608, were jetted to the lean side) and it had some flat spots in the power curve, was rough in transition, and had an intermittent miss at the top end. This was typical of the IDF cars.

Were it me and I didn't have access to a dyno, I would start with 127 mains, 57 idles and 190-195 airs, 200 needles, 35 bleed backs and 55 pumps. Maybe it is a 55 bleed back.

One of the sweetest running, stock 1438s I have seen was in a car I helped a guy with when he went to 40 IDFs. We used 30 chokes, with 127 mains, 55 idles and 185 airs on F11s. The smaller chokes gave it some low end grunt and smoothness, and were just fine for stock cams to let it rev to 6500 rpms. Ran smooth, had some punch, and that 1438 at full song was a delight to hear.

[normark]

Alright!

Thanks for the thorough description and sorry for my late response

What I have is 32mm chokes, F11 emulsion tube, 125 main jet, and I guess the rest is factory setup as well.

So I'll take it from here and let's see where I end up

[normark]

I'm quite slow at this.. but the work is still in progress

I have now taken the carbs apart to see what I got and what to order. I actually have two sets of carbs. I figured I would use the ones that looked best, but they actually look like crap inside. And the crappy looking barn find ones looks absolutely terrific inside! So I guess that I'll make a mix of the best parts.

One set of carbs is marked 13 and one marked 15. What's the difference between these?

[fiat218]

funny thing. i have a 1438 engine with 1608 heads
then i have a 1608 that has 1438 heads. why

[majicwrench]

"Guess that I'll make a mix of the best parts"
It's your carb(s), but I would NOT do this. Keep the parts from carb A with carb A, etc etc. Swapping parts could lead to headaches.
Keith

[131]

One set of carbs is marked 13 and one marked 15. What's the difference between these?

You need one of each, 13 and 15. The difference is the butterfly adjustment between carbs, one is the master, the other the slave.

[normark]

One set of carbs is marked 13 and one marked 15. What's the difference between these?

You need one of each, 13 and 15. The difference is the butterfly adjustment between carbs, one is the master, the other the slave.

Yeah, I realized this shortly after posting...

And also, I'm not planning to swap everything, only jets and such that are bound to be replaced anyway. I have some that would fit according to the suggested 'recipe'

[normark]

Ok, let's get this old thread back to life. There are too many forum threads out there that ends without the original issue being resolved

I started another thread specifically about the throttle linkage, but that is resolved now with a cable instead of the linkage:
http://www.fiatspider.com/f08/viewtopic.php?f=5&t=30248

I'll post some pics later

Anyway, I've actually installed the IDF's and briefly tested the car. It seems to run well without checking the synch and such, but I've only took it for a short spin and I don't know how it should behave because I've never had dual IDF's before

There is one odd thing though. I can't fit my turtleback air filter because it bumps into the back of the engine room. How's that even possible. Did Fiat change something in the engine room or the engine mounting position?
Although, it sure looks like someone have had a turtleback on this car before because the paint was gone just where the turtleback touches the back of the engine room. Perhaps I'll just get some lunchbox filters.

I'll let you know how it goes and I'll post some pictures later!

[rebar1111]

I have a 79 with big bump hood, dual Webers and a turtleback air cleaner. This posed a hood clearance problem. I left the motor mounts stock to eliminate pan interference and reduced the gasket thickness on all intake manifold, carb and air cleaner surfaces. Cut some relief slots in hood reinforcements and was able to get almost complete clearance. Only minor scrapes to air cleaner top and hood persist due to motor mount flexibility when engine rocks. The next try will be to machine 1/8" off of the manifold to carb surface.

As I understand it, the 2L is taller than the 1438 and therefor yours is very achievable. Dip stick clears and sound is muffled to my satisfaction, since I don't want to attract attention when acceleration.