Poor Gas Mileage

[Joe1969Fiat]

Hi All,

New to the forum. Just replace my 26/34 DHSA (could not find replacement parts) with a 32/36 DFEV on 1969 "Big Red' Spider and noticed a 8 - 10 mpg drop. Is this normal with this carburetors? I am amazed by the additional get-up-and-go power off the line...
Big Red grew CAJONES over night!

[vandor]

Those carbs are jetted pretty rich for a 1438 engine. You need a smaller main jet, I think it comes with a 137, I'd replace it with something on the 125-130 range. Check what are the jet sizes in the old carb, it uses the same type of jets.

[RRoller123]

Welcome aboard! You will find plenty of knowledgeable and friendly people here. (Including Csaba, who is nearly always right! )

Here is a thread on how to post pictures directly to the forum:

http://www.fiatspider.com/f08/viewtopic.php?f=4&t=21014

And here is another picture-posting thread:

http://www.fiatspider.com/f08/viewtopic ... 12&t=23084

And here is a link to a map of Spider owner’s locations. Many forum members have listed their locations.

https://www.zeemaps.com/map?group=191825

Pete

[bradartigue]

On the 1438 I found the DFEV idle jet to be too big, the other jets were OK. Change that one first (its the easiest to get to anyway), go down to the next smallest size and tune it.

[majicwrench]

An 8-10 mpg drop??? That is like a huge drop, jetting alone ain't gonna do that.

What was wrong with your OE carb?? Almost anything can be fixed, lots of those around if you need parts.

Somehow the rumor got started that smaller engines require smaller jets. That is not true. Carbs are built so the fuel and air are mixed by how much air goes ithru carb. Less air goes thru, (smaller motor) less fuel gets added. More air (big engine) more fuel gets mixed. The folks that made that carb are pretty dang smart, and good at getting it right.

That said, most replacement carbs seem to err a tad on the rich side, but not 8-10 mpg. Something is leaking or SOMETHING!

[Joe1969Fiat]

I combed the web looking for three diaphragms to the pull assembly and only located one. Most kits do not include these gizmos....any site recommendations would be greatly appreciated.

I plan on changing to smaller jets on the weekend and take it for a ride, will post results next week.

Thanks everyone for advise/info.

Joe

[carl]

Need additional info. While you noticed a fuel mileage drop, you did not indicate what the current mileage is. Could be your original carb was so messed up that you were getting unreasonably good mileage but very poor power. Unless you are driving with your foot to the floor, the idle jets are the ones that affect most of your mileage issues. I had a DFV on my 2000 spider and was getting under 20 miles to the gallon. I kept lowering the primary idle jet size with no affect on performance but a nice increase in mileage. I also dropped the main jet a few steps.

[azruss]

My original spider was a 1438 and the carb was jetted lean from the factory to pass emissions. I was getting 30 mpg but the car bucked badly coming off the line. I drilled out the main jets and my problems were solved. It also dropped the mpg to 23

[bradartigue]

Somehow the rumor got started that smaller engines require smaller jets. That is not true.

Probably from the DFEV as delivered by Redline (and others) have a 55 idle jet; on a 1438cc motor you need a smaller jet.

I agree though; note that the very first carburetor FIAT installed on the Spider was also the largest - and on the smallest engine - the 34DFH was on the 1438cc. The USA didn't get many (or any) - we got the DHSA1 and all the bucking and anemia that comes with it.

[70spider]

I thought it was best for me to post here instead of creating a new post. When I got my new Weber 32/36 DFEV, I ran it the way it came from the vendor but after noticing I was running rich I changed the primary idle jet from the 60 to a 47.5 and readjusted the mixture screw, due to the advice I recieved from the forum. It seems to work, my idle smoothed out a little and I had to back the idle screw out a little to get it back to 850rpms. I was wondering do I need to change the secondary idle jet as well? And what about the mains? The jet sizes that came with the carb are as follows:
Idle Jets (Primary/Secondary)=60/50, Main Jets (Primary/Secondary)=137/140
Note: My altitude here is 950 ft.
Also if everything goes well My wife and I will be vacationing (actually camping )in New Mexico next year at an altitude of 8500 feet. From what I can gather from reading stuff on the web I would need to go lean by 1 size for every 2 to 3k feet of altitude. Anyone have any experience with this. If there is anyone in Denver on the forum it would be great to know what size jets you use.