3,000 foot commute

Bigger is not always better

Recently I calculated my fuel consumption at almost 30mpg. That seemed a bit high for dual carbs, warm cam, exhaust, spirited driving etc. and I suspected I was running lean.

I plugged in my AFR gauge (the wiring resides in the spare wheel well when not in use) and confirmed a general lean condition. Fattening up the 132 main fuel jets to 145s was too much, but 140s were better. But mileage didn't change much and performance felt exactly the same using the time honoured seat-of-the-pants gauge.

Given the somewhat rarified air here, yesterday I decided to rethink the carb set up. Assuming low air speed through the venturis and therefore a weak signal I took out the 32mm main venturis and 140 main fuel jets and installed 28mm venturis and refitted the 132 jets.

The AFR gauge now shows nearly ideal numbers in all conditions, the engine will still rev freely to 7,000rpm, and.....the mid-range torque has been noticeably improved! :shock2: :dance:

Cheers,

Rob
 
Your still 1300 at the moment? If so that makes a lot of sense, 32's in a 1300 is good for 8k+ with 40DCNF's, and if your not revving the thing that hard, 28's would be a better choice for sure in your dellortto's. Do you have 30's for a comparison?

SteveC
 
Yep, still the 1300

I want to work on and finish the 1600 but other things keep getting in the way. It was supposed to be a winter project but I am rapidly approaching 2 years since I started it.

fiatfactory said:
Do you have 30's for a comparison?

SteveC
Click to expand...

I have 28s, 30s, 32s and 34s. But, I can't find the 30s anywhere, so I guess I don't have my full set. CB Performance in California sells them for only 9 bucks each, so I could easily get another set.

Cheers,

Rob
 
I'm not too surprised about the fuel consumption. In the past with twin DCNFs on a 1500cc, commuter fuel consumption was in the mid 30mpg.

While many complain about the lack of power in the exxe and clammering for BIGGER motor, this is one of the hidden great things about this Fiat motor, it is very good for fuel burn-consumption. Another example of Fiat engineering excellence for it's cost... That most never appreciate or realize about Fiat's from this era.


Bernice


rjplenter said:
Recently I calculated my fuel consumption at almost 30mpg. That seemed a bit high for dual carbs, warm cam, exhaust, spirited driving etc. and I suspected I was running lean.

I plugged in my AFR gauge (the wiring resides in the spare wheel well when not in use) and confirmed a general lean condition. Fattening up the 132 main fuel jets to 145s was too much, but 140s were better. But mileage didn't change much and performance felt exactly the same using the time honoured seat-of-the-pants gauge.

Given the somewhat rarified air here, yesterday I decided to rethink the carb set up. Assuming low air speed through the venturis and therefore a weak signal I took out the 32mm main venturis and 140 main fuel jets and installed 28mm venturis and refitted the 132 jets.

The AFR gauge now shows nearly ideal numbers in all conditions, the engine will still rev freely to 7,000rpm, and.....the mid-range torque has been noticeably improved! :shock2: :dance:

Cheers,

Rob
Click to expand...
 
Good design

Rupunzell said:
While many complain about the lack of power in the exxe and clammering for BIGGER motor, this is one of the hidden great things about this Fiat motor, it is very good for fuel burn-consumption. Another example of Fiat engineering excellence for it's cost... That most never appreciate or realize about Fiat's from this era.

Bernice
Click to expand...

Ing. Lampredi was a pretty good engine designer. Even though these SOHC engines do not have cross flow heads, I'm sure the semi downdraft inlet ports help with flow.

I'm clammering to build my bigger motor. :) I think the extra torque will help here on the mountain roads.

Cheers,

Rob
 
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