Gas mileage with 1.6L SOHC and Weber carb

[Banana Bonanza]

37mpg. I was getting 44 or 45mpg with the B3. I have noticed the vacuum advance may not be working properly. Attach a hand vacuum pump and you can draw a vacuum and advance the distributor, but it leaks down quickly. Should hold until released. This is distributor that came with the Japanese B6 and only has the one vacuum connection. I will have to try the one off the B3 or might experiment as I have an old adjustable Chevy vacuum canister for V8 distributor, you use a little allen wrench to adjust the advance amount. Take some adapting to use it with this distributor.

Oh and this engine would really appreciate a 5spd tranny. Its sweet spot with the 4spd seems to be 50mph. It just easily loafs at that speed without seeming effort, uphill, downhill, all around the hill. Dont have a tach to know what rpm that is. But with the extra power over a B3, could pull overdrive easily.

Fixing vacuum advance should get me back over 40 and overdrive probably back to 45 or so.

[bhazard]

Yeah no advance is really hurting your torque, which is what you need for mpg.

The overdrive will help too. Lower rpms are pretty much always better for mpg, and putting more load on the engine with the taller gear helps too, going uphill and stuff.

[TominMO]

Put on some 13" wheels/tires, like 86 - 89 Mazda 323 or later Metro wheels; that will give you higher overall gearing.

[bhazard]

Wont necessarily give better mpg though. Bigger wheels and tires = more weight. Unsprung weight at that, which is twice as bad as sprung weight.

If you want 13's do an aspire swap and get civic vx wheels. They look nice and weigh like 8lbs.

[TominMO]

Wont necessarily give better mpg though. Bigger wheels and tires = more weight. Unsprung weight at that, which is twice as bad as sprung weight.

If you want 13's do an aspire swap and get civic vx wheels. They look nice and weigh like 8lbs.

Yeah, that's something I'm planning on testing next weekend as a matter of fact (didn't get around to it this weekend). I'm replacing my 13" front and 12" rear 155/80 tires with a set of 185/60x14 on aluminum wheels. They are much heavier. I'll come up with exact weights later.

For sure, in the city the mileage will go down; that's a given, because of the extra HP required to spin up the tires from stopped. But on the hwy I think there's a chance of better mileage. As it turns out, my 155/80x13s are the same diameter as these 14s, so it's definitely about weight, and gearing won't play into it.

That's good advice about the Aspire swap and VX wheels BTW. If I had it to do over again I would have gotten 13" aluminums and 185/60s. I think 13" is the perfect wheel diameter for these cars, for most purposes.

[Banana Bonanza]

Slowly converting to 13s just because you cant buy 12 inch tires (other than trailer tires) locally and I never had them last very well anyway though they used to be so cheap it didnt matter. Got 2 Mazda 323 wheels today at junkyard. Fit perfectly. They had one more that matched and several really rusty ones that I wouldnt give $5 for the lot of them.

See what effect a properly working vacuum advance has. A 1.6L in excellent condition with manual transmission and the weber which is properly jetted for a 1.6L should top 40mpg at 55mph. I had figured 41 or 42. An overdrive would probably give it that little boost back to around 45. I really doubt the 155-80-13s are going to make much difference as far as overdrive effect, they are only inch bigger diameter.

I could have special ordered 12 inchers on web for not unreasonable price, but what happens if I need a replacement locally while on the road, stay at motel for a week while they order them??? Knowing me, I'd probably get 12 inch trailer tire just to have some mobility but thats just more hassle and I imagine trailer tires arent great idea on a car far as safety.

[hotfordcat]

I get 38 mpg with my B6 @ 85 mph to and from work. 20 miles each way.

[FestYboy]

yeah, but he's running a carb!

Banana: i run a B6 carbed and typicaly get 36 with my foot in it combined. i would try physicaly advancing the dizzy 4*. If the 4 spd feels good at 50, the 5 spd will feel good at 72-75 (my experiance).

[TominMO]

Slowly converting to 13s...I really doubt the 155-80-13s are going to make much difference as far as overdrive effect, they are only inch bigger diameter.

Yeah there is so much more choice w/13s, and better quality too. Def the way to go.

The diff in diameter btwn 155/80x12 and 155/80x13 is 4.4% (1 inch as you said), or about 2 MPG. It's something; plus the bonus of selecting better tires than what you can get in 12".

[Banana Bonanza]

the 5 spd will feel good at 72-75 (my experiance).

That would be nice! The 4spd is great in town and ok on secondary roads, but sucks on freeway. Especially when Festies get treated like slow motorcycles far as any respect by other vehicles. Now my old F250 4wd, I could drive 45 on freeway and nobody will get close to it.... Looks kinda like a refugee from a demolition derby.

[Banana Bonanza]

I recently replaced bad vacuum advance with an adjustable one for a Chev V8 as per another thread I started. I adjusted it to advance as quickly as possible.

Mileage today, mixed city, hiway (60mph), and rural dirt/gravel roads. [drum roll please] 50MPG. Not bad for a 4spd with 1.6L and a Weber, huh? I have to say I was very surprised. figured low 40s. Needless to say, I am very pleased. Also has nice power, very pleasant to drive.

Got the other Mazda 323 rim and hunted around a bit and found a good Hyundai Excell wheel that fit (think it is/was Excell as car was badly mangled so hard to say for sure) Anyway it even had a brand new 155-80-13 on it!!!

[TominMO]

^^ Whoa, very impressive! My experience with Webers is that they can be as stingy on fuel as EFI, and have more power than the stock carb. So practically speaking, it's a lot like converting your car to EFI, but simpler. Except for the automatic altitude conversion as you go up and down mountains. Which is why it's best to tune it as lean as it will run well.

[Banana Bonanza]

Way back in the dark ages, I had a '77 VW Rabbit with CIS Bosch fuel injection (no computer). It had an automatic (I never want one again in a small car) and got around 34mpg hiway. Fuel injection corroded up (gas wasnt as clean back then) so I bought a carb manifold (the earlier '75/'76 Rabbit Solex carbs were very complex junk) and a little Weber carb specifically jetted for unmodified Rabbit brand new from JCWhitney, had adapters and everything. It got 36mpg. Yep, beat the fuel injection. So much for progress. When Rabbit went to Bunny heaven, saved the carb and its what I am using on Festiva. Knew it was a winner though seems lot of credit goes to the adjustable vacuum advance. Who knew changes in vacuum advance could make that much difference?