I been driving my RX as a daily driver for almost 2years now... this is the first summer since I swapped out the stock 12A for a older 13B 4port w/a YAW carb and HOLY ****...!!!

After doing some quick math: 16 gallons to fill up completly (aprox) and while doing stop and go street driving / not highway, a half of a tank I only got 30 miles. Half of 16 is 8, divided into 30 is 3.75 miles per gallon...

Is this a joke...???

The weather has been the hottest here so far this summer, mid 90's... but dammmm... 3.5 miles is not going to cut it, espically at 4.29 a gallon.

There either has to be something wrong or something I can do to help improve my milage...

Anyone have any ideas... ??? and yes I'm off to searching *after* I made this post.

Thanks in advance.

 

fill the tank maybe your gas guage isnt right? even going wide open throttle 80% of the time you should be getting more than 3mpg...

 

I just don't know about that. My old '82 with a Holley 465 and a Holley blue pump tuned to 6psi, out pounding on it I once got 40 miles on 1/2 of a tank.

Anywho, to the OP, how does the car run? how do your plugs look? are you running rich?

 

Are you leaving a trail of liquid gasoline behind you on the ground?

 

No trail of gas... I wish, then the problem would be easily solved.

I'm going to have to pull the plugs and check them. They've been in there since I dropped the motor which was last August.

I remember reading somewhere about hotter, or colder, I can't remember which... but going one way or the other could help with the hotter weather temps...?

 

Sorry... ^^ hotter or colder sparkplugs.

Doh'

 

You can't trust the gauge. The only way to really find your true mpg is to fill the tank, drive a while or a few days, then fill it up again. Divide the miles you drove by the gallons it took to fill up again, then you'll have your true mpg.

With the Yaw carb, I would expect to see 12 - 16 mpg with mixed driving...




.

 

There must be some thing major going on with your set-up.
I get about 100 miles on a half tank BUT my set-up is with a Holley Blowthru carb pushing 15psi with a heavy foot.....

L8R

 

^ Didn't do this yet... But here's a pic of the sparkplugs:

The ones on the left are Trailing / NGK-BUR9EQ T...

The ones on the right are Leading / NGK-BUR7EQ L...

 

i get 19mpg and i sure somthings wrong with my carb cause i should get better..
i got new motor rebuild nikki msd6al rb header but under 20mpg and somthings up

 

My -SE gets 18.5 to 19. Very little variation from one tank to another. I want to know how the EFI guys get rockin mileage.

 

Alright so I been slowly looking into this problem since I'm busy with other things in life... and here's some info I've come up with to hopefully further help me fix this situation:

- My fuel guage isn't working properly... The needle will not go up past a little over 3/4 of a tank reading, even though it's 100% topped off / filled with gas.

- After completly filling up, clocking milage, and then completly filling-up again to get a gallon reading... here's the math...

Filled gas tank... drove 79.9 miles... filled up w/gas again, 7.968 gallons = 10.02 miles per gallon.

Drove again 152.1 miles... filled up w/gas again, 14.01 gallons = 10.85 miles per gallon.

Both were done while driving on a heavy foot 75% of the time.

After this thread: https://www.rx7club.com/1st-generation-specific-1979-1985-18/gas-mileage-things-i-tried-753513/ I just adjusted my idle and mixture. Following the directions, turning the mixture screw clockwise until the motor wanted to stall... I turned it about 10 full turns before the motor even stumbled a bit. Hopefully this is a good sign..?

The car is now idling at 750ish nicely, so it's off to the gas station to fill up again and clock my miles.

 

Does it idle weird? When I had my OER, I intentionally ran it mega rich and it sounded like a bridgeport. Stock port engine though.

http://ca.youtube.com/watch?v=QchXiwd1toU

 

Why are you running 2nd gen plugs in both the leading and trailing position? Oddly, the trailing plugs look great, leading aren't bad at all. You only run 2nd leading plugs when doing the 2nd gen coil. There really isn't any coil option to run 2nd gen trailing plugs. Is your exhaust color black, is the inside of the rear muffler coated with carbon soot?

Have you checked your timing? At 4k rpm, Yaw recommends +16 leading, +8 trailing, iirc. You can either remark the timing pulley, 1*/mm, or use a timing light that has a dial advance feature that will allow you to use the oem marks.

 

^ I don't have a 2nd gen coil..??? Besides MSD Blaster II Coils the ignition system is stock. I honestly don't know where the 2nd gen plugs came from..??? I bought the motor used from Steve84GS and I think thats what's been in there since, but I could be wrong... I bought the set-up probably 4+ years ago. It's a stock 74 13B 4port.

I don't thinks there's a abnormal amount of soot. Here's a pic. I wiped my finger on the inside of the right pipe.



I'm a little nervous playing around with my timing. I think I'll wait on that one until my pops has a chance to get over here.

It did idle weird, kinda like a lite bridgeport would be the best way to describe it... I just kept doing the adjusting over until it all smoothed out. I think it was about three times.

 

Sorry I mis-read.. I thought u thought I had a 2nd gen coil upgrade.

 

Soot doesn't look bad, My 1/2bp is worse. I figured you didn't have the 2nd gen coil upgrade, that's why I mentioned the plugs

 

So since I adjusted the idle / mixture my milage has definatly improved...it went up from 10.8ish mpg to 13.35 mpg. It might seem like a small improvement but seeing slightly over 200 miles to a full tank to me is huge.

I finally got a hold of my pops today so we could look things over...

I have no vacuum advance on my distributor. The nipples off of each pot are just connected to each other w/a vacuum hose. But the mechanicals are working...

We checked the timing just to see where it's at... My father has the adjustable type timing light and when we hooked up to the Front Rotor Housing Trailing @ 4k rpms gave a reading of being at 50*. From what I've been reading here that's excessive. Front Rotor Housing Leading @ 4k rpms gave a reading of 25*, also seems excessive.

One of the pins on my distributor cap was also bent so I ordered a new one which isn't coming until tommorow. With the new cap were going to then adjust my timing.

 

Alrighty, so my pops and I got into a huge argument and i'm basicly on my own.

I have a few questions, hopefully I have better luck with u guys then I did w/my father... haha.

So I bought my own timing light today. I picked up the adjustable dial type from SEARS / Craftsman and the marks on my pulley don't match what the light is saying when I dial it back to zero or vise versa...???

for instance...

L1 at 4k rpms with the light adjusted to 0, the pulley will read 20*advanced... and then still on L1 at 4k rpms... I turn the dial on the timing lite until I line up the pin on the front cover with the zero marking on the pulley and the dial on my lite reads 34*

Next problem I'm having is my my trailing is not adjusting at all no matter which way I move the pot.

Thanks again in advance for any help...!

Ohh yea also, what is the purpose of disabling the vacuum advance...??? and what does IIRC mean...?

Hope this isn't too much and I'm off to reading more search posts.

 

^^ Just read this while searching other threads... Say it isn't so...

 

check the ignitors and make sure they r both working , i have a feeling you r only running on one good one ,

 

Omgoodness... I found the problem by accident. Trailing is most CERTIANLY moving... when I hook the timing light up to L1.

I'm going to guess I have the coils hooked up backwards...

 

Coils were most definatly hooked up backwards... Switched them up and all seems well as far as setting my timing goes.

I have a Racing Beat pulley and following the specs / marks from the directions I was given when I purchased the thing, I set the timing to 24L 16T,(now forgetting where I picked up those #'s) The forth mark on the far right while facing the motor is 20* BTC. Using my new timing light with it's setting at zero (to avoid using the timing lights advance mechanism) I advanced the Leading until it was slightly past the 20* mark on the pulley, or where I would think 24 should be, so if I'm not exactly at 24 I should be real close... And then did the same for the trailing, ever so slightly past the middle of the 10* - 20* mark on the pulley to give me 16 or at least real close.

So for now it's off to driving and clocking milage again to see if swapping the coils and setting the timing has made a difference.

There's a TON of stuff as I follow links from one thread to the next on fuel economy topics that answer almost all my questions... except, could someone please tell me what IIRC means... it's really buggin me.

Here's a few of the links:

https://www.rx7club.com/showthread.p...ghlight=timing

https://www.rx7club.com/1st-generation-specific-1979-1985-18/fuel-economy-report-since-recent-mods-se-656700/

https://www.rx7club.com/showthread.php?t=753513 (already posted a few posts above)

 

IIRC is an acronym for 'if I recall correctly'

 

Setting my timing at 24L - 16T and swapping the coil hookup off the distributor has DROPPED my gas milage per gallon.

I thought at first it was because I was driving the car a little harder then usual two weekends back, but i've been getting the same milage each tank consistently.