OneRotor

iTrader: (3)

I know, I know. You don't buy nor drive a 7 for it's stellar fuel economy, but my 7 has been ridiculous this summer. I have averaged 15.3mpg without my last two fill ups being added into that average, and they were 11.3 and about 12mpg (haven't done the calculation/put them into my Excel spreadsheet, as I just got home from a long day of driving, meetings, junkyard adventures, and fixing a friend's car for her. I think that it's time for a rebuild of my carb, which is on my list of things to do this winter (along with replace my driveshaft, fuel pump, have my FMOC sealed, track down a massive vacuum leak, fix an exhaust leak that cropped up last week, finish polishing all of my wheels, replace cap/rotor/wires and the list goes on).

Could it be anything else besides a carb rebuild (I know, keep my foot out of the throttle, but my 7 feels really underpowered recently)? My plugs have less than 500 miles on them, my cap/rotor have about 20k on them, and the plug wires have about 30k on them. Mods are below:

RB SP exhaust
MSD Blaster 2 coils
Magnacore 10mm wires
NGK BR8EQ14
FMOC
remote mount oil filter
e-fan
no p/s
no a/c
no air pump
no rats nest
no cats
Casterol Edge 5w50 synthetic
Mobil 1 filter
Kendell 80w140 synthetic in trans
unknown fluid in rear end (whoever replaced fluid last overtightened fill plug and stripped it)
LSD
205/50R15 Potenza RE-11's
-180 treadwear rating

DarrenTRS

iTrader: (1)

I think it's fair to say at least one factor is the super soft tires, granted I don't know how long you've been running them but something like RE-11s are designed to grab and sink down into the road rather than normal commuter tires which are mainly there just to roll ontop of it.

My Dell 48 13B only got about 16mpg as well on a good day with 1 WOT hoon.

Verneuil

are you runnin a stock nikki? If you are thats most likely ur problem. Even with traffic and a lot of WOT i can get 21. Bad day will be 19 or 18. I have blaster 2 coils, Pacesetter header custom exhaust and the direct fire ignition. And this is with a shitty nikki that never seems to run right.

OneRotor

iTrader: (3)

Stock nikki w/ all emissions junk removed.

t_g_farrell

iTrader: (1)

You answered your own question. Its the vacuum leak most likely.

patmac6075

iTrader: (26)

^^^^ T_G beat me to it....get rid of the vac leak first....then check your milage...bet it gets better.

DivinDriver

iTrader: (15)

Yup. Even with fully 100% stock emissions & Nikki carb, my -7's routinely gotten 20mpg average mixed mileage since I've owned it.

OneRotor

iTrader: (3)

So I just checked my carb for vacuum leaks, and it seems as if they're everywhere. I had my choke held open with a set of vice grips and sprayed carb cleaner in these locations:

Drivers Side Rear
Drivers Side Front
Passenger Side Middle
Block-Off Plate on Passenger Side of Intake Manifold
Block-Off Plate on Firewall Side of Intake Manifold

and my engine speed increased each time I sprayed carb cleaner, as if it were getting more fuel, indicating a vacuum leak.

How could I have vacuum leaks everywhere? Bad carb-manifold gasket?

I put vacuum caps on all open ports and zip-tied all of them when I removed my rats nest, and used a lot of RTV when sealing the block-off plates. I'm thinking that I should let the car cool off then re-seal the two block-off plates. Should I attempt to remove the carb and replace the gasket with RTV (since I don't have access to a stock Nikki gasket ATM), or should I go and get some gasket material and cut my own?

DivinDriver

iTrader: (15)

First, check the carb hold-down nuts haven't worked loose, or perhaps have loosened after the carb settled in on the resilient faces of the carb spacer. Base-flange leaks can form that way.

Or your car may be a huff-addict.

There are no "stock Nikki gaskets," remember; the rubberized faces of the carb spacer are non-replaceable, not intended to be removed from the spacer, and can be re-used so long as they're not damaged.

OneRotor

iTrader: (3)

What would happen if I just removed the carb spacer and replaced it with some gasket material? This would eliminate some of the failure points in the system (the nipples that must be capped when removing the rats nest).

What is factory torque for the carb hold-down nuts?

DivinDriver

iTrader: (15)

There are ported vacuum channels that route through the spacer. I've never reverse-engineered which ones are or are not critical- - I know that the vacuum channel for the vacuum power valves used on some models routes through there. Possibly other things. It doesn't just go straight through. How much of it is made unnecessary by stripping emissions I don't know.

If you replace the spacer with a gasket, though, odds are your carb studs will be too long to thread down.

I'll check and see if there's a stock torque; I've always just used one medium grunt past finger tight, since getting a torque wrench on a couple of them would be pretty much impossible.

You can put a VERY (as in translucent) layer of silicone on the spacer faces if you want. Too much will block channels, though.


EDIT: No specific torque mentioned in the FSM for those nuts. Probably only about 14-20 ft/lbs if I had to guess.

Crispin38

iTrader: (3)

I have a Weber 48, and HUGE intake ports, wasted spark and no a/c, or p/s and i've got an E-Fan. I get 12 in the city without getting on it much. But, i've also got Toyo Proxes P888. Which are extremely sticky.
I would fix the vacuum leak, and make sure you always run good oil. I noticed a huge difference in gas mileage when i switched to royal purple. Believe it or not..

OneRotor

iTrader: (3)

I checked to make sure that the nuts were tight, and they are. I have run out of time/energy for today, so this may be a winter project (Sterling maybe?), as I have to work through the start of next week, and if it looks like snow, no more 7.

Verneuil

this is somewhat off topic now. But since my vac secondars stoped working and i did the mechanical secondarys mod. I now seem to be gettin steller mileage. City and highway with some WOT are putting me at 170 Miles to half tank. I used to get 100 miles to half tank. Could try disabling ur vac secs and going mec. You can feel when ur about to open the secondarys. So if you stay off better mileage.

Kentetsu

A few ideas:

Fix the vac leak, which may be from carb, base of carb, intake manifold gasket, or uncapped ports somewhere that you missed.

Any chance of a brake dragging?

Tires properly inflated?

Air filter clean?

If cap/rotor really have 20k miles as you stated, then they are over due for a change.

Ignition timing.

Sticking choke?

And I will second the advice to go mechanical secondaries. That way you can feel when you are about to open them up (pedal gets a bit stiffer at that point due to the extra spring being engaged) so it puts you in control.

Good luck

j9fd3s

iTrader: (3)

my SA was interesting, it was REALLY picky about its tune up, the idle mixture had a very significant impact on mileage. of course the health of the points had a big impact on how lean you could go.

so um with healthy points, or the electronic dizzy, it'll get 22-25mpg no problem. bad points? i think NODE had it down to like 12mpg?

car is STILL totally stock, and basically original

bshusted

iTrader: (1)

When I first got my 7, I averaged about 15mpg in mixed driving (bone stock). I may have gained a mile or two when I threw away the rats nest. 17mpg in mixed driving was tolerable for me. When I replaced my plug wires with the magnecore ones, I noticed that the leading plugs were connected to the trailing ignition and the trailing plugs to the leading ignition. After fixing that, I had worlds more power and 28mpg on the highway.

At this point, my only mods were the rats nest and a racing beat carb hat with k&n filter.

My point is, that you may want to check the simple things before digging into the carb. Ignition coil, fuel filter, air filter, etc.

Rotospeed

iTrader: (8)

^^^^ yes check the simple stuff first, and that vac. leac is killing you.
it sounds like your going to need to pull the carb check over the vac. lines and mounting surfices and re install.

when i first rebuilt my nikki i added a bace gasket that came in the kit and that made a vac. leak, i had to pull the carb remove the gasket and re-install the carb.

OneRotor

iTrader: (3)

Tracking down the vacuum leak will be a winter project, along with possibly a carb rebuild (or maybe the Sterling I've wanted for a couple of years...).

Brakes are not dragging.

Tires are at 32psi.

K&N filter was cleaned in September.

New cap/rotor was ordered this morning. Will be in at Noon at O'Reilley's

Haven't changed ignition timing since I bought the car, and it was bone stock when I bought it, but I'll check it anyways (when I have a helper...)

Choke won't stay open on its own, so it's definitely not sticking.

Verneuil

sounds like you got it covered. You will get worse mileage with a sterling.....Lolz. With mech secondarys and city/ highway with a good bit of WOT i got 22.2 MPG on this last tank. Need to figure out how to get that amazing 29 MPGS....HHO anyone?

bshusted

iTrader: (1)

Once I got everything working correctly and ditched the air pump and rat's nest, I would average 28 on the highway. 90k on the car.

Another thing to check would be wheel bearings. I know you checked if brakes were dragging, but wheel bearings can make a difference and can be difficult to diagnose with our particularly loud cars.

OneRotor

iTrader: (3)

I am tracing the vacuum leak currently, and this is what I found:



I used Permatex Type 1b sealant (pictured below), and it seems to be melting from the heat of my header. I sprayed the block off plate to intake manifold interface, and that is where a huge vacuum leak is from. The sealant was running out of the interface when I hit it with carb cleaner. I'm going to re-cut my block-off plate (it's not perfectly flat) and re-seal with some silicone that is rated to 700f intermittent and see if that helps my vacuum leak.

OneRotor

iTrader: (3)

The Permatex that I was going to use for the gaskets said to not use when the surface is in contact with gasoline, so I went down to the local Ace hardware store (also my employer) and picked up a 12"x36"x.125" roll of cork gasket material. I cleaned the mating surfaces on both of my block-off plates and on my intake manifold, cut my gasket material, put lock-tite on my bolts, and tightened everything down. I started her, and for the first time since I bought her in November of 2008, she idles. Now time to increase the idle from 600rpm to 800rpm and drive. I'll report back with fuel economy statistics until she gets put away for the winter.

T Heller

I'll bet you're feeling good now. This has been an interesting thread to read through. I don't have anything to add (or offer) other than congratulations.

I will admit to laughing out loud when I read someone had discovered their plug wires inverted, since it reminded me of my experience a couple months ago. My '81 regained a smooth idle, a genuinely functional choke (no longer a strangler) and plenty of new power when my mechanic discovered a dead J109 igniter for the leading plugs and replaced it. I suspect it had long been non-functional, probably ever since the replacement/reclaimed engine was installed about ten years ago. Even so, the car ran OK (tho' could never succeed starting it in winter) and I got 23-24 mpg last summer on a long trip with it. To learn I was running on only two of four plugs -and the trailing ones, at that- was simply amazing to me.

OneRotor

iTrader: (3)

I am feeling excellent right now. I had to adjust both my idle speed and idle mixture (both about 3 turns too far out) to get my idle to a point where I'm happy with it. Without any electrical load, I'm about 1100rpm, and with electrical load (blower motor) I'm sitting at 800rpm. If my electric fan is running with the blower motor, the car will basically die, but since it's cold out and I'm about to put her away for the winter, I'm not too worried about the e-fan's load. I'll adjust idle speed and mixture again in the spring.

Back on topic: I'm about to hit 1/2 tank, and I'm at ~110 miles on the tank. For reference, the last tank I ran through her was ~164 miles, and I put 14.5 gallons into the tank, so fuel economy seems to have improved drastically.