I too had a '72 Shadow a few years ago. She was good for about 7 miles a gallon. Cruising at 80MPH or 10MPH around town=7 MPG. You've got 3 tons, 6.7 Liters and just enough HP to drive the AC and motor nicely. If she hasn't been tuned in 10 years, it would be a good idea to do it. The electronic ignition is a good idea. Enjoy her!

 

Mileage Issues! Ouch!

I have a 1976 Shadow with stock electronic ignition, it seems to be average approx. 11 miles per gallon, slightly better on the highway, but we don't drive excessively. I did recently change the plug wires to a heavier silicone wire and converted the spark plugs to the Pulstar Pulse Plug, part number Be1. I e-mailed the company regarding any possible issues with these new style plugs being used in an RR and they were quite confident with their product as several other RR owners have experienced success with them. While some may feel they're a bit costly and not worth the price of $24.99 per plug, I just had to try them.
I haven't checked my mileage after installing them, but I will honestly say, the vehicle runs incredibly smooth. I also balanced both carbs with pot-mount gauges with Sherbourne Mews.
The Shadow passed smog with flying colors three weeks ago, in fact, the smog station owner was very impressed at how clean the engine was running. Overall, I'm very pleased! Our Shadow just purrs, starts easier, runs smoother and the acceleration does feel a bit more responsive. Some may not recommend these new style plugs, but I've since installed them my daily driver (2005 XB) and can actually feel a bit more power If you try them, please let me know what you think. OH!!!! Be careful installing them as I cracked one by accident (front left) while installing in the Shadow and you can only by them in pairs. Well at least I have a spare.

 

Fuel consumption.
I get around 14 mpg (UK) if I don't thrash it, on mixed type driving. I suggest your car has been serviced by someone with a less than satisfactory knowledge of the car. My first purchase had the ignition timing retarded by 20 - yes, twenty, degrees. The result of correcting that was sensational. As someone has suggested, get the ignition and carburration correct, then see what happens. 6 mpg is appalling.
Regards from Alan D.

 

always worth giving it a little tune up. set the timing then the mixture then the idle speed. May help.
Matt.

 

I have a shadow II and will get 275+ miles out of a tank full so there is something very wrong.

 

Wookie I'm curious to hear more about these plugs. Are you still using them? Did you ever measure if they're giving you more mpg?

 

Pulstar Plug Review

Thanks for writing to remind me about the spark plug posting! Well, I changed my old plugs approx 500 miles ago and did switch to the Pulstar #BE1 plug. Definitely not cheap at approx. $24.00 per plug, ouch! With gas costing over $3.00 per gallon, I felt it was worth a try so I bit the bullet and purchased. I e-mailed Pulstar prior to purchase and they responded immediately with the data I requested and they explained about the plug temperatures and how the Pulstar plugs did in fact tend to run cooler, yet disperse a substantially stronger spark. I was worried about burning a hole in a piston or some such event. Overall, I'm very pleased with their performance. The Shadow appears to have slightly more power while accelerating and the fuel mileage seems to have improved. Not much, but I guess .65 miles per gallon increase is quite substantial, especially when you're talking about a motorcar that tends to drink petrol like an ice cold Coca Cola a hot day. The car still has a tiny bit of rough idle during warm up, but once proper heat has been established, she smooths out wonderfully. I guess time and mileage will be the true test, but I'm pleased!
I also changed the oil to a Royal Purple Max Cycle synthetic, so between these changes, hopefully the old girl will keep running for many years to come.

 

Thanks for the update Dale. I was interested to hear the results of your usage as I had a similar experience a few years back with another product that was a premium priced alternative.

When I began putting Amsoil into my BMW E34 M5 I was startled at the change: ran cooler, smoother and faster. So I wasn't that skeptical when you mentioned these spark plugs.

 

I have just bought a 76 Corniche, and although I haven't done many miles in it, I have kept a record of all petrol purchases and miles travelled. Driving through 34 miles through London in clear traffic has resulted in 7.44mpg, and a 90 miles motorway trip gave me 13.45mpg.
According to the poor service record I received when I bought the car, the carbs had just been serviced and reset before I bought it. So the real issue will be tyre pressure. Since doing these trips I have measured tyre pressures and found I was running on 28 and 24 at the back, and 26 and 25psi in the front. I have since put nitrogen in the tyres, which will hopefully keep a stable pressure, and have pumped these up to 30psi at the front and 35 at the rear. I will post my new mpg when I have been able to repeat those same runs in the same conditions.

 

Do you have su carbs or a solex carb fitted the su carbs were very rarely set up correctly and the solex carbs were notoriously going out of tune and the set up in the manual was difficult to follow and rarely done correctly, many mechanics would shy away from the solex carb, so i would guess the carbs aren't set up correctly causing high fuel consumption

 

I've just done the same motorway trip so can now make a direct comparison. With the tyres at the old pressures, I averaged 13.45mpg. With the tyres at the new pressures I managed 15.5mpg. That was over a 50/50 journey of motorway and clear 'A' road. Doesn't sound like much but it represents a 15% drop in my petrol bill. Interestingly when I did a 147 mile round trip into London I got 15.1mpg, so not much of a drop. I should add, that this was driving very carefully, usually around 60mph and avoiding all heavy pedal use except when necessary.
It's possible I can squeeze a tad more out of her by tuning the timing and carbs etc. Perhaps someone could tell us how to tell the difference between Solex and SU carbs. I had a look at my carbs, but can't see any identifying features at all? On the same topic is there a good resource for tuning our cars ourselves, and what tools we'd need?
Stumbler

 

Solex carb is one carb with what resembles a frying pan on top for the air filter. su carbs there are 2

 

Blimey! Something on these cars that's straightforward! I've got SUs. Thanks

 

It seems that some folk are still getting TERRIBLE fuel consumption figures. If you can not get about 14mpg Imperial or, say, 11mpg US, there is something very wrong with either carb setting or ignition timing. I assume that the car(s) are running on all 8 cylinders and the brakes are not glowing red after a few miles. This is what I get on a mixture of fast and slow roads.
The ignition timing is set with a timing light and the carbs are set up by the age-old system of adjusting SU carbs (I don't know about Solex). If you don't know about SU carbs find someone who does - they are a doddle.
Regards from Alan D.

 

I have found here in the US that if Shadows are tuned well you will get from a low of 9 to a high of 15 mpg US. They will only run on HT fuel too. I add 4 oz of Marvel Mystery oil to every 10gal or more at fill up and it has helped my running problems emensly! I have recently spent 2 yrs of my life and over 90K in parts to do a full Shadow restoration. Now everythng is new or rebuilt from the complete engine to rear end. I get 13 mpg tops in perfect conditions. They are big heavy monsters and that is about the best you can do. Even air pressure seems to work the best along with a good hot plugs and good balanced carbs with coated float needle valves so fuel does not run over the top.

 

Actually, Shadows can and do run just fine on regular unleaded. They were designed to allow for a wide range of octane availabilities when they were new and high-test was not available in many areas to which they were shipped. I've been running my Shadow II on 87 octane for years now without any difficulty (and getting much better than 6 MPG).

 

in UK our regular is at 95 octane but recently there is a 10% ethanol mix so it's not recommended to be used on classic cars, instead in UK we use a premium petrol at 99 octanes.

 

I can get 9-12 mpg in normal driving. Can get as much as 15mpg driving it over a cliff.

 

On a long run if I cruise at 55 to 60 MPH I can get 18 MPG (imperial gallons) from my Silver Shadow 11. I've made no modifications, everything is original but I pump the tyres a little harder than the manual recommends, I inflate to 30 PSI front and 32 PSI rear. I don't reckon that the tyre pressure makes a major difference to fuel economy but every little advantage helps.

 

I have recently inflated my tires on my 1970 Silver Shadow coupe to higher than the recommended tire pressure setting of 28 psi up to 31 psi front and rear. The car seems to float along much smoother and faster. It also doesn't wallow around on curvy roads or through the corners as when I first purchased it.

 

That doesn't seem very high for such a heavy vehicle.
High for me would be anything over 40psi on all 4 wheels.

 

You have a point. My car has modern Cooper tires as opposed to the original Avons. I figured I could run the pressures higher as the compounds and components are more up to date with current tire technology. You see lighter weight cars with these low profile, higher pressure tires nowadays. I may even bump up the pressures on the Rolls to 34 -36 psi and see how she handles.

 

1978 Silver Shadow 2 average 10 mpg or 15mpg on motorway using premium petrol at £1.71 per litre so for 62 miles or 100 km at 10mpg it costs me £47.88.
I have LPG conversion and I average the same 10 mpg or 16 mpg on motorway autogas sells at £0.99 per litre , so for 62 miles or 100 km at 10 mpg it costs me £27.72.
Using LPG saves me £20.16 per every 62 m or 100 km (LPG saves 42% compare to Petrol).

 

Hi
I was reading these posts as I took my T2 from Glasgow Scotland to northern France last week. The round trip was 1100 miles. I normally have the tyres at 2.2 bar and following the guidance above put the rears to 2.4. I found this made the car handle a bit differently by being a bit more 'loose' at the back on corners and bad surfaces. Driving a fully loaded car at a fairly steady 70mph ( accurate not speedo) and having mixed traffic, the car average 16.5 mpg ( imperial). I did use Castrol Valve/lead/octane booster at about the correct 25ml per 25 gallons. I know some owners/dealers, claim they can get 20mpg on long motorway trips, but I have never seen anything like that. Om mixed slower driving three years ago doing 1000 miles in a week on the North Coast 500 in northern Scotland, we got 14mpg. My car has now covered about 134k miles. In normal day to day mixed driving my car typically gets 14mpg.

 

Having had my 74 SS1 for a couple of months I have been checking the mpg to see if it is way off as the previous owner stated they serviced the carbs. I seem to be getting between 12 and 15 mpg (imperial) with a mixture of motorway and clear A road driving so roughly 275 to 315 miles per tank. 'Glad' to see that is not far out in expectations. I will now check tyre pressure to see it it adds a little.