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Fuel consumption...

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Brit_Brother

Brit_Brother

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I drive my BN6 for fun and it worked wonderfully well all trough this (cold) european summer.
Most of the time I am cornering and more often pushing on 3rd speed at 5000rpm than cruising in 4th with O/D at 2500rpm.
Only one question : fuel consumption seems to be on the high side: I bmeasured many times 24 liters per 100km and this is somethin around 14 british miles per Imperial Gallon... this looks like almost twice what I am reading here and there.
The carbs work fine, not rich at all, idling at 800rpm even when hot, some dieseling (1/2 secs) when switching off.
No fuel leaks, no smells , no carb overflow.
I mean this is real engine consumption when driving kind of "sport".
Do you think this is normal ? Anything worth checking ?
Thanks for you inputs.
 
your fuel consumption for your BN6 is high, I believe you should be closer to ~ 15 liters per 100km with the type of driving you are describing. With extended driving on the highway you should get ~ 11 liters per 100km

I would recommend that you do a complete tune up. Start with the rocker lash, then points & condensor, then timing, then carb tune up, then adjust timing, and then final tune. It is critical to make sure that linkages are set properly, and linked on the shaft between the carbs at the same set point. In addition, you need to make sure each carb is drawing equal air at idle.

I also notice that your car is idling at 800 rpm. While this ok, your car should be idling about 500 to 600 rpm if it is tuned correctly. Both my BJ8 and BN1 idle at 550 rpms. If you cannot get it to idle at that rpm, that suggests your car is not properly tuned.
 
Thanks, Points Condenser and Timing are OK. I could have idle at 500 Rpm but i thought it was too low, I will change it but I am not expecting a lot from this.
Please explain about Rocker lash how to proceed.

I was thinking about changing the two carbs for brand new ones. The actuals carbs seems to work very well I refurfished both of them with the complete SU kit, but may be they are to be fully changed. What do you think ?

healeynut said:
your fuel consumption for your BN6 is high, I believe you should be closer to ~ 15 liters per 100km with the type of driving you are describing. With extended driving on the highway you should get ~ 11 liters per 100km

I would recommend that you do a complete tune up. Start with the rocker lash, then points & condensor, then timing, then carb tune up, then adjust timing, and then final tune. It is critical to make sure that linkages are set properly, and linked on the shaft between the carbs at the same set point. In addition, you need to make sure each carb is drawing equal air at idle.

I also notice that your car is idling at 800 rpm. While this ok, your car should be idling about 500 to 600 rpm if it is tuned correctly. Both my BJ8 and BN1 idle at 550 rpms. If you cannot get it to idle at that rpm, that suggests your car is not properly tuned.
Click to expand...
 
I also thinks it's a little high, but not terribly so. You might just have to adjust the carb needles a little and make sure they are correct per the manual. The simple "drop test" may suffice. After a long drive check that you don't have any brake shoes dragging as well (hot wheels), that will also affect fuel consumption.
 
Hi Johny,
I purchase a pair of "weak" (think they are marked QW) for HD6, But I went back to standard needles since I could not achieve a good carb tuning with those.
I will try the drop test again.
Thanks
 
Brit Brother, me thinks that your driving technique could contribute a lot to the fuel consumption. My first car, a 100/6 had an engine rebuild and was tuned up by none other than the Guru himself - John Chatham and that returned 13 miles to the gallon around town and 23 on a run. and that is the range. Third gear at top revs or near top revs and you can not expect good returns.

Bob
 
I have been recording the amount of gasoline and miles driven this summer.
I use Shell V power 93 octane most of the time. Reading this thread prompted me to figure out my overall mileage. I have averaged 18 miles per gallon in all of my driving. Some was was highway and some was driving around town and occasionally to work. I am very pleased with this number for an average. I am not bashful about using the throttle and I always down shift when slowing down.
/bcforum/images/%%GRAEMLIN_URL%%/banana.gif
 
Well, since my first reply and curtesy of an administative cock up on taxing my company car I am using my BJ7 instead, 120 miles a day, after a little tweaking I am currently looking at 24 to the gallon, it is dual carriageway and motorway all the way but does include two traffic jams going and one on the way back ( different routes), the bad news is that I need a rebore, oil is running at a litre a day, ouch! but I won't need an oil change for a bit at this rate.

Overdrive went to sleep for 20 minutes last night on the way home but woke up, just in time for the last 7 miles. Seemed ok this morning, and gear box oil level was checked last night and is OK, The front nearside caliper has decided to squeel occassionally and the car has a destinct shimmy at 60 mph, so I drive at 70+ where I can to avoid the discomfort.
Makes driving to and from work a real pleasure, just hope that the tax disc is a long time coming and the company picks up the petrol tab.

Bob
 
brit brother, perhaps in some manner purchasing an expensive new set of carbs may bring you piece of mind but i feel that it is "false economy" a competent in this case s.u. carb re-builder can bring the old set back to snuff, may be a matter of throttle shaft re-bushing, valves, seals, needles etc, but i can assure you its a heck of a lot less expensive. new carbs about $1700.00 vs rebuild $200.00-$300.00 /bcforum/images/%%GRAEMLIN_URL%%/savewave.gif
 
I did retune the carb last week end, I hope weaker... It smells a little different. I wait for a couple of 100 miles to recalculate the fuel consumption. And see if I can achieve something like 18mpg: a good goal to pursue with the existing original carbs.
Thanks
 
Your first post mentioned dieseling on stopping, which implies it adjusted rather rich - it's probably not strictly speaking dieseling (compression ignition) rsther than a build up of carbon glowing and keeping it firing.

I get 20 mpg out and about, and 24-25 mpg on a long run in my BJ8, but that's driving in a gentlemanly manner, not thrashing it. Proper English gallons by the way.

AWEM
 
Andrew,

Since imperial gallons= 1.2 us gallons,
1.2 times my 18 us MPGs= 21.6 imperial MPGs
So it would seem we are getting very similar gas mileage.

/bcforum/images/%%GRAEMLIN_URL%%/cheers.gif

Ed
 
For a comparison, when my BT7 was new I got about 17 mpg. No matter how much I fiddled with the carbs and timing it never got better mileage. The magazine testing reviews at the time gave 19 mgp. Probably depends on how you drive them. Towards the end, before I stored it away after 16 years, It was down to about 12 mpg. Of course with gas at about 30 cents a gallon, I didn't worry about it too much.
 
This is a question we all have in all our LBCs. I have a highly modified BE which has a newly rebuilt motor for a SC. A couple months ago I took it for a 600 mile trip and found I only got about 28 mpg. Disappointed, I still don't know, but it is alot of fun to drive and I think that is the real answer.
 
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