Lemans 1000 fuel consumption

[Bazil]

The back story ( this is not another lemans carb re-jetting thread) :

decided to play with the fuelling on the Mark IV, hopefully to make it a bit smoother between 2000 and 4000 rpm. Changed the carb slides to 50/3 ( from 60/5) and reduced mains to 128, kept the K19 needle at 3 rd notch from top and the AB 268 atomiser. This is with LaFranconi Competzione pipes and pod type filters ( Lynx Ram Flo), but otherwise stock. Certainly made a difference at lower revs, although it does seem a little flat around 4000.

However is looks like this has been at the expense of fuel consumption, which makes senses as I understand the 50 slides are richer low down.  Previously I would be hitting reserve at 300 to 320 km ( about 200 miles) - which I didn't think was that great anyway, but now I'm on reserve at 250 to 260 km (about 155 miles). As far as I can work out that's about 36 mpg (imperial) / 30 mpg (US), which seems pretty lousy. BTW, my riding style is pretty conservative, most of the time the tach is below 5000 ( but not all the time - gotta have some fun). Fuel is 95 / 98 octane, non ethanol, takes about 20 litres to fill from hitting reserve.

So my question is: what mileage are other lemans 1000 users getting until they hit reserve? ( I figure that's an easier question than fuel consumption given differences between US / Imperial gallons / litres)

If my consumption is too high, where do I start looking for answers?

Cheers

Bazil

[chuck peterson]

My buddies  LMV was incredible, up in the high 50s at least...he had the hot rod, but the best mileage...all stock if I remember

Must of been low 50s...all stock...light wrist

[Chuck in Indiana]

This is Milich's recipe for the 40 pumpers..
K4 needle, bottom clip
128 mains
68 idle
50/3 slide
265 atomizers

At any rate 30 us mpg is horrible. IIRC, my LMV was 40-42.

[Antietam Classic Cycle]

I once got 70 mpg, obeying the speed limit (45 mph) on the Blue Ridge Parkway, mostly downhill.  Normal average was more like 45 mpg when the throttle was twisted by a 5' 6", 23 year old, 138 lb. squid. (me). 

[LeRoy]

On longer rides and at a steady speed on the highway (70 mph) I regularly achieve 50 mpg. My riding style is pretty sedate and the bike is completely stock in all respects that would affect fuel economy. When I fit the Hepco u. Becker 40 L bags, fuel economy drops to the middle 40 mpg range probably because these bags significantly increase the frontal area and do nothing to improve drag.

[David 54]

My old 1989 Le Mans 1000 would regularly give 50/54 MPG (Imperial)

[bigbikerrick]

I have been getting average of 40-42 mpg with my 85 Le Mans IV. I am at 4000 ft altitude, and run premium shell gas but it comes with up to 10% ethanol. I have gotten as low as 28-30 mpg a couple of times, but man was I having fun!! 
Rick.

[Bill929]

I never saw 40 mpg (US) with mine (1991 LMV).  32-36 mpg was the norm with 38 being exceptional.  Range was still decent (175 miles) due to the size of the tank.   I did have the K&N filter pods and carbs adjusted accordingly. 

[JoeW]

I don't usually worry about fuel consumption on my bikes, I pay attention to it but, as .long as it  performs well, it's fine with me. I can understand the concern here of a 20% drop in mileage. Many years ago, I transplanted a LeMans 4 motor into my 850T3 sidecar rig. I noticed a serious flat spot at right around 4000 rpm. Many LM IV riders have talked about this but, the extra load of a sidecar and kid exaggerated it. I decided to reduce the carb size from 40 mm to 36 mm. Not only did the flat spot go away but, bottom end power increased and I noticed no difference in pull all the way up to redline. Just my two cents.

[guzziart]

Hi Bazel,

I'm running Ed Millich's recipe and get mid 30's.  The bike starts & runs great all the way to wot.  However, according to my air/fuel ratio meter, we're a little lean at idle and a little rich from about 1/2 to wot. The plug chops indicate as much too.  One of these years I'll try to tweak it closer but for the time being, I'm happy with it.

Art

[Tobit]

This is Milich's recipe for the 40 pumpers..
K4 needle, bottom clip
128 mains
68 idle
50/3 slide
265 atomizers

At any rate 30 us mpg is horrible. IIRC, my LMV was 40-42.

This is the jetting in my LeMans IV as well.  Mild headwork, Bub headers, Emgo Dunstall mufflers, K&N pods.  Seeing 50mpg isn't out of the ordinary on twisty 40-50 mph roads even when working the throttle (with accel pumps).  80+ mph on the interstate will loaded saddlebags gets me about 37mpg, hitting reserve at 185 miles.  Fwiw, I run with both petcocks "on".  I'm as aerodynamic as a buffalo.

Tobit

[mgmark]

My buddies  LMV was incredible, up in the high 50s at least...he had the hot rod, but the best mileage...all stock if I remember

Must of been low 50s...all stock...light wrist

This is what I would get on the highway, steady throttle. They do quite well if you stay out of the pumps. I could go double the mileage between gas stops as my buddies' jap bikes.

[Bazil]

Thanks for all the replies guys.

 Seems there's a wide spread in fuel consumption on the Mark IV / Mark IVs, and while unfortunately mine is down the low end of the range, it's not unknown. I'll probably change the atomisers and needle at some point to see if that helps with consumption and the flat spot at 4000 rpm.

One final thing though - Guzziology suggests adjusting the accelerator pumps or disconnecting them. I'm running flat tops, not bellcranks and don't know the implications of that (if anything) on the pumps, and whether that will make any difference. Thoughts?

cheers

Bazil

[pete mcgee]

Bazel
Time to change the needles and the atomizers.
 These only last around 50,000 miles before they are worn and you end up with a richer mixture and increased fuel consumption.
I've done this 3 or 4 times on my Lemans 3, it always makes a noticeable difference to fuel consumption.
If yours is a high milage unit (arent they all) then new slides wouldnt hurt either especially if you can feel the wear on the side with a finger nail.

Cheers

[guzziart]

Ok, here's my useless two cents worth (lol)

I've got bell cranks, didn't disconnect the accelerator pumps and when I think about it, my wrist hurts!
Some here can orate on the pros & cons to the need for the pumps....
- Under some throttle opening situations the mixture is too lean without the squirt of fuel
- The owners manual states to not blip the throttle, you'll wash the cylinders of lube or something like it.
- The pumps aren't required
- The pumps leak, etc.
to name a few.

I don't think the pumps are a problem for me, therefore, they are still in operation.

[Bazil]

Thanks Pete, that's great info.

Slides are new (ouch!!) but I'll get some needles & atomisers on order - it's got 50,000 kays on the clock, which may or may not be correct.

Bazil

[lazlokovacs]

171 miles until reserve,

runnig ed's jetting but with needle one clip leaner.

Carbs are brand new as are slides and jets.

I don't have the pumpers fitted,

but I do ride the snot out of it pretty much all the time..

mixture of sweeping a-roads, country lanes and superslab.

(shoud mention, new rings in there too and the heads were re-conditioned in december...)

I feel I should get higher mileage, so I'm slapping on a wideband sensor and will address the jetting, float height etc soon.

[lazlokovacs]

ps great thread!

[Arizona Wayne]

On my `87 LM IV I consistently got 40-45 mpg.  Don't know what the carbs were set at.  Easily over 200 miles before fillups.  Rode it from 25K to 50K miles. Had a 2-1-2 exhaust which gave it more midrange torque.