Fuel economy & parts for my 32mm Bings

[Mal S7]

I've started commuting to my new job on the 1977 R100/7 and so far loving it but I have to refuel every day which is good for nothing except working out precisely how much fuel I am using and this is taking away from my riding induced happy zen state.

Precisely 6.9 litres per 100km, which translates to 41mpg (imperial) or, I think, about 34mpg US. Doing over a 1000km per week is costing me $110 a week ( and that's real AUD dollars too, not them mickey mouse ones ). Does that sound bad to you? It sounds bad to me, my SUV gets the same or better mileage.

Bike has done a zillion ks but motor is healthy and has Boyer ignition and is sorta-kinda in reasonable tune considering the current owner doesn't check it much or get too persnickety with things, but it runs OK.

I read lots of posts recommending replacing needle jets as they wear out. But, the Bings .. ahem ... well,.. apart from diaphragms, in 18 years I've pretty much left them be; a PO has been at the jets and jet holders with a pipe wrench or a vice and I never managed to get them mangled things out. Tried again today and have only succeeded in getting a size 150 main jet out, (according to my daughter with good eyes). Does that sound right? 150 main?

And what Motobins cals a " mixture tube" would that be the jet holder? That's the chewed thing that seems to be welded in there. Any tips on getting it out? Any tips on "must have" parts before I place an order from the UK? I notice jets and needles etc are surprisingly cheap at least.

cheers and thanks
Mal

[Roy Gavin]

Force is the last option - it is easy to split the carb. DAHIK.

A good penetrating oil will help - I recently bought a can of Masterproducts "Nutcracker" from Sprint and it has worked well on everything I have tried it on.
Heat everything up, boiling water is probably safest, then spray, and let the oil penetrate when it is cooling -do this a couple of times and then try a sharp tap on the spanner with the carb hot.
If you spray down the larger of the two air bleed passages which run parallel to the intake this will get the release oil to the top of the thread too.

If this gets it out dont forget to remove and clean the emulsion tube which sits above the needle jet - it will probably be stuck in too but a few taps from the top should get it out. It is the brass bit that the slide needle goes into first.

With the petrol that is around now it is hard to get much better than 18 km / L -my twin plug 1000 cc G/S does 10 miles/litre on regular unleaded in normal riding which is not a lot better than your bike, although I have squeezed 612 km out of the 34 litre tank.

Some people recon that they get better mileage with BP Ultimate, but as all our crap except Caltex comes out of the same tanker and tank farm I remain to be convinced.

[Mal S7]

Force is the last option - it is easy to split the carb. DAHIK.

Ooops too late Roy! I didn't split the carb but did manage to crush the brass jet holder. Ewww
mea culpa, mea culpa, mea maxima culpa!

So I pulled some 40mm Bings from my spares cupboard. But they of course don't fit 32mm heads.... sigh as if it would be that easy.

Oh well, its been sitting around on a bench for 6 years waiting for "the day" and I think that's arrived, yes its finally time to raid the R100S engine. Captains Flat is weekend after next!!

I have dropped one head off the S. It looks really good, a bit of the usual carbon build-up, haven't popped the valves off yet. Rockers are good nick. Did they run different pistons in the S v the /7? The piston crown on the S has "96" stamped on it, I presume its original bore then?

[Bob Bennett]

G'day Mal,
http://boxerworks.com/forum2/viewtopic. ... ing+thread
The above is a link to Steve's "Bing thread"
Some way down the first page is a pic of the jet in question,
in the pic from left to right it goes, mixer, needle jet, main jet holder, then main jet,
New needles & needle jets certainly improved the fuel consumption on my R80 as they
seem to wear with vibration, I got an extra 3 or 4 Km per Ltr, worth doing I think.
Thanks to Steve for the thread.

[Mal S7]

Thanks Bob, good info there.
cheers
Mal

[barryh]

I had a seized jet holder and it took a lot of patience, heat cool cycles and penetrating fluid to shift it but out it came eventually without damage to the carb. When you get it out you may see a lot lot of packed in crud around the emulsion tube. In fact it can fill the whole space and this could be partially responsible for your low mpg as it prevents the pre-mixing of air with the fuel that comes out of the needle jet. Together with replacing worn needles and needle jets a noticeable improvement in MPG is possible.

The other thing often not fully appreciated is that the mixture screw setting does not just effect idle. It impacts on fuel mixture at part throttle settings up to 1/4 throttle which for me is 65 MPH cruise. Personally I don't follow the often quoted advice of "adjust for maximum idle revs and then richen another 1/4 turn out" That might be reasonable general carb tuning advice where the base setting is 2 1/2 turns out to start with but for Bing CV's where the base setting is 1/2 -3/4 turns out it's grossly too much in my opinion. I may be exaggerating to make a point here but the mixture screw is more sensitive than it may seem. If you must turn the mixture screw out at all do it in increments of the width of the screw driver slot. I've proved that careful mixture screw setting pays dividends on several bikes over the years. Here's my fuel consumption over the last 5 years or so. The winter/summer cycle is obvious but notice the big improvement in 2008 that's when I cleaned the crud from around the emulsion tube. The gradual improvement in recent years has been down to fine tuning of the mixture screw. Yes the figures are real imperial MPG but you ain't going to get them on an R100. They are from an R45. Same carb type same principles.

[chasbmw]

Barry,

That is some record keeping.....

I go off for a weeks riding with a mate of mine every year and we refuel at the same time with the same pump, and it always seems to be that his bike uses more fuel than mine, when he had a R100R mystic and I was using the 1070 tuned to hilt bike , I was getting 10-15% more MPG, which really irritated him, last year he turned up with a 1100r, and reckoned that he would have me beat, but I was using a newly rebuilt lightly modified R90/6 and I was still about 5% ahead (over 60 MPG imp) at times. Apart from changing the jets things that might make an engine more efficient would be dual plugging coupled with a higher compression ratio, but it's not really a cost efficient thing.

Charles

[Mal S7]

Yes the figures are real imperial MPG but you ain't going to get them on an R100. They are from an R45. Same carb type same principles.

That is amazing Barry. Hmm that sort of fuel economy would buy some kit. Summer / Winter difference due to ..?? What? Warm air making it run richer?

My thread is becoming a bit redundant now as I am fitting S heads, pistons, barrels and carbs. No time for anything fancy, just going to clean off the crud, fit new gaskets, bolt it all on and keep fingers crossed it will get me to work on Monday.
If it all works out OK I may sell the /7 heads, barrels and rubbish carbs.

[barryh]

Summer / Winter difference due to ..?? What? Warm air making it run richer?

In winter the "choke" is needed more and the engine just doesn't get warmed up properly on my short commute. Add to that transmission oil drag. When I tried rotating the rear wheel by hand in neutral at -5 Deg C the amount of drag surprised me and prompted me to change to oil that's a bit thinner at those temperatures. In winter I generally only use the bike for commuting but it gets longer runs as well in summer so that's got to help. On top of all that winter fuel blends contain a few percent less energy due to more volatile fractions being included.

[Roy Gavin]

We dont get a real winter here, so we dont get much seasonal variation, but I have noticed a decrease in mileage since I fitted low tension throttle return springs.

And since the supermarket chains and ethnic minorities got into the petrol retailing business.

Bing USA sell the Colourtune plugs which let you set the mixture screw buy observing the colour of the burning mixture.

When I tried using one correct position was just off too lean, not just off too rich, didnt improve the mileage any, but made a noticeable difference for the first 2 or 3 yards away from a standstill.