fuel cosumption

[timbo]

Hi
After buying a R65 & riding it for a couple of months iv finaly got round to working out my fuel consumption & was a bit suprised to be only getting the low twenties to the gallon. Ive suspected for a while that the bike is running rich as it will never starts with the choke & i have to start it with the choke off and a twist of the throttle, although the bike does run sweetly when warm. Ive bought myself a set of carb gaskets & intend to strip them tommorow, any advise as where my problem might be would be appreciated.
Thanks
Tim

[Luca]

Before you open up the carbs:

1) Make sure your odometer is working.  They are notorious for failing, and that would throw off your calculations

2) It's always worthwhile to make sure that you have a strong spark.  When I replaced the original coil, plug leads, and plugs on my bike, the idle jumped up noticeably.

3) Make sure the enrichener (choke) arms fully return with the handlebar lever in the off position

4) Check for any air leaks around the carbs

After you take the carbs off:

1) Do a compression test if you can.  Engines with poor compression use more fuel.  I think around 150psi per cylinder is good.

2) The jet needles (the pointy bits, as opposed to the needle jet--the brass tube) are adjustable, but I don't know if they bike would even run with them on the wrong setting.  Again, don't have the information off-hand (it's somwhere on this forum), but you can check to see that they are at the stock setting.  They have 4 settings, and each is a pretty drastic change.  While you are in the carbs, make sure that the jets are still the factory size.  (again, seems odd it would run right without an opened up intake/exhaust, but worth a check)

3) Make sure the enrichener discs are not insalled backwards, which will mess up the mixture.  Snowbum www.bmwmotorcycletech.info has an article on this, with pictures

Other thoughts:

A seriously high fuel bowl level could also cause you to use more fuel.  A really rich idle mixture can use more too, but I kind of doubt that either could rob you of 20+/- mpg, nor let the bike run sweetly with such poor economy

How fast have you had the bike?  Any idea of top speed/revs in 5th gear while holding a particular speed?  It's possible the final drive or 5th gear have more reduction (higher gear ratio) than stock.  Either would reduce fuel economy

[Bob_Roller]

That's pretty poor fuel comsumption for this bike .

Previous owners may have put larger jets, moved the needle position, float height is set too high, or the floats have absorbed fuel and are no longer 'floating' as they should .

The enrichment system commonly referred to as the 'choke' may have problems .

There are numbers stamped into a vertical flange at the front of the carb .

Numbers should look something like this : 32/64/325 .

Post those numbers and I can give you what jets, needle position that the carbs came with when new .

[Barry]

Before you open up the carbs:

1) Make sure your odometer is working.They are notorious for failing, and that would throw off your calculations

when I checked mine accurately it was  recording 2.5% low. Not much perhaps but every little helps.

[Luca]

It might be possible that the metal drive wheel in there is intermittently slipping.  Or maybe the odo was replaced with another unit and the ratio inside is incorrect.

I'm a bit flummoxed as to how he could lose around 20mpg and the thing still runs sweetly at operating temp.

My gut tells me this is an issue of compounded problems.

[montmil]

Odd that you say it starts without using the enrichener circuits. Makes me think you are w-a-y rich in the jetting, needle positions or float bowl fuel level. One, both or all.

The final drive ratio should be stamped on the top of the drive case near the drive shaft attach bolts. 32/9 is pretty std for R65s.

Properly tuned, your scoot should get around 40 mpg, depending on your wrist and roads.

[Bob_Roller]

Your unit of measure, is it Imperial gallon ?

[Barry]

I've just realised Tim is in London so it will be imp MPG which is even more diabolical.

I too am having trouble understanding that it runs well with that sort of consumption. Not so much starting without choke because mine does that and still returns 70MPG.  There must be several issues with the carbs as no single fault would drag consumption down that far. Wrong jetting, wrong needle position and or worn needle jets, emulsion tubes blocked solid with goop from the breather, float levels too high.  Could be some or all of those things.

Or could it be a fuel leak  ?

And there has been at least one case of poor fuel consumption that turned out to be someone nicking the fuel.  It's precious stuff in the UK at £6 a gallon.

[Bob_W]

Tim
Make certain the petcocks aren't leaking. My mileage dropped to less than ten after the tank leaked several gallons out over a period of a couple of weeks. The petcock was damp, but no visible evidence of gas dripping. Bike died near the house when the fuel in the carb bowls was used up. It seemed a long walk home pushing a bike.
Also the needle attached to the slide and its associated jet wear. This may be visually obvious.  
It is easy to mix up the enricher discs from left to right or to install wrong. PO could have done this. Snowbum has all the information you need to verify they are correct.

[timbo]

hi thanks for the replies
im sure of the mileage as i only use the bike for work & get the exact mileage from google,
The bike was exstensivly rebuilt by the po as a father & son project & although i originally thought it was done well i have since discovered a few mistakes, i know the carbs were rebuilt as i have the receipt for the parts. a leaky tap is possible & the left carb is slightly discoulored & looks like its had a leak before but i carnt find any sign of one now,
Thanks again & ill let you know what i discover when i strip the carbs
Tim

[timbo]

Hi
back for some more advice
Have stripped the left carb & got the followinng jetting size
The main jet is 148 & had no washer, according to clymer is should be 145
the idle jet is 45  as its an 82 bike it should be 40
the needle clip was on 4th place where it should of been on 3rd
the needle has uneeven wear with one side worrn 5mm higher
The carb no is 64/32/307 & im wondering if its off a pre 81 bike
can the settings from a clymer manual be trusted
As im going to be replacing the jets & needles should i replace the whole needle jet assembly including the attomiser

I read snowburns article on the bing carbs & the choke was assembled propery, but he did include a section about float failure leading to big reductions in MPG, ill check that as soon as i find a drift small enough to nock out the float pin,
 Maybe the bike wasnt running as sweet as i thought, it is my first twin for over 20 years & the first bike with pushrods ive owned.

Thanks
Tim

[Bob_Roller]

When you try to remove the pivot pin for the float, it only comes out one way .

There are serrations on one end of the pin to secure it to the float leg, you're working with aluminum, it won't take alot of abuse, before it breaks .

The serrations are on the side of the pin that comes out first .

There should be matching serrations in the aluminum leg the pin goes into .

Wouldn't be surprised if a previous owner didn't know this, so look it over before trying to remove it .

If by chance the pin doesn't come out and you are replacing the floats, you can get needle nose pliers on the pin and then tap on the pliers with a hammer .

[Barry]

64/32/307 is correct

148 is correct Main jet for UK (US is 145)

45 idle jet is correct for UK (US 40)

4th Clip on needle is correct for UK   (US 3rd)

Needle jet  should be 2.64 (US 2.66)


That 2.64 needle jet size goes some way to explaining 4th position on the needle but if it was me I'd try 3rd position after making sure float bowl levels are correct.

The only jets that wear are the needle jet and maybe the needle itself.  There is no reason to replace idle jets, main jets or the atomiser unless the parts are incorrect or damaged. The missing main jet washer is not the cause of increased consumption unless the jet was loose. Worth replacing though.

[timbo]

Thanks for the information
I take it the clymer manual is for US models
Is there somewhere i can get the UK specs
thanks
Tim

[steve hawkins]

Haynes manual has both

Rev.Light