r80g/s high fuel consumption

[cenn8310]

hi all,

i'm new to the air head seen and need some help.

i have been the proud owner of an 83 r80g/s for about 3 months now and ride it 40ks to work and back each day.

i'm getting about 11km/l with an average speed of 60km/h and its starting to get on my nerves.

the bike starts first go without choke and blows a bit of black smoke when revved. it vibrates a fair bit at idle and even more at low rpm, but runs really smooth at high rpm. the plugs are mostly black except for the very tip.

a previous owner has installed bmw 1000 barrels, but i'm not sure if they did anything to the heads.

i have improved the economy from 10 to 11km/l by rebuilding the carbs (o rings and diaphrams) and replacing the air filter with a k and n unit.

i get about 13.5 km/l on the highway.

i haven't replaced the jets as i'm not sure what size to use, seems it has the bigger barrels. i was thinking of using the same cofigeration as the r100rt as it has 32mm carbs. this would give a 135 main jet and 2.66 needle jet.

what does everyone think about this configeration?

also on cleaning the carbs i noticed that both the float needles were quite worn, the tip has an obvious step worn in it where it seats with the carb body. could this be affecting the ecomomy?

any help or suggestions would be great.

[Frank Warner]

See you have already posted in http://www.horizonsunlimited.com/hub...-problem-30067

.. think the responce from me is similar .. is there oil in the botton of the air cleaner box? Oil blow by into the carbys blocks off some air passages leading to rich running ..

When you overhauld the carbys .. what were the jet numbers? Standard R80?

-----
If the float need le leaks it will lead to fuel leaking out the bottom of the carbs when you park it (with the fuel turned on). In the longer term the stepped ones need replaceing - they will eventually leak.

---- How is the timing ? Advancing and retarding?

[cenn8310]

i haven't had a chance to check the timing and forgot to check the jet sizes when i rebuilt them.

the crank breather seems to exit in the carb inlet not the actual air box, and yes there is oil leaking into the carbs. should i disconnect the crank breather hoses so they exit in the air box or divert the pipe to a small bottle?

the oil level is mid way on the dipstick so its not a matter of draining a bit of oil to stop the problem.

what sort of economy should i be getting?

cheers,

chris

[gsworkshop]

The float needle is just like a valve, it shuts of the fuel supply as the float bowl fills up to a certain level. If the float needle leak, the bowl will fill up to the level of the small overflow pipe and drip out the bottom of the carbs and will not effect the performance of the carbs.
The worn groove in the float needle is not the indicator that they are worn but rather a puddle of fuel under the bike.
Replace the nozzle needle and needle jet with the 2.64 set.
It is very important to replace both needles and jets at the same time as they work as a set. If you fit jets of say 2.66 with needles that were working with the 2.64 jets for instance you will have problems with performance over 4000rpm.
Forget about the main jet as this will have no impact on regular riding.(works only at full throttle)

[cenn8310]

i have moved further from work now (60km round trip instead of 40km) and am having some different problems.
when i first got the bike it would sometimes miss a beat (felt like i was running out of fuel) when it was hot and i was doing 80km/h in 5th gear.
after i cleaned the carbs the problem went away.
however it has started doing it again this week, at around 25km into the trip.
anyone got any ideas? do you think its related to the over rich mixture or could it be and ignition fault?

[gsworkshop]

Ignition control units tend to give problems intermittently so you could be right about the fault being in the ignition system.
There is some test you can do to see where the problem is, but if you have access to second hand units it will help by replacing the components one at a time. I would start with the ignition control box, then the ignition trigger unit below the alternator behind the front engine cover and then the coil and coil leads.
These part will be the same for all BMW models from 1980 till the last of the airhead boxers in 96.
If you know of someone well enough that have one of these bikes.
The first and most important thing to do is to make sure all the components have a good power supply.
And as far as the tests are concerned, they might indicate a fault in one of the components but it will not necessary show a faulty unit. The tests only test for certain problems there might be but even though a test is positive the unit can still be faulty.
My best guess though is to look at the ignition control unit(CDI), you will find it under the tank. It is a black plastic box mounted to a heatsink and have a multi connector at the bottom with about 7 pins.

[Frank Warner]

The ignition control unit (mounted under the fuel tank) is bolted to a aluminium heat sink .. the mounting paste between the two can dry out leading to overheating of the control unit - get some new heat sink compound and apply when dissassembled.

The lead from the 'bean can', 'hall effe3ct sensor', 'trigger unit' or what ever else you want to call it can get traped under teh cover - leading to the wires distorting and when the motor gets hot .. the wires can touch and you get no spark .. for a bit .. works fine when cold. Check the wire routing.

You certain the carbys are not dirty again?

[cenn8310]

could dirty carbs give the symptoms i explained?

they are leaking oil so my guess is yes they are dirty again.

would it be a good idea to reroute the crankcase breather hose so it doesnt blow oil into the carbs?

the engine oil is halfway between the low and high indication marks.

[Frank Warner]

Originally Posted by cenn8310

could dirty carbs give the symptoms i explained?

Did cleaning the cards solve teh problem? Yes
Did teh problem reoccure when the carbs got dirty? Yes

Then yes the problem is related to the dirty carby .. it blocks off some of the air ways .. causes rich running ..

You can reroute the engine breather .. in the longer term finding and fixing what is causing the blow by is the true fix.

[cenn8310]

i am in the process of sorting the problems and have just done a proper compression test and am getting 100 psi in both cylinders.
i put a bit of oil in the cylinders and still got 100 psi.
i am planing on setting the tapets on the weekend and retesting.
my manual incates 109-130 psi to be the normal range does anyone know if bad valve clearances could make 10-39 psi of difference?

[cenn8310]

i checked the tapets on and they were all within spec so i decided to remove the cylinders and barrels to inspect them.

it turns out the previous owner has installed 1000cc barrels and pistons without any modifications. to make it worse he has filed down the tops of the pistons to prevent them hitting the heads.

it gets worse still, the pistons aren;t even the same. one has circlips which you take out using cirlclip pliers and the other has the ciclips you pry out with a screwdriver. the tops od the pistons also have a different shape.

i have decided to put the egine back to stock by buying some second hand 800cc pistons and barrels and then reset the carbs back to stock settings.

does anyone have any tips for checking the valve seats will i have the head off?

oil consumption was low and the bike blows no white smoke so i am guessing the valve guides are in good repair.

a friend suggested turning the heads upside down and filling them with petrol to see if they are sealing. if petrol leaks through them i need to regrind the seats. does this sound like a good tip?

while i am in there i am going to replace the rockers as they are showing signs of pitting, does any one know what year models have interchangable rockers with an 83 r80g/s to make buying a second hand set of rockers easier?

[oldbmw]

Originally Posted by cenn8310

i checked the tapets on and they were all within spec so i decided to remove the cylinders and barrels to inspect them.

it turns out the previous owner has installed 1000cc barrels and pistons without any modifications. to make it worse he has filed down the tops of the pistons to prevent them hitting the heads.

it gets worse still, the pistons aren;t even the same. one has circlips which you take out using cirlclip pliers and the other has the ciclips you pry out with a screwdriver. the tops od the pistons also have a different shape.

i have decided to put the egine back to stock by buying some second hand 800cc pistons and barrels and then reset the carbs back to stock settings.

does anyone have any tips for checking the valve seats will i have the head off?

oil consumption was low and the bike blows no white smoke so i am guessing the valve guides are in good repair.

a friend suggested turning the heads upside down and filling them with petrol to see if they are sealing. if petrol leaks through them i need to regrind the seats. does this sound like a good tip?

while i am in there i am going to replace the rockers as they are showing signs of pitting, does any one know what year models have interchangable rockers with an 83 r80g/s to make buying a second hand set of rockers easier?

It might be cheaper to fit a pair of 1000 cc pistons from Siebenrock. Motobins sell them.
also fit new float valves as the wear you mentioned is not good. At the same time replace the needles and needle jets. My 1985 r80rt went from 280km per tankfull to over 320km per tankful with just the needles/needle jets. the siebenrock pistons will work without modifying heads or carburetters.

[Timo]

I prefer your idea of returning to stock better, unless you need the extra power the Siebenrock kit should produce and are aware of the trade off's. This kit increases compression quite a bit, and is not recommended for fuel of less then 95 octane. Not a problem in most countries, but not always obtainable in much of the world so this is a limitation for adventure touring.

a brand new set (or good used) of 800cc pistons and barrels from Motobins or another good BMW supplier is not a huge expense, and going back to stock will better enable you to sort out the issues with the bike.

The 800cc engine is very smooth and should produce adequate power and good economy if tuned properly. It really depends on your priorities, but if you are wanting to use the bike for long distance travel then be sure you are aware of the potential trade off's with each modification.

Good luck and let us know what you did and how it worked.

[splash]

I owned a R80 for about 40 000km. Consumption should be at least 17-22 km /litre. All I would like to add is to put an inline fuel filter each side above the carb. This is a good idea for all BMW carb models. It stops a lot of problems.

[Samy]

My Basic was already upgraded to 1000 CC.
My bike makes only 450 kms with 35 L gas. It makes nearly 13 km/L. The problem with my bike, repairman doesn't understand how to fix the problem and I can't dare to touch the carbs with fear of destroying it. Many friends who also tried to help you indicated possible problems and how to solve myself. I will have a look how to do it next month.

To you, upgrading to 1000 CC doesn't solve your problems.
Mine is 1000 CC Siebenrock and it is really thurtsy for gas.