I have recently bought a 27 year old R80 G/S which has a 1000cc conversion and four spark plugs. After riding 120 miles two days ago with no problems, yesterday after a short run in the morning the bike, quite suddenly refused to rev. properly and will not accelerate past a certain point. The engine sounds as though it is 'choking' - like it cannot breath or has no fuel when I open the throttle.. Throttling harder makes no difference - the sound gets deeper like i have pulled the choke rather than the throttle.. In neutral it has trouble too and backfires a bit. I was able to ride home with no problems as long as I accelerated VERY gently..?!

At first I thought it was a blocked fuel line as there is some gunk in the tank bottom, so I opened and cleaned the float chambers bu to no avail. Fuel seems to be getting through fine although the LH chamber was lined with ochre coloured powdery stuff..

The bike had been standing for 6 months before I bought it and at first smoked a lot - the previous owner had WD40'd everywhere. This smoke stopped and only had a final burst when i was going up a STEEP hill during the long run..

The bike has loads of mods. R100 (I think) twin disk forks, ALL NEW wiring, a kickstart that nobody can successfully use, a HUGE rear frame for two really heavy STEEL Swiss ammo box panniers..

I am due to carry out a full service, the oil has been clean and steady at half way on the dipstick and there are no leaks other than a very small dirty film over the front of the carbs but I cannot readily see where it is coming from..

Could anyone help point me in the right direction for some diagnostic tests? Or tell me that it is something very common and easy to sort out..?

Toby.

ps. I have the bike as a first boxer to try out for a VERY LONG overland adventure in about 20 months time, so want to learn how to do all my own repairs, maintenance etc. as well as decide whether such a big machine is for me - I am quite small - so far I have succesfull replaced an over-engorged clutch thrust piston and fitted a Halfords £12 speedo to verify that the OEM one is reading 10 - 20% over.. Oh, and I am in North Dorset..

:confused1:

Sounds like the air filter is clogged - the "ochre powdery stuff" might be sand...

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Sounds like the classic symptoms of a split/torn carb diaphram . Or maybe both sides.

Thanks guys! I've only just finished teaching and already two leads! I will examine the air filter right away but the carb diaphragms will take longer.. is this a job I could look at as a careful newbie? or should I think of paying a BMW mech? The guys at CW in Dorchester are expensive but pretty cool and would advise well.. TY

DIY ... take top off carby .. look at rubber round thing for tares .. take it out - hold up to light and look for pin holes..

Buy two carby overhal kits and use them to replace the rubber bits .. you'll learn a good deal by this

could just be dirt in the petrol blocking the jets ..

Good uck.

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Regards Frank Warner
motorcycles BMW R80 G/S 1981, BMW K11LT 1993, BMW K75 G/S

You said you are dual plugged? I would check to make sure you have spark on all four plugs. Check that you have a wire connecting the two coils and it has a good connection. DO NOT turn over the engine in any way without grounding the spark plugs when you check for spark, or you will fry your coils due to the electronic ignition. Your timing at 1080 RPM should be 2-3 degrees retarded (after top dead centre), this needs a timing light. This is a great time to learn about your bikes electronic system!

Thanks for the replies everyone! I am dual-plugged which I know nothing about though I'm looking forward to knowing more. I took the tank off for the first time properly last night and there is a lot of stuff there that ain't in the Haynes.. I'll come back no doubt and ask for help soon..

Hello here is an update..

Having taken an hour from work while no-one was looking I have taken of the tops of my carbs - which are from a R100 or GS100 it seems - and the diaphragms seem fine.. although the LH bowl was and still is fouled by silty mess! I am getting a full service and overhaul kit anyway this week, from Motorworks, and emptying and cleaning my tank and the tap filters.. any ideas as to what is causing problem if the d's are ok? I held them up to the light and they have no holes or tears..

Pics are on

Modified R80 G/S Sudden acceleration problem! HELP NEEDED.. - ::. UKGS'er.com .::

where I am also asking for ideas.. I have got to work now so can't post them here too..

many thanks for any help..

Toby

If you have a blocket ITU; i.e. flyweight restriction - problem is simple; one plug is out.

Simplest test.
Measure resistance across the coils; you should have about 25-30kOhm from left to right plug.
If that thats ok. Check the plugs.

Are you running single or dual ICU's ?
If dual - one may have gone bust => renew.

I have experience a HT-lead to be burnt - so check the coils, HT, plug-caps and plugs.

Which plugs are you running ?

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Drive Safely,
Albert

That comes from parking on the side stand - and the engine oil breather into the air box putting dirty oil down the left side air inlet .. and that goes into the left carby where it finds its way down into the float bowl .. after possibly blocking some jets .. a good clean is recomended .. left carby and air box - under the air fliter ..

Some codes from Mr lindberg post ...

ITU - Ignition Timing Unit - sometimes called the bean can .. as that is what it looks like - on the front of the motor under the alternator. Some details here Second Hall Effect Sensor for an Airhead

ICU - Ignition Control Unit - black box .. ignition amplfier .. you have at least one .. possibly two .. takes the ITU signal and drives the ignition coil/s ...

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Regards Frank Warner
motorcycles BMW R80 G/S 1981, BMW K11LT 1993, BMW K75 G/S

How is it going Toby ?
Did you find the fault ?

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Drive Safely,
Albert

Hi all, it is going ok as far as I have got, which is to remove and clean out the LH carb using the Haynes manual as a guide. It was very dirty with black stuff as well as the ochre powder stuff in the vacuum chamber. The jets were dirty but not actually blocked; but the large screw hole where the main jet holder goes was fouled up with granular black oily stuff!! I cleaned it all out very carefully with a soft brush and a lint-free cloth. There was so much that I thought it was a disintergrated rubber ring, but the Haynes manual mentions none there. I have not disturbed any of the screw settings - the carb top is still on the bike with cables attached. Although the seals, gaskets and diaphragm seem ok I will replace them. Tonight I will do the same to the RH carb which looks less bad at the top.. Oh, and the petrol taps were dirty but not clogged.. I also need to clean out the big plastic tank, hooray! Thanks for all comments, some pics below, ty

dirty tank and electric bar.. ty

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Don't forget to clean the air box - under the air filter .. think you'll find oil in there!

When you have finished cleaning the tank/fuel cocks .. put some petrol in it and drain it through the fuel pipes .. not through the carbys .. but into say an old plastic ice cream container .. should come out clean if you have done a good job .. if not just keep toping up the tank with clean petrol (let the dirt settle in the contanier and then poor the clean top stuff back into the tank).

Once that works .. remove the bottom of one carby and connect up the fuel lines .. repeat the draining process into the plastic ice cream container.


You should now have a clean fuel system .. leaving the ignition system as the next possible cause?

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Regards Frank Warner
motorcycles BMW R80 G/S 1981, BMW K11LT 1993, BMW K75 G/S

Thanks everyone for all the good advice! I think I have cleaned out the carbs well enough and they all work when back together again! That was my day off!! Now back at school so I won't have a PROPER run now 'til next weekend!!


- - apologies for cross postings, this was my first cry for help so I cried LOUDLY. I will have more questions, hopefully of a less worried nature, as the bike is rather no-standard and I plan to get to know it mechanically as best as I can before riding it all over the planet.. and hopefully will put some details of my bike etc up on tobyyarwood.com when I can [it is very out of dat now, having my vanvan on it still!! Thanks again for all the time and advising..

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