R80gs starting problem
 

I've been having some problems starting my bike from cold. I stripped the carbs and rebuilt with new o rings, replaced a bent needle (and new jet). Put it back together, warmed it up for 10mins and went to adjust the idle mixture. I've noticed a weird problem. The right side mixture on adjustment improves the revs. The left side makes no difference when adjusted. I can close it completely and no change occurs to the revs. Doing the same on the right stalls the bike. What is the likely source of the problem? Bare in mind I've had the idle screw out and replaced the o rings and cleaned it already. Have I missed something?

Yes.


Is the throttle butterfly closed.. at least somewhere near closed? If not then the idle bypass won't contribute much to the air flow.

If that is ok then check the passages for blockages..

Correct, about the butterfly valves, they always need double checking, put it up against the light to be sure that they are closing as much as they can.
Also, just check to be sure that the choke is assembled correctly, I remember that it was way too easy to reassemble the linkage backwards.... :oops2:

...been there done that... Spent the 90:ties tuning my carbs more or less every day...

Start all over with your question. There are huge gaps in it.

Need to know exactly what you have done to help you.

The problem / cause is very simple, but to help you address it I will need to know what you did do... and what you did not do...

I'm unable to post photos here on the HUBB. Should you also have problems, start a post at www.maskinisten.net just click on "ny tråd" at:
MC • Maskinisten

Thanks for the pointers guys. I looked at both the choke setup which was badly bunged up (needed a good soak and clean) and reset the butterfly position (looked like it wasn't properly seated after the previous owner's overhaul). Will balance the carbs again tomorrow and see if things have improved. Thanks.

I had a similar problem with one mixture screw - adjustment having no affect on running. I resorted to setting it to recommended position followed by only a little tweaking.

Re. starting problem: There is an o-ring behind the choke rotary valve too. Take care that the choke paper gasket is good; Check rotary valve is fitted the correct way round. Also that left and right are not interchangeable (You probably know that).
Maybe an air leak? Inspect inlet rubbers for cracks/perishing.

Thanks DC. Didn't think anyone would want all the boring detail first off. So here goes.

I bought the bike last year. I had an R80RT before that so I have had one that ran well. I did carb rebuilds on that and some ignition work and it ran very well. Since purchasing this bike there has been issues starting. My ignition trigger unit (bean can unit) failed so I had assumed that most of the problems had stemmed from this. It had newly fitted ignition coils fitted by the previous owner before I purchased.

Since replacing the ignition trigger unit and ignition control unit with a new electronic setup the bike runs better, but has still been a bit rough. Symptoms are it's been increasingly hard to start and never feels quite as smooth as my old 1981 RT. The new bike is an 1989 R80GS.

Round 1 - 3 weeks ago

I stripped the carbs and found that both nozzle needles were bent. I replaced them and the jet with new parts (the bit that sits in the atomizer and receives the needle) in case the bent rod had worn this also. I replaced all the O-rings in the main and idle jets, and mixture screw. I cleaned with carb cleaner. The float bowl gasket was replaced at the same time. I also noticed that the choke gaskets had been partially sucked into the choke housing so removed these and replaced them with new ones. I did not disassemble the choke further. I thoroughly cleaned the carb and sprayed all the passages I could with carb cleaner. There was a fair amount of dirt.

Round 2 - last week

I disassembled the choke housing on the left side (I described above, the left did not change in revs when I adjusted the mixture screw). I noticed the small holes in the choke rotary valve were badly bunged up. I tried cleaning them but with little effect. I had a spare from an old Bing carb (correct side) and so used that instead. I replaced the O-ring on the choke arm. Put the lot back together and balanced the carbs with the engine warm using a mercury type tuner. Runs cleaner with no hops of misses on idle which is an improvement on last time.

I then waited and started the bike from cold. It starts a lot easier but I still need to hold the throttle on to keep it alive until it's warm. My old R80 just needed the choke engaged to start.

I'm thinking that I probably need to clean the righthand carb choke assembly also. After that though I am out of ideas.

Thanks Two Wheels Good. How would I know for sure that I have the correct rotary valve in the correct carb? I have the Clymer manual which shows the Righthand carb in the illustration and my lefthand rotary valve is the opposite of that one pictured. Is that enough to know? I have found some of the previous owner's work done on the bike to be a little erratic so it is possible that he could have done something odd. He did claim to have overhauled the carbs, though many of the O-rings I replaced looked old if not original, so I'm not convinced he did a thorough job.

The bent needle was probably from someone tightening the main jet and atomiser when needle wasn't aligned. Well spotted.

The choke valves are stamped L and R so the only risk is installing them 180degrees out. The photos here should clarify
(I've just read: " it's not a choke - it just acts like one. It's an enricher")

Some other thoughts:
Take some time cleaning the passageways. I've used plastic thread from a strimmer or fishing line with carb cleaner.
Are the needles in the right slots? (Though this caters for wider throttle fuelling.)
Check float height. I find it useful to check fuel depth in floats bowls are equal.
I spent a lot of time hunting a carb problem which turned out to be a sticky timing advance so I'm inclined to say check electrics and earths too.
My R100 needs almost full choke to start but then settles on half choke.

Thanks, I'd forgotten about that biblical 2 post on Bing CV. Very useful.

What's the problem with posting photos Albert? Should be no issue, easy.

if screwing low speed mixture makes no difference. usually low speed jet is plugged. some folks compensate by opening up butterfly enough for main jets to start working.

when enrichening circuit is engaged. having a carb with butterfly open too far will add more air leaning out mixture.

1. make sure your enrichening valves are not backwards. marked R & L. adjust cables to make sure valve is completely engaged.
2. take a can of Berryman's chemtool with long nozzle. put on safely glasses .. place tip on each and every circuit/jet inside carb. if you see carb cleaner coming out other side. proof positive that circuit is clear. use only carb cleaner with nozzle.
3. check diaphragms to make sure there's no tears.
4. make sure ignition timing is correct

to adjust idle is to close butterfly completely. then open by 1/2 turn or barely open. this is only a starting position. rpm will probably be too low adjust accordingly.

start with mixture valve 3/4 to 1.5 turns out depending on which model carb. then after engine starts and runs without enrichener. turn low speed mixture screw out until rpm drops, that's your max rich point. then turn screw inwards, rpm should start to raise. keeping screwing inwards until rpm drops. that's your lean point.

adjust screw until you find the highest idle, then open another 1/8 turn. experiment to find spot for acceleration without hesitation. usually that spot will be slightly richer than peak rpm. if low speed jet has been changed, that will change final position.

if screwing low speed mixture makes no difference with butterly almost closed. something is still plugged up.

Bungle,

Thing with the Bing cars is that they are very simple and easy to work with, but non-forgiving if you make even the tiniest misstake...

You need to check:
- if the stubs are propperly seated and sealing (rings in the heads on which you attach the rubbe hose from the carbs)
- that there are NO cracks in the rubber hoses between the carbs and heads; and that they are soft and flexible.
- the steel-lid at the top of the carb-cover/dome is fully seated and that there is no play nor any leakage
- Which version of the covers that you have, with or without a pressure releef(?) hole drilled between the throttle shaft and the vaccuum chamber.
- The choke needs to be fully disassemble and a cast reidue grinded off; it interefers with choke-return
- the paper gasket to the chokes needs to be well greased with good quallity bearing greas to seal proppely.
- The vaccuum membrane must be in good condition, and made of -rubber- (I tested Volvo/Saab semi-plastic replacement membranes... didn't work so well...) - i.e. you are stuck with BMW originals for a fortune each!

The carbs needs to be cleaned with some detergent (petrol, diesel will do ok) and blown Clean with compressed air, especially all holes and jets...

The butterfly valve is not installed propperly from factory, so you may need to re-set them - it may cost you two new shafts and four new screws... the brass screws are loctited in the brash-shaft...
Makes wonders for the operation to get the butterfly-valves operation correctly :)

As for jets and needle settings - look at the german site:
BING Power Systems GmbH | Motoren sind unsere Leidenschaft
Datenblätter | BING Power Systems GmbH

You may have to change jettings slightly due to climate, wear and tear. To get a good idea of what you may have to do you need the US Bing tuning manal:
Bing Manual

It is highly recommended that you do Clean the air-intake as well with detergent and blow it dry. A new air-filer or re-oiled K&N is also highly recommended.

As for the tuning.
I'm used to vaccuum-gauges, but the counter-balansing hydraulic gauge is by far better!
Manometer, Throttle, Bodies, Carbs, Balancer, balancing carburettors, throttle, synchronization - YouTube

If you experience a problem such as the one you described - something is jamming.
A jet, a wire, a valve - someting is not operating correctly.

If you experence a problem with instable idle, rushing Engine as it gets warm, etc - there is an air leakage (9/10 it will be the rubber hose/manifold; 9/10/1 will be the steel-lid and 1/10/1 will be loose stub).
It happens that it is the choke housing that causes all the problems... Darn rare, but can happen.

I have a couple of good articles on carb-tuning and how to build the gadget - how do I up-load them?

Looks like you did it just fine Albert!

My limited experience of problems with Bing carbs is that if the mixture screw makes no difference one of the pinholes which exit on the engine side of the throttle butterfly is blocked or partially blocked - ultrasonic cleaning may be the only sure way of clearing this.