Go Back   Horizons Unlimited - The HUBB > Technical, Bike forums > BMW Tech

BMW Tech BMW Tech Forum - For Questions specific and of interest to BMW riders only. Questions comparing which bike is best etc go in the "Which Bike" forum.
Contact Overland Solutions for all your custom modifications and setup for overland travel.

Parts & accessories for adventure touring motorcycles including GPS mounts, panniers, luggage, protection, dry bags, camping gear, tools, books & DVDs.

LinkBack Thread Tools Display Modes
Old 6 Mar 2002
Contributing Member
Veteran HUBBer
Join Date: Jan 2001
Location: Gerrards Cross, Bucks, UK
Posts: 150
R100GS running rough

My R100GS is not running so well at the moment and I need some ideas on what might be causing the problem.
The bike idles and accelerates fine, but when I get moving and hold it in the low to mid rev range it runs very rough. The right hand carb is running too rich (sooted spark plug and exhaust) but I can't seem to solve this by adjusting the mixture screw.
I overhauled the carbs with new O rings a short while ago, but not the diaphragms as they seem fine.
I balance the carbs by ear because I'm on the road and don't carry a 'carbtune' or similar, so they may not be perfectly balanced. However, I also balance my girlfriend's R80ST by ear and it runs like a dream...
Does anyone have a good idea what might be wrong? I'm leaning towards the float needle being worn.
no pipe, no slippers
Reply With Quote
Old 6 Mar 2002
mmaarten's Avatar
Gold Member
Veteran HUBBer
Join Date: Sep 2001
Location: South America
Posts: 579

I don't know the BMW very well (actualy not at all), but I guess the mid-range is not affected by the mixture-screw. This screww usually covers 1/8 part of the carb-opening.
The rest is up to the needle and main-jet, so your idea about changing the needle could be a good one.
It could also be the jet itself, I would always change them as a pair. You could try putting the needle a click lower.

Good luck

Reply With Quote
Old 7 Mar 2002
Registered Users
Veteran HUBBer
Join Date: Jan 2001
Location: Nottingham, UK
Posts: 151
I'm no expert - but from what you say it could be a problem with one of the jets that's in use for your throttle setting you're having problems with.

My Haynes manual says that "1/8 throttle setting is controlled by the pilot, 1/8 to 1/4 by the throttle cutaway, 1/4 to 3/4 by the needle position and from 3/4 to full by the size of the main jet.

From your description it sounds like the problem is occuring at the point when needle position is critical. Perhaps this needs investigating and making sure both needles are set-up correctly and aren't worn (they go oval after high mileage)- I seem to remember that if they are removed, the clips that hold them in place need to be put back in the correct groove for both carbs.

Haynes also says the following (under "Poor running or lack of power at high speeds"):

To check that the main jet isn't blocked. Water in the fuel can also be a problem. Condensation inside the tank can gradually create enough water that'll sink to the bottom of the tank and cause running problems (unlikely though). Air bleed holes could be blocked. Check the fuel hoses for kinks or blockages or the diaphragn could be split (hold it up to the light).

Hope some of this helps - most of these suggestions come out of Haynes... Perhaps you have a manual and have already tried these things? Good luck - I know from personal experience how frustrating carb problems can be - it might be worth getting them checked out with gauges, if this is possible? Diagnostic equipment really helps solve these sort of problems I think...

Fuzzy Duck
(I'm quackers about bikes)
Fuzzy Duck
(I\'m quackers about bikes)
Reply With Quote
Old 7 Mar 2002
John Ferris's Avatar
Gold Member
Veteran HUBBer
Join Date: Feb 2001
Location: Reno,NV,USA
Posts: 564
Hi Harvey, Cleen out your carb as much as possable without taking them off the bike.
Check your diaphram and the jet needle.
Sometimes the jet needle clips can wear a slot in between the clip positions.
I am not sure which carbs you have. some jet needles go in from the bottom of the slide and you turn-push-pull to adjust them, some go in from the top of the slide under a screw in the center tube of the slide. I think the needle jet is the mid-range mixture
Let us know what you find. Good luck. John
Reply With Quote
Old 9 Mar 2002
Registered Users
Veteran HUBBer
Join Date: Apr 2001
Location: Canada and the Alps
Posts: 125
Check your floats and float needles.

New floats weigh in at 12 to 12.5 grams. The rubber tip of the float needle may be getting hard and not sealing as well.

Correct float level adjustment is achieved when the floats are parallel to the mating surface of the float bowls on the carbs, at which point, the needles should be sealing.

Did you do a quick overhaul, or did you take the carbs apart completely?

Did you clean the area of the atomizer and needle jet. These items are held in place by the main jet holder. Notee that thye are difficult to install unless the carb is upside down. This area can really get clogged.

Is one choke plate not returning to the "off" position. Rememeber, these are pulled back by springs that may be weak and if the shaft is sticking, you are driving with the choke "on". Check by manually pushing down on the levers.

Let us know what the problem and solution was.
All the best,

Alex's BMW Motorcycle & Global Touring Page
SmugMug Site
Alps Motorcycle Tours - Priced Right

- If motorcyclists claim to be individuals, why then do so many of them ride in packs?
Reply With Quote
Old 2 Apr 2002
Contributing Member
New on the HUBB
Join Date: Apr 2002
Location: Bärenklau, Brandenburg, Germany
Posts: 9
hi harvey,

i dont know if you have fixed your 'running rough' problem in the meantime. but if you dont find anything about the carbs, here's another hint:

i'm not sure what kind of ignition your 89 r100 has, but it might be possible, that the fixing between the camshaft and that part, that tells your ignition to ignite (it depends on model and year but should be a so called Hall-Geber (in german)), is somewhat worn out. with the result that also both ignition-signals are still exactly 180 deg. apart, one is little too late and the other too early.

if you havent fixed the problem yet send me a mail with information about your ignition-system, and we get into it.

long may you run
Reply With Quote
Old 18 Apr 2002
Contributing Member
Veteran HUBBer
Join Date: Jan 2001
Location: Gerrards Cross, Bucks, UK
Posts: 150
Many thanks for all the advice. I tried various different things and eventually narrowed it down when the HT lead failed on the way back from the Tibetan border! A new lead seems to have solved the problem, but I need to get out of Bangkok before I can really tell.

no pipe, no slippers
no pipe, no slippers
Reply With Quote

Currently Active Users Viewing This Thread: 1 (0 Registered Users and/or Members and 1 guests)
Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


NEW! HU 2015 Motorcycle Adventure Travel Calendar is now available! Get your copy now for some terrific travel inspiration!

HUGE, 11.5 x 16.5 inches, beautifully printed in Germany on top quality stock! Photos are the winning images from over 600 entries in the 9th Annual HU Photo Contest!

Horizons Unlimited 2015 Motorcycle Adventure Travel Calendar.

"The calendar is magnificent!"

"I just wanted to say how much I'm loving the new, larger calendar!"

We share the profit with the winning photographers. YOU could be in the HU Calendar too - enter here!

Next HU Eventscalendar

See all events


Latvia to Australia, an inspirational 5 month journey full of unexpected adventures!

Renedian Adventures

Renedian Adventures

What others say about HU...

"I just wanted to say thanks for doing this and sharing so much with the rest of us." Dave, USA

"Your website is a mecca of valuable information and the DVD series is informative, entertaining, and inspiring! The new look of the website is very impressive, updated and catchy. Thank you so very much!" Jennifer, Canada

"...Great site. Keep up the good work." Murray and Carmen, Australia

"We just finished a 7 month 22,000+ mile scouting trip from Alaska to the bottom of Chile and I can't tell you how many times we referred to your site for help. From how to adjust your valves, to where to stay in the back country of Peru. Horizons Unlimited was a key player in our success. Motorcycle enthusiasts from around the world are in debt to your services." Alaska Riders

contest pic

10th Annual HU Travellers Photo Contest is on now! This is an opportunity for YOU to show us your best photos and win prizes!

NEW! HU 2014 Adventure Travel T-shirts! are now available in several colors! Be the first kid on your block to have them! New lower prices on synths!

HU 2014 T-shirts now in!

Check out the new Gildan Performance cotton-feel t-shirt - 100% poly, feels like soft cotton!

What turns you on to motorcycle travel?

Global Rescue, WORLDwide evacuation services for EVERYONE

Global Rescue is the premier provider of medical, security and evacuation services worldwide and is the only company that will come to you, wherever you are, and evacuate you to your home hospital of choice. Additionally, Global Rescue places no restrictions on country of citizenship - all nationalities are eligible to sign-up!

New to Horizons Unlimited?

New to motorcycle travelling? New to the HU site? Confused? Too many options? It's really very simple - just 4 easy steps!

Horizons Unlimited was founded in 1997 by Grant and Susan Johnson following their journey around the world on a BMW R80 G/S motorcycle.

Susan and Grant Johnson Read more about Grant & Susan's story

Membership - help keep us going!

Horizons Unlimited is not a big multi-national company, just two people who love motorcycle travel and have grown what started as a hobby in 1997 into a full time job (usually 8-10 hours per day and 7 days a week) and a labour of love. To keep it going and a roof over our heads, we run events (22 this year!); we sell inspirational and informative DVDs; we have a few selected advertisers; and we make a small amount from memberships.

You don't have to be a Member to come to an HU meeting, access the website, the HUBB or to receive the e-zine. What you get for your membership contribution is our sincere gratitude, good karma and knowing that you're helping to keep the motorcycle travel dream alive. Contributing Members and Gold Members do get additional features on the HUBB. Here's a list of all the Member benefits on the HUBB.

Books & DVDs


All the best travel books and videos listed and often reviewed on HU's famous Books page. Check it out and get great travel books from all over the world.

Motorcycle Express for shipping and insurance!

Motorcycle Express

MC Air Shipping, (uncrated) USA / Canada / Europe and other areas. Be sure to say "Horizons Unlimited" to get your $25 discount on Shipping!
Insurance - see: For foreigners traveling in US and Canada and for Americans and Canadians traveling in other countries, then mail it to MC Express and get your HU $15 discount!

All times are GMT +1. The time now is 14:56.