Go Back   Horizons Unlimited - The HUBB > Technical, Bike forums > Yamaha Tech
Yamaha Tech Originally the Yamaha XT600 Tech Forum, due to demand it now includes all Yamaha's technical / mechanical / repair / preparation questions.
Photo by Mark Newton, Mexican camping

I haven't been everywhere...
but it's on my list!

Photo by Mark Newton,
Camping in the Mexican desert

LinkBack Thread Tools Display Modes
Old 1 Jan 2007
*Touring Ted*'s Avatar
Contributing Member
Veteran HUBBer
Join Date: Jul 2005
Location: Wirral, England.
Posts: 5,666
Why does the XT have twin carbs ?

Just thinking why ???

Iv had loads of large singles and none of them have had twin carbs. I know they dont have many problems but surely 2 is less reliable than 1. Iv had excelent fuel economy on single carbs too.

So why cant the XT function on a single carb ?

Can anyone explain the whole twin carb set up to me ?

Thanks guys
Did some trips.
Rode some bikes.
Fix them for a living.
Can't say anymore.
Reply With Quote
Old 2 Jan 2007
Registered Users
HUBB regular
Join Date: Jul 2006
Posts: 52
Well, consider that the XT and the XR 600s are very similar bikes. I brought my XT into a shop with an XR enthusiast mechanic and he asked me what year XR it was. In any case, they were competing models and both ran dual carbs. The simple answer is "airflow," as for the real answer, I don't know.
Reply With Quote
Old 2 Jan 2007
Registered Users
HUBB regular
Join Date: Aug 2006
Location: UK
Posts: 45
I believe the answer is something like this .....

CV Carbs are more efficient but suffer some problems on big singles.
1) They do not perform well at low revs when the venturi vacum is inconsistant and "pulseing" with each stroke
2) Again, at low revs, they do not respond to rapid opening of the throttle, because they rely on the venturi vacum.

So, Yamaha fitted a slide carb to deal with small throttle openings, and a CV to provide more efficient carburation when the throttle is wider open.
.... an attempt to have the best of both worlds.

Fow my part, I would rather just have a single big slide carb, my Suzi SP400 never seems to have a problem. But then, I would rather the XT had a nice heavy flywheel on the crank rather than that nasty chain driven counter weight that gets all "confused" at low revs
Reply With Quote
Old 4 Jan 2007
Registered Users
HUBB regular
Join Date: Sep 2006
Location: Western NC, USA
Posts: 25
the XT500 had one big carb.

mine worked well for 20+ years, but I heard they had lots of low speed stall issues, opening the big carb too fast lost flow and dropped the engine.


on the XT550, they went to a big carb with a smaller carb for low speed ... like a pilot valve next to a flow valve. the small carb would handle idle to 25% the bigger carb started opening around 20% and went on to 100%.

they also went to the 4 valve head for better flow.

with the monoshock, they also had to maintain space, going from a single carb to a 2-to-1 intake to feed the two valve head requires more room.
Do one thing every day that scares you. Baz Luhrmann
Women and cats will do as they please, and men and dogs should relax and get used to the idea.
An armed society is a polite society. Manners are good when one may have to back up his acts with his life.
Robert A. Heinlen
Adventure is discomfort recounted at leisure. Flash / GSWayne
Chrome don't get ya home. Rob Nye
1995 XT600E - 1992 TDM850 - 1984 GPz750
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

Similar Threads
Thread Thread Starter Forum Replies Last Post
Africa Twin fuel economy LordStig Honda Tech 12 18 May 2006 23:08
How do you keep Boxer carbs tight? locodog BMW Tech 3 5 May 2004 15:21
EFI vs CARBS TONY BRAICO Which Bike? 6 6 Jan 2003 02:30
found a twin in usa! tomrsewell Honda Tech 4 27 Oct 2001 11:46



Thinking about traveling? Not sure about the whole thing? Watch the HU Achievable Dream Video Trailers and then get ALL the information you need to get inspired and learn how to travel anywhere in the world!

Have YOU ever wondered who has ridden around the world? We did too - and now here's the list of Circumnavigators!
Check it out now
, and add your information if we didn't find you.

Next HU Eventscalendar

HU Event and other updates on the HUBB Forum "Traveller's Advisories" thread.
ALL Dates subject to change.



  • Queensland is back! Date TBC - May?

Add yourself to the Updates List for each event!

Questions about an event? Ask here

HUBBUK: info

See all event details

World's most listened to Adventure Motorbike Show!
Check the RAW segments; Grant, your HU host is on every month!
Episodes below to listen to while you, err, pretend to do something or other...

2020 Edition of Chris Scott's Adventure Motorcycling Handbook.

2020 Edition of Chris Scott's Adventure Motorcycling Handbook.

"Ultimate global guide for red-blooded bikers planning overseas exploration. Covers choice & preparation of best bike, shipping overseas, baggage design, riding techniques, travel health, visas, documentation, safety and useful addresses." Recommended. (Grant)

Ripcord Rescue Travel Insurance.

Ripcord Rescue Travel Insurance™ combines into a single integrated program the best evacuation and rescue with the premier travel insurance coverages designed for adventurers.

Led by special operations veterans, Stanford Medicine affiliated physicians, paramedics and other travel experts, Ripcord is perfect for adventure seekers, climbers, skiers, sports enthusiasts, hunters, international travelers, humanitarian efforts, expeditions and more.

Ripcord travel protection is now available for ALL nationalities, and travel is covered on motorcycles of all sizes!


What others say about HU...

"This site is the BIBLE for international bike travelers." Greg, Australia

"Thank you! The web site, The travels, The insight, The inspiration, Everything, just thanks." Colin, UK

"My friend and I are planning a trip from Singapore to England... We found (the HU) site invaluable as an aid to planning and have based a lot of our purchases (bikes, riding gear, etc.) on what we have learned from this site." Phil, Australia

"I for one always had an adventurous spirit, but you and Susan lit the fire for my trip and I'll be forever grateful for what you two do to inspire others to just do it." Brent, USA

"Your website is a mecca of valuable information and the (video) series is informative, entertaining, and inspiring!" Jennifer, Canada

"Your worldwide organisation and events are the Go To places to for all serious touring and aspiring touring bikers." Trevor, South Africa

"This is the answer to all my questions." Haydn, Australia

"Keep going the excellent work you are doing for Horizons Unlimited - I love it!" Thomas, Germany

Lots more comments here!

Five books by Graham Field!

Diaries of a compulsive traveller
by Graham Field
Book, eBook, Audiobook

"A compelling, honest, inspiring and entertaining writing style with a built-in feel-good factor" Get them NOW from the authors' website and Amazon.com, Amazon.ca, Amazon.co.uk.

Back Road Map Books and Backroad GPS Maps for all of Canada - a must have!

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 R80G/S.

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 all over the world with the help of volunteers; 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, or ask questions on the HUBB. 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.

All times are GMT +1. The time now is 03:32.