XT600E carb tuning. Any bright ideas?

[Mr Skid]

I'm currently looking to improve the economy of my XT. They're reputed to return 20km/L with normal useage, and I've heard of 26km/L on the open road.

At the moment I'm getting between 15.5km/L and 17km/L fuel economy, depending on if I thrash it or not. Usually I'm around 16km/L.

The bike has 66,000km on the clock, and I'm not sure if there's been any work done on the carbs since new. I have dismantled and cleaned them and they looked to be in good condition internally.

I suspect that there may be wear in the needles and needle jets and possibly the jet/valve that the float actuates.

Any thoughts whether this would be a reasonable diagnosis given this bikes milage?

Can anyone with a XT600 offer their fuel economy figures?

Alternatively can anyone suggest a methodology to use to diagnose the issue?

[Brian d marge]

does it have the single or twin carb set up???

kind regards Stephen

[Motu]

Have a close look at the secondary diaphram - if it doesn't lift the piston high enough then the air speed across the jet increases,sucking in more fuel.Sometimes they sorta get too big with age and don't fit onto the carb body so well,sometimes they are too still....and holes of course.

[Mr Skid]

does it have the single or twin carb set up???

kind regards StephenIt's a twin carb setup. The left carb is a slide carb, and the right carb is a cv carb.

the slide carb operates full time, and the cv carb starts to operate around 1/4 throttle. The right carb shares a common float bowl with the slide carb.

Here's a link to an exploded diagram of the carbs.
http://www.imagessite.com/OEM_Images/Yamaha_db_images/90XT600EAB1.gif

[F5 Dave]

presume you have been to the Factory (http://factorypro.com) website. They make replacements emulsion tubes for many bikes. My RF ones were ovalised at 40k & a single should be worse.

[Brian d marge]

Yup I would agree with dave there ..First I would make sure everything is up to scratch ..chain sprockets etc ,,,and with a new plug ,,,start testin

With a slide carb ,,,I use a chopstick cut to length so that you cant open the throttle anymore ,,,,
For example ,,I need to set up my bike at 1/4 throttle ..so I cut a chopstick so the slide can only open a few mm..

go for a ride ,,do a plug chop ( kill engine and coast to a halt ,,remove plug .....I install a spare to ride home with actual plug in pocket with that little bit of cardboard to protect the colour ..)

Well there you go ..

Depends what you want ...but if you want punch of the line jet the pilot and needle of the slide carb

Feul economy ,,,,,drop the float height a bit ,,,,,and if I think Motu is saying that the diaphram is old and the slide isnt lifting ,,,...if the needle and emulsion tube is worn ,,then the cv carb will tend to go rich on you ,,,,

one last thing ,,,,,If you use a stronger spring in the CV it will tend to lean out the mixture at cruising and max rpm ,,,

Kind regards Stephen

! though make sure all compnents up to scratch before trying to tune ,,,otherwise you chase your tail .....

sorry hope this is of some help ,,they arent tricky ,,,but Its difficult to explain in a short email

[XTC]

My XT has never had better than 18km/l from new.

[MacD]

My XT has never had better than 18km/l from new.

I had about the same from my SRX600, same dual carb/engine set-up.

[XTC]

They say that the XT660R gets better economy from it's fuel injection... Same with the F650GS. Think i'll get the 660 in about 90,000km's time. :ride:

[Mr Skid]

presume you have been to the Factory (http://factorypro.com) website. They make replacements emulsion tubes for many bikes. My RF ones were ovalised at 40k & a single should be worse.Excellent! They have a 'drop-in' kit available for the XT600 listed at ~USD$79.95.

Supposedly it's a direct replacement for OEM parts, I'll email them to enquire exactly what bits it contains. Yamaha OEM prices for for 2x jet needles and 2x emulsion tubes is NZD$203.70..


They say that the XT660R gets better economy from it's fuel injection... Same with the F650GS. Think i'll get the 660 in about 90,000km's time. :ride: I was talking to a chap on Sundays ride with a F650. Apparently it returns 33km/L. I think my next ride will have to be fuel injected.

Thanks for your fuel economy figures too.

[Mr Skid]

Unfortunately it looks like Factory Pro are out as an option, here's the email I recieved from them:


the kit we have for this bike is for the single carb version and comes
with an adjustable needle, main jets of 125 and 128 and replacement
float bowl screws. We dont offer emulsion tubes for this bike. If the
picture on our website shows any additional parts, its because we use 1
generic picture for all ti pro kits.

This kit sells for $69.95 actually, and the shipping would be $22.50 US
global express.
That's got me slightly confused, as it's listed as a kit for '89-'95 XT600's and as far as I'm aware they were all twin carb'd. Mebbe the kit only contains parts for the CV carb..

It's amazing how much of an orphan the carbs are on this bike, considering how long it's been in production.

I think the options so far are replacing the suspected worn parts with OEM, or swapping them out for a set of gpx250 carbs, which the SRX6 tuning sites suggest are a more or less direct replacement..