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Yamaha Tech Originally the Yamaha XT600 Tech Forum, due to demand it now includes all Yamaha's technical / mechanical / repair / preparation questions.
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Old 29 Jun 2010
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84 XT600 poor fuel mileage. (now with pictures) 56k=death

this one is new to me.

my 84 XT seems to suck down about a gallon of gas in 20 miles, gentle riding, no hard on the throttle runs or anything, just gentle acceleration.

I know the carb is clean, pretty sure float height is right, only thing I saw is it looks like the secondary carb has had some sort of mod where someone attempted to enlarge the hole a little, and its all kinds of a mess. now I dont THINK this could cause the issue, but I've been surprised before. when I can I'll take a picture of the inside for anyone ineterested.

I'm just looking to know if this fuel mileage is normal or not though. sure doesnt seem it should be.

Last edited by bobthebiker; 1 Jul 2010 at 04:20.
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Old 29 Jun 2010
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20 mpg that's unreal!
Mine's a 85 bike,I reckon it does about 60mpg.
What colour's the plug? Have you got a fuel leak?!
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Old 29 Jun 2010
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Thats 3.0L 4x4 mpg

You need to pull the carbs and 'reset' everything back to standard. The only way i can see the mpg going on is that the fuel/air mix is shot and/or both carbs are working all the time at the same time.

Can you smell fuel when its running ? is it 'pulling' through the revs ok or is it spluttering or backing off?

Pictures would be nice.

on the other hand, do you have a locking petrol cap? are there teens with scooters living near you hahahah

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Old 29 Jun 2010
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I'm pretty confident fuel theft isnt an issue, as I rode i 20 miles and burned a gallon roughly.

Soon as I have an opportunity, I"m going to reset the carbs, but I'm not sure exactl what must be done.

plug looks SLIGHTLY rich but not excessively. while riding, theres a slight surge at 3000-3500 rpm. Generally though I can twist the throttle and this thing will either lift the front end, or leave a trench behind me, or both with no hassles.

Is there a way to know if both carbs are working full time?
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Old 29 Jun 2010
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The first carb with the slide is there for low end running. the second card is of the CV Vacuum type. This CV carb comes into opperation when there is a high demand from the engine.

This will happen approx around 4-5000 rpm.

Seeing as the plugs are a little dark and its gulping fuel, i think i would still look at both carbs working 'all' the time rather than slide carb first then the cv.

A thing I sometimes do, the older the bike the more i do it, is run the bike then tap the carb bowls and see if the engine note changes, misfires, or revs. then take it upto 3000rpm and try again. it may give you an indication that things may be stuck/worn.

However either way, your going to have to pull them in the end.

There are pdf files of the xt all over the web so you should be able to get one for the carbs.

Good luck and get back when you have more info, photos or carbs out.

I have a pair in a box i think, will go have a look over them and see if i can give any pointers.

Do you have a fuel pump on your xt?

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Old 29 Jun 2010
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No fuel pump on my bike. the CV carb though, I have to get a pictue, bt the pressed in jet, looks like someone did make an attempt to enlarge it for some unknown reason. I'm probably gonna need a whole new CV carb honestly, but I'm not certain yet.

I've been through the carbs before, and not noticed anything dirty, or out of place/spec, but at the time, I hadnt looked at float height, as I have no tool to measure that.
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Old 1 Jul 2010
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ok, I pulled the carbs off, the jet on the right side sure does look like some less than smart hick decided to "rejet" the thing his way.

Does anyone have another one of these jets I could snag up for cheap? it sure looks like this one is FUBAR.

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