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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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  #1  
Old 30 Jul 2006
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Fuel problem

Hi my xt 600 3aj seems to be not getting enough fuel at about 4500rpm. I want to remove the fuel taps to clean the filters.
I am traveling in Estonia at the moment and dont have any spare gaskets or seals and am worried that if I take the taps off the seals may be damaged and not be able to be re used is this likley to be a problem
Also on my other bike TTR 600 there was a small filter in the carb which used to get blocked causing fuel problems is there a filter in the 3aj carbs again dont want to take them apart unless necessary incase I damage gaskets.
Thanks
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  #2  
Old 30 Jul 2006
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Check first

If the problem is indeed the filters in the taps, check this first by pulling the hoses, opening the taps. If a firm jet of fuel comes out, this is not it.
Further, does the problem only manifest itself at 4500 rpm, and not above this speed, because at higher engine speeds the engine needs even more fuel, so your problem should be worse then.

The 3AJ also has this filter on the float needle seat. The gasket of the float chamber increases in size when wetted with fuel, and decreases when drying. So, when you remove it, just put in the sun to make it smaller to fiit again, or soak in petrol.

From the description of your problem I think it is something else. At what altitude above sealevel are you? It might be, if around 1000 m, that the compensation valve has opened already but overcorrects a bit.

Auke
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  #3  
Old 2 Aug 2006
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Hi Bolla,

Are you sure it's not just your air filter clogged up.
It's easier to clean an air filter that chase possible fuel supply problems.

Good luck

Mark
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  #4  
Old 2 Aug 2006
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Hi and thanks for replys
The problem seems to appear if travelling at 4500 for more then about 20 minutes some times it will get better if I increase the revs but only for a little while then probem wll continue at above 4500.
The last time it happened I had filled up with fuel, started riding when problem started again I stopped filled up again. I had used 7 litres of fuel and every thing seemed ok again for about 60km .
I will cheak the air filter and also the breather in the fuel cap tommrow I have a tank cover and tank bag fitted and the fuel cap is very tight the cap is also half coverd by the tank bag.
I am riding at pretty much sea level at the moment and is not a problem to keep the speed down for a few days .
Thanks John
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  #5  
Old 2 Aug 2006
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I dont think this is a fueling issue. Its too RPM specific.....

What exactly is the problem, if the bike losing power or cutting out ??

What gear or throttle positions does the problem occur and what helps the problem ??

remember.... Throttle position is NOT rpm.

It sounds like a carb, tuning issue to me which suggests your feeling of "fuel starvation"
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Old 2 Aug 2006
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Quote:
Originally Posted by tedmagnum
I dont think this is a fueling issue. Its too RPM specific.....

What exactly is the problem, if the bike losing power or cutting out ??

What gear or throttle positions does the problem occur and what helps the problem ??

remember.... Throttle position is NOT rpm.

It sounds like a carb, tuning issue to me which suggests your feeling of "fuel starvation"
The bike does not cut out but will just miss a beat like it is coughing, some times it will clear if I go past 4500 but only for a little while.
There will be less power if I want to over take slower traffic, it will have less power and hesitate when I increase the throttle but if I stop and put a bit more fuel in it seems ok for a while so not sure if its petrol or if the engine just cools down a bit when I stop to refuel or a problem with the breather in the petrol cap .I had a look at the petrol cap and all seems ok.
It allways happens in top gear after I have been at constent speed for a while.
Thanks john
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Old 2 Aug 2006
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hmmm !! Hard to diagnose this one !!

take the cap off and check the breather is clear... give it a blow through to check.

Pull off the fuel line to the carb and see if the fuel flows freely too, theres no need to take the taps off unless the fuel isnt flowing.

What your suggesting does sounds like a possible fuel lock due to vacumn.

How long has this problem been going on for ?? Are you running the correct grade fuel ??
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  #8  
Old 2 Aug 2006
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I took the fuel cap apart tonight and all seemed ok.
I have been using the fuel pump with 95 on it .
When I am at home I just use any unleaded fuel as am just riding around town and seems fine. Since I have beeen traveling have allways gone for 95 should i try the higher grade.
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Old 2 Aug 2006
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well... if its been running on 95 for years then its probably fine as the XT has a low compression engine anyway.

If your sure that the tank is breathing properly (also try riding with the fuel cap very lose and see if it helps- dont lose it though)

Has the tank got a seperate breather bike ? is that breathing correctly ??

Clean out your air filter too, these are all simple checks that you have to do before diagnosing a more serious problem.
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  #10  
Old 2 Aug 2006
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I've been having a similar hickup as you described, It seemed to be worse if I was driving in heavy winds. I found that servicing the air filter helped and recently I replaced the vent tubes on the carb so they extend all the way down behind the engine, the old ones were cut off really short. Have not put a lot of miles on yet but It has not hicuped since.
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  #11  
Old 11 Aug 2006
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Thanks for replys
I have cleaned air filter, changed spark plug checked fuel supply from taps by removing pipes and was ok cleand the mesh filter in carb, removed fuel cap when bike was runnig bad and continued riding still ran bad.
The bike will run ok but if I stay at constant speed above 90kph or about 4500 rpm it will start to splutter and hesitate if I increase the throttle it will not accelarate. If I continue to ride it will get worse at lower revs down to about 3500 if I stop for 10 minutes I can usually pull away and bike will rev freely up to 6000rpm but only for a short while. If I am riding on twisty roads or alot of start stopping there is no problem.
When the bike is running bad and I close the throttle I often get a back fire I think this is comming through the carbs.
I have 2000 kms to ride home so would like to sort this problem
So any ideas please
Thanks
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  #12  
Old 11 Aug 2006
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ill have a think on this one...

In the meantime, most this problem with as much detail as possible on www.visordown.com in the workshop section..

Theres some excelent mechanics on there and you will get answers in minutes rather than hours.

im tedmagnum on there.

You may have an obstruction in your carb or perhaps the diaphram is damaged. I woudl suggest stripping the carb and giving it the full treatment.

This problem can be down to the CDI too. It does sound like a starvation of either fuel or air at open throttle.
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  #13  
Old 14 Apr 2007
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How did the story end?

Hi Bolla.

Im an 3AJ -88 owner with some of the same symptoms as you describe.

Did you eventually sort out the problem?
What's the solution?

Norway
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  #14  
Old 24 Apr 2007
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similar fuel system issue

I was some time ago experiencing a similar issue with my XT600e.
After about 15 minutes of riding at high revs (4000 RPM or so) the buike would surge and splutter in the same way as they do when your runing out of fuel. (yep just before you cut over to the reserve).
I tried putting a couple of fuel system cleaners in to the bike, even ran it down to reserve and put a full bottle of cleaner into the tank then ran it for 30KM, therefore almost to empty.
I do think this improved the issue but a few thousand KM later it was doing it again.
I then stripped the carby(s). The carb was dirty but not significantly. I therefore adjusted the float, this did resolve the issue..
Another thought.
I recently stripped the motor, she's old and tired, time for a rebuild.
When I pulled the carbs off I found the carby to head flanges were both split. It's possible that after sustained high speed running these may get very hot and possibly leak more air I guess..
Here's the part numbers
43F-13586-01-00 JOINT, CARBURETOR 1 (Carby to Gead Flange) $82.68 AUD
1VJ-13596-00-00 JOINT, CARBURETOR 2 (Carby to Gead Flange) $112.31 AUD

Or in my case the split flanges may have been the entire cause, adjusting the float may have just been a temorary resolution.
Does anyone know of a method to rebond the rubber flange to the alloy spigit. They are quite an expensive little item.
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  #15  
Old 26 Apr 2007
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Quote:
Originally Posted by Norway View Post
Hi Bolla.

Im an 3AJ -88 owner with some of the same symptoms as you describe.

Did you eventually sort out the problem?
What's the solution?

Norway
Hi Norway
I have sorted the problem
I got an after market stator from Electrex when this was fitted the top end improved and the missfire was gone I could hold the throttle open no problem but the bike felt very low on power when pulling away from stand still untill it got to about 3000 rpm.
I had also bought another 3AJ which had an after market stator. I swapped the complete side casing stator and pick up coil and my bike was fixed.
I think the pulse coils were breaking down when they got hot this was fixed when I replaced the stator but the pick up coil was also breaking down at low revs.
I am now trying to find a second hand pick up coil for a 3AJ as Yamaha only sell them complete with the stator at about £400
Good luck with your bike
Its alot easier to diagonise these problems if you have another XT to swap parts with
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