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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 17 May 2007
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xt600 weird starting problem

After getting my needle and set fixed my problem now is the motor will not start when its cold i have to use aero start to fire it up. Once its warmed up then i can stop it and restart it with out probems. Whats the deal? Choke seems to be fine(no sticking)

It also has a hickup (backfire)while its running once every few secs.
Can any body help out?

niko.
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  #2  
Old 17 May 2007
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Read on

Hi Niko,
You are where I was about 2 months ago; new bike (to me) and an issue with poor starting and a newbie on the HUBB.
I am no expert on the engine and I don't want to try to diagnose your problem but I do advise you to read the back-threads in this technical forum for some great advice from others who do know what they are talking about! It sorted me out. It is a simple design and one of the guys out there on this forum has seen it before. Look at the threads for both the XT and the TT (my bike) - the engines are much the same.

For quite some time I thought my bike had a fuelling problem but it turned out to be electrical (the earth and, maybe, a dirty spark plug).

Thing is to change one thing at a time and look for the effect that has, be methodical and patient also; if you have a spark and good fuel then it will fire up and then you can adjust/fine tune.

Hope this helps,

Dave
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  #3  
Old 17 May 2007
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Idle mix

If before the replacement of the needles etc (why did you do that anyway, never seen an XT where that was necessary), the engine ran, and you did not change anything else, I'd guess the idle mix is now too lean, as you have installed new, not worn jets.
The easy fix is to adjust the idle mix, see earlier posts.

Always a good idea to have a good, new spark plug BTW.

If the above doesn't work, start worrying about the following:
Further, to install new jest you have taken the float bowl off. You sure you did not bent the float or something?
Is enough fuel arriving in the float bowl?
Are the connections between carb and cilinder head airtight?

Auke
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  #4  
Old 17 May 2007
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thanks guys for replying, first off its got a new battery(drycell) a new spark plug, and new needle and seat( old one was worn out and had stuck)
the float is ok and not bent and the rubber manifolds are good.

Now it could be an earth problem(will test that out tomorrow)
One thing it does do once its running is if i put my hand over the air cleaner hole the motor starts to really rev this normal??

Or maybe the spark plug gap is not right or idle screw not adjusted right(its 2 turns out now)

niko.
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  #5  
Old 17 May 2007
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Idle screw

Niko,
My idle screw is set at near enough 3 turns out from fully in; there are two different values in the cd information that I have and this is the average of those recommendations; all of this for the 3AJ engine in a TT600R. Set at 2 turns it would be running lean I guess, but I don't know how sensitive the idle screw is to one whole turn!!

Cheers,

Dave
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  #6  
Old 17 May 2007
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Choke

Hi,

in the swimmer chamber is a channel where the pipe for the choke fits in. I check that channel with some water drops and look if they make it through the channel into the chamer. If the channel is blocked, this is often the problem if the XTs don`t like to start when it is cold. This happens often after bikes did park for a long time with fuel in the carb.

regards Thomas

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  #7  
Old 17 May 2007
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again thanks guys , i'll try the idle screw at 3 turns and see how that goes.
One thing ive noticed with the spark plug its blackish not gray once i remove it this means its running rich?

Also motor has bee sitting awhile with out been started so water could be an issue.
niko.
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  #8  
Old 17 May 2007
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Niko,

I would not want to send you down a dead-end road! Everything so far sounds like a fuel problem (but it could be electrical!!)

As aukeboss says, have a look back (do a search in here) at the past threads about setting the idle screw; there is loads of good information for the XT and TT (so look for both) with lengthy descriptions of what to do.

Good luck. If you are systematic and change one thing at a time and look for what happens it will get sorted out,

Cheers,

Dave
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  #9  
Old 18 May 2007
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well today i tried to start it again with the same problem. I had a look at the spark and it was there and didnt look to strong(not blue)
I went over the earth conections and made sure they were clean.
Once it started it again with aerostart and once warmed it ran(still backfiring) Took it for a drive and had a few misses when i gave it a boot full.
Next thing im going to get rid of the old fuel(98oct) and put some new 95 in.
See how that goes.

niko.
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  #10  
Old 18 May 2007
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Plugs and things

Again, as mentioned before, it's worth fitting a new spark plug - I am getting a spark with my old one but I don't know how old it is so I have a brand new one ready to fit the next time I have the tank off (and that won't be long!!).
It's an Irridium type which are supposed to be better at starting as well as running and they don't cost too much here in UK.

My earth problem was sorted by cleaning the back of the coil where it touchs the frame - it was dirty/greasy - once that was sandpapered the bike was much easier to start!!

Cheers,

Dave
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  #11  
Old 18 May 2007
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sparkplug is a new one, and i did the same sanding the area under the coil mounting.

One thing Dave, what gap did you use on the plug?

niko.
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  #12  
Old 18 May 2007
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0.8 mm

Hi again Niko,
The recommendation is 0.8 - 0.9 mm. I used 0.8mm on the NGK DPR98EA plug.

I was not sure if cleaning the plug made any difference as well as "re-earthing" the coil - I did both at the same time, hence my comment about changing one thing at a time and checking for the result.

Cheers

Dave
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  #13  
Old 20 May 2007
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thanks Dave, ive set that gap right, set the idle screw to 2.5 (3 no good)turns and took it for a test drive and well its till not happy. Its fine running around in 1st and 2nd but as soon as you floor it it bogs down bad.
Must try again.

niko.
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  #14  
Old 20 May 2007
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`One thing it does do once its running is if i put my hand over the air cleaner hole the motor starts to really rev this normal??`

No, not normal. It means two things: 1) the idle mix is way, way too lean and 2) the idle speed setting is way, way too high.
If you block part of the air intake, apparently the mix gets better ...., ie richer.

When you said you replaced needle and seat, did you mean the float needle and seat or the needle and jets in the carb throat(s)?

Just presuming you mean the float needle, I'd go back to the float level setting, check that one by either removing the float bowl and measure or by using the way described in the manual with a piece of transparent hose.
Or the check the other possibilities for the lean mixture: false air drawn in somewhere, blocked jets etc.

Auke
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  #15  
Old 20 May 2007
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thanks for that,i'll have another look tomorrow does sound like theres must be another air leak somwhere. Yes you were right i did replace the float needle/seat. I did use the air compressor to clean the inner workings of the carbie so im sure the jets are fine.
Could be the manifold rubber inlets leaking.
So to richen up the mixture the idle screw needs to wind out more to 3.5 will try that tomorrow too.

thanks,
niko
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