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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 4 Apr 2007
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Inconsistent tickover on 34L XT

Hi,
I'm currently heading along the North of the Niger from Niamey to Timbuktoo via Gao and Bourem; I've had a few ignition problems and have replaced the CDI on the bike twice and the coil once; occasionally it ticks over just fine, then 10 minutes later it will be surging and eventually will cut out. The bike has also started back-firing quite badly on the overrun. Does anybody have any ideas how to rectify this?
Cheers.
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  #2  
Old 4 Apr 2007
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I would check the carb' if you are getting surging - partially blocked pilot jet, air leaks around inlet rubber/carb joint, poor seating of the float needle etc. Take the float bowl off and see if there's any dirt lying in the bottom which isn't good as it can subsequently block the pilot/needle jet holes.

is the choke coming off fully?

backfiring on the overrun is normally due to air leaks in the exhaust, especially at the cylinder head.

I'd look at these things before you go back to the ignition

good luck!
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  #3  
Old 5 Apr 2007
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There are similar discussions in the threads here - suggest you take a look at those for more advice (same as I am doing right now!!) if you need it.

rickg,
are there any points to look for with the float bowl off, apart from muck lying in the bottom and does the bowl come off with no problems while the carbs are on the bike?

Also, how can I tell if the choke is working properly? e.g. returning to the fully in position.

Apologies for these basic questions, but I am very new to this engine.

Dave
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  #4  
Old 5 Apr 2007
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Dave

Ok, it's been a while since I had my XT so this is from memory. There are at least 4 cross-head screws holding on the float bowl. They are tight and made of cheese. The inner screws are probably hidden by the secondary carb body. If you have a good cross-head screwdriver of exactly the right length you may be lucky enough to get them out but it's vital that you don't mess up the heads else it'll subsequently be very difficult to get them out, even with the carb' off the bike. You would probably be better off resigning yourself to taking the carb' off the bike and taking the opportunity to look over the carb' thoroughly, there's not much you can do or see with just the bowl off, though you may be able to remove the floats and then look at the float needle which shouldn't have signs of a groove around it - wear could alter the fuel level in the carb' or allow fuel to leak in and make the bike run rich

there ought to be drain screw facing outward on the base of the float bowl. It may be worth draining the bowl into a clean container and looking to see if any muck gets flushed out. If it does (and I assume you too have poor tickover?) the next thing is to check for any dirt in the pilot jet. The hole in this is tiny, so it doesn't take much to block it.

As long as the choke returns to the fully-in position it should be ok but there is I think a seat on the end which bungs-up the choke-circuit to cut off the fuel when running normally. Clearly this seal needs to work or it'll run rich at tick-over when hot.

The carb' is a complicated jobbie, it'd really be worth your while tracking down a manual from the 'net. I think there have beens some posts on this site in the past with places you can download.

cheers

rick
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Old 5 Apr 2007
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Rick,
You are a star; confirms my reservations about taking off the bowl while doing handstands! I've had that experience already just fiddling with the pilot jet adjustment screw.

This connects with my own thread about poor/difficult starting - an ongoing tale as of today - From memory, I think you have been contributing and helping me there as well.

The choke definitely does not return all the way in; there is about 20 mm of "bare metal" showing when the control knob is pushed in - any thoughts on that?

I do have a manual for a TTR and I have a feeling I will be stripping the carbs once I have seen a good spark!!!!! (Got to do one thing at a time - can't multi-task nowadays!!). I will try your drain suggestion first of course.

Toecutter,
Sorry for hogging your thread; I hope that these discussions on here are of some use to you as well.

Regards,

Dave
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  #6  
Old 6 Apr 2007
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I'd say if the choke goes in until it won't go any further and doesn't pop out when you let go ther's nothing much wrong with it. There will be some 'spare' rod left even when fully in

Don't pull the carb' to bits until you are happy you have a decent spark.

You say you've been fiddling with the pilot screw too? Was that before or after you had problems.... :-)

Rick
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  #7  
Old 9 Apr 2007
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Inconsistent tickover etc

Cheers for the quick reply Rick and Dave,
I checked the exhaust and inlet rubbers etc, and all was well. I've just ridden it hard through a lot of sand along the Niger and now it seems to be running just fine. Maybe just some sediment floating around in the bowl which has now come out in my multiple tumbles!
I'll strip the carbs when I have regained my energy, 'cause I'm sure it's just some crappy blackmarket fuel.
Thanks and good luck with yours Rick. The carbs are pretty easy to get off and on, especially if you soak the rubbers in hot water before putting them back in to soften them up a bit.
Bye for now,
Darryl.
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  #8  
Old 11 Apr 2007
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Quick update............

.......for anyone interested!

Glad to hear that Darryl/Toecutter is sorted out; for myself, I still need to get the spark plug out to check the ignition (a whole story on my own thread!). I don't yet have the right spark plug spanner, which seems to be a tad specialist, to fit under the frame.

In the meantime, I have run quite a bit of fuel out of the drain screw on the float bowl and it is perfect - no muck showing at all. Thanks for the advice about the choke etc. All very useful as and when/if the carbs have to come off the bike. I certainly won't be doing that until the spark is assured though!!

As a point I could not get a pipe onto the drain of the bowl (no room for that against the oil tank) so I used a bit of tin/cooking foil as a makeshift funnel and ran the fuel off into a jamjar.

My fiddling with the pilot jet was after the poor starting appeared - pretty recent in fact and was based on other advice in my thread.

You can tell from the above that the bike still won't start; glad I am not on the Niger at the mo!!

Cheers,

Dave
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