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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 22 Oct 2009
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Carburetter overflowing/ not starting TT600R '03

hi all,

A couple of days ago the bike cut out on highway speed a couple of times, but after kicking it (the kickstarter i mean) it went on. I suspected and airlock: tankbag blocking fuelcap vent.

day before yesterday when crossing the border into Paraguay i noticed that my carb was leaking fuel. So i drained the carb and that seemed to work.

This morning i didn't start at all, so draining again. Didn't help. Took the old sparkplug out, was dry, which i think is weird after trying to start it for a few minutes. Put in an old spare sparkplug, checked if it worked first. No sign of life. Then the carb started overflowing again.

I have an inline fuelfilter.

Before i take the carb apart i really like to have some idea what might be the problem.

Oh, before all this happend i did a lot of bad washbordy roads through Bolivia a about two weeks ago. Bike worked fine after that till yesterday.

Can it be that due to vibrations etc. the carburettor bowl level changed?

Any info highly appreciated.

Sander
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  #2  
Old 22 Oct 2009
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Sounds like sh*te in the carb - Probably a build up of dirt in the fuel tank - got shock up and into carb...
Check fuel filter isn't blocked up - Disconnect fuel line and run fuel thru filter to see if its flowing OK. My 04 RE runs OK, but the fuel flows quite slow out of the tap - without a filter.
It only takes a small bit of dirt to hold the fuel float valve open and make it leak/over flow! Carbs will need a good clean out - look for sediment in bottom of float bowl - it may have by-passed the filter?
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  #3  
Old 22 Oct 2009
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hi,

fuel is flowing ok. i took the carb off and opened the floater chamber. looks clean.

so....

i read in my manual that the floaterhight should be 27-29mm and there's an other figure 'swimmerstand' which translates as floateradjustment of 6-8mm.

How do i measure that?

thanks,
sander
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  #4  
Old 22 Oct 2009
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Fuel level: 6.0 ~ 8.0 mm Under the edge of the carburetor body. Thats when you measure the actual fuel level in the working carb as fitted on the bike, using a special adaptor with a clear tube - like a manometer.
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  #5  
Old 22 Oct 2009
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float level

Sander,

The two values are different:
1. Floatheight 27 - 29 mm: measure with float bowl off, carb upside down, then distance between float bowl mating face and top of float must be 27 - 29 mm.
2. Fuel level 6 - 8 mm: as Pigford says, with running engine the fuel level above the float bowl mating face (carb installed of course) to be 6 - 8 mm.

The first one works for me.

While opening the float bowl, did you check the little filter on top of the float needle seat, better to remove anyway. When this is blocked it gives the symptoms as you described at first (stops at highway speeds, starts again etc)

Good luck
Auke
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  #6  
Old 23 Oct 2009
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Guys,

Thanks for the answers. i found the measuring method in a TTRE manual. Same carb.

Took the carb off - i think i found an almost non-violent way to do this ;-) - and it measured 25mm. Adjusted that and put the whole thing back together.

Inside of carb was clean.

So. The good news is: It stopped pissing nafta The bad thing is : It still doesn't start. I have a bit of action, more than before, but is doesn't fire upenough to catch on.

Played with/without choke and idle speed screw. Doesn't help.

Tomorrow i'll check valve clearance.

Airfilter is ok.

A bit more background: My TTR always had cold start problems in Hot and humid environments on sealevel like beaches in CA and Colombia/Ecuador or here in Iguazú. The last few months i spend in Equador, Peru, Bolivia and north chile/ north Argentina. So either dry, or on altitude or a combination. Always easy to start. What does that say about idle mixture?

Also, now i'm thinking of it, lately i give a wee bit of gas when starting. This developt over time, don't know when i developed this habbit.

Anyway, to be continued...

sander
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  #7  
Old 23 Oct 2009
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idle idle

Hi Sander,

Having cold start poblems in hot environments tells me that your idle mix setting is on the rich side (assume you use the choke for cold starts). (Humidity, unless under water, does not really matter). Remember that the 'factory idle mix setting' does not apply for older bikes: on my older Tenere the setting is 4,5 turns out and that works fine. Same for all other XT and the like that I know.

I'd recommend you try to start it with different settings: 3, 4, 5, 6 turns out; do not be shy ... BTW; the further out, the richer the mix.

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Old 23 Oct 2009
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hi Auke,

i never touched the idle mix screw, so i might give it a try. BTW. 'she' kicks back when starting on choke on sealevel and tropical environments.

i don't know sh*t about carbs and mixture and such, but on altitude it starts fine with choke. and on altitude, mixture is rich due to less oxygen in the air, right? So how can it be too rich on sealevel? If it works allraight on altitude, i expect it to be too lean on sealevel. Or does my logic fail here? :confused1:

Quite eager to understand this stuff actually... please elaborate!

One good thing about kickstart only bikes, you do need to understand more about the technicalities!

thanks,
sander.
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  #9  
Old 25 Oct 2009
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well,

looked at valve clearance and that was ok.

Current symtoms: If i crank it a few times with choke and kick it without choke the bike fires up a little before it dies and doesn't get up to idle speed, if I give a bit of throttle it dies immediately.

Can this be the effect of a too low fuel level in the floater chamber? My guess would be that on idling the fuel consumption is so little that it doesn't affect running at idle speeds.

...still puzzled.

sander

Last edited by sanderd; 25 Oct 2009 at 21:11. Reason: refine text
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  #10  
Old 26 Oct 2009
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Hi all,

just to let you know. it starts again. appantly adjusting the floaterhight with the carb. upsidedown doesn't do the trick, since the floater compresses the valve a bit. Adjusted it again holding the carb on 45 degrees. seems to work, it fired up nicely and i have idle again and it revs nicely.

ergo, too low fuel level in the floater bowl affects starting and idle too.
will take it out for a spin tomorrow and see how it holds up....

thanks for all the responses!

sander
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  #11  
Old 26 Oct 2009
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not quite ok...

yes, it does start, but has a very high idle. if i rev it a little i see smoke from the exhaust and i sputters when i let go of the throttle. sounds like too rich mixture right?

how does that relate to a wrong fuel level in the floaterbowl?

to be continued...

sander
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  #12  
Old 26 Oct 2009
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mix, lean and rich

Hi Sander,

Was busy in Pasto getting new crankshaft bearings ...

Quote:
Originally Posted by sanderd View Post
hi Auke,

i never touched the idle mix screw, so i might give it a try. BTW. 'she' kicks back when starting on choke on sealevel and tropical environments.
*** kicking back: decompressor cable correctly set? all plugs in the ignition system nice & tight?

i don't know sh*t about carbs and mixture and such, but on altitude it starts fine with choke. and on altitude, mixture is rich due to less oxygen in the air, right? So how can it be too rich on sealevel? If it works allraight on altitude, i expect it to be too lean on sealevel. Or does my logic fail here? :confused1:
*** Two opposite effects: 1. hot intake air: engine sees a richer mixture; cool air; engine sees a leaner mixture - the engine only sees the gas that has been evaporated, for which the hotter air is a better agent obviously
2. going up from sealevel the air pressure decreases (according my GPS 770 mbar at 3000 m - that is almost 25% less!) which makes the mix indeed richer.
In general, effect 2 is stronger, while effect 1 compensates, depending on temperature.

Quite eager to understand this stuff actually... please elaborate!

One good thing about kickstart only bikes, you do need to understand more about the technicalities!

*** Seems to me you have now 'adjusted the idle mix by adjusting the float level. Nothing wrong with that, but would recommend to also adjust the idle mix with the appropriate screw - makes a world of difference in starting.

thanks,
sander.
Good luck!
Auke
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  #13  
Old 26 Oct 2009
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yeah well.... it starts getting annoying to be honest.

it runs, but the idle needs to be high and feels sort of weak. like i'm back on 4000m again. on sealevel i'm used to more powerful thumps from the exhaust. if i leave it idling it cuts out al of the sudden, with a 'pffsst' sound.

still confused.....

yesterday an german couple with their two kids showed up on their old airheads. guy was a bike mechanic. will talk to him too.

will go fiddle with the idle screw.

good luck with the bearings!

sander
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  #14  
Old 28 Oct 2009
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Hey Sander, carb rubbers haven't gone have they? Mine was doing similar things with Knackered rubbers.........
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