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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 1 Jun 2008
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Trouble with hot starting

I'm having trouble again with the Tenere ('86),this time with kick starting hot.Now when I say hot,I mean in the range of 170-200 degrees centigrade as measured on my trail tech vapor.
If it's ridden and sat a while,say 10mins and you try to restart it will "catch" but even with or without throttle it'll die.Then you're left with a flooded engine and a near heart attack as you spend 5 mins kicking it over!Also it'll do a massive backfire and flames out the exhaust when trying to find tdc occasionally and sometimes spit back into the carb and a nice wee explosion in the airbox too.
After my trail ride yesterday,I decided I've had enough of this.
I have changed my pilot jet to a #50,the main jets have been drilled out,head has been ported,airbox opened up etc etc.
When I added the new pilot jet,I ended up with a near stock setting of the idle mixture screw of about 2 turns out.It ran fine at this until about 2 weeks ago.
I adjusted it tonight back to 1 turn out and the bike didn't like being on the idle circuit when riding,surged and farted a wee bit.So adjusted it to 1 1/2 turns and it's running fine.
I tried a few times to get it too play up and not start hot,but it was starting perfectly.
I have found when I tried the mixture screw out more than 2 1/2 turns,when the bike is idling for too long,be it in traffic or on the sidestand,the revs would drop and the engine would die.Most likely it'd flooded itself.
One thing I am wanting to try also is a new float valve,but I'd imagine it'd be a Yamaha only part.

Anyone got any suggestions?
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  #2  
Old 1 Jun 2008
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Why #50?

I'm having trouble again with the Tenere ('86),this time with kick starting hot.Now when I say hot,I mean in the range of 170-200 degrees centigrade as measured on my trail tech vapor.

*** Just out of interest, what is a trailtech vapor?


If it's ridden and sat a while,say 10mins and you try to restart it will "catch" but even with or without throttle it'll die.Then you're left with a flooded engine and a near heart attack as you spend 5 mins kicking it over!Also it'll do a massive backfire and flames out the exhaust when trying to find tdc occasionally and sometimes spit back into the carb and a nice wee explosion in the airbox too.
After my trail ride yesterday,I decided I've had enough of this.
I have changed my pilot jet to a #50,the main jets have been drilled out,head has been ported,airbox opened up etc etc.
When I added the new pilot jet,I ended up with a near stock setting of the idle mixture screw of about 2 turns out.It ran fine at this until about 2 weeks ago.
I adjusted it tonight back to 1 turn out and the bike didn't like being on the idle circuit when riding,surged and farted a wee bit.So adjusted it to 1 1/2 turns and it's running fine.
I tried a few times to get it too play up and not start hot,but it was starting perfectly.
I have found when I tried the mixture screw out more than 2 1/2 turns,when the bike is idling for too long,be it in traffic or on the sidestand,the revs would drop and the engine would die.Most likely it'd flooded itself.
One thing I am wanting to try also is a new float valve,but I'd imagine it'd be a Yamaha only part.

Anyone got any suggestions?

All the modifications you have done have a neglegible impact on idle running - I checked and the original idle jet is #46, so what was the reason you changed it to #50? I'd say, open the float bowl, check float level and install the original idle jet again. Then, on older XT's, the standard idle screw setting is too lean. Normally, 1 - 1,5 truns out more makes it start nicely under all circumstances. To set the idle correctly, see other posts.

Good luck,
Auke
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  #3  
Old 1 Jun 2008
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Quote:
Originally Posted by aukeboss View Post

*** Just out of interest, what is a trailtech vapor?





All the modifications you have done have a neglegible impact on idle running - I checked and the original idle jet is #46, so what was the reason you changed it to #50? I'd say, open the float bowl, check float level and install the original idle jet again. Then, on older XT's, the standard idle screw setting is too lean. Normally, 1 - 1,5 truns out more makes it start nicely under all circumstances. To set the idle correctly, see other posts.

Good luck,
Auke
The Vapor is a digital speedo with a few extras made mainly for trail/enduro bikes.
Trail Tech Home is their website.

Reason I changed the pilot jet was because I had to wind the mixture screw pretty much right out to get the bike to run right,which shows the pilot jet was too small for the mods done.
Who ever had ported the head had set up the carbs due to the float level being set as low as it can be,around 17mm I think from memory.
Any moving of that setting back towards standard resulted in the bike coughing and running out of fuel when given anything more than 1/4 throttle.
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Old 3 Jun 2008
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Interesting

So, if you increase the float level and open throttle more than 1/4, bike coughs ... that does not point to too lean (running out of fuel) but to too rich!
From a technical point of view, correcting jetting problems by adjusting the float level is horrendous ...

Anyway, when you are happy with the settings of everything except for idle, still beg to ask you ... why the step from #46 to #50? Try #48 for instance?

Auke
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Old 3 Jun 2008
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Quote:
Originally Posted by aukeboss View Post
So, if you increase the float level and open throttle more than 1/4, bike coughs ... that does not point to too lean (running out of fuel) but to too rich!
From a technical point of view, correcting jetting problems by adjusting the float level is horrendous ...

Anyway, when you are happy with the settings of everything except for idle, still beg to ask you ... why the step from #46 to #50? Try #48 for instance?

Auke
I don't see how raising the float level back to near standard,eg making the carbs get less fuel than what it is now and then running the bike like that with it coughing and surging can be running too rich...Especially when it would now be getting less fuel into the float bowl.The reason I think it's been set that way is someone previous has drilled the main jets.Out to what size,I have no idea,but it certainly doesn't lack any power.

I went to the #50 pilot jet due to them being priced at $24NZD and ex Australia.
But it seems I may have fixed the problem with the 1 1/2 turns out on the mixture screw.Will have to wait until I go trail riding again to get it super hot and see if the problem comes back,but for now it's starting normal again.
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  #6  
Old 4 Jun 2008
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Aha

Quote:
Originally Posted by Yobbo View Post
I don't see how raising the float level back to near standard,eg making the carbs get less fuel than what it is now and then running the bike like that with it coughing and surging can be running too rich...Especially when it would now be getting less fuel into the float bowl.The reason I think it's been set that way is someone previous has drilled the main jets.Out to what size,I have no idea,but it certainly doesn't lack any power.

I went to the #50 pilot jet due to them being priced at $24NZD and ex Australia.
But it seems I may have fixed the problem with the 1 1/2 turns out on the mixture screw.Will have to wait until I go trail riding again to get it super hot and see if the problem comes back,but for now it's starting normal again.
Aha - let's check: are we talking the same thing: float level: fuel level in carb, or something else?
If we talk fuel level in the carb: if it increases (goes up), bike will run richer. If it decreases, bike will run leaner.
If you measure float level, what exactly do you measure?
Normally, to measure, float bowl open, carb upside down, measure distance from underside float to edge of float bowl mating edge. Indeed, if this measure increases, the mix becomes leaner.
Or is it different in NZ you being on the other side of the great pancake?


Auke
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  #7  
Old 4 Jun 2008
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Quote:
Originally Posted by aukeboss View Post
Aha - let's check: are we talking the same thing: float level: fuel level in carb, or something else?
If we talk fuel level in the carb: if it increases (goes up), bike will run richer. If it decreases, bike will run leaner.
If you measure float level, what exactly do you measure?
Normally, to measure, float bowl open, carb upside down, measure distance from underside float to edge of float bowl mating edge. Indeed, if this measure increases, the mix becomes leaner.
Or is it different in NZ you being on the other side of the great pancake?


Auke
The 17mm I quote is from turning the carb upside down and measuring from where the bowl meets the carb to the bottom or top when upside down,of the float.
The fuel level(measured with clear hose running up the side of the carb,coming from float bowl drain)at this setting is within standard specs also.
Just to reassure you a bit more,when I set the float level to 21mm,still richer than stock,the plug turned a nasty white with pink speckles.
Another thing I think might get overlooked is heat soak.
With the tank covering half the engine,I'm sure that would hold a lot of heat when the bike is stopped.
I have started to cover the fuel lines and fuel pump with heat reflective matting in hoping this will help also,as I noticed the fuel pump was warm when I had come home from work one night.
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Old 6 Jun 2008
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Sorry ...

I'm lost as to the cause of the bad starting. Someone else has an idea?

Auke
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