YBR dies when throttle is released.

Ok folks, here's a good one for you all...

My girlfriends 2008 (injected) YBR.

Symptoms:

Absolutely fine when cold. Once warned up after 2 minutes or so, it dies when the throttle is released, not when it is backed off but released back to it's start point. The bike hasn't actually stalled electrically, the engine doesn't completely stall until you come to a stop as normal, but there is no power at all. When it has died trying to get it going with the clutch is worthless and to get it going you need to put it back into neutral and push the starter. It is rideable but you can't set the throttle to 0, ergo using the back brake to adjust your speed and change gears without releasing the throttle. I believe it is an idle issue as the revs on idle are ~700 and I can't adjust it due to the screw being a bast*rd. Ordered a new throttle body for this reason.

Note that the other day, it didn't start at all and has no spark. At this point it would not bump or kick start. I changed the coil, played about with the spark plug cap and it now starts no problem but has the above issue.

So far:

-changed plug, coil and air filter.

-used a high concentration of petrol cleaner additive.

-cleaned spark plug cap and changed with my one (Work) fine)

-doesn't appear to be any hoses disconnected.

About to:

-change the throttle body to see if the other one is A) dirty and B) adjust the idle to the right amount.

So that's where I'm at right now, I believe it to be the idle speed since it works well when cold and revs are higher but what do you folks think and is there anything else I should be thinking about?

It does sound like it's the idle position set too low.......I don't know the setup on those bikes, but if it has a Throttle Position Sensor, that may need setting up.

Valve clearances? A valve not seating correctly when the bike warms up.

Air filter? Clogged could be causing it to run too rich?

Just a couple of ideas......

It does sound like it's the idle position set too low.......I don't know the setup on those bikes, but if it has a Throttle Position Sensor, that may need setting up.

Valve clearances? A valve not seating correctly when the bike warms up.

Air filter? Clogged could be causing it to run too rich?

Just a couple of ideas......

Cheers Bob.

Valves have been checked, all good. Air filter has been changed and there is no TPS, it's just a cable that attaches to the throttle body. I was thinking fuel pump too but it primes ok...

She had an issue involving her Z750 and that cutting out, gave the idle 200 more RPM and it was sweet. Hopefully this is the same. If it's not though, I've ran out of ideas lol.

there is a common fault with the fuel pump on that model year which could cause similar problems

although it wouldn't be isolated to just at idle

adjust idle first and go from there

Oh yeah, forgot about this little bit of info...

Before fuel cleaner was added, 100% of the time of you went to 7K THEN backed off it would cut out and around 20% of the time the same would happen above 5K.

Now the fuel has been mixed with, it's more like 100% above 3K.

may well be that the fuel pump is on the way out!

when you say backed off do you mean close the throttle fully?

may well be that the fuel pump is on the way out!

when you say backed off do you mean close the throttle fully?

Yeah, if you keep it at 10%, it will keep running, will only cut out at 0% then when you give it the has again, nothing.

have you got an air screw on the throttle body?

this should allow enough air through to keep it running when you close the throttle to 0%

if it has an air screw check the setting in the manual and adjust it if necessary

Yeah I think you're talking about the idle screw which will in effect change the base mixture?

That's the reason we bought a new throttle body - because the other brass one in the current TB is unscrewable...

Hopefully I'll install the new TB, adjust the idle and all good... If not - fuel pump?

No I am talking about the air screw

you cant alter base mixture on an injected bike you are talking about a mixture screw on a carbed bike

the idle screw opens the butterfly slightly to increase the RPM

but you also have an air screw this bypasses the butterfly and allows air past the butterfly when closed

they use a combination of an air screw setting and idle screw setting to get a nice idle

when you close the throttle the air screw allows air past to stop it stalling and to keep it running it acts as a dampener so you dont starve the engine of air

not all throttle bodies have them though

If not... Tighten the throttle cable to prevent it closing fully?

Don't think so Stu - there's only one screw to play about with and that's the idle adjustment.

If not... Tighten the throttle cable to prevent it closing fully?

That doesn't really help the problem and makes it fairly dangerous to ride...

Don't think so Stu - there's only one screw to play about with and that's the idle adjustment.

 

sounds like your butterfly is at a fixed setting then

its will still be an air screw and yes altering it will adjust the idle

the idle screw and the air screw both have an affect on the idle

the air screw and the butterfly have the same affect they both allow air through

Just suggesting adjustment to cable to keep the rev up to 800/900 enough to stop it stalling

Don't think so Stu - there's only one screw to play about with and that's the idle adjustment.

 

 

sounds like your butterfly is at a fixed setting then

its will still be an air screw and yes altering it will adjust the idle

the idle screw and the air screw both have an affect on the idle

the air screw and the butterfly have the same affect they both allow air through

I'll have a look around when I leave work for this air screw then... Alternatively... Stick a sock in the intake I guess!

Don't think so Stu - there's only one screw to play about with and that's the idle adjustment.

 

 

sounds like your butterfly is at a fixed setting then

its will still be an air screw and yes altering it will adjust the idle

the idle screw and the air screw both have an affect on the idle

the air screw and the butterfly have the same affect they both allow air through

I'll have a look around when I leave work for this air screw then... Alternatively... Stick a sock in the intake I guess!

Now that's dangerous, sock could come out and get wrapped in the chain and lock the back wheel.

You say it runs fine for 2 mins ?

Just a thought, but does the engine have a temp sensor ?

Wonder whether the ecu isn't getting a signal back to tell it the engine has warmed up and leaned off the mixture.

Not sure what to make out of your comments about it wont start or bump these days so will ignore this.

Sounds a bit of a weird one though

You say it runs fine for 2 mins ?

Just a thought, but does the engine have a temp sensor ?

Wonder whether the ecu isn't getting a signal back to tell it the engine has warmed up and leaned off the mixture.

It does mate and I'll include that with my next diagnostics if it isn't the throttle body. That should come tomorrow and I expect that when I take the old one out, it will be black as my cat! We shall see...

Funny thing happened tonight though...

Been riding it whilst she uses my bike (I'm a bit more clued up how to ride a F**k'ed up bike lol) but because I was riding the back brake to manage my speed, I have overheated the brake shoe and now need a new one since there's no more on it lol... stank horribly.

Are you sure it doesn't have a throttle position senson??

Symptoms do sound consistent with a dodgy TPS.

An ex lady friend of mine had a 125 with the exact problem.

Turns out while it was injected, it was so simple that its idle was controlled by the throttle cable adjustment.

I adjusted the cable when warm, and the bike started revving at 1500rpm idle, and 2500rpm cold which seemed right.

This was an Aprilia RS4 125 though. And it was quite unlike any other 125 I've worked on.

For a start, it used a magneto to charge itself up

Sounds electrical, so the sensors aforementioned are a good place to go next if what I said doesn't fit your bike.

Are you sure it doesn't have a throttle position senson??

Symptoms do sound consistent with a dodgy TPS.

Nah, just a cable

An ex lady friend of mine had a 125 with the exact problem.

Turns out while it was injected, it was so simple that its idle was controlled by the throttle cable adjustment.

I adjusted the cable when warm, and the bike started revving at 1500rpm idle, and 2500rpm cold which seemed right.

This was an Aprilia RS4 125 though. And it was quite unlike any other 125 I've worked on.

For a start, it used a magneto to charge itself up

Sounds electrical, so the sensors aforementioned are a good place to go next if what I said doesn't fit your bike.

That's what I'm thinking. The adjuster on the throttle did nothing but that's just free play adjustment, I'm hopeful the idle screw will sort it.

You should be able to tighten the cable adjuster enough that it puts the throttle on, you just have to take all the free play out of it and then some.

Is there just a control level adjuster, or does the cable have an adjuster lower down the line?

You should be able to tighten the cable adjuster enough that it puts the throttle on, you just have to take all the free play out of it and then some.

Is there just a control level adjuster, or does the cable have an adjuster lower down the line?

Did that... didn't help. Did raise the idle though but that's Just applying throttle so didn't think it would ...

tightening the throttle cable is not a good move!

this removes the free play the cable needs when you turn the bars and can increase the revs!

tightening the throttle cable is not a good move!

this removes the free play the cable needs when you turn the bars and can increase the revs!

Yeah that's the only reason I did it - makes it easier to ride in it's current condition. I didn't event tighten the locking nut because I'll put it back again soon.