R6 stalling when coming to a stop

[m-v-b]

Hey everyone

I've got a 2002 Yamaha YZF R6, this bike has been nothing but trouble since I bought it. A few months after buying it, there was a discovery of two hairline cracks in the cylinders. So I bought a used engine and had it fitted. Shortly after this I got it run on a dyno, they discovered a couple issues, in the end the carbs were balanced and the crank case breather pipe was routed up to the back end of the bike.

Now on paper it looks good, and to ride it's great. However, is has now started stalling on me once its warmed up and I come to a stop at traffic lights, or crawl at very low speeds. It did it around 4 times today one after the other at every stop, around 100 metres in between. The first 3 times were at round abouts. When trying to start, it turns over, but just doesn't seem to fire, I have the throttle open, then suddenly it'll fire up, it can take around 10 seconds on average to start these times. The final time was when I was parking up, I popped it in neutral and it fired up right away.

I have tried adjusting the idle screw as a couple times after stalling it seems to idle a little low, however this doesn't make much of a difference as it still stalls. Normally there is no issue to start from cold, I just put the choke on, press the switch and it fires up right away.

Any ideas?

After spending a fair amount of money I'm losing faith in the bike, and I'm struggling to decide if I get a new one or try and sort this issue...

[Stu]

has it only recently started doing this as the weather has got cold?

[m-v-b]

Sorry! Here's some info I forgot to mention...

It's not an issue I had after the engine change. I took it a trip to Oban, in which I got absolutely drenched, stopped at Tyndrum, and it wouldn't start, would turn over but wouldn't fire up. Called recovery, after 2 hours no one arrived, so I tried again and it fired up.

It stayed in my garage for a couple weeks after that, where I tried to get it to start, it occaisionally fired up, but when I test rode it, it would splutter and run rough after a few hundred metres and stall constantly when stopping.

That's when I booked it in for the carb balance, and to have a look at the starting and stalling issue. However after several weeks of being there, no one had any trouble with it starting or stalling.

It wasn't cold at all when the issue originally started.

[Stu]

I was going to say if its only just started since the cold spell it could have been carb icing

[Guest]

I was going to say if its only just started since the cold spell it could have been carb icing

Or running a bit weak

[Tango]

A blocked idle jet?

[Stu]

I was going to say if its only just started since the cold spell it could have been carb icing

Or running a bit weak

 

I would have assumed the dyno run would have picked that up but you never know!

[m-v-b]

I was going to say if its only just started since the cold spell it could have been carb icing

Or running a bit weak

 

I would have assumed the dyno run would have picked that up but you never know!

 

Yeah that's what I would also have assumed. They told me everything was great, and re routing the breather pipe had made a massive difference. But as you say, you never know.

[Guest]

I was going to say if its only just started since the cold spell it could have been carb icing

Or running a bit weak

 

I would have assumed the dyno run would have picked that up but you never know!

Set up in warm weather they can vary a lot, or it could just be daft as an air leak

[Stu]

yeah true

alsoa dyno operator can also make it read what they want so everything looks "good"

[Mississippi Bullfrog]

Can you pull the plugs and see what the tips look like. That can tell you quite a lot about an engine.

[Guest]

I would first clean the carbs. Sounds like a classic case of dirt in the jet(s).

If that didn't cure it but it probably will... I'd check to see why it was running rich. Perhaps the pilot screws aren't set properly or in line with other mods.

[Tango]

Dunno.....has it got CV carbs on it?......maybe a split diaphragm on one carb?

[Joeman]

Is the idle smooth or lumpy?

If the idle screw makes no difference to tick over speed then it's likely a carb issue with the low speed jets. The dydno guy was probably only running high engine speeds so didn't notice.

Check the rubber boots that connects to the air box to make sure they haven't popped out. Also if you can get hold of a infrared thermometer measure the exhaust header temperatures from cold to see if one cylinder is running colder than the others.

Carb rebuild and balance with a new set of plugs should see you running fine.

[Guest]

Just a thought...

Have you left your choke on? That would kill it at idle...

[Grumpy Old Git]

My guess would be blocked idle jet (as the idle screw has little to no effect).