Problem when bike gets hot

[Bubb]

My R80st bitsa has started to misbehave…
Starts and runs fine for first 20 minutes or so, then misfires, and eventually stops.
Left to cool, it will start up again, but same thing happens as it gets hot again.

I’ve checked the plugs (and tried new ones) and checked the valve clearances…..so I’m left thinking it’s the coil breaking down as it gets hot.

Can the far more technically minded on here tell me if I’m looking in the right direction please…..or is there something else that may give these symptoms.
( I have wedgetail ignition, and that’s set as per the instructions….. not sure if it’s coil, or could it be HT leads?)
Oh, coil is a dual output Dyna coil from Motorworks, 0.7 ohms as said fits the g/s and ST…….
Plugs, non resistor bp6es NGK….new


Thanks

 

[Pukmeister]

Could it be a blocked fuel tank breather, causing it to draw a vacuum in the tank when running and then lose fuel flow ?

 

[Bubb]

Pukmeister
Like the thinking…..but doubt that’s the cause. I have a Monza style cap fitted.
It doesn’t just stop straight away, but misses when revved….. so I think it’s coil rather than fuel.
I have inline fuel filters, and have cleaned them (all okay) as I first thought dirty fuel…..haven’t seen any water or dirt in bottom of float bowls.

 

[DrFarkoff]

Have you one to swap out to test the theory ??

Seems about all you have left

The Wedgetail should cover everything if you have the timing unit and the Ignition amp

 

[Bubb]

DoctorF

Sadly, no other coil to swap out, but one ordered from motorworks, as I do think that is the problem

The wedgetail unit is set up fine as per instructions, and was fine….so doubt it’s that (well I do hope it’s not that)

Will update once i get the new coil from works…

Thanks

 

[mikeyboy]

Just a thought,
I have no idea if the wedgetail is susceptible to excess voltage,
But I had a bike with the seimens ign and it started misbehaving after a while once the battery had regained full charge,
After mucho head scratching we found it was charging at nearly 15 volts and the ignition module did not like it.
Might be worth looking into if the new coil doesn’t remedy your problem

 

[Bubb]

Mikeyboy

Many thanks. This is a new issue that has just started, even tho the wedgetail has been fitted for over a year.
I will look at the reg/rec charging rate if the new coil doesn’t fix it.

Many thanks for all the ideas so far.

This place is great for the amount of knowledge freely shared.

Thanks all

 

[Steptoe]

Pukmeister
Like the thinking…..but doubt that’s the cause. I have a Monza style cap fitted.
It doesn’t just stop straight away, but misses when revved….. so I think it’s coil rather than fuel.
I have inline fuel filters, and have cleaned them (all okay) as I first thought dirty fuel…..haven’t seen any water or dirt in bottom of float bowls.

I’ve had inline fuel filters which blocked due to water contamination which restricted the fuel passing through, even though they looked clean and fuel appeared to be flowing through as normal. Easy to check, next time your bike starts to splutter and stops, quickly turn the fuel tap off and check if there’s fuel in the float bowl.

 

[Bigcats]

I would have to agree with Pukmeister here...fuel starvation. Start with the simplest of issues!!

Could run it with the full cap open see what that does??

 

[Bigcats]

Sorry for jumping in here but I'm trying to send a private message to Bigcats and I can't get through. Would you mind sending me one so I can reply?
Thanks in advance

You're not a paid up member so you won't be able to send or receive them.

 

[SBD]

As an aside, if it is fuel starvation due to a blocked breather or filters, it’ll be hotter due to running weak.

 

[The Other PaulG]

If not the fuel, my £5 says a hairline crack in the coil. Had exactly this on an R80, only manifested itself when hot and the crack was very nearly invisible.

 

[DrFarkoff]

I’ve had inline fuel filters which blocked due to water contamination which restricted the fuel passing through, even though they looked clean and fuel appeared to be flowing through as normal. Easy to check, next time your bike starts to splutter and stops, quickly turn the fuel tap off and check if there’s fuel in the float bowl.

Simple diagnostics for the win every time It needs fuel and an Ignition source

As soon as it dies Turn the fuel taps off! as Steptoe says BUT Hold off on the next bit re float bowls for a moment, as there are sparks involved (or maybe not!)

1) Carry a known good spare plug in your pocket, once the bike stutters and stops just unclip a plug cap and stick the plug in and rest it on the cylinder base (To ground it ) and spin it over, Any Spark ??

2) Because you have turned off the fuel taps as soon as the motor quit, if the bowls were empty they should still be empty (Or not) So drop off the bowls and check the fuel level

One answer Should be Yes and One should be No and then you have a direction to follow

N.B I suggest a spark check first, Because no matter how careful you are there is always a chance of fuel spilling on your glove or trews or somewhere and igniting (Better to be safe for a minor inconvenience, however remote a fire may be !!!)

 

[Steptoe]

If not the fuel, my £5 says a hairline crack in the coil. Had exactly this on an R80, only manifested itself when hot and the crack was very nearly invisible.

Ahh, the old original bmw dual output coil, they were so prone to cracking I’d have i thought they’d have all been replaced by now

 

[timeandtide]

You're not a paid up member so you won't be able to send or receive them.

He is now!

 

[SBD]

Simple diagnostics for the win every time It needs fuel and an Ignition source

As soon as it dies Turn the fuel taps off! as Steptoe says BUT Hold off on the next bit re float bowls for a moment, as there are sparks involved (or maybe not!)

1) Carry a known good spare plug in your pocket, once the bike stutters and stops just unclip a plug cap and stick the plug in and rest it on the cylinder base (To ground it ) and spin it over, Any Spark ??

2) Because you have turned off the fuel taps as soon as the motor quit, if the bowls were empty they should still be empty (Or not) So drop off the bowls and check the fuel level

One answer Should be Yes and One should be No and then you have a direction to follow

N.B I suggest a spark check first, Because no matter how careful you are there is always a chance of fuel spilling on your glove or trews or somewhere and igniting (Better to be safe for a minor inconvenience, however remote a fire may be !!!)

I like this approach, but it won’t tell you if the spark is ok in fresh air but fails under compression.

Tbh, I’m not sure how likely that is.

 

[Nin]

I had this problem on the old R100GS Bumblebee.

It was the grey dual output coil - cracked. Gave all the symptoms of running lean.

On one of my trips to Wales I was sat in a lay by waiting for it to cool down and work again, a very nice gent stopped on his RT, diagnosed it immediately.

I went home, replaced it with the black/red job and it worked perfectly. For years.

 

[Bubb]

Thank you to all who have taken the time to respond.
This place is a fountain of knowledge, for which I am very thankful

I will Try some of the suggestions, and will update when the solution s found.

Again, thanks to all

 

[Steptoe]

I had this problem on the old R100GS Bumblebee.

It was the grey dual output coil - cracked. Gave all the symptoms of running lean.

On one of my trips to Wales I was sat in a lay by waiting for it to cool down and work again, a very nice gent stopped on his RT, diagnosed it immediately.

I went home, replaced it with the black/red job and it worked perfectly. For years.

I used to fit a K100 coil to customers bikes when their original grey coil failed. Bullet proof and a used one was the tenth of the price of an R series twin output.

 

[Nin]

You’re 10 years too late for me, with that excellent advice


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