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Bike over heating after 40 mile ride
K2-K6:
--- Quote from: Ken4004 on May 04, 2026, 06:22:21 AM ---I noticed yesterday that no 2 exhaust pipe warmed up a little slower than the test although it seemed to start OK so I believe the cable / plug on no 2 is occasionally breaking down.
The leads on all plugs are a bit short like they have been shorted a number of times so time for new hardware .
--- End quote ---
That rings alarm bells for a poor running cylinder. Given that your other investigations have not given anything confirmed as probable cause, that partially missing cylinder needs investigating for both ignition and idle circuit fuel supply.
If you have a borescope it would be worthwhile looking in there to see if there's anything untoward. The cheap type for phone, with front & side facing camera are really good value to get decent inspection.
Hope you have a good holiday, anywhere interesting ?
Ken4004:
--- Quote from: K2-K6 on May 04, 2026, 12:19:56 PM ---
--- Quote from: Ken4004 on May 04, 2026, 06:22:21 AM ---I noticed yesterday that no 2 exhaust pipe warmed up a little slower than the test although it seemed to start OK so I believe the cable / plug on no 2 is occasionally breaking down.
The leads on all plugs are a bit short like they have been shorted a number of times so time for new hardware .
--- End quote ---
That rings alarm bells for a poor running cylinder. Given that your other investigations have not given anything confirmed as probable cause, that partially missing cylinder needs investigating for both ignition and idle circuit fuel supply.
Off to Kefalonia in Greece for three weeks , going around the whole Island staying one or two nights in several places so should see the whole island,
I was looking at endoscopes a couple of months ago and thought it might be useful bit of kit and it appears that I was right , I did a very detailed and meticulous clean of the carbs when I had them off the bike but as I said before I am not ruling anything out.
I was going to change the coils anyway in the future because of the dodgy looking leads so this is a good a time as any to get it done and cross another possibility off the list.
Thanks for the advice regards Ken
If you have a borescope it would be worthwhile looking in there to see if there's anything untoward. The cheap type for phone, with front & side facing camera are really good value to get decent inspection.
Hope you have a good holiday, anywhere interesting ?
--- End quote ---
Ken4004:
--- Quote from: exvalvesetdabbler on May 02, 2026, 11:54:30 PM ---
--- Quote from: Bryanj on May 02, 2026, 11:19:51 PM ---I think you have an electromechanical gremlin that stoped the engine and starter didnt work
--- End quote ---
Still in gear and clutch lever not pulled all the way in. We have probably all done it much to the annoyance of cars behind us.
Dave
--- End quote ---
I have just got back from holiday and went out for a ride and 10 miles in the bike overheated again and died at a junction and you were spot on Dave , the bike would not initially start but I then remembered what you said and realised that I was in gear and started it again straight away but it was hesitant and would stall at low revs so nursed it home.
I did have my suspicions about no two cylinder not firing properly and so decided to look at the plugs again and every plug looked fine except no two cylinder which was sooty.
On another post I did talk about changing the HT leads on the coils as per Ash’s modification and have bought all the parts needed for the mod.
So just to let you know what I found , whilst preparing the coils reading for fitting the new cables I thought I would first check the resistance between the leads between 1 and 4 which came out at about 24 ohms with the caps fitted and 14 ohms with cable only so what I expected.
When checking the 2 and 3 coil no resistance so open circuit and after stripping back the insulation found that the HT lead was broken half way down and showed signs of corrosion, just pulling on the lead it was stretching so I knew the wire had completely broken.
So in a nut shell when originally checking for a spark all plugs looked good so assumed the leads were OK but a little short , when starting the bike for the first time noticed that number 2 cylinder exhaust pipe was not getting hot straight away then finally after a few minutes got up to temp leading me to suspect the HT lead.
Bike has done about 200 miles after the rebuild and didn’t seemed to me to be pulling as it should so must have been only running on three cylinders most of the time which would explain a lot.
Anyway in the process of repairing / replacing all HR leads on all coils which will take a couple of days due to waiting for expoxy and putty to dry and then I’ll get it all back together clean the plugs check the HT resistances and take it for another spin and see how it goes.
I am not really sure if running the bike on only 3 cylinder would cause the engine to overheat but sounds very plausible because the other working cylinders are working extra hard .
K2-K6:
Hopefully you'll get to the bottom of it with the coil rebuild, then verify its firing properly on all 4 cylinder.
Running on three will cause it to be a heat risk, as you've found. They've only about 24 ft/lb of torque @ 7500rpm when healthy, so starting with approx 18 lb and running below peak torque will likely bring about 15 lb at a, licked finger in the wind, estimate.
Trying to pull uphill like that will severely compromise its output, ultimately to cause lean running through that set of circumstances. Essentially, the crank rpm can not "follow" throttle opening as there's insufficient torque to accelerate the bike and rider. That causes you to open the throttle further, which drops the vacuum affecting jets, to then run permanently lean (if the crank rpm never catches the throttle slide position) up gradient being the biggest risk, as it can never catch up.
"Lean" running, in and of itself doesn't necessarily increase heat as a cause. What happens as the combustion chamber reaches its ability to burn fuel as it approaches the 14.7:1 ideal (stoichiometric) the propagation of flame front outward from the spark plug begins to break down such that the burn phase doesn't spread out to far reaches of tbe periphery of piston/chamber. This results in unburnt "gas" mixture in a ring around that periphery, which then explodes rather than burns as piston comes to tdc. Its this uncontrolled event that gives a shock wave that breaks the boundary layer protecting the piston crown from exposure to high heat and subsequently raises the overall temperature if left unchecked. When more extreme, we can hear this as "pinking" but it starts in virtually inaudible levels before we become aware of it in more severe form (we're isolated from source & with helmet sound insulation too) but it happens and significantly shifts the temperature accumulation, that also being relative to the ambient air trying to cool tbe motor and it's capacity if moving more slowly. Detonation is the process, as there's loss of control thats fundamental to how the fuel air mix is supposed to combust, rather than explode. Essentially it has the effect of advancing the timing to detriment of the engine's desirable running condition.
There's another phase going on from this as too much of the above will likely bring pre-ignition, which is usually catastrophic, and in short time frame too :o this will definitely put a hole in tbe piston for you!
Seems like you've got away with it in recent description, but quite close to serious damage though.
Ken4004:
--- Quote from: K2-K6 on June 02, 2026, 09:37:32 AM ---Hopefully you'll get to the bottom of it with the coil rebuild, then verify its firing properly on all 4 cylinder.
Running on three will cause it to be a heat risk, as you've found. They've only about 24 ft/lb of torque @ 7500rpm when healthy, so starting with approx 18 lb and running below peak torque will likely bring about 15 lb at a, licked finger in the wind, estimate.
Trying to pull uphill like that will severely compromise its output, ultimately to cause lean running through that set of circumstances. Essentially, the crank rpm can not "follow" throttle opening as there's insufficient torque to accelerate the bike and rider. That causes you to open the throttle further, which drops the vacuum affecting jets, to then run permanently lean (if the crank rpm never catches the throttle slide position) up gradient being the biggest risk, as it can never catch up.
"Lean" running, in and of itself doesn't necessarily increase heat as a cause. What happens as the combustion chamber reaches its ability to burn fuel as it approaches the 14.7:1 ideal (stoichiometric) the propagation of flame front outward from the spark plug begins to break down such that the burn phase doesn't spread out to far reaches of tbe periphery of piston/chamber. This results in unburnt "gas" mixture in a ring around that periphery, which then explodes rather than burns as piston comes to tdc. Its this uncontrolled event that gives a shock wave that breaks the boundary layer protecting the piston crown from exposure to high heat and subsequently raises the overall temperature if left unchecked. When more extreme, we can hear this as "pinking" but it starts in virtually inaudible levels before we become aware of it in more severe form (we're isolated from source & with helmet sound insulation too) but it happens and significantly shifts the temperature accumulation, that also being relative to the ambient air trying to cool tbe motor and it's capacity if moving more slowly. Detonation is the process, as there's loss of control thats fundamental to how the fuel air mix is supposed to combust, rather than explode. Essentially it has the effect of advancing the timing to detriment of the engine's desirable running condition.
There's another phase going on from this as too much of the above will likely bring pre-ignition, which is usually catastrophic, and in short time frame too :o this will definitely put a hole in tbe piston for you!
Seems like you've got away with it in recent description, but quite close to serious damage though.
--- End quote ---
Many thanks for the detailed explanation , I have modified the coils just waiting for the Milliput epoxy putty to dry then just a matter of rubbing down and painting then checking coils and fit back on the bike snd see what happens.
Will probably check the timing again and the carb sync because this will all be affected if I was only running on three cylinders some of the time.
I did notice that when setting up the timing with a strobe it was occasionally jumping around which was probably due to the misfire on number two spark plug.
This has been an interesting problem and it’s very easy with any issue to jump to the wrong conclusions.
When I originally bought the bike and rode it home from Barnstable to Copthorne Sussex it seemed ok but when I got around the stripping down the engine I found a piston and I think it was two had quite a bit of heat damage where the head of the piston was partially vaporised.
I originally believed was due to a piston ring being broken but it’s all making sense now.
Obviously during the rebuild I did change piston two and fitted new piston rings to all cylinders.
I will try and see if I can get hold of a endoscope camera to look at the head of the pistons thru the spark plug hole to see if there is any damage .
This is my first bike rebuild so it’s been a learning curve , I originally just checked for a spark on all cylinders and didn’t check the coils resistance so lesson learned .
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