Engine problems - due to heat?

[Loo Kahs]

Hello, (long read, sorry)

This has been going on for a while now, but I've been desperate to see some logic in it. Hopefully I am not inventing it.

Every day of the week the bike ran perfectly fine in the morning. It turned on without any problems and idled nicely.

Upon finishing work, I'd get back on it to go home. I'd cross tower bridge and get onto the highway and almost as a rule the bike would start having problems all the way to home. I may be imagining, but I thought it got even worse when I was going through the long tunnel.

I have been thinking whether this is heat related. The bike sits and cools down in a bicycle store (air ventilated). In the morning while the engine's cool it runs nicely for 15 minutes that it takes me to get to work. It then is parked outside in +20C and perhaps some sun. Upon my return home, it takes 5 or 10 minutes to warm up and the problem starts. If I stop, and idle, or turn the engine off... it will start running better... and then start again once on the road again.

To prove my lame theory.. I thought will it happen today again? It rained at lunchtime and was generally a bit cooler in the afternoon than the previous days. I thought, what are the chances that I might get to ride it problem-less for longer than the previous days? And so I did. I almost managed to get home without any issues until the very end when it started having problems! I missed home and rode for another 5 minutes and the problem simply persisted.

I tried to show the problem to agentpinapple. Stopped at his house, chatted for half an hour and then he had a go on the bike. It ran perfectly. Eventually I left and got onto the highway and just before hitting the tunnel the problem started.

Symptoms
- It will be running well and suddenly the sound of engine will get duller as though a cylinder, or both are not firing right. This will mean I will have to keep higher revolutions to maintain the same speed and also keep playing with the clutch for the times when it momentarily runs fine and gives a burst of power.
- The problem has a 'range of shitness'. It isn't on and off where the engine is running perfectly and suddenly it's really lacking power. It may be juddering a bit, but with a twist of throttle it will accelerate quite well. Other times it may be so bad (for example when going through the tunnel) that even fully opening the throttle barely does anything other than maintain current speed.
- If I stop for a bit and either idle at 1k or turn the engine off. It will after a while start running nicely. However, the problem will come back soon enough.

[Loo Kahs]

Photos during CCT change






Photos 1 or 2 weeks after sparkplug change





Peacock

I cleaned that bit of filth off. Otherwise seems perfectly fine.

[fabiostar]

if that was my engine id be thinking its running weak looking at those plugs.. check the airfilter/carbs are tight and you have no air leaks. also give your carbs a good clean.

[freeridenick]

if that was my engine id be thinking its running weak looking at those plugs.. check the airfilter/carbs are tight and you have no air leaks. also give your carbs a good clean.

Or, from the carb tuning guide in the welcome in:
NOTE: A rich problem gets worse as the engine heats up. If the throttle is lightly "blipped" at idle, and the rpm drops below the set idle speed, then rises up to the set idle speed, the low speed mixture screws are probably set too rich: try 1/2 turn in, to lean the idle mixture.

Either way. I'd say start where Fabio said and work out through balancing, cleaning and jetting.

[VTRDark]

Something is not right there. Change the plugs as a matter of precaution....cheap enough to replace and I have known plugs to be bad even new ones. You also have to make sure the HT leads are seated securely too. It takes a bit of force sometimes to get the front on. Sounds more electrical or fuel starvation to me. Plugs yeh maybe a little week. Weird how it happens only when hot though....almost like it's overheating. What's you temperature reading like and have you heard the fan kick in. Fuel mixture is a tricky one as it's very easy to get caught up in whether it's running lean or rich. You could try turning your mixture screws out a 1/4 turn to richen and see if things improve. It's a bit of a pain in the butt though because to do this accurately requires carb removal in which case you might as well strip them down and give them a squirt through with carb cleaner. While you at it...note what the jetting is.

[Loo Kahs]

- Sparkplugs were changed after the problem was noticed hoping for an improvement. Thus, a 2nd change unlikely to solve the problem. However, I suppose even if I was to change them and see no difference.. I could still use the existing ones in the future.

- "If the throttle is lightly "blipped" at idle, and the rpm drops below the set idle speed, then rises up to the set idle speed, the low speed mixture screws are probably set too rich" - I don't think this is the case. I will double check tomorrow. Also, the motorbike when started cold runs better with choke on, and better without choke when warmed up. Would this not suggest that the mixture is fine? Lastly, if the mixture was to blame, it wouldn't quite explain the scenario where the bike is fine after a couple minute break as I had described previously.

- HT leads are on properly

- From what I recall the temperature reading has always been fine and the fan does kick in when needed.

I'd like to avoid carb removal for the time being. Hence, why I was wondering whether replacing the ignition coils and ht leads could perhaps solve the problem at little cost. If that were to be of no use, then carbs could be next.

[xeris]

Do you still have the stock R/R? When it starts to go bad, strange and random symptoms occur. Check battery voltage at rest and when running at start of day and then when you arrive home or when running poorly.