Hey everyone,

I have an 05' CBR RR with about 49000km on it (30k miles for you yanks)

Occasionally when I try to start it at a hot temperature, the engine will crank a lot slower than normal, as though the battery is dying. Sometimes it will crank a few times before firing up, rarely it won't. I notice this most after I've been riding for about 45 minutes flat.

It will -always- fire up crisp from cold right away.

Any ideas? It's inconsistent which is what I find troublesome

 

That's normal for most engines. When an engine is hot or on the hot end of warm, the pistons are expanded making a tighter fit and rings as well. This is what was explained to me.

Just now thinking about, I bet the oil is thicker also. A 10w-30 would be at its 30w viscosity.

 

Interesting! I don't know a tremendous amount about engines, however what you say would seem to make sense, and would explain both why it happens intermittently and why the bike will always fire up if I let it sit for 10 seconds or so...

 

I don't think it's normal. Warm engines with warm oil should crank better than cold.

You say it's like the battery is low. I'd start looking there. Maybe the charging system is cutting out intermittently or just not at 100%. Check for burned connections... Maybe you have battery cables that are no good and have high resistance that gets worse when they are hot. Maybe the starter motor itself gets resistance as it heats up.

 

Thanks, that is also good insight. I will take a look at the battery connections / cables as you suggest, and mention it all to my shop. Thanks!

 

I have never owned a bike that would crank fast when hot.

I found this LINK interesting.

I would guess that, if your thermostat or cooling system was not up to spec, when you shut it down it may be hotter than normal making it harder to start or taking longer to cool down.

Yesterday I took a 340 mile ride with 9 other bikes. I was the last one to fire up on a few occasions because my big air cooled twin was cranking to slow to start. Its got a compression release due to the 927cc pistons and higher compression. It will bump up against the compression stroke and stop dead if not spinning fast enough. If I press the start button and it cranks but stops dead, I press it again and again until I get it past compression and it fires up. Usually 2-3 tries and its running but only when hot. One a windy or breezy day I have no problems what so ever. If it sits for 10 minutes, it fire right up any day, 5 minutes on a hot day it may not fire up first try.

My CBR almost never cranks up when hot.

 

WOW thank you for this! That is tremendous insight into what could very well be the issue / cause of the problem.

What you describe sounds exactly like what my bike is doing; if I leave it for 10 seconds it will fire right up, but on occasion it will crank very slowly and then fire.

I will clean the battery connections and take a look at the starter to see if it's shielded. If it's not, will some insulating tape (the silver metal stuff) work? Any ideas?

 

I don't know until you try. lol

 

hehe good point, thanks again