CB650F Cold start problems, maybe difficult rich mixture? Or fuel pump?

Pikappa · Nov 28, 2021

Hi everyone, I'm facing some trouble with my CB650F 2017 ABS with 17000 km

I've noticed that, more and more frequently, the engine starts (cold start) with some problems: it seems that the engine is having difficulty getting to the right rpm (that are more high when it's cold, of course). Seems that it has difficulty to arrive to a rich mixture, I suppose (sorry for my bad english). It starts with low rpm, then go high with a few seconds of process.

Since now, when I've started the engine (cold), it went quickly to the right rpm without any problems. And of course went lower when it become hot.

When it's started, the engine is perfect, idle and running, cold and hot.

What can be the problem? Fuel pump? Spark plug?

Thanks for your help!

xorbe · Nov 29, 2021

17K km / 11000 miles ... time for valve adjustment inspection maybe? But that's a bit early per the maintenance chart. However I had one bike that needed adjustment way early.

Brammers · Nov 30, 2021

I was thinking valves as well. Possible if oil has not been changed or lots of short cold journeys wearing the engine more - possibly.

Worth checking the clearances to be safe.

J

baugustine · Nov 30, 2021

What is the fuel pressure at start-up and when its at operating temperature?

Pikappa · Dec 8, 2021

baugustine said:
What is the fuel pressure at start-up and when its at operating temperature?

How can I check that?

Anyway, i always do at least 20km when I take the bike. Valves at 17k km? It is possible? Or iat sensor?

Oil changed ai 1000km, 8000km and 14000km with motul 10w40

If I take the bike every day, it seems that the problems disappeared.

Today, after 3 days of stop, the problems appeared again.

Atucker · Dec 8, 2021

Did you test the battery?

Pikappa · Dec 8, 2021

Atucker said:
Did you test the battery?

Yep, tested with another battery, a new one, same problems.

One more info, when a turn on the bike, i smell a little fuel, not so heavy, but i smell it.

No smoke from the terminal, no smell during the trip with hot engine

baugustine · Dec 8, 2021

Pikappa said:
How can I check that?

Connect an fuel pressure gauge to the fuel rail before you start it up. When you power the bike on, the pump will prime. I believe the spec is ~35psi but its listed in the service manual along with the required tools.

Pikappa · Dec 8, 2021

Ok I did a video, please give me some opinions:

accensione Honda cb650f, miscela che si ingrassa lentamente

Enjoy the videos and music you love, upload original content, and share it all with friends, family, and the world on YouTube.

youtube.com

Atucker · Dec 8, 2021

I'm not sure what I'm missing, but that seems 100% normal?

miweber929 · Dec 9, 2021

Atucker said:
I'm not sure what I'm missing, but that seems 100% normal?

Agreed.

The high idle that the bike does cold isn’t really a “set” thing, instead the ECU monitors it’s multiple sensors and sets idle based on what it sees. So there are times when the motor is cold you’ll see idle wander a bit as the ECU tries to figure out where it should be set and it may vary a bit or even sound like a misfire as it figures out where to set itself at. And it’s always trying to run as lean and efficiently as possible so it’s trying to have a lower idle as soon as it possibly can.

What you posted sounded and seemed normal to me.

JRinKtown · Dec 9, 2021

Pikappa said:
Ok I did a video, please give me some opinions:

accensione Honda cb650f, miscela che si ingrassa lentamente

Enjoy the videos and music you love, upload original content, and share it all with friends, family, and the world on YouTube.

youtube.com

Listening to that, it sounds perfectly normal. Since new, my 650F 2018 starts the same way. It'll hold those high rpm's for about 2 minutes before gradually reducing. I always wait about 2 minutes before riding on a cold start. If I don't wait that long the bike will be very sluggish for a half mile or so. Honda techs told me it's all normal and common on many of their models.

Flashpoint · Dec 22, 2021

Pikappa said:
How can I check that?

Anyway, i always do at least 20km when I take the bike. Valves at 17k km? It is possible? Or iat sensor?

Oil changed ai 1000km, 8000km and 14000km with motul 10w40

If I take the bike every day, it seems that the problems disappeared.

Today, after 3 days of stop, the problems appeared again.

Hi

I ride a CB650f from 2017, 15 000km. I have an IXIL aftermarket exhaust without the db killer and I did not have an ECU flash/remapping. My bike also has a lot of trouble when trying to start in cold/humid weather. I ride to work daily in spring and summer, so it's about 80km per day on the bike. Still, with certain weather conditions, the bike will not start in the morning.

This has happened at least 3 times the last few months! Seems to be when the nighttime temperature drops below 10°c and the bike stands outside.. Battery is fine (I always make sure to charge the battery when I don't ride for a longer time, the battery's health is also fine).

There is nothing I can do to get it to start, I just wait a day or 2 and then it suddenly comes back to live again. This is frustrating.

At the moment, my bike is with the garage to try and figure this problem out. He said that we maybe can solve this by putting in a different kind of sparkplug. But I'll keep you updated.