CB550F Gradually losing power and stopping...

[Steph550]

Hi all,

I've also posted this on the US forum so apologies if you've already seen it there.

Went out for a nice evening's ride on my CB550F yesterday, and broke down no less than 4 times on the way home!! I'm just about to start investigating the problem and wondered whether any of you guys would be able to shed any light on it...

The bike hasn't been out a lot recently, has been sitting in the garage and run occasionally. Got her out on Tuesday, filled her up with petrol and went for around a 15 mile ride. No issues at all. Then on Friday went for a 50 mile ride and the bike didn't miss a beat. Yesterday, rode for 5 miles with no problems, and stopped off at a pub.

After that, things started going wrong. Left the pub, got around 2 miles down the road and started losing power. Then she stopped completely, and I pulled over. At this point I realised I'd been an idiot and forgotten to turn the fuel on when leaving the pub, so turned it on and tried to start the bike. Strangely, she didn't start after several attempts... I wheeled her over to a safer spot, sat and contemplated for a bit then tried again, and she started immediately. I rode on, thinking "that's a bit strange" but she seemed to be behaving herself. However, another two miles down the road I started losing power again, losing one cylinder at a time. It would pick up if I opened the throttle fairly sharply, but got progressively worse, then stopped. This time the fuel was definitely on. Pulled over, tried to start, no joy. Fiddled with things, tried switching the fuel onto reserve, made no difference. Waited a few minutes, and she started normally.

Another two miles down the road, repeated the same process. And then again just before I got home!

It's not a battery issue because the electric start is turning over perfectly. Trying to kick start her makes no difference.

Has anyone had anything like this before? Just about to go and break down again then see if there's a spark or not...

I'd be grateful for any advice.

Thanks,

Steph.

[Bitsa (Ralph Wright - RIP)]

Steph
Sounds to me fuel starvation.Check the vent in the filler cap is clear because as you say when leaving it a few minutes it fires up again that's because the carbs are slowly filling up again.While you are at it I would check all the fuel system tap filter etc.
Hope this helps you
Bitsa

[LesterPiglet]

I'm with bitsa. Unscrew the carb drains and see if any crud comes out. Do you have an inline fuel filter? Maybe this is blocked.

[Bryanj]

Another p[ossibility is the charging system not working and after a while the battery recovers enough to allow a re-start. I've had it happen to me

[matthewmosse]

A friend of mine had his bike do this several times, he'd far more expirience and knowledge of bikes than me but still ended up stranded. I went back up there with him to collect the abandoned machine and after some head sctatching I spotted the fuel pipe had a slight kink in it which was restricting fuel flow. Also check fuel cap vents, tap might be in need of a clean as said above.

[Steph550]

Thanks for the replies,

It is looking very much like a fuel starvation problem. I have since filled the tank completely and the bike's done 80 miles without missing a beat...!

The vent in the filler cap is fine, I'll have a look at the filter when I get a chance.

Cheers

Steph.

[Bryanj]

Could just have been going on reserve, how much did you put in to fill it?

[Steph550]

Tried running it on reserve and had the same problem. It took about £10 of premium unleaded (about £1.59 a litre )

Steph.

[LesterPiglet]

I've just reread. This happened after you forgot to turn the fuel on. Carbs possibly sucked up sediment in the bottom of the float bowls, I would check the bowls first. If there is crap in there you will need to clean all your jets out.

[Bryanj]

What you put in is about the quantity before you go on reserve so i would suspect that the reserve part of the tap is bungeded up mate

[LesterPiglet]

except she says she's done 80 miles since filling the tank up without it missing a beat

I don't see that stated.

[LesterPiglet]

Post 6 Lester

Thanks for the replies,

It is looking very much like a fuel starvation problem. I have since filled the tank completely and the bike's done 80 miles without missing a beat...!

The vent in the filler cap is fine, I'll have a look at the filter when I get a chance.

Cheers

Steph.

Hmm, I must have skipped that second post..sorry. 

[Steph550]

Thanks again for all your help.

Bryanj, you were right, the reserve part of the tap was blocked. All sorted now and running sweetly again after having also decided to pour oil all over the garage floor that is...! (fortunately just a seal gone!)

Now back on the road, hoping I can enjoy a bit more riding before winter really sets in...

Steph.

[singleoverheadbraincell]

I suspect I have a similar issue to deal with - if you look at my post under "unusual teething problem" from about two weeks ago I eluded to having a similar problem which I thought might have been related to 'stale' fuel. I'm convinced now I have an intermittent issue with my reserve tank tap position (getting blocked) and I'm going to drain the tank to remove the tap for a closer inspection.