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CBF500 loss of power at high revs

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foxylad85
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CBF500 loss of power at high revs

Post by foxylad85 on Thu 02 Jul 2015, 12:04 pm

Hi All,

I have recently bought a 2004 CBF500 as a starter bike having passed my direct access tests.

It starts absolutely on the button and with hardly any choke and rides lovely up to 5000 revs.

However, when I try to go above 5500 revs it is really juddery, hesitant and completely lacking in power. It gets worse in higher gears as well. Sometimes when you can get up to 7500 revs it picks up again, but this still leaves most of the 'fun' rev range unusable. I'm finding myself not wanting to overtake anything because I don't know how the throttle is going to respond.

I have tried the following so far...
- Fuel system cleaner as additive to fuel.
- Checked and cleaned air filter.
- Checked spark plugs and reset plug gaps with feeler gauges.
- Removed, checked and cleaned carbs. Diaphragms are ok. Needles don't show any damage or wear. Jets cleaned out with carb cleaner and compressed air.

After this it is still acting the same.

So I have now replaced the carbs with a set I know have come from a perfectly running bike. Symptoms are still exactly the same.

I suppose my next step to try would be HT leads & coils....

Any help and ideas will be greatly appreciated as I'm at a bit of a loss now.

I'm dreading that it's going to turn out to be a timing issue!!


Thanks,
Chris
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eternally_troubled
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Re: CBF500 loss of power at high revs

Post by eternally_troubled on Thu 02 Jul 2015, 1:32 pm

That sounds annoying.


I know it sounds obvious, but have you checked that the battery terminals and screwed down well? This can screw you over in ways you might not appreciate. While you are looking at the battery, check that it is charging correctly (as per Haynes - 5000 rpm, headlight on, battery voltage should be 14.4 - 15 volts).

Also, it is just about possible that the air-filter may be past its best but still *look* OK - however I doubt this would cause the kind of problem you are having.

Checking the HT leads and coils is not a bad idea - the snag is that the coils can measure-up fine with a multimeter when cold but then breakdown as they get warm through use.

Have you checked the carb rubbers for damage? If there is any air getting in it won't help the situation.

Can you hear any difference when you rev the bike to 5000 while it is standing still, or is the problem only obvious when under way?
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foxylad85
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Re: CBF500 loss of power at high revs

Post by foxylad85 on Thu 02 Jul 2015, 2:37 pm

Hia,
Thanks for your reply!!
Yea battery terminals are definitely screwed in ok. Had the battery off when swapping the carbs out. I've not checked the voltage at high revs though, I'll do that.

Like you said, air filter looks ok and have given it a clean with an air line. Have also ridden the bike with no filter in & the same symptoms exist.

Checked the carb rubbers over when swapping the carbs last night & they appear to be fine. In pretty good nik actually. 

When just revving in neutral it seems to rev fine. Only happens under load and is worse the higher up the gears you go.

Cheers,
Chris
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Beresford
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Re: CBF500 loss of power at high revs

Post by Beresford on Thu 02 Jul 2015, 5:15 pm

When you checked the carb rubbers, did you look to see if there were any power limiting washers stuck up inside them ?
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louiscaron
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Same problem on a 2003 CB500

Post by louiscaron on Thu 02 Jul 2015, 8:22 pm

Hello,
Actually, I am facing exactly the same problem with a 2003 CB500.  I have done the same checks (replaced air filter, replaced carbs with good ones) but it does not go away.

I measured the battery voltage at various rpm and with different light configuration and here it is very strange: around 13 with engine off, then 13.2 at low rpm, and drops to 12.8 when accelerating beyond 5000 rpm.  With the headlights one, the voltage is a little bit higher but the shape is the same.

Could this be the cause of the problem?  How can I investigate any further?

Thanks
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ANDYC
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Re: CBF500 loss of power at high revs

Post by ANDYC on Thu 02 Jul 2015, 9:41 pm

Normally this is a sign of either a duff battery, or an alternator on it's way out. Crying or Very sad

On the CBF model, try making sure that the TPS (throttle position sensor) which is the electrical part at the side of the carbs is secure and clean. On my XJ900 diversion it would show those symptoms, but gain a new lease of life after the TPS was cleaned and treated to some WD40.
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eternally_troubled
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Re: CBF500 loss of power at high revs

Post by eternally_troubled on Fri 03 Jul 2015, 1:33 pm

@ANDYC wrote:Normally this is a sign of either a duff battery, or an alternator on it's way out. Crying or Very sad

I can be caused by a duff regulator/rectifier too, but probably less likely, essentially it is caused by the battery not charging correctly.

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mcalvert39
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Re: CBF500 loss of power at high revs

Post by mcalvert39 on Fri 03 Jul 2015, 7:40 pm

This is weird. . . im also having the same problem. Just arose a few days ago. Completely standard CB500s. Had the tank off, plugs out, air filter. saw no faults at all. Its only just started to happen so it cant be a restrictor. Im thinking coil pack is starting to break down. It did start though on the hottest day of the year though but didn't overheat. Im going to take it out again tonight now its abit cooler and head to southport for a run out. Ill report back.

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Re: CBF500 loss of power at high revs

Post by Guest on Fri 03 Jul 2015, 9:32 pm

Being an absolute beginner I may quote Haynes:


2 Poor running at low speeds
Poor acceleration
° Timing not advancing. Pulse generator or ignition control module at fault.

3 Poor running or no power at high speed
Firing incorrect
° Ignition control unit or ignition coils defective.

Neutral ... possible?!
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submarinex1
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Re: CBF500 loss of power at high revs

Post by submarinex1 on Tue 11 Aug 2015, 9:00 pm

odd thing I'm having his problem it gets stutter like fuel out,if can get past the point it clears as if nothing happened.

no issues lower gears then hit the 6k revs and stutter, no issues starting or running normal, no funny noises
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submarinex1
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Re: CBF500 loss of power at high revs

Post by submarinex1 on Wed 26 Aug 2015, 9:09 pm

after checking seems not just cb500 having issue, one suggested redex in tank, Its hard to say if fixed or not but after putting small amount in and running bike for 2 days the issue I had with loss power has not happened.
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dave jones
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Re: CBF500 loss of power at high revs

Post by dave jones on Wed 27 Dec 2017, 10:46 pm

Hi there, im new to this forum, i have a 2004 cbf500 non abs and im having exactly the same issues as you mentioned, has anyone found a cure for this? i have tried the following...
new coils
new plugs
new air filter
and the problem is still there, pulls fine up to 5000rpm then stutters upto 6000rpm once past that its fine, it revs out fine standing still, only when its under load as such.
can anyone please help me out? 
cheers in advance
Dave
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eternally_troubled
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Re: CBF500 loss of power at high revs

Post by eternally_troubled on Fri 29 Dec 2017, 8:15 pm

@dave jones wrote:Hi there, im new to this forum, i have a 2004 cbf500 non abs and im having exactly the same issues as you mentioned, has anyone found a cure for this? i have tried the following...
new coils
new plugs
new air filter
and the problem is still there, pulls fine up to 5000rpm then stutters upto 6000rpm once past that its fine, it revs out fine standing still, only when its under load as such.
can anyone please help me out? 
cheers in advance
Dave

I don't think anyone fixed this particular problem. Did you check the battery-charging and terminal connections (as mentioned above)? Also I think Andy's TPS tip is probably worth a shout too...

I would warn you in advance it's quite difficult to resolve these things remotely; you might have to get a real-life mechanic involed at some point (or at least a mate who's good at fixing things).
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skyrider
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Re: CBF500 loss of power at high revs

Post by skyrider on Sat 30 Dec 2017, 2:13 pm

could this be a restrictor problem and do any of these bikes have one fitted
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dave jones
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Re: CBF500 loss of power at high revs

Post by dave jones on Sun 31 Dec 2017, 8:31 pm

thanks for reply, ive been through every connection etc and given them a clean, nothing jumped out at me. whilst doing checks i checked the windings and none of the three yellow cables go to earth, so that would suggest they are ok, how ever when i was testing the charging i got the following which looked strange to me...
12.4v on tick over
14.6v at about 2000rpm
13.6v at about 5000rpm

if i put my heated grips on and leave it on tick over it stuggles to reach 12.0v.
does anyone else get readings like this?

cheers Dave
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eternally_troubled
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Re: CBF500 loss of power at high revs

Post by eternally_troubled on Mon 01 Jan 2018, 11:25 pm

@dave jones wrote:thanks for reply, ive been through every connection etc and given them a clean, nothing jumped out at me. whilst doing checks i checked the windings and none of the three yellow cables go to earth, so that would suggest they are ok, how ever when i was testing the charging i got the following which looked strange to me...
12.4v on tick over
14.6v at about 2000rpm
13.6v at about 5000rpm

if i put my heated grips on and leave it on tick over it stuggles to reach 12.0v.
does anyone else get readings like this?

cheers Dave

I've seen the voltage go up and down like that; it seems odd, but I don't think it is anything to worry about. The current draw for the ignition system will be more (on average) at higher revs which may well be why the terminal voltage of the battery goes down a bit (less current to charge the battery).

From my experience with heated grips (bog standard oxford ones) on a CB500: the charging system doesn't generate enough energy at tickover to charge the battery AND power the grips AND power the headlight. End result (if you do a lot of idling with the headlight and grips on) a flat battery and poor starting.

My commute used to consist of a fair bit of filtering through town so I ended up switching off my headlight and/or heated grips where possible and the situation with my battery got better.

If you only every use the grips on longer journeys with higher revs you won't have this problem...
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ANDYC
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Re: CBF500 loss of power at high revs

Post by ANDYC on Tue 02 Jan 2018, 5:05 pm

I upgraded my alternator to supply enough power to run heated grips, a heated jacket as well as always running lights. No problem at all.
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wornsprokets
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Re: CBF500 loss of power at high revs

Post by wornsprokets on Tue 02 Jan 2018, 5:40 pm

What alltenator did u use andy...from what bike
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Jameshambleton
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Re: CBF500 loss of power at high revs

Post by Jameshambleton on Tue 02 Jan 2018, 6:29 pm

@wornsprokets wrote:What alltenator did u use andy...from what bike

vfr800fi/cbr1100xx, same as what I run.
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ANDYC
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Re: CBF500 loss of power at high revs

Post by ANDYC on Wed 03 Jan 2018, 9:49 am

Yes mine was to suit the cbr1100xx.
I do believe that it's now available for sale as I stripped the bike.

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