Bike loses power sporadically

[skinny]

What would cause a bike to loose power while riding? this is inconsistant and speed / gear and load seem to have no relevance. It just doesnt have power sometimes usually while riding along and trying to give it gas it sounds like the bike all of a sudden starts running on 3 or less cylinders (due to exhaust note change).

Is this likely to be electrical or fuel related?

[koba]

Most likely electrical.
Pulse coil, Ignition coil or Black Box.

If it last for a reasonable ammount of time it would be good if you could check for spark while its going on...

Start reading...

[FJRider]

Most likely electrical.
Pulse coil, Ignition coil or Black Box.

If it last for a reasonable ammount of time it would be good if you could check for spark while its going on...

Start reading...

What he said ... check the plugs for crud / gap ... it doesn't take much to rob a few horsepower ...

Fuel filter blocked ... ?? kink in the fuel line ???

I would say fuel ... electrical is usually all go or NOTHING ...

[koba]

I would say fuel ... electrical is usually all go or NOTHING ...

True.

I had a particular incident in mind, If it is an instant drop in power and stays at the same low level of power which causes it to struggle to even do a hundie kays look at the pulse coils and ignitiopn cols because one half of the engine isn't working.

It it is more of a cough and splutter and is less sharp/consistant I would look at a fuel problem.

Its real hard to relate stuff like this though a keyboard!

I would check everything anyway, starting at the fuel tank breather... there can be some real obvious things like fuel filters etc but less obvious ones like a damaged carb diaphragm.

[stify]

I would say fuel ... electrical is usually all go or NOTHING ...

well how can I top this gem of an internet diagnosis....

[FJRider]

Start it in the dark ... and look for spark where there SHOULDN'T be spark ... a short in the leads ...

A dodgy lead would cause probs like this ...

[CookMySock]

Does it do it after riding for quite a while? Does it come right for a while if you stop? Worse at night or in cooler weather? It might be the fuel tank vacuuming down.

Steve

[YellowDog]

I have had incredible results from similar problems by changing HT leads.

Good luck.

[stify]

[QUOTE=DangerousBastard;1129646699 It might be the fuel tank vacuuming down.
[/QUOTE]

ok the last internet diagnosis isn't anywhere near this gem....I've been a mechanic for the last 20 odd years and never heard of this one....maybe you should stick to what ever the fuck you do during the day....

[skinny]

Its a discussion i did ask for peoples opinions. Obviously not everyone is a mechanic and its the risk i take for starters when people cant even see it or ride it or knowing its history.

[skinny]

do you test the spark like a car with a screw driver in the lead and arc it against the engine?

[skinny]

its pretty instant i will have trottle and then all of a sudden i have sweet F all. then i can hold throttle in the same position and after a few seconds it will come back and other times i need to change gear. Even tho none of these always work. Could be i just go over the right bump and the powers back again.

[koba]

its pretty instant i will have trottle and then all of a sudden i have sweet F all. then i can hold throttle in the same position and after a few seconds it will come back and other times i need to change gear. Even tho none of these always work. Could be i just go over the right bump and the powers back again.

Either be prepared to spend ages checking everything and doing lots of learning or take it to someone who already knows, you really aren't going to get too much useful diagnosis over the internet.

[skinny]

for someone whos hands on it can be a money saver too. Ive been to mechanic before who wouldnt have a clue what they are doing but charge you to go through all the options that i can do myself.

[Ragingrob]

Could also be reg/rec failing. I've had this problem and experience similar symptoms. There is a troubleshooting flowchart for the reg/rec if you have a search around, sorry bit busy at the moment to look myself.

[koba]

for someone whos hands on it can be a money saver too. Ive been to mechanic before who wouldnt have a clue what they are doing but charge you to go through all the options that i can do myself.

Ok then, your best off looking for a service manual, it will tell you how to test all the specific components.

[CookMySock]

ok the last internet diagnosis isn't anywhere near this gem....I've been a mechanic for the last 20 odd years and never heard of this one....maybe you should stick to what ever the fuck you do during the day....Shoot filthy mouth off? much? Stick to talking to your women like that ay? Jerk.

Steve

[crazyhorse]

Too technical for me - I'd take it to a bike shop :wari:

[stify]

Shoot filthy mouth off? much? Stick to talking to your women like that ay? Jerk.

Steve

oh no I've got hurt feelings....and I stand by awaiting more usless information from you...dick

[YellowDog]

Hey Skinny, I did have something like this happen on my XF650. It would just lose power jerking on and off at around 100kph.

The solution turned out to be the battery terminal screw being a bit loose. I tightened it and all was sweet for a week or so and then it did it again. I stripped and cleaned both terminals and then did them both up tightly. The problem was completely cured.

Hope you problem is something as simple as this.

[FROSTY]

Skinny given your description I'd be STARTING to look at the carbs,fuel pump fuel tap area.
Look at it this way if I'm right you're ahappy camper if I"m wrong you've given the carbs a good huck out which on an older bike is never a bad thing.
From thereI'd have a look at the plug leads and caps,--seeeing as the tanks off anyway.

[SS90]

oh no I've got hurt feelings....and I stand by awaiting more usless information from you...dick

Dangerous Bastard just chose his words wrong.
By "vaccuming down" (sic), I took it to mean that he was suggesting that the breather on the fuel cap could be blocked, so, when the fuel level decreases, the fuel tank cannot equalise with the ambient air pressure, creating a negative pressure in the fuel tank, essentially stopping the flow of fuel to the carb (the carb cannot equalise this pressure, because of the float valve, so you have air pressure (thereabouts) in the float bowl, and a negative pressure above the float needle.

Positive pressure will always try to equalise negative pressure, not the other way round, so in effect, there is more chance of fuel going upwards (except for the float valve stopping it) to the tank than from the tank to the carb in this situation, like when you pour petrol from a 20l plastic container, you have to undo the little "breather cap" on the top to allow the fuel to flow faster the little piddle that comes out

That's what I took from his statement.

It is a possibilty (but these engines are well known for problems with the emulsion tubes wearing out, and flooding the airbox,giving similar faults).......and, quite common.

[CookMySock]

[....] That's what I took from his statement.He's just taking a (small) opportunity to abuse a person because it makes him look big.(sic)

Steve

[GOONR]

Skinny given your description I'd be STARTING to look at the carbs,fuel pump fuel tap area.
Look at it this way if I'm right you're ahappy camper if I"m wrong you've given the carbs a good huck out which on an older bike is never a bad thing.
From thereI'd have a look at the plug leads and caps,--seeeing as the tanks off anyway.

+1 for looking at the carbs my bike would start to run on 3 cylinders when it was hot, my emulsion tubes are buggered but George from Motorcycle Doctors sorted them out and the bike runs sweet now.

[blossomsowner]

tend to agree with frosty on this one. check carbs, plugs and leads.
Can you tell which cylinder is dropping out by header temp or plug condition?