Motorbike looses power when I give it throttle

SweetCaliber

Hey all,

I'm completely baffled. Got the bike back on the road yesterday, drove great for a couple of mins and then started to loose power.

I pulled in and let it idle, which it did perfect but when I attempted to go near the throttle it just lost power, almost to where it would cut out but then it would stutter.

Funny thing is, if I leave the bike to go cold, start it, nothing wrong when I give it throttle, but the minute I give her throttle when shes warm, she looses power and it happens all over again.

The bike was lying up for 2 months and after cleaning out the tank it was full of rush and dirt, I know the problem is probably in the carbs, which I am going to strip and clean tomorrow, but it still doesn't explain why the bike will only do it when its warm.

Any idea?

Skill Magill

Is the choke on?

Pawwed Rig

Is there a kink in the fuel line?

SweetCaliber

Skill Magill wrote: »

Is the choke on?

Tried it with choke on and off makes no difference the bike will rev high with the choke on when warm but still when i give it throttle dies down then stutters

SweetCaliber

Pawwed Rig wrote: »

Is there a kink in the fuel line?

Nope it is vaccum pumped though, seems to be operating grand though, tried it without the tank and good suction on the host that goes to the tank.

Krusty_Clown

What kind of bike?

I've had similar problems in the past, down to a failed fuel pump relay (bmw), faulty kick-stand switch (bmw), throttle position sensor (Suzuki) and muck/water in the carbs (cbr250).

SweetCaliber

Krusty_Clown wrote: »

What kind of bike?

I've had similar problems in the past, down to a failed fuel pump relay (bmw), faulty kick-stand switch (bmw), throttle position sensor (Suzuki) and muck/water in the carbs (cbr250).

Hyosung GT125R.

kaimera

TPS set too low?

Wossack

any better if you leave the cap for the fuel tank open?

SweetCaliber

Wossack wrote: »

any better if you leave the cap for the fuel tank open?

Tried that, no difference. I still find it odd how it only does it when the bike has warmed up.

SweetCaliber

Okay update guys.

Finally took the carbs out today and gave them a good soak and clean. There was a small bit of dirt in them so got them spotless, cleaned all the jets etc.. also.

Took out the spark plugs, they were jet black so gave them a quick sand to clean them.

Checked the fuel pump, all works well, checked all hoses and all clear.

So put everything back together and she started running well.

Brought her off for a half hour spin and she ran like a beauty. Never seen so much power out of her.

All was well until the problem has suddenly reappeared.

Just made it home and once again once I give it any bit of throttle, she loses power and stutters.

Absolutely pi***d off right now, this is starting to do my head in now

I can rule out the carbs and the petrol pump, also cleaned the tank and that so no dirt has gotten back into the carbs.

The only thing I can think of now is the spark plugs? I'm going to sand them down again when they cool and see and I'm going to get new ones tomorrow but does anyone have any idea whats wrong?

Thanks

BlackWizard

What about shims? Are they okay?

If they need replacing they would reduce the cylinder compression and really give the symptoms you are experiencing. But it would more of a consitent problem.

Next time it happens would you be able to check if it's firing on all cylinders? Maybe it has a faulty spark plug or cable. But you would notice a difference in the spark plugs if it had problems with firing.. although if its inconsistent maybe not?

ZX7R

If your spark plugs are black i.e black from sooty build up could be caused by a faulty choke cable ,or more likely your fuel/air mix is to rich this would cause loss of power when you open the throttle.
If it black and oily damp your piston rings could be on there way out, also the fact you have cleaned your carbs they might need to be ballenced.
If your bike is a two stroke it could be using too much 2/stroke in the petrol mix.
hope this helps.

CJhaughey

Do you have an inline fuel filter between the carbs and the tank?
Its very worthwhile fitting one, especially as there is already rust and dirt in the tank.

Are both plugs the same colour or is it just one cylinder?
It could be electrical, when CDI units get warm they sometimes break down, is it a single cdi unit or one for each cylinder?
Sorry for the Q's I haven't seen many Hyosungs.

kaimera

Missus had a prob on her fazer a good while back; would idle fine but die when the throttle opened (fun trip to rosslare that was)

Adjusting the TPS (throttle position sensor) higher sorted it before the return trip.

SweetCaliber

kaimera wrote: »

Missus had a prob on her fazer a good while back; would idle fine but die when the throttle opened (fun trip to rosslare that was)

Adjusting the TPS (throttle position sensor) higher sorted it before the return trip.

I dont think i have one tbh haha where abouts would i find it?

kaimera

hmmm

on hers, left side of the engine, looked like a plastic nut with a X (or +) on it, turning it with engine idling would increase/decrease revs.

BlackWizard

Is the TPS not different to the Idle Control valve?

I think the idle control valve has a + sign on it. Or maybe its the other way around.. heh

SweetCaliber

BlackWizard wrote: »

Is the TPS not different to the Idle Control valve?

I think the idle control valve has a + sign on it. Or maybe its the other way around.. heh

Was in honda center today and he said to clear a hold undrr the petrol cap apparently it runs down through the tank and gives air, he also recommended that i get the tank sealed when i told him about the rust, will give it a go first!

kaimera

BlackWizard wrote: »

Is the TPS not different to the Idle Control valve?

I think the idle control valve has a + sign on it. Or maybe its the other way around.. heh

ah feck, I think I'm confusing work I did on my old bike and hers.

I hit my head this one time

Me thinks you are right

SweetCaliber

CJhaughey wrote: »

Do you have an inline fuel filter between the carbs and the tank?
Its very worthwhile fitting one, especially as there is already rust and dirt in the tank.

Are both plugs the same colour or is it just one cylinder?
It could be electrical, when CDI units get warm they sometimes break down, is it a single cdi unit or one for each cylinder?
Sorry for the Q's I haven't seen many Hyosungs.

Theres a fuel filter fitted on the vaccum operated petcock, its clean.

Both plugs were black but after taking her for her recent spin before it happened again the plugs were fine.

It could be, I got advice from the Honda center first, if not they will take it in and run a diagnostics so that might show some results.

It's a single CDI unit.

Thanks for all your help everyone soo far Hopefully I'll get it sorted out soon.

CJhaughey

SweetCaliber wrote: »

Theres a fuel filter fitted on the vaccum operated petcock, its clean.

Both plugs were black but after taking her for her recent spin before it happened again the plugs were fine.

It could be, I got advice from the Honda center first, if not they will take it in and run a diagnostics so that might show some results.

It's a single CDI unit.

Thanks for all your help everyone soo far Hopefully I'll get it sorted out soon.

Those tap mounted filters are only OK, better fit a proper paper element type one TBH, they filter finer particles better.
I'd be thinking electrical problems, Coil, Pickups and CDI and also ignition leads from the coils to the plugs and plug caps.
Check them in a dark place or use a fine water spray to see if you can see sparks.

SweetCaliber

Hey guys,

Long time no see! Well she seems to be working again

After a long and committing time and not giving up, I finally found the problem, well problems. One of them fixed it!

First off, the vent hole on my petrol tank under the cap was blocked, yep its a vent hole, not overflow!

Second, the carbs were out of sync, so I put them back in sync.

Third, well my bike has an "automatic vacuum operated pet cock". Yep that's right, no tap or nothing, its a lazy man's way of shutting the petrol off. Well the diaphragm in that was gone, I presume. I tried bypassing it by sealing off where the vacuum hose goes in and removing the diaphragm.

After doing all them, well she's running like a charm again

I'm going to replace the diaphragm as I don't like the fuel staying on, my floats work and she's is started every morning so its nothing major, but just in case.

So yeah. One of those three things I did worked, which, I'll never know but it really sounds like the pet cock was the main issue, after all its what gives petrol and cuts it off, duh!

Thanks for all the help guys, hopefully she will run right now, once the cold weather in the winter doesn't f**k it up! :P