Bike quirks

Luimni

Hello all,
Im enjoying the crap out of riding my bike at the moment, roll on the long bright evenings.
But when i am driving along minding my own business on a straight road in 4th/5th gear with gentle throttle on as needed, suddenly the engine starts to loose revs as if i let off the throttle and continues to loose revs no matter what i do with the throttle.
But the strange thing is, is when I change down gears to try and remedy the situation, I pull in the clutch and the engine goes silent and it only kicks back in when i let go the clutch (whether i change down gear or not)
I usually have to stop, turn off the bike and restart then everything is grand again for another few days.
The garage looked at it and couldnt find anything.

Tank was 3/4 full
Throttle cable seems fine
But the engine stopping when the clutch is pulled in and comes back when i put the clutch out again baffles me

Has this happened to anyone else and if so what was the problem.

Any help much appreciated.

Laserface

possibly a bit of water in the petrol tank?
due to the ****in rain when filling up.

This happened to me recently...but not the clutch part...so I dunno

Slaanesh

My bike took ages to warm up the other morning. If I pulled the clutch in the engine would die. When releasing the clutch this turns the engine over and starts it again (When moving).

My bike just wasn't warmed up enough, didn't leave the choke on for long enough I think.

Idleater

Luimni wrote:

Has this happened to anyone else and if so what was the problem.

Sounds very much like Carb Icing to me.

I would recommend using this as an opportunity of upgrading your bike to an ECU based bike

L.

Elfish

Luimni wrote:

But when i am driving along minding my own business on a straight road in 4th/5th gear with gentle throttle on as needed

Does giving throttle cause engine cutout?

Luimni wrote:

suddenly the engine starts to loose revs as if i let off the throttle and continues to loose revs no matter what i do with the throttle.

Does it lose revs irrespective of whether or not you have clutched?

Luimni wrote:

But the strange thing is, is when I change down gears to try and remedy the situation, I pull in the clutch and the engine goes silent and it only kicks back in when i let go the clutch (whether i change down gear or not)

It is possible that the engine is dying as you pull the clutch, then when you release it, its like bump starting the bike at whatever speed you are doing. So its not really the clutch that is causing the the engine to stop - something else is causing it to stop and letting out the clutch just bump starts the bike.... try getting into neutral next time before letting out the clutch - will the engine still come back to life when you let out the clutch?
Be careful with this lark, bike can get slidey with too much engine braking.;)
Need more info - if you don't bother clutching, will the bike just die?

Possible carb icing, although I think people here are very quick to point the finger at carb icing as the root of all problems - what bike do you have?

Elfish

nereid wrote:

I would recommend using this as an opportunity of upgrading your bike to an ECU based bike
L.

Every bike nowadays is ECU based.
Even if it wasn't, how would it help anyway?

The fella is looking for help, not sidetracking with misleading uninformative posts.
If you asked a mechanic to upgrade your bike to an ECU based bike, he'd laugh at you.

Going by this post, I don't think you know what you are talking about Nereid.

Hotblack Desiato

OP, those are classic, 100%, solid-gold symptoms of carb icing (and fuel injected bikes can suffer icing too)

What bike is it? Is it an import? Imports from countries where bikes hibernate in winter don't have carb heaters fitted and can be endless trouble in damp cold weather

If the bike is under warranty bring it back, it's not fit for purpose and it's not safe to have a bike cutting out unexpectly or losing power (icing can even cause the throttle to stick open, or a surge of power).

If you have to pay for a fix yourself, try Silkolene Pro-FST fuel additive (I think Mountjoy Motorcycles have it) - if that doesn't work and lack of carb heaters is the problem, you'll have to source a set of heated carbs off a UK/Irish spec bike.

Hope this helps

Idleater

Elfish wrote:

Going by this post, I don't think you know what you are talking about Nereid.

Bugger, I apologise - Fuel Injection was what I meant.

Sorry. It was only an attempt at humour anyway. The main part of my post was to highlight Carb Icing to the OP which as it certainly does sound like from the OP's description.

However, you are correct and I am not a mechanic, I was merely providing my opinion on what the symptoms as described in text format over the internet were to the OP.

Ninja, I was unaware that FI could suffer from Icing - cant find explanation on the winternet either.

Elfish, relax... Just biker banter, nothing malicious.

L.

Luimni

Elfish wrote:

Does giving throttle cause engine cutout?


Does it lose revs irrespective of whether or not you have clutched?


It is possible that the engine is dying as you pull the clutch, then when you release it, its like bump starting the bike at whatever speed you are doing. So its not really the clutch that is causing the the engine to stop - something else is causing it to stop and letting out the clutch just bump starts the bike.... try getting into neutral next time before letting out the clutch - will the engine still come back to life when you let out the clutch?
Be careful with this lark, bike can get slidey with too much engine braking.;)
Need more info - if you don't bother clutching, will the bike just die?

Possible carb icing, although I think people here are very quick to point the finger at carb icing as the root of all problems - what bike do you have?

Sorry Im not able to do the quote thing to reply to individual responses but anyway..

Giving throttle doesnt cause the engine cut out, last time it happened i had the throttle open 1/4 way on a straight with constant speed and the engine just gadually lost power.
I loose revs no matter what i do with the throttle but when i clutch, the engine goes silent and i let go the clutch the engine comes back but doesnt bump or kick back in, it is like slowing down with the throttle closed and clutch pulled in when the clutch is actually out.
The engine looses power and cut out whether clutch is in or out.

Carb icing could be the culprit as another symptom is the throttle sticking from time to time as Ninja pointed out as this has happed a few times to me.

The bike is an Aprilia 125 cruiser, and its not in the best of shape but it has got me started on two wheels. I find it very hard to start in the mornings.

I saw a thread about carb icing before so i will have a look through it. But at least I now have a name to the possible problem that i can go back to the dealer with instead of 'i think my bike is haunted':)

Great stuff
Thanks

Interceptor

It could be several things and I think carb icing gets too much press. I had the very same symptoms on my bike a while ago and it turned out to be a loose connection on the 12v supply to my HT coils - the engine died at whatever revs vibrated the connection enough and it always started again straight away - nearly drove me nuts.

I thought carb icing would prevent the bike re-starting straight away? Your bike isn't haunted but if its a poorly looked after Aprilia then it needs some extra love or it will develop faults like this.

'cptr

Hotblack Desiato

Interceptor wrote:

It could be several things and I think carb icing gets too much press. I had the very same symptoms on my bike a while ago and it turned out to be a loose connection on the 12v supply to my HT coils - the engine died at whatever revs vibrated the connection enough and it always started again straight away - nearly drove me nuts.

There's your clue right there. If it's related to engine revs (goes away if you hold the same speed in another gear) then it's likely electrical. If it's related to throttle position (happens in any gear in the same circumstances) then it's likely fuel.

I thought carb icing would prevent the bike starting straight away?

No. The ice only builds up after the bike starts. Sucking lots of cold damp air into an engine, which is what a carb does, cools it down - evaporating fuel cools it down even more, so it's easy for it to go below freezing and the moisture out of the air can block fuel jets, air flow or freeze the throttle in position!

The best thing to do is (a) get the choke off as soon as possible, more fuel = more cooling (b) if the air temp is below about 5C then let the bike idle for 2-3 minutes after shutting the choke off before riding away. This gives the engine a chance to warm up a little, hopefully enough to keep the carbs above freezing. If carb icing does strike, then turn the engine off for a minute or two and let the engine heat reach the carbs. If you leave the engine running you're still sucking cold air into the carbs so the ice is much harder to melt.

Your bike isn't haunted but if its a poorly looked after Aprilia then it needs some extra love or it will develop faults like this.

Hmmm I never heard a good thing about Aprilia strokers when they were new, never mind 10 years old
As it is a 2-stroke, carb heaters are unlikely to be an option and the Pro-FST additive may not be an option either (could bugger up engine lubrication). My first bike was a 2-stroke and prone to icing as the carb is further away from the engine heat than on a 4-stroke. Only answer was to let it warm well up before riding off on a damp cold morning.

Luimni

Interceptor wrote:

It could be several things and I think carb icing gets too much press. I had the very same symptoms on my bike a while ago and it turned out to be a loose connection on the 12v supply to my HT coils - the engine died at whatever revs vibrated the connection enough and it always started again straight away - nearly drove me nuts.

I thought carb icing would prevent the bike starting straight away? Your bike isn't haunted but if its a poorly looked after Aprilia then it needs some extra love or it will develop faults like this.

'cptr

I really must give the connections another check, just in case. It could be something obvious i have over looked.

I try to give the bike as much love as i can but technical & mechanical love is much more difficult for a beginner like me but the bike is slowly getting that too with the help of an owners manual and Haynes books.
But at the moment its a one way relationship, I thing she is still mad at me at nearly wearing out her starter & battery when stalling the bike so many times while learning.

Laserface

haha..nothing a good spanking wouldn't take care of!

show her who is the boss!!

bushy...

Those bikes can have a few faults as they get a bit older , the rubber between the carb and engine can get porous/split , the magnet in the rotor can break up and move out of place, nipping the wires going to the generator.