can anyone diagnose this?

[nuad]

hi all, hope someone can advise me on this.

 

my bike just came back from an overhaul, its running well and going fine.

 

good power and smooth delivery, no exhaust smoke either.

 

however there a strange problem, and it only developed after i started hard running in the bike.

 

 

after a 15 mins +/- ride, then parking at my destination, when running idle, it would cycle between 8 secs of smooth idling then 3 secs of the engine 'bogging down' (the idle gets weak) then this cycle would repeat for 3-4 times and then the engine would die off. however, no problems starting it up immediately

 

its strange because its perfectly fine when i start it cool.

 

i went around googling online and the closest diagnosis to the symptoms i could find was bad fuel lines.

 

 

went to a shop for diagnosis and the mech told me it was the carb settings, but i really doubt so, as i serviced and tuned it before getting it back, also no lean or rich symptoms ie popping, flat spots and it passed the throttle blipping tests.

 

 

hmm... so does anyone know? thanks in advance.

 

oh also ia am currently using mineral oil for the break in process, is it possible it dosent handle high heat temp well?

Edited November 3, 2009 by nuad

[scubasimon]

Doesn't sound like engine problem...probably air/fuel mix consistency...could be carb setting...could be air hose hardened or have leaks...could be fuel line obstruction...

 

...oh...could it be clutch loose??

[mepkoh]

well it seems to be a combustion issue....

i would check the following...

-air filter...is this dirty?? is it time for a change??

-a choked/dirty carb where the idling rpm goes up and down seems likely..

-bad fuel..possibility is there...check your fuel tank..filter or signs of tank corrosion/water leakages into itor debri etc

-could be as simple as a fouled plug.

 

if the above is okay..maybe it could be a electrical problem...dying component??

 

good luck

[Terrible One]

U can only do hard run-in for brand new engine.. Not newly overhauled engine.. I'm not sure what your problem is tho,hope u can solve it and enjoy your ride asap..

[nuad]

hmm good suggestions all, i do think its a combustion issue. i guess i should double check the air and fuel supplies and delivery.

 

thanks guys.

[SunnyBhai]

If your bike has CV Carburettors, get the diaphragm checked. This issue particularly happens if the diaphragm has worn out. Be warned - It'll be expensive to fix it.

[NightPhantom]

i had this problem with uneven idling.... sometime the rev abit higher, sometime low... at times e engine would just die off...

 

in the end i tried my luck and chagne the tensioner and it solved my problem.... now my rpm is stable... btw e bike is honda wave...

[w00t]

Do check your spark plug cable too. I had one such problem which cost 100bucks for relieving the symptoms and just cost 8 bucks elsewhere for solving the problem.

[laxstylad]

Cheers!

Valikie

Out of the many posts, this one attract my attention. I believe it is possible for anyone to participate.

Excellent ! I like it very much.

 

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[nuad]

Hi all just an update, and possible help to people that encounter symptoms similar to mine in the future.

 

reliable mech informed me that it be a possible problem with the carb floats. not too sure though.. cos i don't smell/see any overflowing from the carbs.

 

but i trust my mech, will get it fixed.

[nuad]

oh ya and thanks all

[scubasimon]

so did you figure out what the problem is?

[Raptor]

This is what I can offer you from my experience.. take it if want to.

 

The idle jet is a fixed diameter jet, and the fuel air mixture screw regulates the fuel/air mixture going into the combustion chamber at idle ie throttle closed.

 

Cold air is denser than hot air coz the molecules are closer together.. so you could say cold air causes the fuel/air ratio going into the cylinder to be leaner... (more air than fuel). When the engine is hot or when the ambient air is hot... air is thinner... so now more the fuel / air ratio going into the engine is now richer.

 

Lean mixtures produce more explosive burning thereby producing more power. Rich mixtures tend to burn slower and hence produce power on the low end but poor on the high revs. Rich mixture is great for low rpms and acceleration but suck with regards to top speed.

 

Proof that leaner mixtures are better is... don't you guys feel that your bikes seem to run smoother and is more responsive in the early mornings or late nights or after the rains??? The air is cold and dense at those times.

 

So your problem could be as simple as just adjusting the fuel screw a 1/4 turn leaner to have steady idling when the bike is hot.

 

How I know all this?? I have blown 3 cylinder blocks / pistons on my race Y125Z to understand what has tuning a carb got to do with power and performance.

[mepkoh]

a word of caution to those who intend to lean mix...

 

yeah you will find lean mix runs better...yeah combustion is better than rich mix.. your FC will be better..

 

but the irony is that running a lean mix..u are just going to bust your piston..

as the combustion is so hot..u end up with a hole in the psiton..

 

there is where the irony is...we need to cool down the piston ..how??

yes..by making fuel mix richer..run away temperatuer in cylinder will have seizure or worse hole in piston..IMHO

[Marcheline]

a word of caution to those who intend to lean mix...

 

yeah you will find lean mix runs better...yeah combustion is better than rich mix.. your FC will be better..

 

but the irony is that running a lean mix..u are just going to bust your piston..

as the combustion is so hot..u end up with a hole in the psiton..

 

there is where the irony is...we need to cool down the piston ..how??

yes..by making fuel mix richer..run away temperatuer in cylinder will have seizure or worse hole in piston..IMHO

 

http://i35.tinypic.com/i1yx3p.gif

[Silent Hunter]

Yap, if the ratio is too lean the engine gets overheated, in the worse case scenario, it burns up the engine oil, then piston sized and rear wheel lock. Then Bam! Engine gone.

[JbAtRaCeR]

U can only do hard run-in for brand new engine.. Not newly overhauled engine.. I'm not sure what your problem is tho,hope u can solve it and enjoy your ride asap..

 

Hard run in can be done also on a overhauled engine. Depends on what is being changed. If full overhaul, new crankshaft bearings,piston,piston rings,piston pins,cylinder block etc etc...(almost every moving parts) then the engine can be hard run in..If just top overhaul(cylinder head) then dont need to do..

[mepkoh]

Hi all just an update, and possible help to people that encounter symptoms similar to mine in the future.

 

reliable mech informed me that it be a possible problem with the carb floats. not too sure though.. cos i don't smell/see any overflowing from the carbs.

 

but i trust my mech, will get it fixed.

 

carb float problem...

 

carb float is sticky..causing the float..so to speak..unable to float up and down..

easily..

carb float say slow/dificulty in moving up or down...than the petrol coming in will be restricted..sometimes okay sometimes insufficient petrol in carb.

 

u wont be able to smell the petrol as it is all in the air tight carb..

if the float stuck or dirty ..unable to stop petrol from coming in and over flow it..it will somehow end up in the intake line and this will make combustion very dificult..it even stalls engine.starting will be no go.