difficult little engine!

[skatefreak]

Hey there,
So i'v had a bike since mid last summer (1999 Kymco 125 Stryker) as a cheap bike to get some experience on. It ran great for a while and i got a good 1200km on it without any trouble at all.
I started out easy but ended up riding it between luton and cambridge occasionally and the bike does require WOT to keep up on some of the bigger NSL roads...

Problems began as the weather started cooling down, at first it was a little spluttering and the engine didnt run great one chilly morning. I put this down to the cold weather and not leaving the bike long enough to warm up (which i didnt do much to be honest).

In a short space of time the bike went from spluttering a little to becoming unridable. From cold the bike ran fine but after it had warmed up a little when being ridden it would lose power above 4000rpm and then not go above that in any gear.

If left to cool it would run again okay but only untill it was warmed up.

After this the engine decided it would start fine and idle from cold but not rev up at all (as the throttle was opened the revs wouldnt increase much and die if lowered).

So having abandoned riding it i started tinkering, cleaning the carb and spotting a leakage from the head gasket.

After getting the engine out, replacing the head gasket and getting the engine back there is little change, it will start and idle from cold but any increase in the throttle will make little difference if not stop it. (taking the filter out did help the revs and it would rev up but once it had warmed up, back to sq 1).

I did start it and let it idle for a good 20 minutes and noticed that the engine came off the choke from around 4000 rpm as it used to and although sticking to 2000 rpm for the first 5-7 minutes it then wonders a little from 1500 to 2500... I poked everything on that engine with no effect on the idling.

When i had the engine open i did notice quiet a bit of carbon on the piston and on the exhaust port side of the head.

The bike does not have the original air filter so i cannot be sure if its to much or little air getting in there (just waiting for one of the originoals in the post) but i'm not sure if this will make much difference as the bike rode okay for 1200km with what it has at the moment.


From an R/C helicopter backgroup i would have sworn the problem is a fuel mixture issue but that doesnt explain how the bike rode fine originally unless the engine was running lean and is now genuinely knackered


Much appreciation for anyone that has read this thread through. These problems appeared 2 months ago and due to the gasket taking a while to get hold of and a lot of tinkering, this whole situation is getting very frustrating

There is another engine from a breaker for ?140 delivered and i'm starting to feel this engine might beat me, just thought it would be worth having a couple more shots before calling it a day on this. I'v spend about ?35 on the engine so its not been to expensive so far...

Any thoughts would be much appreciated.

Best regards

-Jvr

ps, the picture of the head, i used some plastic to scrape some of the carbon off but gave up as i got near to the valves.. dont want to bugger them up...

[temeluchus]

Sounds like its runing the rich.

did you check the float height? Are the carb gaskets in good shape?
____________________
Some shite cruiser. Now with guns and FREEDOM!

[skatefreak]

Hey there.
The gaskets in the carb are in good shape
To be honest i have no idea how to check the float hight let alone where it should be. When i checked out the carb it moved freely and was in good shape to (no leaking).

Another person said he thought it was flooding to actually, not much else but i think that might be a valid train of thought there.

The mistery is that the *air filter* on there at the moment is just a tube with gause over it, if i take the gause off to let more air in the engine is happer but it dosnt solve the running issue when it gets warm. I was under the impression that there was to much air getting in there causing it to run lean.

I really dont get it though as the bike rode great before. I am really concerned about letting the engine run lean (from modeling with nitro engines, one tough lean run and yr engine's toast), are these 125's as sensitive?

Does anyone think the buildup of carbon could be a contributing factor? Would it be worth removing it?

Cheers for the input, will google floats and have a look in the morning again though.

Best regards

-Jvr

[Noxious89123]

From what you describe, and that there is so much carbon buildup, I'd say it was running rich, not lean. The fact that removing the air filter makes it run easier and that it starts easily from cold would also indicate this.

Check that the choke isn't stuck on!
____________________
'06 Honda CBR125RW-6 ~ '00 Honda CBR600F-Y ~ '07 Honda CBR600RR-7 ~ Bikeless
'53 Ford Ka 1.3 ~ '03 Vauxhall Astra SRi 1.8 ~ '52 Vauxhall Astra SRi 2.2 ~ '53 Vauxhall Astra GSi

[skatefreak]

I am certainly starting to think its a running rich problem.
I was reading that overly rich mixture can cause a dry, tougher to remove carbon buildup which seems to be what i have in there...

Its an automatic choke and i have looked at it before but for the life of me i cant figure that one out.

However, that being said i think the choke is doing its job, when the bike starts from cold it runs at 4000rpm for a while and then drops to 2000rpm once its warmed up.

I have a feeling that its either been running rich or lean and whichever it was has taken its toll over time

The input is much appreciated though !

-Jvr

[Noxious89123]

4000 and 2000 sounds too high to me.

Would expect it to be more like 2~3k for a fast idle on a cold start, and about 1200~1500 once warm.
____________________
'06 Honda CBR125RW-6 ~ '00 Honda CBR600F-Y ~ '07 Honda CBR600RR-7 ~ Bikeless
'53 Ford Ka 1.3 ~ '03 Vauxhall Astra SRi 1.8 ~ '52 Vauxhall Astra SRi 2.2 ~ '53 Vauxhall Astra GSi

[temeluchus]

Yup sounds like your auto choke is on the fritz. Certainly explain the issue.

As to fixing it i dont know. You may be able to replace the carburettor with a japanese carb from a similar bike, or get spares for the carb.

Stick a pic of the offending carb on here and lets see if we can find summat.
____________________
Some shite cruiser. Now with guns and FREEDOM!

[skatefreak]

Buggery.
It took a while ago but i managed to track down the exact carb i have, hunted down an exploded view a while back when i was stripping it down but i cant seem to find it now...

I will pull it out in the morning and track it down again...

Interesting you suggest its a bit fast, i thought it was a bit high @ 4000 with the choke but its my first bike...

I remember when i stripped the carb down it all looked okay inside etc.

After a quick look around, this carb, although for a 250 scooter is pretty much identical to mine.

https://www.kymcopartsonline.com/catalog/diagrams/200903041943530.Grand_Vista_250_2008_Carburetor.JPG

All the diaphragms were intact and everything looked clear and good. Will get it off in the morning though.

Any suggestions as to what to look for?

Best regards

-Jvr

[temeluchus]

i'd guess that the bits on the left with the electrical connectors relate to the auto choke.

They would be the bits to have a look at.
____________________
Some shite cruiser. Now with guns and FREEDOM!

[Ichy]

Are the valves seating correctly and are the gaps correct? Did you check for air leaks around the manifold?

[skatefreak]

Carb off,
making stew for dinner so have a little time
Will check out the carb, seals and will have a little hunt around if i can find any distances but alas i dont have any calipers to accuratly measure anything at the momemt

-Jvr

[skatefreak]

Okay,

Earlier today i did try altering the air mixture, this would help smoothen the idle somewhat but did nothing for anything above idle.

This evening i took the carb apart and it all looks good in there,
i took some pictures that i will throw down on the bottom so u guys can have a look but sadly it looks fine
Might pick up some carb cleaning stuff and put it through all the little passageways that riddle this carb like cheese heh...

I'm beginning to think it could be a tuning issue, it looks like the air mixture screw on the side has been fooked about with quiet a bit as its literally 30% stripped (looks like its brass?!?).

I cant seem to find a fuel mixture screw, the only other screw i can find is on the very bottom of the float chamber (although it has a shallow point) seems to let all the fuel out of a nipple that looks like it may want a pipe on it but there wasnt on there when i got the bike

I had a look at the *tubes* in the carb, the shorter of the two i took out as it doesn't seem to be ajustable but the longer of the two (well, lower) looks ajustable and i dont want to mess around with the ajustments on that!

The float all seems to be mechanically sound, in good condition (clean, free moving etc) but i will have to look into this as this bike is very obscure and i doubt i'll find any measurments (and there dont appear to be any ballpark markings inside the chamber),
that being said, i'm still not 100% sure how to measure this one.

I dont suppose anyone knows of a website for diagnosing issues with little 4 strokes, i know muchos about R/C engines but accrued all that knowledge through experience and clubs over many years but i'm mighty eager to learn asap as i feel like somewhat of a t*t constantly harrasing the online comunity...

Any thoughts much appreicated

Best regards

-Jvr

Ps, Attachments not working at the moment, will get onto that first thing

[Noxious89123]

Your not harrassing, your asking! You won't find out or learn if you don't ask, so don' worry about it

The screw on the botom of the float chamber is for draining the carb, appropriately named the drain screw.
____________________
'06 Honda CBR125RW-6 ~ '00 Honda CBR600F-Y ~ '07 Honda CBR600RR-7 ~ Bikeless
'53 Ford Ka 1.3 ~ '03 Vauxhall Astra SRi 1.8 ~ '52 Vauxhall Astra SRi 2.2 ~ '53 Vauxhall Astra GSi

[skatefreak]

Well,
Picked up some carb cleaner today,
thoroughly spreyed it through all the passages in the carb,
left it for 5 and spreyed through again,
then back onto the bike and let it run.
What a difference it made

She would sit and idle and even get up the revs comfortably, even got the bike up the road (uphill !) but alas after she had warmed up she was back to playing up again.

Runs a lot better but just not right now.

I well get a propper recording in the morning but have a really short one just so you can hear.

I am convinced its running really rich!

I would just like to ask if anyone can figure out what else i can twiddle to tune the engine somewhat, i was going to give the air screw a few cautious 1/8's either way to see what happened but alas it was to dark to see.


Sound bite from today at the bottom, short but it was a last second idea and after that short run she wouldnt run properly..
will get better one in the morning!

Thought much appreciated here

Best regards

-Jvr

[Ichy]

[skatefreak]

Yeah,
I might be a little obsessed with this carb i'll admit heh.

Intake manifold seems good (between carb/engine) as well as exhaust side, valves in the carb all look good, seals seated well and in good condition.

The gaps? Not 100% sure what you mean by gaps?

There is still a slight leak of oil from the crank case (altenator side) which came about 2 days ago (long story heh) which i'll seal in the morning if i can find some JB weld or anything simular

best regards

-Jvr

[Ichy]

The valves in the cylinder head are probably operated by rockers? These should have a specific gap to the actual valve when the cam is in a particular position. It could be that there is a minimal gap when the bike is cold but once it starts to warm up the metal expands, closing the gaps. The valves in the head need to seal all the way round for the bike to run correctly. Hard carbon deposits can stop them working properly if they get on the valve faces.

Its worth just checking that the camshaft is in the right place and hasn't skipped a tooth.

[temeluchus]

A leak in the inlet would lead to high but lean idle.

Overtight valve clearences may be an issue but on a screw and locknut head, the opposite is more likely.
____________________
Some shite cruiser. Now with guns and FREEDOM!

[skatefreak]

Another recording, this time one from cool and the second one is when she was warm and picking up and then copping out.
The idle is quiet high in both.

I discovered reving her quiet high produced black smoke but only at the very top end (which seemed to help the top end a little) but by the time i got the phone cam out and reved it up again the smoke had stopped and she copped out and wouldnt start very well again.

Once warm the bike will only start with throttle and wont pick up the revs. I really dont know how to interperate the sound of the engine here

The cylinder valves has the cam chain config (SOHC?). When putting the bike back together i was pretty careful and re-checked the position of the chain and went over the valves to check if they sealed but again, not sure about how much they should open, not that i can open them very far heh.

Re-checked the rubber inlets between the carb and engine, all seems good

Interestingly, managed to get the bike up the road and the bike does pull somewhat in first but cops out in second gear.
Generally running very rough

Cant play with the air screw to much (soft metal and was half stripped when i got the bike), it doesn't seem to have to much of a positive effect on the idle, it will make it worse but it seems the optimum achievable is still pretty rough...

Will try get a more knowledgable friend out soon.

thankyou for you patients!

Best regards

-Jvr

[temeluchus]

its almost certainly your auto choke, or some other carburettor issue.

Id meausure the inside and outside diameter of the spigot (that goes into the engine) on the carb, and look for a replacement carb. It doesnt have to be from the same bike, but one from a similar bike (GS125, Hyosung GF125 etc etc) would probably do the trick. Manual chokes whilst not as convenient are less likely to cause trouble.
____________________
Some shite cruiser. Now with guns and FREEDOM!

[skatefreak]

Hmm,
I think you might be onto something there...
The bike certainly runs fine when its cold with the choke on, Will try and ride it and see how it goes.

Just a question though,
On a bike operating normally what would you look for when riding the bike before its warmed up (aka on the choke)?

I will look out to see if it rides properly or overly rich (as it should if its working fine). Only issue is i dont really know what i'm looking for on an overly rich run on a 4 stroke.

Best regards.

-Jvr

Ps,
Jst tried it out, the bike is ridable when started from cold... but probly got a great idea to ride the bike like that whilst the engine is cold
A little hesitation but the bike pulls quiet well so i think the choke may be something to look at.
Time to do some serious googling and figure out how this choke operates!

[stirlinggaz]

hi,
i had the very same carb on one of my previous chinky bikes.
i can practically guarantee that your issues are carb related +
the auto choke is known for failing.
iirc, in theory theres a pin thats eletrically controlled, that moves up + down the choke passage.
i think it can be tested off the bike with a 12v supply, + you should see the pin move.
theres no user serviceable parts in the auto choke though, its replaced as a unit.
might be worth sourcing another carb.
the guys over on the chinese bike forum will be able to tell you more,as that particular carb is fitted to umpteen chinky scoots + bikes.
but definately sounds like the carb is needing to be set up correctly + maybe needs the choke unit replacing.
the auto choke unit had stuck on mine before i got it, + the previous owner had fiddled about the carb settings (mixture & idle) to compensate for the dodgy choke.
i removed it with the intention of replacing it, but found that a good clean with cheap brake cleaner freed of the pin in the auto choke.
then once it was put back on, i had to return the carb to stock settings.(got these off a guy in the chinky bike forum)
cheers,
GAZ

[skatefreak]

Hey,
I'v tried googling but cant seem to find this chinese bike forum.
I found the chinese bike and scooter forum but that has closed due to lack of members apparently

Any direction would be fantastic

I did *test* the choke by unpluggnig it but that shows how i should have investigated further before trying as unplugging it simply means it will remain in there...

Muchos gracous though

Best regards

-Jvr

Ps, Nope, its a CVK carb...

[temeluchus]

https://cgi.ebay.co.uk/GY6-24MM-ATV-MOPED-SCOOTER-GOKART-CARBURETTOR-CARB-NEW_W0QQitemZ190318443885QQcmdZViewItemQQptZUK_Motorcycle_Parts?hash=item2c4fdcfd6d

looks like the same carb.
____________________
Some shite cruiser. Now with guns and FREEDOM!

[0l0dom0l0]

from all the symptoms and the sound clips, that thing is running horriby rich. auto choke = failed.

just dismantle the whole auto choke unit and seewhat that brings. worst case is you have t buy a new one. im sure thats the problem though. (as everyone else says)

hope this helps