Help needed! extreme bogging and terrible performance :(

[ghost_Shark]

Hello, I've got a Kinroad XT50GY, it's a road bike, but the engine is from a Chinese pit bike, it's a 50cc horizontal engine with 4 gears and a manual clutch.
P.S. I'm not good with 4 strokes, this is my first 4 stroke bike, and i wan't to learn how to diagnose and fix 4 strokes as well. And i'm very sorry for the long post, but i wanted it to be as detailed as possible.

The issue
The problem is the bike runs OK for about 20 meters then all the performance is lost and the bike won't even pull on flat roads, let alone hills, it will come to a full stop as it pops once or twice and it then has to be cranked several times in order to start again, then i can drive for another 20m, and then repeat.

The throttle response is very bad, i can twist the throttle alt the way and it will some times die and sometimes rev up very slowly. I've put a new carburetor, inlet, air filter, fuel hose and spark plug.
At first i thought it was the float bowl getting emptied and then of course the bike would stall and it would have to fill up again, but I've tried putting the fuel tap off and then removing the float bowl, but it's full, so i thought maybe it was the float sticking causing the engine to flood (i haven't ruled this out yet) as it drove better when i put the throttle needle clip in the center (it was on the bottom), so i tried moving it one up, but then it drove worse again, so now it's on the middle, and the air screw is set to 1 turn out, and that's the best setting i can get, but the idle is still not good, it will stay at about 2.5k rpm for a while then suddenly drop causing the bike to stall, i can put the idle screw farther in to make it stay at 2.5k rpm but that's too high for my taste. i don't understand this, i don't have any other jets, i will try to find some (there aren't any Chinese bike shops in the area) the jet in the carburetor at the moment is a #72, it's a 20mm carburetor and I've got a foam air filter on.

Another theory i've got is that the valve clearance's need adjusting, but the bike has only done 1000km but i don't think they've been adjusted after the break in period which i think you're supposed to, i didn't buy the bike new so i don't know for sure.
If it is the valve clearance, i'll need to get a valve tool. There is some debate about the optimal clearance level, some say the inlet should be .004 and the exhaust .006, and some say inlet should be .003 and exhaust .004, i want the best performance but i don't want to break anything.

I've been thinking it might be the electronics, but all the lights, kill switches and starter work perfectly fine, so if it is i'm guessing the stator or the coil, the cdi has been swapped out several times with no difference, i don't have another stator or coil so i don't know how to test this, but maybe the coil is getting warm and cutting out or something?

Notes!
Some notes that i thought might be worth mentioning. The exhaust is leaking, i don't know if this could do much on a 4 stroke, i know on a 2 stroke it can do heeps of difference.
The engine ran without oil once for about 20mins, there doesn't seem to be any damage caused by that, although there is a weird knocking noise in 1st, 3rd and 4rth gear, but that has come very recently, and this was a while back.
When rolling down a hill in gear, if i give the throttle a little twist nothing will happen, but if i twist it all the way it will really slowly gain some speed.

At this time I'm completely lost as to what i should do, I've tried everything to my knowledge and nothing has come even close to a decent running bike so I really hope someone can help me with this bike, as i really like it.

 

[my67xr]

Have you tried taking the fuel line off the carby and open the fuel tap to check that the filter on the inside of the tank isn't blocked.
The filter is usually found when you remove the fuel tap from the tank

Do you have a plastic insulator/spacer between the manifold and the carby ?
Is it fitted the right way around, the rubber o ring side face's the manifold.
Did you overtighten the bolt's that hold the carby to the manifold?

Try starting it up and let it idle, spray some degreaser or wd40 onto the join's where the carby meet's the manifold
Listen to the engine rev's, if they change in any way then there is a vacuum leak there.
If it changes and you have a leak, you might be able to fix it by making a new paper gasket to fit where the leak is.
You can use gasket paper and cut it out to the same shape as the manifold face and fit it between the carby and manifold or manifold and spacer.
Then try the spray trick again ^ and see if it make's any difference

The air filter did you oil it with foam filter oil, running it with no oil will make the fuel mixture lean and can cause some of the symptom's you have mentioned above.
It also help's to not let dirt/dust etc through into the carby/engine

The needle clip on the carby should be set on the centre notch from the factory.
And can be adjusted to suit once you start tuning it
The standard starting point for the fuel mixture screw adjustment is roughly 1.5 full turn's out.
You will need to adjust your mixture's again after oiling the air filter and adjusting the valve clearance's




The exhaust leak will affect the way the engine run's a bit,
You might be able to fix the leak by simply tightening the 2x nut's underneath the head where the exhaust pipe flange bolt's on.
If it doesn't fix it by tightening them you will need to fit a new gasket, the copper one's seal a lot better than the fibre ones and cost about $2 or $3

The valve clearance's should be checked before you even start the engine for the first time, people rarely do this though.
You will need a set of 17mm spanner to undo the rocker cover, some feeler gauge's, some pointy nosed plier's and a 9mm spanner
We recommend to set the inlet clearance to .003" (.076mm) and the exhaust to .004" (.1mm), this will give you the best performance, and checking them every 5-8 hour's and adjusting them if neccessary will give your valve's a long service life
This video will help explain the process needed to do it

[video=youtube;QJciyJRJh8Q]https://www.youtube.com/watch?v=QJciyJRJh8Q[/video]

How many km's has the engine done roughly ?
The knocking noise might be the rubber's in the Primary driven gear have worn out.
They aren't really replaceable (but can be done), or you could just buy a replacement gear off ebay etc
It's the big one behind the guy's hand here
They are fairly simple to replace, and shouldn't cost you too much

 

[ghost_Shark]

i havent checked the filter, but i've checked to see if there's coming fuel from the tank, i will go check for good measure. The carburetor doesn't have a plastic bit in the middle, just an o-ring, i haven't put oil on the filter, I'll have to go buy some first, i will check for leaks as well.
The exhaust is fixed, it was missing a gasket. And the nocking sound is almost gone, i don't know why, but after i put the 17mm carby back on it knocks a lot less.
I need to find my feeler gauge's, can't remember where i put them

I'll check all this and report back ASAP

 

[my67xr]

Ok you will need to get a new plastic spacer/insulator otherwise the carby wont seal very well to the manifold.
If you have trouble finding one a Honda dealer should be able to help you out, one of a CRF50 or CRF70 should fit


The Kinroad XT50GY looks like a big bike for the little 50cc engine

 

[ghost_Shark]

Shouldn't the o-ring keep the carby sealed? if the carb is moved farther back it wont fit because the electric start is in the way you said spacer, does the inlet need a specific length in order to run properly?

 

[ghost_Shark]

Also, here's a video to hopefully show the issue i'm having (sorry for the bad audio quality)
[video=youtube;VRYqKGJ-1mc]http://www.youtube.com/watch?v=VRYqKGJ-1mc[/video]

 

[my67xr]

Yeah the o'ring should seal against the manifold,
but if the carby bolt's have been done up too tight it can warp the mounting face of the carby, when fitted together it can cause a vacuum leak.
The plastic insulator/spacer's also help's to stop the heat from the head travel into the carby as well.
.

This is an old part's carby similar to your's



You can see the slight bow across the front (left) face



Here you can just see the warpage across the mounting face
The white in between the carby and flat steel bar is the gap where it's warped



Use a flat hard sanding block and piece of 180 grit sand paper to flatten the warp





Mark the mounting face of your carby with a permanent marker to show how warped the face is



after 5 pass's you can see the end's are bowed in toward's the manifold



10 pass's it's getting there



20 pass's almost there



30 pass's and it's now flat again





Blow any filing's off the carby well, and refit the carby.
Use some gasket paper there as well to help it seal.
Some thick cardboard from an old cereal box will work too if you don't have any gasket paper
Don't over tighten the bolt's holding the carby to the manifold
And retune it once it's all back together.

 

[ghost_Shark]

Thanks, i will take a good look at the carby, and also replace the gasket between the engine and inlet, because i have a new one anyway. I should have some gasket paper so i'll put that between the carby and the inlet as well.

 

[my67xr]

Yeah just make and trim up a new gasket using the manifold as a template to cut out a new one

 

[ghost_Shark]

i've put new gasket's on, the carby was warped pretty badly, but i fixed it, but the problem is still there. I'm going down to the local bike shop, to buy new bulbs and ask them if they've had similar problems before, and if they've got valve adjustment tools and tips.
I'm thinking it must be electrical because no matter what i do there's no change, i can put the fuel screw all the way in, or all the way out, it only changes the idle which only lasts a few seconds anyway, the needle doesn't do much either but still a little difference. So i will try to find a new coil to see if that changes anything.

 

[my67xr]

Do you have a multimeter, i can tell you how to test the ignition coil

I reckon the pilot jet is blocked up, the smaller jet toward's the manifold side of the carby, not the central main jet.
Or it could be a blocked the hole at the bottom of the thread's where it screw's into in the base of the carby.
You need to use a strand of copper wire taken from an off cut of automotive wiring
Poke that though the holes of the jet's, and there are hole's that run across the jet's too make sure they are all open
If the pilot jet is partly blocked then it won't idle too well, the mixture screw adjustment's wont do much, and the bike will hesitate and pop when you try to rev it.


When you adjusted the mixture screw, you need to let the bike warm up
Raise the idle speed by a couple of hundred rpm by turning the idle speed screw in a bit.
Then adjust the mixture screw in until it start's to stall.
Listen to the way the engine rev's, you want to find the point where it run's at the smoothest/fastest rpms
Turn the mixture screw out 1/4 turn at a time, then let it settle for 10 seconds or so
Then turn it out another 1/4 turn and let it settle, etcc etc
Once you have it running at the smoothest/highest rev's then adjust the idle speed screw back out till it idle's at a normal speed.

 

[ghost_Shark]

i just took the spark plug out to see what colour it was, and i then checked the spark because i had it out anyway, and the spark was very very weak, i almost couldn't see it, and i checked some other plugs as well so it's not the plug. The guy i spoke to at the dealer also said that he had a similar bike with the same problem and it turned out to be the coil, so i'll change that next and see if there's a change.

 

[my67xr]

Try swapping the 2 wire's around on the ignition coil and see if the spark come's good.
Wired one way it will give a weak spark, and the other way around it will be 5 time's better

 

[ghost_Shark]

i will clean the jets and switch the wires, hope that works

 

[my67xr]

it's worth a try.
Is the ignition coil one of these type's ?

The small hole here on the left/inlet side of the carby is the one that let's the fuel/air mixture through for the idle circuit.



I think the small hole may be blocked, or the jet that screw's in there is blocked.
When a carby has been sitting with fuel in it and it eventually evaporate's it turn's to a gum/varnish, and can restrict the hole size.
It's pretty hard to see, and poking some copper wire through the hole's may dislodge the varnish, it'll fall out as thin flake's and is a clear or yellowish colour
This is why the bike wont idle at a lower speed as it's not getting enough fuel.
With you turning the idle speed up, the engine is now only running off the main jet instead of the idle circuit, and the main jet is set up to start working at 1/4 throttle and above.

 

[ghost_Shark]

i have already cleaned the carby, but i will try once more with a wire this time. I'm also on my way to pick up a new coil so i'll be putting that in later. And yes i have got a multi meter. I'll write back when i've done this.

 

[ghost_Shark]

i changed the coil, but there's no change, but that got me thinking, could it be the stator that's fried? the battery doesn't seem to charge now that i think about it, and the lights are getting dimmer than before, i think i will pull the cover off and have a look. but the bike now idles ok.

 

[my67xr]

Ok to test the stator have a read of this thread- http://www.miniriders.com/electrica...neto-igniton-coil-source-coil-pulse-coil.html
Use the reading from the first stator to test your's
The testing detail's are just below the picture, write down the reading's from your stator and post them up here
The headlight's and battery run off a seperate coil on the stator.
To test the Lighting/Charge coil set your meter to 2000 Ohm's, put one lead to the yellow and the other lead to the white wire

Your stator will look like this one

And has your bike got a 5 pin cdi or a 6 pin cdi ?

 

[ghost_Shark]

i will try this and write back.

P.S. i've got a 6 pin plug just like the 5 pin one only with the top middle one there.

 

[ghost_Shark]

looks like my multimeter doesn't work, so i think i'll just pop the cover of and have a look, maybe it's visible.