Bike goes to rev-limiter right away

[KevariMan]

Hello there people of the internet !

You might remember me from such hit as:''starter issues''. Lets call this a part 2 to that problem.
I did not feel like continuing it onto the same topic since this is not related to starter anymore.

So, the problem i have is that the bike runs straight to rev-limiter, if i turn off the choke/half-choke.
The problem is less noticeable if i'm actually trying to ride the bike and thus put more resistance for the engine. Riding the bike i can use throttle aswell. The bike will still want to rev, without touching the throttle at all, this all happens with half choke, it will just die if i'm running on full choke.
I never turned off the choke fully while riding, partly because i was concentrating on staying on the road.

My intake port on the cylinder is: 25mm
Intake manifold is: 27mm
Carburetor is: 22mm

My question is, does the oversize carb/oversize intake manifold cause the engine to suck more air and thus start to rev it.
But then again, it will rev even without touching the throttle.

The throttle slide on the carburetor doesn't go all the way down in the carburetor, but then again the idle screw is fully open and the mark of the idle screw on the throttle slide is as high as it will get, so this suggests me that the throttle slide was never meant to go lower in the carburetor.

As you might have guessed, the intake manifold doesnt sit perfectly on the carb/cylinder, could it cause the engine to suck more air and start to rev ?

Leave questions, give suggestions

[GS_in_CO]

Going to the limiter suggests to me that you do not have an intake leak because excess air would tend to lean the mixture and it wouldn't run very well.
Stuck open throttle slide? Throttle cable not letting the slide go closed? Does it do this with the throttle cable disconnected? Can you see into the carb while it's running to see what the slide is doing?

I've never seen anything like this so just giving ideas of where I'd start looking.

[KevariMan]

The throttle slide does move up when turning throttle.
The throttle/carburetor doesnt have any modification done to it after it was last working.
So this is the carburetor that was functional with the other engine that i had on the bike.
But, i guess i could try and check what the slide is doing, while the bike is running.

Also, the choke valve keeps twitching when on full choke, so the choke valve is moving when intake is happening. I don't know if its supposed to move, almost loosely you could say. It jumps between full choke and half choke with every intake. So i have to manually by my own hand hold the valve shut/control the valve, to get the bike to ''idle'' at lower rpm.

And i tried releasing the throttle cable from the throttle handle and the cable didn't move anywhere. But again, i didn't check the slide when i did that, so i guess it could have moved without me even noticing it.

It feels to me aswell, like the engine would be sucking too much gas, but would the oversized intake manifold cause the engine to suck more air/gas?
Maybe even too big jet ? or would that just drown the engine and kill it?

I will go and find out tomorrow if the cable does actually hold the slide a little bit up.

[GS_in_CO]

The pipe and hole and carb sizes wouldn't have any detectable effect.
Wrong jetting would make it run badly - not way faster.
Choke in the form of a flap inside the carb body ahead of the throttle plate could wiggle a little without a problem if it is nearly aligned in free air flow.
An enrichener lever (the NOT a choke plate option) probably shouldn't.
The slide should be very nearly closed for idle as it takes very little air to idle.

[KevariMan]

Yes, i will conclude this with that the throttle cable was too short, luckily i had ''repair kit'' at hand, so i was able to replace it and the slide went further down.
It still baffles me how it was running just fine with the other engine, since i haven't touched the cable/carburetor area in any way to make the cable shorter.

But i guess it had something to do with the fact that the intake port was alot bigger on the chinese engine, so it might have needed more gas to idle properly (?)

But all is well now, except i can't get the damn thing start again, but the problem is more likely weak battery, since i checked that the engine was getting spark and i dont think it will just loose all the compression overnight haha.

Thanks again, for giving me suggestions and giving me advice with my ''minor'' problems.

[GS_in_CO]

The problems are almost always "simple" after you know the answer.
Which is why it's best to start with the simple possibilities first. (Then among those you choose the easiest ones to pursue first)