Predator 212 idles erratically and cuts out when throttle is opened

[Onebean]

My son and I are trying to finish a mini bike build, and we are struggling with the 212 Predator. Here’s what we’ve done.

We removed the Predator fuel tank, air box, and exhaust, and replaced them with a custom made fuel tank, stage 1 intake and KN style air cleaner, and a header with a screw on muffler. I also installed the smaller jet and emulsion tube that came in the stage 1 kit. We did not install the beefy valve springs or offset flywheel key.

We did not run the engine in factory form. When we tried to fire it up, it would not start. I verified we are getting spark, it’s a very light spark, but it was sparking. We finally got it to start by squirting some starting fluid into the carb. Once it started it was smoking and running poorly. It would not idle smooth, and the engine would speed up and then slow down to the point of almost stopping running unless I bumped the throttle. Also, when any throttle above just a crack, it would cut out like it was running out of fluid. I suspected our gas tank was the issue, because the cap was not vented. I added a vent to the cap with no change to the poor idle or cutting out.

Then I assumed the jet and emulsion tube was the culprit, so I swapped the stock jet and emulsion tube in, and it ran the same. Then I started to think it was a vacuum leak, so while the engine was running (poorly) I sprayed some starting fluid between the carb and plastic plate it mates up to, to see if the engine would speed up, but no change. I also made sure I had the thick steel and rubber gaskets on both sides of the carb.

I have another Predator I plan to put on another bike, so I unboxed it and pulled the stock carb off of it. I installed the carb from the fresh from the box engine, and it will start without starting fluid, but runs the same (poor idle and cuts out with any throttle applied).

I’m out of ideas. I assume it’s something simple, but I have no idea how to fix it.

Should I install that offset key? Is that my problem? Surely the stock valve springs are not the issue, but I’m not ruling anything out at this point. Anyone have an idea what my problem is with this engine???

 

[Onebean]

Here’s a video clip of it running. I did not touch the throttle during this video.

 

[ole4]

Your governor should be reacting when the revs drop low and its not moving at all. It looks like it is not working correctly.

 

[Onebean]

@ole4 After watching a guy on YouTube use the governor arm for throttle linkage, I did that. I assumed using it as throttle linkage would override the governor. I have spring tension on it to close the carburetor when the throttle is released. Here’s a picture of how I have it hooked up.


The throttle cable comes from the bracket over the carb and hooks into that aluminum clamp hooked to the governor arm. Then I have a spring running to a brass bracket I made. The throttle works super smooth.

 

[ole4]

I have no idea on how that is supposed to work other than you have a spring on the throttle cable so at least the govenor can try to close it if you rev it too high. When a motor is stock the throttle sits open when it is not running, when it starts the govenor arm closes the throrrle and controls the idle. That said if your carb is set correctly, it should idle ok with the throrrle arm resting on the idle adjuster. If you start the engine and with your hand hold the throttle closed, does it idle steady or does it speed up and slow down? If it is idling eratically with the throttle held closed either you have an air leak or carb needs to be tuned.

 

[Minimichael]

I have no idea on how that is supposed to work other than you have a spring on the throttle cable so at least the govenor can try to close it if you rev it too high. When a motor is stock the throttle sits open when it is not running, when it starts the govenor arm closes the throrrle and controls the idle. That said if your carb is set correctly, it should idle ok with the throrrle arm resting on the idle adjuster. If you start the engine and with your hand hold the throttle closed, does it idle steady or does it speed up and slow down? If it is idling eratically with the throttle held closed either you have an air leak or carb needs to be tuned.

Have you tried disabling the governor altogether? There's a zip tie trick out there that doesn't require opening the crankcase. It seems the way you've set up the spring between governor and throttle could be your problem. With the governor taken out of the equation, your throttle cable spring can hold the throttle closed; then adjust your idle screw to open the throttle just enough to hold a steady idle rpm. This will at least let you determine whether the governor mod may be to blame.

I'm not advocating the governor's removal here. That's against the policy and safety concerns of this site.

Still, it seems the mod you implemented may be disrupting the governor's ability to correctly operate because the spring may no longer have the correct tension to work the butterfly properly. If disabling allows you to achieve a steady idle, you might then go about reincorporating the governor somehow (eg: with a lighter spring tension, or different configuration).

 

[SAS289]

The throttle on the carb is being held closed by the former throttle spring. The startup and idle should be identical to starting and idle of an engine without a governor. There's no way that the governor will regulate the idle like it does with the stock linkage.

If you want to test the governor action or inaction when opening the throttle, remove the throttle (your return) spring. Have someone else pull start it while you rev manually with the governor arm. If it revs better the governor was interfering with reving it up. If it runs the same then you could rule out governor action.

With this kind of test make sure the chain is off or the back wheel is off the ground.

Also. With the stock carb you will need to crack the throttle open a touch to start it easier without the stock throttle linkage arrangement.

 

[toomanytoys]

I’m not quite sure why you set the throttle up like you did.


Clamp cable at red. Attach wire at green. Take yellow off. Remove the friction washer and put nut back on.

my first step would be hooking it up like this using the factory parts. Spring tensions play a huge role in how it all works together.

or remove what you’ve installed for return springs and throttle cable and see if it runs properly.

 

[Onebean]

I’m not quite sure why you set the throttle up like you did.

View attachment 293835
Clamp cable at red. Attach wire at green. Take yellow off. Remove the friction washer and put nut back on.

my first step would be hooking it up like this using the factory parts. Spring tensions play a huge role in how it all works together.

or remove what you’ve installed for return springs and throttle cable and see if it runs properly.

I originally hooked it up as you show, but I wasn't happy with the way it worked. I couldn't get it to move smoothly, and it seemed to be too many points of "linkage" to work smooth and reliable. Moving the connections to the governor shaft made it simple and smooth.

 

[Onebean]

I had some time tonight to work on this, and here’s where I’m at. I removed the spring from the governor and it didn’t change the erratic idle. I decided to put the throttle back to stock configuration, so I could rule out the governor throttle issue completely. I swapped it back to all the stock parts and fired it up again. It ran a little better, but basically the same. I was running it with the air cleaner off, and put my hand over the intake hole assuming it would kill the engine. I could feel it sucking on my hand a little , but the engine continued to run erratically. Now I’m sure I have a vacuum leak. I pulled the intake, carb, and plastic plate off, and put it back together paying close attention to the gaskets and orientation of everything. Here’s the order from the head out:

green gasket with D shaped hole to match the head

black Plastic plate

steel gasket with rubber insert (should I swap this out for a regular Cardboard gasket?)

carb

steel gasket with rubber insert

aluminum air cleaner adapter

I tightened the whole stack as tight as I felt I could go without stripping a stud. Runs exactly the same.

It makes sense it starts hard and cuts out under throttle, because the fuel to air mix is way off due to the vacuum leak.

how can I chase down my vacuum leak. I assume it has to be between the carb and the head, but how do I pinpoint it? I’m

 

[Bigjake]

Check coil gap to flywheel just so you can say you tried everything and different spark plug
I had one ran fine i put it up for year and a half drag it out and same problem your facing did everything you did and still same thing
gap was wide from the factory new ngk plug and ride on hope thats the problem

 

[SAS289]

I had some time tonight to work on this, and here’s where I’m at. I removed the spring from the governor and it didn’t change the erratic idle. I decided to put the throttle back to stock configuration, so I could rule out the governor throttle issue completely. I swapped it back to all the stock parts and fired it up again. It ran a little better, but basically the same. I was running it with the air cleaner off, and put my hand over the intake hole assuming it would kill the engine. I could feel it sucking on my hand a little , but the engine continued to run erratically. Now I’m sure I have a vacuum leak. I pulled the intake, carb, and plastic plate off, and put it back together paying close attention to the gaskets and orientation of everything. Here’s the order from the head out:

green gasket with D shaped hole to match the head

black Plastic plate

steel gasket with rubber insert (should I swap this out for a regular Cardboard gasket?)

carb

steel gasket with rubber insert

aluminum air cleaner adapter

I tightened the whole stack as tight as I felt I could go without stripping a stud. Runs exactly the same.

It makes sense it starts hard and cuts out under throttle, because the fuel to air mix is way off due to the vacuum leak.

how can I chase down my vacuum leak. I assume it has to be between the carb and the head, but how do I pinpoint it? I’m

I don't know if it's your issue but you should have only one steel gasket with the rubber insert. So swap out the one you mentioned. That gasket is not used in between the plastic plate and the carb.

I guess some guys use carb cleaner or other sprays to verify an air leak. I would use a small propane torch to see if the idle changes when hit with propane.

 

[desert rat]

I don't know if it's your issue but you should have only one steel gasket with the rubber insert. So swap out the one you mentioned. That gasket is not used in between the plastic plate and the carb.

I guess some guys use carb cleaner or other sprays to verify an air leak. I would use a small propane torch to see if the idle changes when hit with propane.

WD-40 with the straw is the safest.

 

[Onebean]

Update - I got this fixed!!!

So based on recommendations here I restored the original throttle components and governor, I even put the hand throttle back in place to make sure nothing was influencing the throttle or governor. The motor ran exactly the same, terrible. Frustrated from all the effort I turned my suspicions to a vacuum leak. I placed my hand over the intake of the carburetor basically sealing it off. The engine continued to run just like when my hand was not covering the intake on the carburetor. Now I new what the problem was. When installing the carburetor, I had the factory paper gasket against the head, then the plastic plate I call the intake manifold, then a steel gasket with rubber, then the carb, then another steel gasket with rubber, then the aluminum air cleaner adapter. The leak ended up being the metal and rubber gasket between the carb and plastic intake manifold. As soon as I swapped that for a paper gasket, the engine started easily and idled perfect. I still had throttle cut out as the engine rev’d up, but that was because of the stock jet and emultion tube. I pulled the carb off one more time, and replace the stock parts with the recommended emultion tube and jet. The bike runs great! Hopefully this explanation helps someone else struggling with the same problem. I feel like I’ve almost worn out the threads on the carb studs as many times as I had it apart and back together. Problem solved now.

 

[Onebean]

@SAS289 I just saw your message, and you are 100% correct. Thank you!

 

[SAS289]

@SAS289 I just saw your message, and you are 100% correct. Thank you!

Good to hear that you got it running well. The governor works great to limit max RPM with the stock engine internals. It's safer to run that way at first. If later you want higher RPM you could then build the engine for it and include a billet rod and upgraded flywheel.

 

[Onebean]

@SAS289 this will be all the motor my son will need for ripping around the neighborhood. My bike might be a different story.