Predator 224 Issues Starting/Idling

[Luttrell850]

Hi all, first post here. Been building a custom bike using a predator 224 for the past 6 months or so. Finally got everything together, but I'm having some major difficulties getting the bike started and idling. One major thing that most of you will notice immediately, is that the motor is tilted at quite an angle. I have run 212's like this with no issue as well as Coleman 196cc motors (what was originally on this bike before the motor blew), so I don't believe the angle of the motor to be the underlying cause of my issue in this situation specifically. (Not to say that it won't potentially cause issues down the line or be down on power relatively speaking).

On this motor, I have removed the governor, as well as the low oil sensor. After reassembling the motor, I was able to get it started with the chinese vm22 carburetor I purchased, however the pull start was noticeably heavy and would kickback hard. When I would finally get it started, it would throttle upwards of ~3500-4000 and act like a runaway motor. After cleaning, jetting, and rebuilding that vm22 carb I still was unable to alleviate the issue. At this point, I figured that it might be a fueling issue as I confirmed spark and compression, and with that I went ahead and bought a PWK 24mm nibbi carburetor.

With the new carb, I went ahead and fabricated a new intake runner to clean up my work and hopefully get a better seal. With that I went ahead and re-lashed the valves to .003/.003. The pull start felt brand new, no kickback and only heavy from the compression, no noticeable oddities. However, now I am completely unable to get the motor started! I was able to finally get it to turn over with a small spray of lighter fluid into the carb with the slide opened before pulling. Although, once it started running with the new carb, it had the same issue of running away!

After digging through this forum and all the other minibike forums I could find, I have found that my most likely option is a leak at the intake manifold to the carb and or intake manifold to the cylinder head. This leak is either a surfacing issue with the flange, or my welds have pinholes that are leaking. I have confirmed a very small leak as trace amounts of gasoline can be found on the outside of the flange to the motor of the intake manifold, however I feel that a small pinhole of this size that isn't even leaking enough to drip wouldn't cause the issues I'm facing.

One other possibility I have thought of but couldn't prove, is that my custom intake manifold is potentially too long and or that the bend it takes, makes it difficult for the fuel to make it to the motor from the carburetor. Any thoughts on this especially would be very appreciated.

If any of you have any insight as to why I cannot get this motor to idle, or even start up, it would be greatly appreciated. This bike is still a work in progress, but I am very eager to finally get this thing moving under its own power and out into the world.

I understand that with custom work and fabrication, issues and problems will arise, but this is how improvements in skill and knowledge are made. I am by no means a master fabricator, just an enthusiast honing his craft.

sidenote: The nibbi carb has not been opened up yet to check float level, jetting, or factory assembly quality.

 

[Denny]

Any poor sealing surfaces or holes in the intake will make it not run or run lean. It all must be sealed perfectly. Are you sure the cam is not off one tooth from the crank when you re assembled the engine? The hard pull sounds like the compression release is not working also.

 

[Luttrell850]

Any poor sealing surfaces or holes in the intake will make it not run or run lean. It all must be sealed perfectly. Are you sure the cam is not off one tooth from the crank when you re assembled the engine? The hard pull sounds like the compression release is not working also.

Checked internals and everything is as it should be, compression release looks fine and operates as intended. At this point I believe it might be a leaking intake manifold allowing air to bypass the carb. This probably results in the carb not having enough vacuum to actuate the jets properly, which would prevent me from starting the bike. Makes sense that some lighter fluid got it to start, and from that maybe if it is not pulling the fuel properly from the float, running in a lean condition and revving out from that.

 

[Hellion]

Your mind is nicely analytical, kudos on the possible causes.
I do think (maybe) the intake is too long with an unsupported mass out there, way out there, on the end. Shorter is better based merely on the fact that on most potent applications, there's not much distance between the carburetor and the block. I don't think it is your problem but perhaps a contributing factor. You do need to eliminate all the vacuum leaks and ensure the intake manifold is good to go.

Keep in mind all these engines need CHOKE to start, sometimes even when hot ...but that is usually due to EPA jetting (designed to run leaner than the norm, you know, to "save the planet").

COMPRESSION
SPARK
FUEL
*All at the right timing*

Did the engine run fine right out of the box or was it immediately taken apart for mods?

I like the configuration of the engine. The standard configuration I am not a big fan of because of the inefficient footprint and vertical cylinders are an aesthetic that looks best. I imagine it takes a different amount of oil to run it this way? I mean you want the oil dipper to have full contact with the oil "pool".

 

[Luttrell850]

Your mind is nicely analytical, kudos on the possible causes.
I do think (maybe) the intake is too long with an unsupported mass out there, way out there, on the end. Shorter is better based merely on the fact that on most potent applications, there's not much distance between the carburetor and the block. I don't think it is your problem but perhaps a contributing factor. You do need to eliminate all the vacuum leaks and ensure the intake manifold is good to go.

Keep in mind all these engines need CHOKE to start, sometimes even when hot ...but that is usually due to EPA jetting (designed to run leaner than the norm, you know, to "save the planet").

COMPRESSION
SPARK
FUEL
*All at the right timing*

Did the engine run fine right out of the box or was it immediately taken apart for mods?

I like the configuration of the engine. The standard configuration I am not a big fan of because of the inefficient footprint and vertical cylinders are an aesthetic that looks best. I imagine it takes a different amount of oil to run it this way? I mean you want the oil dipper to have full contact with the oil "pool".

Thanks for the response! The motor was indeed taken apart immediately, probably an oversight on my part to not break the motor in on an entirely stock configuration.

To test my theory of a vacuum leak I will be applying JB weld over my welded areas tonight to see how that affects this issue. This weekend I plan on welding up a new intake runner with a shorter design (and potentially a slight venturi around the bend to promote a faster air speed around the turn, unsure about this concept still) to hopefully get a better weld down.

In terms of oil, I do overfill the motor slightly in order to raise that oil level to an approximately appropriate level. One major thing I have been working on constructing for this specifically is a 3D printed clear side cover so that the oil level can be visualized and allow for me to see the dippers position during a full revolution of the crankshaft. From here, I can measure that amount of oil, and fabricate a new dipstick to gauge the new level accurately. I have also considered a clear sheet of acrylic with a 3/4 hole for the crank vs the 3D print route but either should work.

 

[Hellion]

You can also try doubling up your gaskets (or using thicker material) on the intake manifold on both ends. Sometimes these composition gaskets are poor and quite honestly a lot of overseas manufacturers just can't get it right. It may look the part but functions poorly. We even have German toolmakers outsourcing their manufacturing to China and Vietnam, sad times.

To judge optimal oil level, I would place the bike on a level surface with the side/sump cover off and then place a carpenter's level against the block making a straight level line across the block (mimicking the oil level) and making sure the dipper is buried at the bottom of the piston stroke. You can experiment from there deciding on what's the best amount. The racing guys typically use quite a bit less oil than the manufacturer's recommended amount. It's all churned up and mistified at 9000+ revs anyway.

Don't forget to use a strong light to look for pinholes in anything you weld. You could also try sealing the flange ends, applying air pressure and plunging it in a bucket of water to check for bubbles.

 

[SLM]

i

Your mind is nicely analytical, kudos on the possible causes.
I do think (maybe) the intake is too long with an unsupported mass out there, way out there, on the end. Shorter is better based merely on the fact that on most potent applications, there's not much distance between the carburetor and the block. I don't think it is your problem but perhaps a contributing factor. You do need to eliminate all the vacuum leaks and ensure the intake manifold is good to go.

Keep in mind all these engines need CHOKE to start, sometimes even when hot ...but that is usually due to EPA jetting (designed to run leaner than the norm, you know, to "save the planet").

COMPRESSION
SPARK
FUEL
*All at the right timing*

Did the engine run fine right out of the box or was it immediately taken apart for mods?

I like the configuration of the engine. The standard configuration I am not a big fan of because of the inefficient footprint and vertical cylinders are an aesthetic that looks best. I imagine it takes a different amount of oil to run it this way? I mean you want the oil dipper to have full contact with the oil "pool".

was gonna ask about that cuz i am building a similar bike, with the engine canted too, the thing that worries me is the oil dipstick, my engine is angled back quite a bir, so much so that the base of the engine is slightly leaning back, prob by like 9 degrees, is that too much? any other problems i should know about for this amount of lean?

 

[Luttrell850]

Well, it's been a while since I posted and unfortunately, I do not have much of an update on the runaway issues I had been facing.

Not long after this post my gas tank sprung a bad leak. I decided to take this opportunity to fabricate a proper gas tank which certainly has been quite the learning process. The previous tank was slapped together and was more of an experiment than anything as it was held together with jb weld and had a red-kote liner on the interior. I'm not surprised that it did spring a leak, as I figured the gasoline would breakdown the jb weld over time.

I am making this new tank by hand with 20-gauge aluminum and will be torch welding it together. I have now finished fabrication of my buck and will begin shaping my metal this weekend. Hopefully when the tank is finished, I will be able to address the runaway issue properly. I have a new intake runner already fabricated that is ready for testing. I have ensured that this runner does not have a leak present already. Hopefully with that and the new gas tank I will have eliminated a lot of points of failure within the system and can finally get this bike running!

One thought I've had over time is that potentially the WPC-01 pulse fuel pump is potentially supplying too much fuel to my carb. Has anybody ever had any issues like this with their pulse pumps on 212's or 224's? Especially when used with a Nibbi PWK carb (24mm).

Anyways, I'll be sure to update with some pictures of the buck and tank once those are done and I can finally address this runaway issue!

 

[Denny]

You need to add a return line with a valve to regulate fuel pressure.

 

[Darren]

Our karts run Mikuni pulse pumps with return lines, a simple fish tank air clamp is used to fine tune the fuel pressure

 

[Luttrell850]

You need to add a return line with a valve to regulate fuel pressure.

What do you mean exactly here? Are you T'ing off the line from the pump to the carb as a return line to the tank?

Our karts run Mikuni pulse pumps with return lines, a simple fish tank air clamp is used to fine tune the fuel pressure

With the clamp, where is that being placed along the system? I would assume it is being used to restrict flow to the carb. For your return line, how is it routed?

 

[Denny]

T the line near the carb.