Hello everyone. I have been working on my predator 212 swapped dirt bike recently and have been having alot of issues. So it all started with this thread here. https://www.diygokarts.com/vb/showthread.php?t=44168 I was having issues at full throttle and it was flooding on me. Some carb settings were suggested and I tried them and it wouldnt start for me going any leaner than it was. After that I tried cleaning the chinese mikuni carb I had on the engine as well as checking jet sizes so i could order a bigger size but when I put it all back together the engine would no longer start at all for me even on my old settings that used to work all it will do is backfire out the carb. To eliminate spark as an issue I tried starting the engine with no fuel in the bowl with ether and then I could clearly see that the spark is firing but its sending all my power right out the intake valve. My first thought would be that somehow the ignition timing is very far off but as far as I can tell theres no way to change the ignition timing on this engine besides changing the magnet position on the flywheel. Has anyone had this issue before or have any suggestions? My engine is completely stock and has never been opened or had any valve adjustment since it came out of the box besides the chinese mikuni that is on there and it has only about 20 hours of use on it so I cant see it being valve timing and the valves on intake and exhaust are not bent and seem to open and close alright. If it helps I can provide pictures or videos of what I am describing just ask. Thanks for reading!
Predator 212 backfiring out carb and wont start
- Thread starter jonlasaga
- Start date
Brianator
Gettin' er done!
Have you reset your valve lash? If not that's a great place to start. Another thing that comes to mind is the possibility of the flywheel key being sheared or partially sheared (which does change the spark timing), I've had the same thing happen for that reason.
Ah shoot I hope its not the flywheel because I dont have the tools to pull that to check it out. Ill verify valve lash is within spec tomorrow and post back but that shouldnt be it because it ran fine before and I havent messed with it. Would definitely be preferable to a sheared flywheel though. Do you have any suggestions for a flywheel tool that can be purchased at any hardware or autoparts store?
Brianator
Gettin' er done!
As long as your flywheel has threaded holes for bolts then a standard general purpose puller should work (the kind with 4 "fingers") BUT you may need to scrounge up your own bolts to use IF none in the kit work, they usually do though.
Honestly though I've only ever needed a puller for one flywheel, the rest I was able to pop off with a couple tight fitting wedges of wood between the flywheel and the block and a hammer (to tap the end of the crank snout). The trick is to set the nut FLUSH with the end of the crank so when you hit it with the hammer you are hitting both surfaces as equally as possible and you won't damage the threads. With good pressure on the wedges, 1 or 2 decent taps and it should pop right off! The kind of swing you can get with your wrist should be enough you don't want to wail on it. A standard carpenters hammer is sufficient.
Honestly though I've only ever needed a puller for one flywheel, the rest I was able to pop off with a couple tight fitting wedges of wood between the flywheel and the block and a hammer (to tap the end of the crank snout). The trick is to set the nut FLUSH with the end of the crank so when you hit it with the hammer you are hitting both surfaces as equally as possible and you won't damage the threads. With good pressure on the wedges, 1 or 2 decent taps and it should pop right off! The kind of swing you can get with your wrist should be enough you don't want to wail on it. A standard carpenters hammer is sufficient.
Any suggestions on how to hold the flywheel steady while I remove the 19 on the front? I tried putting a bar in the pull start ring and I bent it up a little bit
Brianator
Gettin' er done!
I use an impact gun but a long ratchet strap would probably hold the flywheel, don't use the ratcheting part just wrap it really tight in the same direction as you need to go to loosen the bolt then find something solid on the motor to hook the hook to. A little water on the strap will help it be "stickier". You could always just try holding the flywheel by hand then smacking the ratchet or breaker bar with a hammer, I've done that with success several times on various moving parts.
mckutzy
Well-known member
Cotton or any other natural rope/cord, stuff as much as you con into the combustion chamber through the sparkplug hole... make sure its jammed in there good enough. crank against that....
An other Idea, is get a sprocket/ pulley or hub w/key that can fit the shaft, make a handle to attach to that, and leverage against that to loosen the nut, likewise, use that to hold against the nut when tightening.... I made a tool like this... Was a bar welded to a hub and tacked a key in place to crank against the flywheel....
An other Idea, is get a sprocket/ pulley or hub w/key that can fit the shaft, make a handle to attach to that, and leverage against that to loosen the nut, likewise, use that to hold against the nut when tightening.... I made a tool like this... Was a bar welded to a hub and tacked a key in place to crank against the flywheel....
Brianator
Gettin' er done!
Great ideas! I forgot about the rope in the cylinder trick I haven't used it in so long! And yup I made a bar to remove the water pump pulley on my truck, it still hangs on the wall!
Karttekk
Well-known member
I use a piston stop to keep the crankshaft from rotating. Thread it in the spark plug hole then manually rotate the engine until the piston hits the stop. You can then remove the nut without the engine rotating.
https://www.ebay.com/itm/Tecomec-Un...roke-4-stroke-engines-10mm-14mm-/382049095159
https://www.discountlawnparts.com/piston-stop-700-820
https://www.ebay.com/itm/Tecomec-Un...roke-4-stroke-engines-10mm-14mm-/382049095159
https://www.discountlawnparts.com/piston-stop-700-820
I might have to get one of these if not for my predator definitely for my honda prelude that engine is almost impossible to get the timing belt on right because it spins over so easily. Thanks for the suggestion and links.
So It took me a while to get the engine off in this heat but today I removed the flywheel to check it and the ratchet strap trick worked like a charm. Thanks for all of the other suggestions as well on how to keep the engine in place this is a common issue I run into working on my cars. The flywheel looked good as well as the key and I reinstalled it. The valve lash seemed to be alright but I got it as close to .0015 as I could and after that it seemed much more eager to start and the backfiring ceased except when I gave it ether. I think it was only backfiring with ether because it can combust at a wide range of afr. It is afterfiring now so i think it just needs more valve adjustment to make sure that exhaust is closed once it fires up and it should go. I will update if thats not the case but its looking good so far. Thanks for all the suggestions brianator the valves would have been the last thing I would have checked normally.
my guess (since it's more likely) is a misaligned camshaft..
if you ever opened up the crank (to remove the governor for example)
you might have installed the cam the wrong way around
(aligned the dots at BDC not TDC for example)
'sid
PS walls of text are a huge PITA.. please use some paragraphing ..
your initial post is essentially unreadable on a full size PC (I still haven't!)
So ditch the phone-habbits, we're no short message service
if you ever opened up the crank (to remove the governor for example)
you might have installed the cam the wrong way around
(aligned the dots at BDC not TDC for example)
'sid
PS walls of text are a huge PITA.. please use some paragraphing ..
your initial post is essentially unreadable on a full size PC (I still haven't!)
So ditch the phone-habbits, we're no short message service
Brianator
Gettin' er done!
Np at all and I'm glad you made the ratchet strap work! They're useful on so many levels! Sounds like you're close to getting it running smooth, keep up updated, this info will help others as well I'm sure.
my guess (since it's more likely) is a misaligned camshaft..
if you ever opened up the crank (to remove the governor for example)
you might have installed the cam the wrong way around
(aligned the dots at BDC not TDC for example)
'sid
PS walls of text are a huge PITA.. please use some paragraphing ..
your initial post is essentially unreadable on a full size PC (I still haven't!)
So ditch the phone-habbits, we're no short message service
I will keep that in mind but I believe what I typed was a paragraph considering it had punctuation and was formatted in sentences but if it makes it easier to read I can make sure to add a space between every 4 to 5 sentences. I am also a pc user. I don't own a phone so I don't quite understand your analogy. Is there a certain format that you all like to stick to around this site?
As far as the engine it has never been opened the governor is still inside the engine but is not attached to anything outside of it because of the chinese mikuni. I wouldn't be surprised though if it somehow came out of time considering how far out of spec my valves were after only about 20 hours runtime. But if it did that probably means my engine is toast anyway. I tried adjusting the valves again today and got it to fire over for a couple turns but its still not going so it might be time to take it all apart and see what has been happening inside.
uhhh you left the governor in and disabled it??
that's a baaad idea.
remove it ! NOW before it detonates inside the engine and locks your running engine from 5k rpms to zero in the blink of an eye.
Really.. that thing either has to do it's job or must be romved, no inbetweens
(that's essentially a cherry bomb, you either have it unlit in your pocket, or a safe distance apart.. lit in your pocket is waiting for injury)
Now that that's out of the way.. the analogy comes from the 'observation'
that most users posting walls of text, like you did above;
are indeed using their phones to visit and participate;
and what looks okay on 2" wide screen and even a 4" wide screen a foot from your face,
So they tend to not think ahead but just type as they would type on whatsapp or whatever.
Anyways back to topic..
that cam is still untouched.. so valve timing can not be the issue,
the flywheel and it's key were fine, and I'd bet you checked the magneto's air gap as well already.
I doubt it's really possible to overheat the magneto itself to have it missfiring,
so you have a sticky valve for some reason..
valve lash might be an option, but an unlikely one..
a bent valve stem or a contaminated port is more likely to prevent it sealing up.
Since even on zero lash, the intake port would be fully closed when the spark ignites.
at least when trying to start.
Oh... wait a minute....
Here's an idea (maybe far fetched, but hear me out)
what if that governor already decided to desintegrate inside your engine,
and instead of spittings it's bits and bobs
into the cog gears of your crank and cam to lock the engine up,
it decided to spit one part unter the lifter with the oil acting to glue it under it
to essentially add a bit of lift to the intake valve at all times..
taking up all slack and even cracking the valve seal open at least most of the time.
Since that governor has to go anyways.. that'd be the very first thing I'd check atm;
to be sure by no means of firing the engine up the next time (or trying to that is)
I'd cause a much bigger issue.
cleaned and checked internals with a properly reset (just to be sure) valve lash
would certainly rule out all internal issues within less than 45mins of work.
And since that governor -again- has to go anyways, even if everything is in perfect order internally, that time wouldn't be wasted at all,
and we could concentrate on the 'externals' then.
Running an engine too lean means overheating and depending on how lean an engine runs,
it could also cause the spark plug to overheat of course,
and once that's hot enough it can certainly ignite incoming fuel/air mix already..
unlikely during pulling the rope of course,
and that also should be dealt with with the choke setting to at least have it trying to fire up
and then dying out after just a few minutes acting that way.
BUT check your spark plug insulation colour to dial in the fuel mix anyways..
a too lean engine is worse than a too rich one (you rather foul a plug than having the plug drop ceramic shards into the cylinder when it cracks from heat)
that can only be done properly with a running engine though..
so that'd be part two in my book
'sid
that's a baaad idea.
remove it ! NOW before it detonates inside the engine and locks your running engine from 5k rpms to zero in the blink of an eye.
Really.. that thing either has to do it's job or must be romved, no inbetweens
(that's essentially a cherry bomb, you either have it unlit in your pocket, or a safe distance apart.. lit in your pocket is waiting for injury
)Now that that's out of the way.. the analogy comes from the 'observation'
that most users posting walls of text, like you did above;
are indeed using their phones to visit and participate;
and what looks okay on 2" wide screen and even a 4" wide screen a foot from your face,
So they tend to not think ahead but just type as they would type on whatsapp or whatever.
Anyways back to topic..
that cam is still untouched.. so valve timing can not be the issue,
the flywheel and it's key were fine, and I'd bet you checked the magneto's air gap as well already.
I doubt it's really possible to overheat the magneto itself to have it missfiring,
so you have a sticky valve for some reason..
valve lash might be an option, but an unlikely one..
a bent valve stem or a contaminated port is more likely to prevent it sealing up.
Since even on zero lash, the intake port would be fully closed when the spark ignites.
at least when trying to start.
Oh... wait a minute....
Here's an idea (maybe far fetched, but hear me out)
what if that governor already decided to desintegrate inside your engine,
and instead of spittings it's bits and bobs
into the cog gears of your crank and cam to lock the engine up,
it decided to spit one part unter the lifter with the oil acting to glue it under it
to essentially add a bit of lift to the intake valve at all times..
taking up all slack and even cracking the valve seal open at least most of the time.
Since that governor has to go anyways.. that'd be the very first thing I'd check atm;
to be sure by no means of firing the engine up the next time (or trying to that is)
I'd cause a much bigger issue.
cleaned and checked internals with a properly reset (just to be sure) valve lash
would certainly rule out all internal issues within less than 45mins of work.
And since that governor -again- has to go anyways, even if everything is in perfect order internally, that time wouldn't be wasted at all,
and we could concentrate on the 'externals' then.
Running an engine too lean means overheating and depending on how lean an engine runs,
it could also cause the spark plug to overheat of course,
and once that's hot enough it can certainly ignite incoming fuel/air mix already..
unlikely during pulling the rope of course,
and that also should be dealt with with the choke setting to at least have it trying to fire up
and then dying out after just a few minutes acting that way.
BUT check your spark plug insulation colour to dial in the fuel mix anyways..
a too lean engine is worse than a too rich one (you rather foul a plug than having the plug drop ceramic shards into the cylinder when it cracks from heat)
that can only be done properly with a running engine though..
so that'd be part two in my book
'sid
uhhh you left the governor in and disabled it??
that's a baaad idea.
remove it ! NOW before it detonates inside the engine and locks your running engine from 5k rpms to zero in the blink of an eye.
Really.. that thing either has to do it's job or must be romved, no inbetweens
(that's essentially a cherry bomb, you either have it unlit in your pocket, or a safe distance apart.. lit in your pocket is waiting for injury
Now that that's out of the way.. the analogy comes from the 'observation'
that most users posting walls of text, like you did above;
are indeed using their phones to visit and participate;
and what looks okay on 2" wide screen and even a 4" wide screen a foot from your face,
So they tend to not think ahead but just type as they would type on whatsapp or whatever.
Anyways back to topic..
that cam is still untouched.. so valve timing can not be the issue,
the flywheel and it's key were fine, and I'd bet you checked the magneto's air gap as well already.
I doubt it's really possible to overheat the magneto itself to have it missfiring,
so you have a sticky valve for some reason..
valve lash might be an option, but an unlikely one..
a bent valve stem or a contaminated port is more likely to prevent it sealing up.
Since even on zero lash, the intake port would be fully closed when the spark ignites.
at least when trying to start.
Oh... wait a minute....
Here's an idea (maybe far fetched, but hear me out)
what if that governor already decided to desintegrate inside your engine,
and instead of spittings it's bits and bobs
into the cog gears of your crank and cam to lock the engine up,
it decided to spit one part unter the lifter with the oil acting to glue it under it
to essentially add a bit of lift to the intake valve at all times..
taking up all slack and even cracking the valve seal open at least most of the time.
Since that governor has to go anyways.. that'd be the very first thing I'd check atm;
to be sure by no means of firing the engine up the next time (or trying to that is)
I'd cause a much bigger issue.
cleaned and checked internals with a properly reset (just to be sure) valve lash
would certainly rule out all internal issues within less than 45mins of work.
And since that governor -again- has to go anyways, even if everything is in perfect order internally, that time wouldn't be wasted at all,
and we could concentrate on the 'externals' then.
Running an engine too lean means overheating and depending on how lean an engine runs,
it could also cause the spark plug to overheat of course,
and once that's hot enough it can certainly ignite incoming fuel/air mix already..
unlikely during pulling the rope of course,
and that also should be dealt with with the choke setting to at least have it trying to fire up
and then dying out after just a few minutes acting that way.
BUT check your spark plug insulation colour to dial in the fuel mix anyways..
a too lean engine is worse than a too rich one (you rather foul a plug than having the plug drop ceramic shards into the cylinder when it cracks from heat)
that can only be done properly with a running engine though..
so that'd be part two in my book
'sid
"
I think I understand what you mean with the walls of text now. I see that my browser is zoomed out to 75 and when I zoom it in to 100 or more my text is very difficult to read. Ill try and clean up my writing here.
That is an interesting theory though with the governor coming apart I have heard alot online about how it is a bad idea to leave it in but I figured since the governor arm is still there and bolted on it shouldnt be able to back out any easier than with it connected to the assembly. But since my engine doesn't run anyway I think I will take it apart to take pictures of the governor assembly and remove it as well as my internals just to show what happens if you leave it in for all the people like me who figured it would be fine.
I know that my spark plug fires pretty consistently but it is very worn out and battered the plug wire is cracked on the plastic piece that holds the plug and the plug has cracked ceramic insulator so I may as well replace that since the engine is off anyway.
I think you are right that it is likely a valve issue though as coil gap is good flywheel is good and the valve lash made it better. If its not something on the cam side causing the valve issue Ill make sure to check the seal between the valve and the head when closed to look for bent valves.
Post Teardown Update:
https://imgur.com/a/7kIqlki Here are the pictures of my tear down. As I would have thought the governor was still intact as well as the oil sensor. After looking at it today I wouldn't be worried at all about it coming out under use as just trying to get it out by force was hard enough. There is not only the bolt holding it in but also a pin holding the arm on.
Outside of that I found nothing unusual besides the block is cracked around the oil port shown in the photo gallery. I rolled the push rods across the concrete and they are perfectly straight still and the cam and rockers look fine as well. It was all perfectly in time too. The crank was discolored from heat because torque specs were too tight on the rod so I took them off and re torqued to spec.
Tomorrow I will check the valves to make sure they aren't bent but I assume they are fine because the push rods are as well. I will also polish up the engine while I'm at it and tap the holes for the oil sensor and governor arm.
I was kind of hoping to find my solution here but it all seems just too in its place. At least I can rule out issues with the internals for now though. (at least as long as the valves are straight when I check them)
Last edited:
Karttekk
Well-known member
An extreme lean condition could also cause backfiring. I would look for a cracked intake manifold or gasket, restriction in the fuel delivery system such as a clogged fuel filter, fuel line or debris in the tank. Seems odd you would go from flooding at WOT to what appears to be a lean condition. Do you still have the original carb that shipped with the engine? Maybe try another cheap factory style carb instead of the Mikuni.
Follow the diagnostic steps in this guide. It's for a 150cc engine but the same principals apply.
https://absolutelyscooters.net/pdf/CGen_GY6_50cc_Service_Manual.pdf
Follow the diagnostic steps in this guide. It's for a 150cc engine but the same principals apply.
https://absolutelyscooters.net/pdf/CGen_GY6_50cc_Service_Manual.pdf
I have heard this as well but I don't quite understand how a lean engine causes a backfire. Do you have any resources that explain this? I could try putting the stock airbox and carb assembly back on to see what happens but I cant get it to run on ether either so it might be some kind of vaccum leak on the intake side I do know that the manifold is intact though. Unfortunately I have already tried everything in the troubleshooting guide with no luck but now that I know that everything is mechanically in order it has to be my fuel and air or spark causing it to not run.
Brianator
Gettin' er done!
If a engine is running lean it automatically is going to run hotter, when the engine gets too hot "pre-ignition" occurs. Pre-ignition is when the fuel/air mix ignites earlier than it should (while the intake valve is still open) and can cause a "backfire" out of the carburetor, not to be confused with an "afterfire" from the exhaust which occurs when there is a too much fuel coming out of the exhaust side.
I'd do what 'sid said and remove the governor, what happens is the arms inside in engine case grenade and scatter about. Running stock components as a test is great process of elimination!
I'd do what 'sid said and remove the governor, what happens is the arms inside in engine case grenade and scatter about. Running stock components as a test is great process of elimination!
still kikn
Member
I do have a replacement coming in for the plug as well as materials to build a new spark plug wire since it got cracked in the first place because it is very difficult to get the stock wire off on my frame. Now that I have checked out all of the other parts it can definitely be narrowed down to either my spark isn't right or my air fuel isn't right.
Ah you must not have seen my photos? Just finished removing oil sensor and governor yesterday and got the block polished up and tapped today. Probably should have done it sooner but it didnt end up causing any damage at least.
That does make sense though now that you have explained it thanks! I always do love to learn more about engines.
Alright so today I got the engine all back together after an internal inspection and it all looked good. I am going to make a checklist here for my own reference as well as for anyone who is new to the thread so they don't need to re read everything.
1. Ether start attempt it did fire when the plug is on and not fire when the killswitch was off. Would not run on ether though.
2. Valve lash reset it was at .0030 set the lash to .0015 and it gave a couple turns but wouldnt fully start.
3. Checked flywheel key was intact as well as the flywheel itself
4. Opened the engine to check on governor as well as cam and valvetrain. Pics here https://imgur.com/a/7kIqlki governor removed as well as oil sensor.
Tomorrow I will check the intake side of the engine for anything out of place. I remember the gasket fitment wasn't the best and I trimmed on them a bit so I will be remaking gaskets and shortening the bolts to make sure I have a tight seal to the engine. If that doesn't work I may try the stock carb and filter assembly but I really hate that whole assembly so I hope it doesn't come to reinstalling all that garbage.
I will also replace the plug though I don't have the materials to replace the wire just yet. I have heard that when switching to a mikuni it might run better with a different plug. Does anyone here suggest any plugs besides the stock one?
Thanks for all the suggestions so far everyone I hope soon I will be riding again.