Honda CRF 250 Dirt Bike Backfires But Won't Start. What's Wrong With It?

[@jrchaidez2143]

I just want to come and say that.. thanks for all you’re content man, legit I’ve been learning a lot of thinks from you’re videos man. I appreciate what you do just to entertain us and teach us too.

[@mikespain8655]

The compression release on a small engine accounts for about 30-40 psi of lower compression when testing. Takes at least 500 RPMs to take the compression release out of the equation. Owner had the exhaust valves set tight, not loose. How you are only getting 10 psi on a compression test and little leakage on leak down test is both concerning, and odd. If you suspect worn or stuck rings, simply add some oil down spark plug hole and if compression increases, then rings are most likely the problem. Funny how the owner installs a new fuel injector, sets the valves, but does no compression or leak down test.

[@todascaaurelian3570]

Hello! Last year I had a 2008 crf250r at my garage. After a full rebuild of the engine the bike would start first or second kick but then shut off as the revs went down. The problem was caused by the decompresion spring which was having too much tension, bent it a little and the bike run like a dream. I am suspecting that this bike is having the same issue and I suggest you to take off the mecanism and bend the spring so it does have enough tension just to move the decomp. weight back to the center of the cam. Mine would also make a ticking noise before shutting off every time. Good luck!

[@chrisheath7500]

After a Full OEM rebuild, my does the same thing. When the revs start to fall back to idle, I here a little ticking noise but only for just a second and it shuts off. Can you give me a little more of an explanation? Take the mechanism off and bend the spring to make it harder to work? Make the spring tighter so it has more tension? Thanks!

[@ashharurot7082]

Make the spring softer is the answer.

[@tedh7543]

I just found your channel recently and really like how you take the time to explain how engines and transmissions function & the steps necessary to repair them properly. If I lived in Wisconsin near you I would certainly buy a machine you repaired with confidence.

[@thevoxofreason8468]

Nice bikes when new-ish. When older, they can be a bit difficult to work on and diagnose. This is one of the reasons why I stick with 2 strokes with carburetors for my *personal* machine. They're so darn simple and still tons of fun.

[@MaNNeRz91]

I don't understand how people say carbs are so simple 🤔 maybe never had to tune a brand new one from scratch without the original jet and needle sizes. Injection.... you can literally see... Visually indicated... On a gauge.... What your fuel is doing. With a carb you could be bombing down a road and have your slide get stuck or a jet slightly block without even realising and completely alter your mixture and hot spot the piston. Injection would either cut out before it did damage from irregular parameters or it would adjust those parameters to bring the mixture back to 14.0:1 or wherever it needs it to be 👀

[@thevoxofreason8468]

@@MaNNeRz91 That's true. I do own carbureted and injected bikes. What I mean by simple, in this case, is everything can be worked on with hand tools. No computer needed. I would be the first to admit though that it's easier to map my Power Commanders than to rejet a carb... but I can do one of those things on a trail in the middle of a forest with just my tool kit, the other I can't.

[@MaNNeRz91]

@@thevoxofreason8468 that's a fair enough example mate but with tech getting smaller and smaller you now have the ability to do ECU stuff over Bluetooth with a module over your phone etc. I wouldn't want to carry a laptop around although I do in my car for mapping reasons but a phone would be ideal on the bike. My bike is carb. I've worked on all sorts of carbs and engines including RC, classic cars and bikes. But I definitely prefer EFI for the reasons in my last comment. I know you can have a wideband sensor on a carb set up too which is super helpful but then an efi system would read that information and adjust accordingly whereas a carb you then have to adjust stuff yourself. I mean efi you can go from say a #50 jet up to a #200 jet without changing the jet 👍

[@thevoxofreason8468]

@@MaNNeRz91 For sure. I agree. EFI is certainly easier to adjust, but my point was just that carbs are simpler. I can make a carburetor out of a tin can...like Harley did on their first machine (although I think that story's apocryphal). Anyway, I'm just thinking worst case. In the mountains, bike stops running, no cell service, just my tool kit that I carry. I find out it's my carb or EFI that's the problem. I'd rather it be my carb.

[@MaNNeRz91]

@@thevoxofreason8468 to be fair if it's serviced well there shouldn't be any problems with the efi or carb. I think for mountain riding efi all day long though. If you're riding around a certain altitude then carb will do too. Personally I'm always adjusting my carb slightly depending on time of day. The dense air on the morning when I go to work at 5am allows me to run richer but when I finish work it will not run right until I lean it off slightly. Could definitely do with a efi system but I cba to retro fit one 😂😂 The tin carb thing is intriguing lol 🤔🤔

[@reaper20015]

To me fuel injection and dirt bikes seems really silly. Too many electronics to possibly fail. And yeah, that spark plug.......pretty sure it goes through the bottom of the crankcase. Damn!

[@MaNNeRz91]

Injection requires less changing in regards to altitude and weather conditions which it does itself. Carb is more reliable at the conditions it'd tuned for providing nothing gets blocked or stuck. Injection can be programmed to change spray amount and timing and will work more efficiently providing you keep the fuel sensors and injector clean

[@Davido50]

They run far better & are proven in racing an off rd riding! My 2 newer Yamaha sport quads are fuel injected..no probs!

[@Davido50]

@@MaNNeRz91 FI is proven & better by far now in '22.

[@rogersemple3122]

We were all worried when cars went to FI now how many cars out there have carbs

[@Ty-NY8vp]

Love the channel definitely should do more modern and newer bike and atv builds on the channel. I love the modern builds.

[@stevencoleman1557]

My yx 140 pitbike was doing that and it turned out to be the inlet valve was Bent

[@BrennZy96]

Love your videos man! There's never a video I don't learn something new, thanks!

[@Haydenluptonbmx]

To me when you pulled the rocker cover off the camshaft did not look like it had the lobes facing up like it should with correct timing. I would definitely be re checking the timing

[@eschrader]

My pilot jet fell out on my 450r and it would only run at WOT. Broke my arm that day 3rd gear pinned up a rocky hill climb. Def got some carb or valve issues if it doesn't start easily

[@louis3576]

I had an xr350. Also a washer was missing at one cylinder bolt, which left me with no compression. The cylinder head then pulls skewed while tightening the cylinder head bolts.

[@cesargallo7424]

Joe, if the compression is going out to the crankcase, I think it is not because of the decompression system. My bet it is because the headgasket was blown on the timing chain side.

[@soupdragon5555]

Thats what I was thinking too. Interesting video.

[@antoniobednjanec4787]

exactly my first thought

[@benmiller5015]

Yup. I'm sure if he'd bumped the air pressure up to something like 40 psi it would have really made a difference on the leak down test n prolly even would have started leaking air into the coolant too

[@1991enduro]

what gasket mate im not sure can you explain further thanks

[@cesargallo7424]

@@benmiller5015 maybe the gasket is blown but not on the coolant passages, instead on the timing chain sid and this is why it leaks to the crankcase, this is my theory

[@IronriverVlogs]

I feel like he like fixing more than riding hope he opens a shop one day. His subs would be there first day ready to get shit fixed

[@2vintage]

Hopefully in the near future! That would be awesome!

[@IronriverVlogs]

@@2vintage you got this man just keep up the hard work

[@farmermann2335]

I can't help but notice, usually when you kick things over you crack the throttle a little. From my experience most bikes especially race bikes don't like that

[@rogersemple3122]

The Accel pump throws fuel into carb.Each bike has a starting routine which you must learn.My old 490 Maicos liked to be laid over until gas came gushing out,then they started right up

[@dannyjamison8337]

If you had a problem with the compression release, the leak down test would have shown a leak through the exhaust valves. It's leaking into the crankcase, so it's either rings or a head gasket. Also, when the compression test is that bad, squirt some oil through the spark plug hole into the cylinder and retest it. If the compression comes up, the rings are bad.

[@rickyparrish2570]

the leakdown should be done at tdc so the lobe of the compression release should not be engaged with the valve.

[@isaiahthomas4906]

how do you know all of this sir. wow

[@blaisesarate6729]

the oil in the cylinder after bad compression test is a new one to me… will be trying that.

[@RioterRides]

@@isaiahthomas4906 practice

[@mtbridingog9083]

Not all the time … it could be the decompression seating is not set right or the shims for the exhaust is out of clearance

[@hanneseichler5108]

I had the same issue with mine. In my case is were the inlet valves. There were worn out, new ones in and it runs again

[@PaulHigginbothamSr]

Since he adjusted the valves and she never ran since my idea is also the compression valve, or mechanism. Since those rings could have been put in a racing bike you would wish for no leakage but that is tilting at windmills. With new rings and different valve adjustment she will run and scare you good.

[@motomechanic5711]

You need to do 80psi for the leak down test. 20psi isn’t enough.

[@dyanmarks7926]

We need a video of a ltr450 that’s like the last one we haven’t seen you work on 😢

[@fredrikahlinder5055]

My crf250r 2011 had the same problem and it was the TPS on the throttlebody that was broken.

[@rickyparrish2570]

very first thing you should have done is spray it with ether and see if it would light up. I've built countless honda unicam motors and that one looks healthy enough to run. check fuel pressure. should be around 50 psi

[@cooperdonner4520]

Awesome video Joe. Love seeing dirt bikes on the channel.

[@bricehale6593]

My 05 crf250x supermoto just locked up few weeks ago im about to halfto go through all this same stuff

[@2vintage]

ah bummer! I hope you get it fixed up!

[@darreng2639]

you can't get a proper reading doing a leak down test with 20psi.. you need 60psi min.. you need to hold the engine from turning over once you put higher psi to it. you should put the cam caps on when you're checking for valve clearance on the bench same as you should on the bike

[@benmiller5015]

Cars are often checked at 100 psi or more. If your on exactly TDC you shouldn't have to hold the crank, which you shouldn't do anyway unless you want a ratchet ripped out of your hand. But even if he just ran 40 psi leak down test he prolly would have found that the head gasket was blown. A proper leak down tester would go a long way as opposed to just pressurizing straight from the compressor. They are stupid easy n cheap to make

[@tervosalminen191]

@@benmiller5015 And if you perform leak down test at TDC, the automatic decompression system is not active, and does not have any effect to leak down.

[@bigcaputo09]

With leak down test some air will always go past the rings. The actual leak down tester has a gauge that tells you if it's too much leaking past.

[@joey-gb5md]

I'm glad someone finally said it and especially with a single ring .

[@anthonyf4439]

Watching you drain fluids is oddly satisfying.

[@mattbrown5511]

I have not worked on this particular model, but I'm thinking the head gasket was a bit dodgy. I don't see the rings, jug, or piston being an issue. The decomp mechanism is definite possibility.

[@bengilbey04]

Is this the worlds first Honda that don’t start. I’m impressed

[@MM_in_Havasu]

Probably a worn-out piston and rings. The pistons in these throwaway 4-stroke MX bikes are basically an aluminum wafer with 2 ring grooves and a tab on each side called a piston skirt. Titanium valves that stretch under high RPM also start leaking and cause low or no compression. Head gaskets can also fail, but not as common a problem as the wear-out parts.

[@eddieconner7302]

Can't do a compression test on a 4 stroke with auto decompression.

[@souvlakiisnijs7331]

check valves , re do the timing ( guess its off ) if the valves seat all the way( so you dont have leaks ) and it gets gas and timing is 100% right ( check spark ) then it should run

[@Davido50]

Def confirm that plug is proper size & REPLACE!

[@devinaudette2635]

Had a YZ 450 with a key way problem on the crank.. Hard to remember the details, but a new keyway and it ran again. Easy enough to check..

[@AliasTekTV]

Piston tells a tale. It 100% kissed a valve at one point.

[@jaredk777]

I like these videos but I have OCD and almost wish you’d wait until the machine is fixed before you post the video, the cliffhangers are killing me!

[@2vintage]

Yeah sorry about that The videos would be over an hour long if I waited.

[@jaredk777]

@@2vintage no problem man, I get it. It’s like a good tv show, “to be continued” always keeps you coming back to see the final episode! I gotta also say, your video editing skills are much better now than they used to be. I need to learn how to edit so I can start posting my repair videos!

[@kolegibson1723]

I have a question I see you lube up the cylinder invites quite a bit with oil I was wonder what exact oil that was

[@rhiantaylor3446]

Backfiring might mean spark taking place at wrong time when inlet valves are open. Similarly good compression requires cam timing to be correct with respect to crank and piston position. Is it possible crank/flywheel keyway has failed ?

[@rogersemple3122]

@@greatest_bumble_bee_dude 100 dollars a hour and this young man is as good as most mechanics.

[@prayzal9343]

Every time Joe finds a problem he be like “that’s not good” 😂😂😂

[@mikeschlup5279]

When I put mine back together the timing chain tensioner as I tightened it up threw my timing off...still do not know what I did wrong...hopefully when you put it back together I will learn something.....

[@davidpalmer287]

Your marks should be lined up when the chain is tight i always push the chain guide with my finger to double check that. It sounds like you may be a tooth off. Another thing ive seen is cam chain was stretched throwing the timing off

[@Tyemuck18]

Any amount of wear on a gasket could cause a small Leak. Large leaks that build pressure in the lower end and cause damage would more then likely been a catastrophic failure like a crack. Your decompression chamber was probably adjusted after the leak first became present that's why it was adjusted, as you said the owner got it to fire once. I would clean all gaskets and re seal them with new adhesive. I had a Suzuki bandit that had all the same issues and it was a result of the gasket leaking into a oil chamber building pressure in the bottom without leaking in to coolant.

[@ShoreTime]

First things first. I like your channel and just subscribed. I think u r a good mechanic. I agree with your assessment. A tip from my experience - when someone tells me they did a valve adjustment, that's the FIRST thing I check because most folks don't make it perfect, but "good enough." And when I do valves I also do rings because I am there and rings are cheap. I am not sure I wouldn't hone that cylinder too because why not?

[@fisiipeautameilau1728]

I just noticed you didn't check the camshaft timing

[@2vintage]

I did, I forgot to film it unfortunately. It was spot on. The cam has two lines in it that need to be parallel with the head. Theh were.

[@fisiipeautameilau1728]

@@2vintage thanks for replying and love your channel cheers

[@WujoCaZa]

For future :) Crf got automatic decompression, so the value don’t gonna be big. Standard compression for 250 17’ is 13,8:1. and the tested value is gonna be only around 600kPa/87psi. So keep that in mind! But either way this value is too low 🤣

[@jamiewilliams2261]

Awesome video man Keep up the awesome content

[@DrivenPHPOV]

having the same issue right now on a project KLX Kawasaki 250 to 300cc conversion. the bike was stock up for about 15+ years. i changes the block and valves and machine shopped the head. my feet is swollen from the kicking. gaskets are new and the seals as well

[@mtbridingog9083]

Timing off most likely g .. it’s firing but most likely off time .. make sure it’s not off by a tooth .. check compression and make sure the bike is holding at least 100 psi if not then see if the valves are out of spec ( seats needs to be recut if the valves aren’t sealing then the shims need to be replaced ) ….

[@richgwozdz8580]

My warrior bent its second set of rods from the compression mechanism spring failing

[@devincarr9049]

Iv Ben watching ur videos for years now sence beginning u the man u can fix anything

[@Davido50]

Valves out of spec? Worn top end? It looks well used & not very well taken care of sadly!

[@tomnekuda3818]

Other than it's a miserable 4-stroke, perhaps timing or valves too tight. BUT, it could be low on lighter fluid or need a new flint! LOL After watching this upload it brought back memories of 4-strokes.....mostly bad, and; I remember why I am a 2-stroke freak. Excellent analysis with logical step by step. I'll never figure out why a fella needs a decompression device on a small bike like a 250.

[@danssv8]

Might be decompression problem so the valve stays open a small bit and that's why it back fire throughout the exhaust and valve

[@krotchlickmeugh627]

Careful with that brand of shim kits. I get the urge to spend less and make more bud. But hot cams or prox kits actually last. Rather than those amazon kits. Been at this sake job just a larger scale and larger shop with more turn over for 10 years. That bike will be back for a valve adjustment very soon. Not to mention honda uses titanium valves that wear through the seats very quickly

[@craigcamb5598]

That's got "Someone's been here before " all over it . washer missing from the head bolt? were they even torqued down ? Didn't see you remove them in the vid ,20 psi is not a lot to use on a ldt thats why you could barely hear it comming out the crankcase.

[@johnhicks9529]

Check the head gasket over good to man also.

[@andy5786]

Honda CRF awesome vintage you are great can sort any bikes out love your channel class👍💯🙂🇬🇧

[@MaNNeRz91]

Did you check ignition timing? 👀 Seemed to me like it wasn't firing for a while then when it finally pooled up enough to backfire it backfired. Could be firing too late

[@rickyparrish2570]

the only way for ignition timing to be off is if the flywheel sheered the key. possible but unlikely.

[@MaNNeRz91]

@@rickyparrish2570 not the only way if something is shorting/giving a false signal on the flywheel. Some metal on it or its been fitted wrong or without the keyway?

[@rickyparrish2570]

@@MaNNeRz91 have never seen a cdi give a false signal

[@MaNNeRz91]

@@rickyparrish2570 interference or shorting would be false signals or discharges

[@rickyparrish2570]

@@MaNNeRz91 iterference of what?

[@cheto2952]

Great find boss roll with it nothing to lose, but get a new piston and rings you got the head and cylinder off might as well do it anyway

[@iannsr125]

Well while you have the head off take the valves out and clean them and measure them to see if they are in spec and the valve stems are OK as well , if they are all OK I would say it uas other issues but can diagnose over a video but look for black tracking on the head and cylinder as this will show where the gasses were going if the head gasket had blown

[@johnhicks9529]

Check the reed valves.& seals., the decompression relief valve. Know as pop off pressurerelief valve. It most likely is. Those intake valve has to be set at .005 to dead on. It would not be labeled in the book if you could leave at .006 theit .001.& yes there is A bigger clearence in the intake valves to now.

[@frontlinemedia4270]

Why are you saying that the compression is low? So what was the issue?

[@kittenfat2207]

NGL I cringed a bit when you were checking the oil, these models have two oil compartments 😅. One for clutch gearbox etc, and one for Crank and head

[@murrayminimotors1674]

Still pumping out great content 👌!!

[@mariusfitzgerald9217]

Can u show how to step by step fix it because my bikes doing the exact same

[@Tommy-vd8uh]

There are 4 things a motor needs. Air, rule, compression,and spark. If a 4 stroke back fired it has spark. And by watching the first 30 seconds I can see u have compression. So it is probably a fuel problem. Because I don't think that a lack of air would not let it start. That is the best that I can say in watching about 1 minute and only being 13.

[@rogersemple3122]

I suggest you watch allot longer than one minute young man.Every good rider must know mechanics very well.

[@dietznutz1]

My first guess would be timing but I don't know much abt new bikes like this, more of a vintage Villiers guy

[@TroyRosenbaugh]

Or in my experience ring gaps are in line with each other.

[@mattoaida]

I feel like it's the head gasket or I think the valves aren't seated properly. I know you did a leak down test but I'd pour some gas in the intake port and exhaust port and see if any gas leaks out the valves

[@stewartgriffin3192]

23:25 It looks like the exhaust valve was contacting the piston. See how one valve relief is black and has soot. The other valve relief has the perfect circle of the valve in it. Almost like it was contacting at some point. I would definitely make sure the piston is not cracked and that the exhaust valves are sealing. Pour some rubbing alcohol on the top of them and make sure it doesn't leak through.

[@stevenhanson5782]

I'd put money on the sprocket has spun on the cam.. have seen it a couple times

[@andyyarrington6401]

valves are out of adjustment ,,very very common issue with crf250r ,,needs shimmed ,,and when it happens its pretty instant

[@1176hambone]

Maybe Honda built in a safety to no-start when valves lashed too tight. Sounds like a Honda-esque engineering technique.

[@ALDA2479]

Need to put a case saver on it everytime I see someone without 1 I cringe thinking of what could happen

[@j-beatsimaginationstudio1987]

Your theory sounds right to me brother. Be safe :)

[@bradrush45]

Excellent videos!

[@tphvictims5101]

Valves are to tight ? If I worked on that two minutes in you’d have an expensive piece of scrap metal. Holy Mackerel.

[@jeironamobey8136]

my bike backfired and wouldnt start. My klr650 had bad exhaust valve seals and i was consuming oil daily. One day my bike wouldnt start after a previous days ride. It just backfired. I heated the cylinder with a heat gun and the bike started right up and idled at 3000 and i coult start it every time only when the cylinder was heated up first. What do you think it can be???

[@18wheeler77]

Very interesting! Glad you found the problem.

[@vwsandvettes3253]

Not sure your thoughts on it, but I like to reuse the coolant that I drain if it looks good. No sense letting it go to waste. It is different than oil which is quicker to get contaminants in it. Coolant in theory doesn't go bad, at least not for quite some time, unless it gets oil in it.

[@benmiller5015]

Drove me a lil crazy when he drained the coolant n oil from the plug to rotate the engine was dripping right into the coolant

[@jeffkenyon7084]

I have to wonder if the decompression mechanism dumps compression till the bike starts then a compression test would only tell you what it leaves in their not its real compression I think your rite and it's dumping off to much

[@lukesousa7010]

Happend to me after rebuild. Had to re shim exhaust valve

[@trevorchapman1078]

Yea I’d recommend changing airfilter after every ride or 2 because Hondas eat valves tbh

[@stevemayo1175]

AT 23:31 see where the Right Ex valve has Touched the Piston?

[@leviphipps269]

With these race bikes don’t hit the throttle pump it a few times to get some gas in there and let it be if you hit the throttle all it’ll do is pop and crack just for future reference

[@tonythompson9049]

Never seen a plug that long dam

[@joshdrifts8843]

I'd say try to push start it a few times bit if your looking for a permanent fix get that compression checked

[@yonnierenton6177]

friend, nice vids🤩... I have had this issue lol, first time I ever noticed valve's Grow?... Valve seat's are to soft and the slamming of the valve eat's it?... lol Good luck

[@TheCuttingtorch]

theres separate gearcase oil? the oil on the dipstick was new but looked like shit when you pulled the plug off

[@davidcorder95]

Heck yeah brother when my bike get paid off I was looking at a 250 nah im getting an atv fast one too

[@paulfranklin7891]

Love your vids dude my son has the 2020crf150r too get the spark plug out I use a piece of garden water hose works a treat can you give that a go and see how you like it

[@robertcamden224]

I've never seen a spark plug that long

[@jamarionjohnson5130]

I have the same bike and the motor needs to be rebuilt and I don’t know how to 2vintage do you think you can do it for me

[@lukelloyd1765]

Love ur vids

[@TroyRosenbaugh]

Need the oiler rings.

[@stevenhanson5782]

I'd put money on that the cam sprocket has turnt on the came.. I have seen it quiet a few times on crf250's

[@stephenmooreguitaruk8365]

Did you find the problem in the end? And did you get it started.

[@user-nb7qt6uw5r]

I have a 1990 CR125R an when it start it it revs out high. Do u know what I can check to solve this?

[@canadian_boyz_tv9811]

You can hear the valves from a mile away you might have to shim them

[@Flow-like-Water777]

clean the fuel injetion or carb...

[@petenikolic5244]

Highly suspicous of the cam timing and you did not check it as for that decompress thing it's a dang 250 ye gads there is only 1 250 with enough compression to need decompression one of the Older Ducatti Desmo 250 singles that was an ankle braker but humm Honda weld it up not needed

[@Drum3rboy14]

i mean was i right or? you think the rings were really contributing to the compression loss?