Freshly Rebuilt $1200 Big Bore Racing Dirt Bike Won't Start 

I definitely think it's the hot cams. Probably to aggressive of a cam causing lack of vacuum while kicking it. It needs higher rpm to create enough vacuum which would explain why it can be bump started. Put stock cams in it

With regard to push starting on your driveway you might want to try a higher gear and I found that it helps increase traction if you jump higher and drop the clutch just as your butt hits the seat rather than after you are settled in coasting. Lastly hook up a harness to the cute little dog and let him pull you....he clearly has excess energy!

I own an 04 WR250F and have learned more about my bike in the last 2 videos then I have in owning my bike for 6 months. You rock.

Is it just me or does the sounds the paper towels makes when he wipes down stuff give y’all cold chills too? Lol it’s kinda like scratching something on a chalk board for me lol

Decomp, and hot cams. 🔥 I'd burn them both to the ground for how much time I spent chasing that same issue. Run stock cams and a new decomp.

I admire your patience and I am totally confident that you will get that bike starting and running great

Do it the Mustie way, gas straight in the cylinder. If it doesn't fire it's ignition prblm

That shiny ring on the old piston was probably caused by a way too narrow squish or even the piston hitting the head. Always check the squish with aftermarket pistons. It is normally done with solder tin. You can stick it on to the piston edge with greas and do a dry fit of the head with the old head gasket (head bolts torqued to specs). Turn the engine over by hand, remove the head and measure the thickness of the compressed solder tin. Adjust the squish with a (probably) thicker bottom cylinder gasket

at 30:00 you started it, then changed the jetting at 33:40. Imo its a air/fuel ratio problem. Don't give up on it ! great video :)

When bump starting jump on the back of the seat to put a lot of weight and traction on that back tire

Love the channel, always a learning moment. Vinny monitoring progress, better not be dipping into Alpo budget

#1 I'd be suspicious of that cam, and might consider putting a stock one back in (or change the timing on that Hot Cam just for testing purposes). Next I'd connect a clamp on the plug wire and test the actual ignition timing to TDC. What if the coil/magnet were set incorrectly and the timing was off (need a scope to test that, and not sure if you have one.... I find them invaluable). The fly in the ointment is it sounded strong when it was running though.

I would do one size pilot changes at a time. One size makes a big difference. It may need a bigger starter jet, needle clip position adjustment, and it wont hurt to check the ac pump squirt timing

I know that my 2001 yz426f had a certain starting process and if you didn't do it just right it would never start, but also that cam looks to be adjusted a little much maybe adjust it to the middle of the slot

Runs exactly like my 250f. It's the carb is super lean...the compression blows out the spark. Tighten the plug gap and put a known good carb from any running 250.

its awesome when you try to teach us when you have no clue

Wow that the first time I've seen you not get a bike started.. you are great I can't wait to see what it is keep up the great vids

I am emotionally invested now... DON'T GIVE UP YOU GOT THIS!!!!!!!!

I had a Honda that would only bump start. Turned out to be a weak magnet. Kicking it over didn’t produce enough spark but once I pulled it up to 3rd gear on a bump start, it fired immediately. Don’t try and bump it in first or second gear. Pull it right up into 3rd and pop the clutch. Do some testing on resistance and find out which ignition component is weak. Most likely not the cdi, as they usually either work or don’t. No in between. Have jade pull you on a quad or side by side lol. Or have chuck get off the squat rack and help his big brother out lol. Good luck joe

I had a 2014 YZF250(last year of the carb bikes), It would NEVER start if I twisted that throttle first or while kicking it, NEVER !. I always had to be careful to not activate the accelerator pump when starting that beast, it would not even burp if I touched the throttle. Leave the throttle alone, use the choke only and see if that helps (?). Aside from that id be looking at the decompression mechanism After that the timing & hot cams keep up the great Vids !

Intermittent spark Bump start allow more crancking time than kick start. Try a drill on the crank nut to test spark with test light for a longer test spark confirmation.

love your videos man, just got heavily into bikes again since i was a kid about 3 years ago. ive learned a ton on how to maintain and work on bikes from your channel. huge thanks, keep up the great content!

Check the cam and decompress spring. I had a 2001 yam 426 that I put the auto decompress kit in. I Had to play with the cam and like once year replace the comprs spring for some reason. Was acting the same way that one is. Love the channel. It's so cool watching other techs work and pick up tips and tricks. Your get it.

That intake side cam is out. It's fully clocked.

Twisting the throttle while kicking a 4stroke especially one with high compression is a sure way to damage your shin, kick back can sometimes be no joke!

the problem is with the compression release on those bikes. That's why it only bump starts. They don't come with an auto compression release on the cam. If you kick it like all the newer 4 stroke it will flood out on you. Before you kick it make sure you're on the compression stroke. The older bikes like that yzf have a compression release lever on the handle bar area. Look at the front of the head on the right side you should see a lever where the cable attaches to.

Thanks for this, was thinking about a 4 stroke dirtbike, i'll guess i'll keep my yz125 😂😂😂😂

Teach Vin to drive the tri-sport, then have him tow ya with a strap.. it'll bark off.

First I would put the jets back in that you took out, reason being it did run there, even though you had to bump start. So i am thinking lean. When it was running and you reved it, the engine didn't return to idle crisply, it lingered before returning to idle, that usually means vacuum leak some where. Have you verified ignition timing using a timing light, check it. After trying to start was a plug pulled to see if flooding was occurring, you said you fed gas straight in, try again and pull plug. If wet then ignition problem. I don't fully under stand adjustment on the cams, but using a dial indicator you verified cam timing to TDC. Don't go by the marks do it by finding TDC then check marks. Marks could be wrong. Good luck

If you aren't already, bump start in 2nd gear, it'll turn over on the gravel drive...

You'll get there eventually mine had a problem that happened to be the valves being to tight for it needed a similar way to start using bumpstarts and would only start kick when hot

Next time you kick on it try this, no throttle what so ever sometimes it's best to put your hand on the bars instead of the throttle to avoid temptation lol. Slowly turn the engine 3 or 4 times. Then find compression, after you find compression ease down on the kick starter until it gives a notch and gets tight again. Then let off the kick starter let it return to home position, now give it a good hard kick and it should fire after a few times of doing this repetition. That is the only way I can get my 01 to fire up. If I kick it like I mention her it fires the first kick or two. Hope this helps man. Love your content, I watch all your videos. You have taught me alot. Good luck.👍

Sounds like it could be the decompression mechanism, not releasing at the right time due to the big bore kit maybe. Had the same problem with my raptor 660 with the BB kit, had to order 2 new carbs as well as change the head gadket thickness.

Maybe try adjusting the intake timing since is adjustable. It looked like you had it turned all the way to once side of the slot in the gear. Try it in the center?

I had a similar issue w a RM250. Made spark and got fuel... The cdi box was the issue, it was failing. Also, check to see if the pulsar pickup (stator pickup) has a slot for the timing adjustment, if so, make slight adjuments either advancing or retarding the timing. I've been there bud, these types of issues can be extremely frustrating. Good luck!

I would suggest moving that cam timing back some and also change that pulse coil because it probably got hot when they ran it low on oil I had 1 test good but be weak and only crank with a bump on my ktm

Did you ever figure it out? I am dealing with a very similar issue. Bought bike with a stiff crank/con rod bearing. I did a Fresh rebuild, new Pro-x crank, WIseco top end, new cylinder. Head disassembled, cleaned, inspected, measured. New valve seals and valves shimmed. Carburetor thoroughly cleaned. Problem is a no start, backfiring occasionally through the exhaust. Got it started twice after kicking forever and it ran for 1 second each time (sounded fine). Ok, gone over everything several times with a fine tooth comb, as they say. Nice crisp blue spark, swapped out the coil and cdi just to be sure that wasn't the problem. Compression is as good as new, leak down test passed as new. Checked cam timing again and again and again as well as valve clearances. Ohm tested, coil, stator, CKP sensor, kill switch, neutral switch and TPS, all good. Pulled the carb and shot fuel directly in the engine, nope. Looked at the cams to be sure that the gears hadn't spun, that's good. Checked to make sure the woodruff key was in the crank, perfect. I'm lost. Can't think of what I might be missing.

Im not really into 4 stroke dirt bikes but that intake cam looks to be adjusted as late as possible.

I can watch this guy all day. Used prices of videos on my 04 ktm105.

It ran strong and crisp when it ran, the decomp spring could be the issue. Worn, overheated spring. Jetting and cam timing would be an issue running. Bumpstart bypasses the decompression system.

Joe, I would check the keyway on the flywheel. Make sure it’s not sheared a little bit or totally. Definitely sounds ignition timing related. As others have said, could be CDI. As a secondary problem, when it was running, I could hear hanging idle. That is usually a lean condition. On my KLX 450. It was a dirty pilot jet. When you went from large pilot to small pilot I think that may be the wrong direction. Also, possibly air leak. As others have said, bump start it in second or third gear. Last tip, when kickstarting it put the bike on the frame stand so that you can stand on the pegs while kicking it over. you’ll get a lot more leverage on each kick and not wear yourself out as fast. Ask me how I know.

Those old 4 strokes are super specific to start! Great find!

Try maybe new stator. Idk had the same problem on a 600cc Daytona 04, didn't let us bump start it. Same sound when you tried to bump start it sounded like it wanted to kick over but jus died out. Prob not the reason but maybe worth a try. Always a great time watching you rebuild engines! Keep up the great work!

You need to teach Jade how to tow you on a four-wheeler to bump start. I'd start with an OEM carb and get rid of that eBay junk. If you're like me, it's going to eat at you until you figure it out. Good luck, and thanks for the great content.

Hey Joe my wr426 had spark compression and fuel ended up the resitor in the spark plug cap was reading 11ohms should be 5 ohms or less as soon as I got replacement resitor it fired up 1st kick and everytime try look inside Ur spark plug cap the resitor looks like a fuse take Ur resitor out multimeter it see how many ohms it is if it over 6 ohms then there's the problem hope that helps you

Check the timing. / redo the timing. Look for a short in the harness. Check the decomp spring.

Been patiently awaiting this Joe.. Good job

When you started it and blipped the throttle the idle was high. You adjusted it and it dropped but when you blipped the throttle it went high again. Or it could be a sign of too lean mixture. Maybe some leaky carb or carb-cylinder head tube has some hair crack on the rubber. I'd check the spark plug gap and the spark plug type. Perhaps it is a hotter one. Definitely checking the stock jetting for that big bore, the engine should at least run with it. I think the cam timing is correct, maybe a bit noisier but the throttle response was good. Bigger compression needs higher ignition energy to ignite the mixture. There are a lot of ways to start investigating the source of the no-start issue.

I rebuilt alot of yfz450 crf450r trx450r kfx700 all started right up good luck

I have that bikes big brother the 2001 Yamaha yz426f I bought 6 years ago running beautifully and great condition for 1200 im glad you are doing this bike I've always wanted to find one of these to have bothe the 250 and the 426. I still have my 426 starts first or second kick every time. Would love to meet you some day brother! -Brad -B-Eazy

Being that it has a bigger bore and piston kit, many big bore bikes that I owned 450cc 500ect when they didnt start' I layed the bike down and flooded the carburetor for a brief moment. Then they started a couple of kicks. Maybe it's a fuelling issue' was the plug wet when removed. Keep at it, love the content.😂

I had an 01 just like that one except the headstock cams in it. I put in a high-compression piston and it would not. I contacted the manufacturer of the piston and I had to rejet it's super lean.

Try 2nd or 3rd gear when bump starting. Maybe timming on Hot cam is wrong. It looked liked it was all the way advanced.

Chin up Mr. You took on a tough project with many variables. There's only one way to test one's skills. The Best

love the vids keep it up man

Great video as always

I find the absolute best thing to do when a bike acts just like this one is to kick it to the ground put it into a corner for a week then revisit it when it’s smartened up

The decompression valve may me clogged with carbon build up, or the decompression valve spring itself may have just given out. Keep doing what you do‼👍

watching you kick that thing is making my knee hurt LOL

A lot of people are talking about timing. Just curious one thing to check is the key way on the crank shaft. Make sure it’s not sheared or messed up

Just completely rebuilt a yfz450 while doing so went ahead and for what I thought was a good idea I put a Chinese carb on it would not stay running or start consistently to save my lift. Had the oem Kehin rebuilt for same price as Chinese carb and started and ran instantly no problems after that

I had one like that a couple years ago and it turned out to be an intermittent kill switch. Pulled it and it started every time.

If she did not pop over on starting fluid, it's a pretty safe bet the problems within the ignition system.

I have a 2004 YZ250f stock. When cold it does not like any throttle at all when starting. If you even tweek the throttle while kicking it over it will not start. But if you leave the throttle alone it will start in 1 or 2 kicks everytime. With your big bore fancy cam I doubt my advise will help much.

When you bump start, put it in 2nd or 3rd gear. It will go easier. I am thinking the ignition timing is off a bit. Not sure there is a way to check that.

I'm a new subscriber.....I'd love to see a bike being fully detailed. Like a good washing, steam cleaning. Possibly powder coating a frame or two.

Still waiting on that Goldwing to fly down the road my friend 😊🇺🇸good job on the yammy don’t give up!!! Bump start it in 4th gear

I've never seen you not start a motorcycle. It's ok don't worry be happy

Its always great when he posts a video

I had a buddy build one of these and he had to use higher octane fuel in it to get it to run correctly

I was thinking the same thing. Possibly running lean. Or that adjustable hot cam. I think the rebuilder before you had problems with that also.

1 - Reset the carb to all original jets to have a good starting point. Check the seals on the choke and the hot start plungers. Check the slide aswell. Run the bike and spray on the carb some brake cleaner to check for air leaks. 2 - Check the timming of the intake cam. Maybe its a litle off, but it looked correct to me. 3 - Check the tps condition and position. On the wrong position it will mess with the timming. 5 - To kick start this bike is much easier, if not only possible if you turn until the decompression makes a click. Kick the bike on this position. 6 - Good luck and take your time.

If it was mine I’d go with a cam kit that I knew the specs that matched with the new piston and came with setup instructions and recommendations for carb resetting, or tech support for it.

Soon as you pulled that side cover off I said to myself "I be damn, that kinda looks like a Hinson clutch" can't believe I was actually right tho 😂 lol...seems like you've found another nice bike!! Saying this as your replacing the piston so hopefully after rebuild im right about that haha

I admire your persistence. I'd be tempted to reach for the matches. Thanks for sharing and BTW does having an air filter make any difference?

Mayve you could explain the hot cam concept, thats new to me. Why would you want it?, and how to adjust em. Thanks.

Try putting the 48 pilot back in and let it warm up. Once it's warm, use the choke and hot start to determine what way to jet. Higher rev with choke, up the pilot size. Higher with hot start, lower the size. It may be worth picking up a stock used cam to put in place of the adjustable intake cam. You can try turning up the idle when starting it to get it started, then down once it starts to tune it in. Just a few thoughts.

Very reminiscent of my XT500. I gave up after tearing motor down multiple times. It’s something with the carb. The guy I gave it to took it to Yamaha shop and they discovered a screw missing in the throttle body. I did not notice it and it ran great after that. So check vacuum leak or wrong carb. I’ve been there.

can you sand the pickup ignition ? just an idea to see the amount of spark.

You could try lowering the compression by changing the deck height, (extra base gasket) might be worth a try, great video as usual 👍👍👍👍👍

Really like your videos, but isnt it better to wash the bikes before you start working on it ?

While I have no experience with this particular motorcycle my thoughts are....Adjustable Cam timing (it appeared the adjustment was at the extreme end of the adjustment range?), malfunctioning compression release, ignition timing....good luck, you always figure it out.

Ring gap to small to high of compression. Big drag bikes use a big drill to start high compression motors. It was running so everything works it just takes more rotations to fire, or maybe there's gremlins in the carb. Super stumped if it's not either of those. Just for safety don't give it any gas after midnight.

My old 2001 yz250f had a decompression lever. Where you had to pull and kick before you released it and gave it a real kick. Started every time but only if you used that decompression lever. But you could get it to bump start without it. Maybe that’s the issue, also had a weird hott start deal. Not sure it that could effect anything either.

So I’ve rebuilt the 400f version of this bike using the same carb. I replaced it with an OEM carb with the same exact size jets and it fires up. Idk if it was the carb or what but definitely try the oem keihin carb with the oem jetting and you should be good

Joe.remeber the xt 500. Don't touch the go go until it fires.just my experience with thumpers.cheers mate.

Try. Checking the stator coils resistance. I’ve had it where one coil is dead but you still get a nice fat spark but under compression not great.

I had a stage 2 hotcam in my 350x. Made it hard starting. Like bad. Impossible when really cold! Went back to stock. Maybe this helps. Luv your content. Thanks

When you bump start, run way faster then when you pop the clutch jump down on the seat to get traction and give it gas, I have a 03 yz450f and those are the tricks to get these stubborn things to start.

Compression is ok judging by bump start trouble. When cold you want it to be rich so smaller jets are no use. Big bore kits use more air so bigger jets are required I would have thought. Keep in mind emulsion tube stabilises mixture as vacuum increases. It runs when bumped ok. Carb is the issue, it's not fuelling at low rpm when kicked. Starter fluid will prove this although accelerator pump works you say? Give it loads of pumps? Substitute the carb for another.

Are the rings on the correct way? Also try bumping in 2nd or 3rd and not 1st

I think ya flooded it before it started bud. I've got a yz426f with the same carb and it takes 2 pumps of the throttle and it fires right up. Any more and it floods. Ya gotta kick it till it backfires, give it 2 pumps and try again. Any less and it'll stumble a sec and die or not fire at all.

Check cam degree settings and decmp. spring and valve along with timing. Inspect ignition wiring for shorts ... safety cut offs... grounds.. You did the right thing. Set it aside and go to something else. Then come back fresh. It will be something simple it always works out that way.

The old four strokes are a pain in the ass to start if you don’t ride it everyday.

this one was a toughie - maybe think about an o2 sensor you can stick up pipe and see if you are getting good afr - this will help you dial things in and id issues with jets? i agree with people below who deal with these all the time - go back to stock parts and chek decomp spring, maybe try a little ether? you will figure this out - you are eliminating causes - keep dx and troubleshooting and it will help in future corner cases like this #modded bikes

Bro I have the same bike no it’s a hard bike to start don’t never hit the gas and the little pull button near the clutch pull that in when the bike not starting it helps it start it’s called a hot start

Frustrating for sure. One positive is your right leg is a monster. I wonder what Vinnie thinks??? He usually has the correct solution. Can't wait and see the end result. Great rebuild

Replace the spark plug. High compression engines need to have perfection with the plug to make a proper spark. Lower compression engines need less spark. A plug will have visible spark outside of the engine but once under high pressure it will not spark. These plugs are usually a one shot deal. The rules of starting these bikes is no throttle. In fact keep your right hand away from the throttle when learning to start. When doing a hot restart, the stock carb had a bypass air valve to assist with the hot restart. I know that to start this bike with a flooded plug it would be pulled by a car for quite the distance before it would fire. Very dangerous but had to do it a few times. New plug is the answer.

A tip. When you bump start, stand up and hit the sadel and then put the gear in and release the clutch.

When joe uses that 1/2 impact with a 3/8 adapter to 1/4 adapter to 8mm it makes my stomach turn