What’s the worst you’ve ever gotten your ass beat trying to troubleshoot a dirtbike ?

Lacing a wheel and keeping it true.

Trying to properly jet an 2003 Gas Gas 300xc. Pulled my hair out only to realize some were shipped with wrong slide in the carb which made a burbling mess at low r's.

Hahha I got worked on an old cr250, could not get it going rebuilt the engine twice, new carb, correct compression and spark, just would not start sold it and told the kid to never tell me what it was...fml

Did you forget to turn the fuel on?

88 Rm250, full restoration….totally disassembled carb, vapor blasted, all oem rebuild kit. Set to factory specs…. Bike would not clean out, ran like choke was on, when it wasn’t…. Had carb on/ off 10 times, doubled checked everything…Eliminated everything else I could think of….finally turned pet cock off while running, ran great right before it ran out of fuel…. Out of desperation I installed a well worn 96 CR250 carb that I just happen to have laying around…..fired right up, ran perfect, didn’t even have to change 1 jet….that Keihin is still on that 88 RM250 ..But I have a mint looking Mikuni TMX slingshot carb sitting in a box….Assume carb body had a small crack or the rubber body gasket was bad, I did separate the body of the carb and the rubber gasket looked ok…

6+ hours to find an intermittently-disconnected wire at a 32-pin ECU connector.

I left a rag in the air box once and it took 10 minutes of trying to start it before I figured it out. 

Not me, but I paid the price for the same issue.

Early 80's my friend was trying to start his YZ125 to go out for practice on race day. Would not fire, so we tried to push start it. Pushed that freeking thing for what felt like miles, trying to bump start it about a hundred times. 

Oops, he changed his air filter the night prior and left a rag in the airbox. I wanted to kill him but I was too tired. 

I did that recently with the fuel line not being completely coupled. I punched myself in the face.

Not a dirtbike, 2008 f150 with a 4.6. Dropped a 7mm deep socket down the spark plug well right after I got the plug out and moving on to the next coil over plug. 2.5 hrs of using a magnet to fish it out. 

Just reading that gave me anxiety, fuck I hate electronics, and they hate me back 😐  

My wifes 90 CR250 would quit when we'd get far enough out of camp to be a concern. I swear I could ride it around camp for 45 minutes with zero issues, get 5 miles away and it'd get ebu.  EEeeeeeeeeee......boooooo..... nada.   Then start after it cooled down. Wound up being the cdi box. 

Carburetors.  All of them. 

My wifes 2005 crf250x. Had the top end rebuilt. It was a little lean before and getting it right, step by step is a total PITA. The jetting part isn't a big deal. Getting to the carb .......

Probably not the worst, but the most stupid.

In 2003, parents had bought a new CRF150F when they first got released. That weekend we were loading up to go ride some trails, and it won't start. Checked for spark, checked for fuel, and everything checked out. 

Drove it 2 hours back to the dealer, and about 30 minutes later they have it fixed. The ceramic portion of the spark plug had failed so when you pulled it out of the bike, and flipped it upside down to look at it, it looked good and would show spark. When you put it back into the motor, the ceramic would fall down not allowing it to make spark...

2009 YZ450F spark plug cap ate my lunch for a couple days

Spent weeks trying to jet around a clogged vent hose cap

Dealing with a weird one now!

2018 KTM 250xc from new never ran right and over time it progressively got worse.

I narrowed it down to transmission fluid making it's way into the crank case.

After 2 leak down tests, two right crank case seal changes and some frustrating diagnosis hrs, I finally found the oil was getting in through the center cases.

Long story short, the cases from the factory were not properly machined.

There were 2 serious low spots where the center gasket would eventually fail.

I placed a lit q-tip at a transmission window while the crank case was under 8 psi of pressure and sure enough air flow was blowing out the flame.

I bolted the cases together without the center gasket and back-lit the crank area and saw the gaps.

Flexi flash light in the transmission cavity, picture taken from the crank case side.

Now, onto the fix....

I have a couple.

After I sold my Xr75 to my brother, it ran like crap.

I rebuilt the top end, cleaned out the carb (it was fine), made sure it was getting fuel, made sure it had spark, gapped the points, made sure the intake boot wasn't cracked, everything I could think of.

This went on for a couple of months.

Then one day, one of the 2 gas stations at the bottom of the hill was closed, so we went to the other station.

It ran perfect!!

After that we put a high lift cam in it and gave it a few more ponies.

I also tore it down to the frame, got mounts welded on so it could have layed down shocks, then gave it a custom paint job.

Fun times when you're 14.

Probably my worst too, did the same thing on my RM 125 the night before a race. I had serviced the air filter earlier in the evening and then could not get the thing started. Spent several hours trying to figure it out and finally removed the seat and took the air filter off and wala -  rag stuffed in the carb. 

I once rebuilt a KX 500 motor (1983 model) from scratch. Everything new...bearings, seals, crank rebuilt and balanced to perfection. 

I was pretty chuffed when it fired up on the second kick. Sitting on the bike warming it up thinking that I gotta repack the tail piece...when I decided it was warmed up good I slipped her into 1st gear and let the clutch out....next thing I know is I'm going over the bars...the top of my head was on the front fender ..legs in the air and then hit the ground.

The bike ran in reverse. 

I knew my jetting was pretty close to spot on so I started checking timing.

The thing had me stumped. I was working for a Kawa dealership the time and I got Rob involved who had more experience than me. He was also stumped.

We tested everything electrical and found nothing faulty.

Out of desperation I sent the stator away for rewinding. When I got it back i fitted it and set the timing. She fired up and this time the motor ran in the correct direction.

That Damn stator caused me so many sleepless night and unnecessary stress.

I left kitchen towel...that toilet paper stuff in my riders YZ450 airbox...when I got it started I noticed pieces of towel flying out the exhaust 😂 

Freshly rebuilt 1983 xr200r ran great for 30 mins then died. Lost spark friend gave it to me to troubleshoot. It was maddening because it would sometimes get spark back. 

I checked everything timing electrical even bought. Used electronics cdi coil to try. I didn't think it was the stator since it had a brand new one. 

I finally went to check the stator to find out. My friend didn't tighten the flywheel nut it was finger tight. It had sheared the pin on the crank and spun. Occasionally it would catch. Ruined the crankshaft end. 

Ok I’ll play…

I had Yoshimura build a complete head for my son’s 2006 RMZ250. The cylinders were on back order so Yosh got one from the Kawasaki guys for me, since the bikes were the same. 
Put it together and warmed it up in the garage. It sounded like a monster, so stoked. Next day we went to the track and took two bikes. I warmed the new motor up and had him ride it. He made it onto the track and it blew up. He ride the other bike and I tore the head off of it. The piston hit the valves… I called them and I had another head in a couple days. 
It blew up in less than 3 corners. Same issue. 
Drove the bike down there the next day and they tore it apart. Turns out the Kawasaki cylinder had a different part # and they had cut the head to work with the Suzuki measurements. 
We all learned something that day. 

daughters kx65 couldnt be jetted right. change jets, gas back n forth. got it decent enough to run. first day out wouldnt start, pulled carb, kicked for half hour. figured out i ran all the gas out then ran.

fast forward another few weeks trying get it to run right. rebuilt the carb twice over and finally got it running right

Intermittent ECU connection due to a pushed pin on the harness side. FML. Lost a three day holiday weekend full of riding to that one.

I got a couple:

YZ 250. Trackside at a race, I go out for practice and bike is running terrible. Won’t clear out and gargling everywhere. It was a new track at higher elevation so I pull off and start switching jets like a mad man so I can get a few laps in. Wouldn’t you know it…I left the choke on. I still can’t believe I did that. 

2000 KX 250 rebuild. Fully rebuilt with a freshly plated cylinder, bike starts up after rebuild and runs amazing. Go to ride it around the block and it’s getting hung up between gears. Dang it. Resplit the cases twice trying to figure out my transmission error and it ate my lunch. Never figured it out and sold the bike at a loss. Live and learn. 

If you can... depending on location...

Try JB weld or an aircraft quality 2 part aluminum epoxy and see if that seals it up.

If you go that route it must be super clean and I'd give it a 48 hr cure time.

Had a Honda MR175 when I was probably 14-15 years old… low hr bike, sometimes would  run great most times it could barely get out of  its own way…my brother & I tried everything, brought to local Honda dealer, they couldn’t find a problem…I was paying the bill with my paper route money…. Had to go back to Honda dealer several times, they still could not find any problems…. …the Honda dealer mechanic was an old miserable prick, I hated going there and they were not cheap…I”m not sure how we finally figured it out….but the internal baffle in the exhaust pipe had broken, intermittently it would clog the exhaust and make the bike barely run…bought my first aftermarket pipe from Bassani…..got it running good and sold it… my next bike was a used 78 YZ250, it was aweome!