2003 yz125 won't kick start but will roll start

[rparrish2]

OK guys, my younger brother managed to put a quarter sized hole in the gearbox of his 2003 yz 125. After letting the bike sit for a couple of months he sorced a complete bottom end off eBay including: both case halves, transmission and crank off a used bike. He also ordered a top end kit and a few miscellaneous gaskets needed to complete the build. Well since I've rebuilt a few bikes and he can barely get a cap on a coke bottle, I offered to do the work free of charge. I inspected the new/used bottom end and was surprised with its condition. Zero play in the lower rod bearing or crank bearings and the tranny shifts flawlessly. So I tear down the old engine and swap everything over to the new/used bottom end. Everything goes together flawlessly. I also put a new top end on the bike. My brother had bought the bike used from some redneck idiot who clearly didnt take care of it about a week before trashing the cases. Thus I was surprised to find a flawless hinson clutch

and new reeds on the bike. Anyways, I get the bike back together and it won't kick start but I can run it down a hill and bump start it but just barely. When it does start it runs awful and bogs terribley and essentially has zero power. Now I know what you're thinking... "Don't assume anything, test the compression." Well I did and it sits at about 165lbs cold WOT. Now that isn't an enormous amount of compression but it is well within spec. I'm also getting a nice fat blue spark and fuel is certainly getting past the reeds and into the cylinder. On yea and the reeds look brand new and are tight. I really can't get the bike to run long enough to get a good read on the plug but it is wet so I know its flooding. But that could be from kicking the piss out of it over and over. Regardless I pulled the carb apart and cleaned it thoroughly and jets and passages got a nice squirt of carb cleaner and were blown out. Still doesn't kick start and runs like hammered crap when I can get it to bump start. I don't have the equipment to do a leakdown test but both the airbox boot and intake boot are secure and the carb is fully seated in both boots. What is going on here! I thought maybe the right side crank seal is bad causing a rich condition but I'm not seeing any excessive smoke. What do we need for an engine to run? Fuel, air, fire and compression. I have all of those and she still won't run. I'm by no stretch of the imagination a top rate bike mechanic but I've rebuilt some engines with some success and I have a pretty good understanding about how these bikes work. But I am absolutely stumped. So, here I am asking for help from those of you that are smarter than me. (That's a pretty inclusive category) why won't this sucker run. Thanks ahead for reading and for your opinions.

[YZJ]

What are your current jetting specs?

[rparrish2]

I'm not sure, I'll pull the carb back apart tomorrow and see. It was running prior to the rebuild. However, someone's been into this carb a number of times, the bowl screw heads were striped to the point to where I had to use an impact driver to get them out. The carb was pretty funky before I cleaned it but I left it spotless.

[SellYour4Stroke]

Ive found towing to start is common from weak compression or a bad plug.

Might be worthwhile to check the coil and timing as well, since u just did a bottom end.

Does it leak gas out of the bottom of the carb? An inlet needle can also stick and just drown your bike.

Also

I was checkin leakdown stuff today. Just for shits.

Homemade stuffs not too rough.

https://www.thumpertalk.com/topic/1164419-making-my-leakdown-tester/?p=12805369

https://www.thumpertalk.com/topic/432226-pressure-testing-a-2-stroke/

[rparrish2]

In regards to timing, how could it be timed poorly? The flywheel can only sit in one spot due to the woodroof key and the stator plate timing mark is lined up with the timing mark on the case. I'm not saying it can't be timing I just don't know how it would be.

[SellYour4Stroke]

In regards to timing, how could it be timed poorly? The flywheel can only sit in one spot due to the woodroof key and the stator plate timing mark is lined up with the timing mark on the case. I'm not saying it can't be timing I just don't know how it would be.

Loose or rotated or somethin.

Shot in the dark item to take a look at, since you were swappin bottom end parts.

[rparrish2]

There is what seemed to be a timing mark on the flywheel, where should this line up

[SellYour4Stroke]

There is what seemed to be a timing mark on the flywheel, where should this line up

It lines up with the mark on the stator plate at a particular part of the stroke...the factory manual goes into it in detail. You need a dial indicator and adapter to get it perfect.

Many people just line the stator plate back up where the mounting screws have made marks.

Generally it is a pretty solid unit as long as its fairly close and tight and clean...I would continue with the carb/crankseal/compression troubleshooting.

[rparrish2]

I have good compression at 165lbs. It could be the right side crank seal but wouldn't that cause excessive smoke from burning gearbox oil? If it were the left side crank deal then I could expect to see fuel in the stator/flywheel compartment. (I don't) this would also cause a lean condition which I don't have. (wet plug) moreover, an air leak causing a lean condition USUALLY results in a high revving idle and this bike won't even idle. The carb is clean but seems to be dumping fuel into the cylinder. What would standout as a cause for this. Btw I really appreciate the dialogue. Just bouncing ideas off somebody is helpful.

[rparrish2]

So I got it bump started again today and noticed that I have an exhaust leak between the exhaust port and header could this be my problem. Could this cause hated starting, bogging and extreme loss of power

[YZJ]

Yes definitely a problem that needs to be fixed.

[rparrish2]

Found a tiny bit of fuel in the stator cover. I think I'm just going to order new crank seals BC I am suspecting that they're both bad. I'll let you guys know something when I do.

[YZJ]

New crank seals and pipe O rings and you should be in a much better spot than before.

[Rohill100]

On 12/24/2015 at 4:13 PM, rparrish2 said:

Found a tiny bit of fuel in the stator cover. I think I'm just going to order new crank seals BC I am suspecting that they're both bad. I'll let you guys know something when I do.

I know this post is almost 3 years old, but I'm having nearly a dead on same issue, but wanted a little more insight before I tear apart the bike. How did it turn out with new crank seals?

[rparrish2]

16 hours ago, Rohill100 said:

I know this post is almost 3 years old, but I'm having nearly a dead on same issue, but wanted a little more insight before I tear apart the bike. How did it turn out with new crank seals?

Crank seals were fine. Woodruff key sheared.

[broberts814]

16 hours ago, Rohill100 said:

I know this post is almost 3 years old, but I'm having nearly a dead on same issue, but wanted a little more insight before I tear apart the bike. How did it turn out with new crank seals?

Now that's using the search engine... Awesome you got a good answer and nice to hear what the final result was for you rparrish2.  

[Rohill100]

22 minutes ago, rparrish2 said:

Crank seals were fine. Woodruff key sheared.

That definitely makes sense actually. My issue is that when trying to push-start down a hill, the engine would run, but only to the speed of how fast the bike was moving down the hill. once the hill and movement stopped, it sounded like it was getting bogged down and/or flooded just as you described. (i.e. not engaging with the gearbox at all)

Thought I heard an unusual pop on the first kick or two when starting it up that day. That should have been my indicator to go home right then and there. Thanks again for the heads up on the woodruff key. Hopefully someone else searching the interwebs falls on this chain to have a quick fix if they are also having the issue of not able to kick start or get going off of a push start, or "engine not starting from roll start"; bike not starting from push start, or hill start. (hopefully that's enough SEO keywords there lol)

[rparrish2]

54 minutes ago, Rohill100 said:

That definitely makes sense actually. My issue is that when trying to push-start down a hill, the engine would run, but only to the speed of how fast the bike was moving down the hill. once the hill and movement stopped, it sounded like it was getting bogged down and/or flooded just as you described. (i.e. not engaging with the gearbox at all)

Thought I heard an unusual pop on the first kick or two when starting it up that day. That should have been my indicator to go home right then and there. Thanks again for the heads up on the woodruff key. Hopefully someone else searching the interwebs falls on this chain to have a quick fix if they are also having the issue of not able to kick start or get going off of a push start, or "engine not starting from roll start"; bike not starting from push start, or hill start. (hopefully that's enough SEO keywords there lol)

If you have fuel, air, compression and spark then this may be the case.  What threw me off was that i had a nice fat spark. Unfortunately the flywheel had turned just enough on the crank to throw off the timing. Truth be told this wasnt even the biggest head scratcher I've had working on bikes.

Roughly a year later a friend brought me his ktm 250 freeride because it wouldn't start.  These bikes are electric start only so the only way to get a feel for compression was to use a compression tester.  It tested at 70psi. I thought it had to be a faulty guage so i tested again with a different guage and got the same result.  So i tore the top end down. The piston was a little scuffed and there was some blowby but nothing out of the ordinary.  New piston and rings go in. Bike still wont start. Test compression, 75 psi.  Im stumped.  The plating was still good on the cylinder and it measured within spec with a bore guage.  New gaskets throughout the top end.  It sat in the shop for a week. I would literally go in the shop and just look at it for hours thinking of what it might be? It pissed me off so i just left it alone for a couple of days.  

Im driving home from work a few days later thinking about it (it haunted me) and it come to me.  These bikes come stock with a spark aresstor and he had been complaining about the jetting being rich.  I speed home, remove the spark arrestor and it starts as soon as i hit the ignition. The spark arrestor was covered in carbon letting very little air through thus letting very little air in causing a low compression reading.  

Ive never been so happy and pissed at the same time.  Now when a bike doesnt start i always ask if it has a spark arrestor.