Odd issue starting my BTX200

[Aerindel]

Hi all, again.

Over the winter, my bike developed a strange issue with the engine.

If I run it long enough to get hot....10+ minutes.....and then shut if off for 10 minutes.....It becomes VERY hard to turn over, almost feels like is hydrolocked or something...very strong compression, to the point where you almost can't turn it over, if you aren't sitting on it, you could lift the bike off the ground trying.

If I pull every hard, and slowly on the cord and let it slowly turn through a few strokes, it will loosen up enough, that I can get a regular pull on it, and once I do, it starts up and runs fine.

And if it sits for a few hours, its fine and normal, its only after riding for a least ten minutes, and then waiting about as long. Right after driving, its fine for awhile, but go a little longer and I hit this issue everytime.

Any idea's? Is this the excuse I need to put a Predator in it?

 

[sparkwizard]

Try checking the valve lash, or clearance.

 

[superflea]

Try turning the gas off and let it run die and die. See if that helps upon restart.

 

[Studeman68]

Check the oil, overfilled? Smells like fuel?

 

[Harquebus]

Try checking the valve lash, or clearance.

Ding ding ding. Had this about 3 years ago on a riding lawn mower. It would barely turn over except with extreme difficulty. I thought it was the battery or the starter but it turns out the valves needed adjusting.

I've also had hydrolocking on it, due to a worn needle and seat in the carburetor. This means the float/needle/seat no longer cut off the fuel flow, so it would flood the crankcase with fuel, dilute the oil (not good) and cause hydrolocking. Since the cylinder is oriented horizontally on a vertical shaft engine, it was that much easier to flood the cylinder.

 

[DaddyJohn]

Ding ding ding. Had this about 3 years ago on a riding lawn mower. It would barely turn over except with extreme difficulty. I thought it was the battery or the starter but it turns out the valves needed adjusting.

I've also had hydrolocking on it, due to a worn needle and seat in the carburetor. This means the float/needle/seat no longer cut off the fuel flow, so it would flood the crankcase with fuel, dilute the oil (not good) and cause hydrolocking. Since the cylinder is oriented horizontally on a vertical shaft engine, it was that much easier to flood the cylinder.

That’s super-common with horizontal single-cylinder Briggs tractor engines. They have a decompression mechanism on the cam that doesn’t tend to bump the exhaust valve open enough for the starter to push the piston past TDC on the compression stroke if the lash isn’t adjusted within spec. The other thing that can happen is the little decompression dohickey can break off, then the only remedy is to split the case and replace the cam.

 

[Aerindel]

Sorry for not getting back earlier. It became winter again here and I wasn't messing with the bike.

Checked the valves today, they where loose, I re-adjusted to spec, and tested, no change. Same issue. Run for 10 minutes or so, stop and wait more than a minute, and extremely hard to turn over while hot, if I work it slowly for awhile, it seems to 'loosen' up and I can get it restarted but its a process. Wouldn't want to take it anywhere the way it is.

I will try turning off the gas. The hydrolocking theory seems plausible.

Of course, I'm also eyeing a Tillotson 212cc..........so if I can't figure it out soon I might just go that way. I run this thing a lot in the summer so need it to be up and reliable soon.

 

[Aerindel]

Just ran it for half a mile, shut off the fuel, drove it until it died....a surprisingly long time....same issue. Very hard to turn over, maybe 150lbs of force on the rope needed to get it to kick over TDC. Impossible to start like that.

 

[Aerindel]

Just warmed it up, confirmed the issue, removed the sparkplug....no issue....replaced the sparkplug, and the resistance is back, so its definitely resistance from air compression rather than some kind of mechanical binding.

 

[sparkwizard]

When you adjusted the valves, was the piston at TDC, or slightly past TDC?
At TDC, the exhaust valve may still be on the compression release. There should be no clearance on the compression release, as the valve is slightly open. turn the engine slightly past TDC and check your valve lash again. I suspect you will find the exhaust valve is loose after TDC.
Look closely at the rocker as you slowly turn the crankshaft. That rocker should get tight right before the piston reaches TDC, then loosen up a tiny bit after TDC. That is when you should adjust your exhaust valve. Right after the bump at TDC. Sometimes, I adjust at zero lash just so I can be sure that I have gone past the bump on the compression release at TDC, it is easier to see the bump with the lash set tight, then adjust it to specs after you verify where that bump is. I hope that makes sense.

Now, if you do that and you do not see that little lift or bump on the exhaust rocker, you may need to open the engine and see why your compression release (on the cam) is not working.

 

[Aerindel]

It may be tricky to sort out, because it ONLY happens when the engine is hot.

Which seems to mean it has to be a issue with the compression release sticking, rather than valves out of spec.

 

[sparkwizard]

Not necessarily true. When the engine is cold, the piston and cylinder allow more bypass that after warm up. If the compression release was broken, it would be broken always, not just when hot.
You can tear the engine apart and see, or you can try what I suggested and maybe you won't need to take it apart. Your choice.
You asked for help, I offered help.

 

[Aerindel]

I find few things break in that binary of fashion. Unfortunately. Mechanicking would be a lot easier if they did.


But I will try it your way.

 

[ole4]

So if it pulls ok when plug is removed then it is a compression issue either exhaust lash too loose or cr broken. More likely lash not set a few degrees after tdc on compression stroke.

 

[sparkwizard]

If you read the instructions I posted, you will see if the compression release is working without taking it apart. No guess work, either it's working, or it's not.

 

[Harquebus]

This "replace it with a brand new motor if you can't fix it" attitude is very commonplace. It's hilarious and troubling at the same time. Glad we are not at that stage yet and are working through it. If you can't fix things, that's a lot of motors piling up.

It became winter again here and I wasn't messing with the bike.

You must be in the southern hemisphere. Happy winter.

 

[Aerindel]

This "replace it with a brand new motor if you can't fix it" attitude is very commonplace. It's hilarious and troubling at the same time. Glad we are not at that stage yet and are working through it. If you can't fix things, that's a lot of motors piling up.



You must be in the southern hemisphere. Happy winter.

No, just the more northern parts of the northern one.....MT.... where at this moment its 41º and dropping slush from the sky on me.

The replace it attitude bugs me as well....but its hard to avoid when motors are so much cheaper than time.

 

[Aerindel]

Tested cold, the compression relief is working. Easily seen actually, more so than I would have thought. I can even hear the air escaping when it bumps.

Now I'm going to let it run for 10 minutes and see if I can take the valve cover off without burning myself too much and check while hot.

 

[Aerindel]

And there we have it. Clear as day. No compression release when hot.

Thanks everybody. I never would have suspected there was a automatic compression release without you guys.

 

[Strigoi]

The replace it attitude bugs me as well....but its hard to avoid when motors are so much cheaper than time.

I see it as people not wanting to learn why something isn't working. They just want it to work. Minibikes are a hobby and something you tinker with. Figuring out the why is part of the fun of having them as a hobby. It can get annoying, but it is rewarding when you get a bike running right.

That's why you see so many posts on Reddit with people just wanting all the info given to them. They don't want to do any of the leg work to try and figure things out for themselves. That's a huge reason why I quit posting in the subs on there. I'd tell them what they need to buy and they'd reply back wanting links without so much as a thanks. Also getting told you're wrong for doing things the right way got old pretty quick. I'm an adult and I have money for toys so I don't do things the cheapest way possible. I do them the correct/safest way. Can you do X? Sure. Should you do X? Absolutely not.