Lotto Machine Sound From 2 Smoke

["Dangerous" Dan K]

Some of you may remember my thread about rebuilding my KX125, detonation had the head & piston looking like they'd been a backstop for a shooting range. I rebuilt the thing with wiseco stuff and it runs great, probably twice the power as before. Powerband lofts the front end in almost every gear now.

The downside: Under load, 3rd gear and above, lower part of powerband it sounds like there's a lotto machine shuffling those stupid numbered ping pong balls in my engine. The bike will rev right past it, but i think it's safe to say the noise can be filed under the "bad things about to go catastrophically wrong" category.

My first thought was detonation, but 6 fingered man rode it and said it doesn’t sound like detonation. He knows his shit and I don’t, so I’m inclined to believe him. I’m still going to pull the head and have a look, but I’m thinking maybe something in the bottom end isn’t liking all the power the new top end gave it? Any suggestions, anything to look for? I was hesitant even posting with such a crappy description, but I don’t know how else to describe the sound. Aside from that the thing runs tops. Gobs of power, first kick every time (unless it falls over in the trailer and sits that way for god knows how long, then it needs Daniel to push-start it the first time and it goes right back to first kick).

I’m all ears to suggestions on anything I should check out/look for.

edit: Does it with Mobile 93, which I usually run, and Shell race fuel (guy @ stimilon said it was equivalent to C-12)

[SSearchVT]

Check the stupid stuff first... Engine mount bolts, expansion chamber mounting springs, etc...

["Dangerous" Dan K]

Check the stupid stuff first... Engine mount bolts, expansion chamber mounting springs, etc...

Good call, and never even crossed my mind. I could have done something stupid putting it all back together after the rebuild, and had a pipe spring pop off or something. I'll give it a good looking/shaking/tightening over tonight to see if there's anything stupid and obvious that I messed up. Thanks.

[richw]

Look at the sparkplug see if its hot white or light beige

Did you rejet after piston by by ?

Could be lean

["Dangerous" Dan K]

I'll check the plug tonight. I expect it to be a touch fouled looking only because my first time out after the rebuild was Dunbarton/Clough, and the bike was not in powerband nearly as much as it likes to be due to the severity of the trails and my lack of skill. I did a little bogging along with a whole lot of powerband @ Stimilon too. I'll check it and report back all the same.

I did not rejet after piston replacement. I don't know the first thing about jetting, and have never rejetted anything I've owned. This bike has the jetting I got it with. Same pipe, different silencer, and I replaced the piston with the exact same Wiseco model I took out.

[Paul_E_D]

Well, the spot you describe (low in the powerband) would be where the powervalve would open. I'd inspect and clean that system.

[gregp]

In my experience, the most common problem with any well used 125, besides needing a top end job, is the lower connecting rod bearing. The symptoms generally sound like the discription you have offered (loud knocking), and will get worse very fast. Of course, I would check all of the obvious stuff previously mentioned, but do not be surprised if you end up doing a crank rebuild.

["Dangerous" Dan K]

Paul:
OK, about the powervalve. When I did the rebuild, before it started making this sound, the powervalve was completely stuck together with gunk. There's no way that thing had opened in years, it took me a couple minutes with tools to break the two pieces apart (it came out so solid that I thought it was one piece for a second). Cleaning it took another 20 minutes, easily. So it very well could be happening when the powervalve opens. Pre-lottomachinesound there was no opening of the powervalve. I cleaned it so that now it opens/moves/acts as two parts rather than one solid gunky part, and since then we have lotto machine sound. Adding powervalve to top of list of stuff to check (after stupid stuff, only because it's easier than opening up the engine).

Greg:
I was warned about the connecting rod bearings when I attacked the rebuild, and because of that I did grab the shaft and see if it had play that indicated bad bearings. I found none, but that doesn't mean I didn't just F up and miss something. I'll keep that on my list of stuff to watch as well. It has not gotten any worse from when I first heard it @ Clough/Dunbarton to the last lap @ Stimilon, for whatever that's worth.

[Paul_E_D]

Go back into the powervalve. Dissassemble fully. Look for grooves worn on spindles etc. replace anything with wear you can feel. Also check for tightness in any bores in the cylinder.

Go through the actuation system (parts that make the valve open) as well looking for wear in those parts. If you bike was making top end power, the valve was opening, but something is worn and its better to replace cheap parts than wait and have to replace the cylinder...

["Dangerous" Dan K]

Go back into the powervalve. Dissassemble fully. Look for grooves worn on spindles etc. replace anything with wear you can feel. Also check for tightness in any bores in the cylinder.

Go through the actuation system (parts that make the valve open) as well looking for wear in those parts. If you bike was making top end power, the valve was opening, but something is worn and its better to replace cheap parts than wait and have to replace the cylinder...

Thanks. This actually makes a lot of sense considering the condition of the powervalve when I did the rebuild. I forgot all about it after I de-gunked it and got it to move/slide again. It never even crossed my mine the noise could be related to the powervalve (told you I don't know my shit).

I'll open it up and check it out this week. I'm heading off for vacation for a couple weeks at the end of the week and doubt I can get parts in that fast, so it'll probably have to wait until I get back to be taken care of, but I can at least tear it down and see what I need for parts.

Thanks.

[richw]

If the old piston melted because of detonations then new one in same risk

Never ran better is the
"Famous Last Words of 2 strokes"
as too lean causes heat and detonation but best power.

It also sometimes causes double cycling where there is insufficient fuel for the motor to fire every stroke and starts firing every other stroke rough idle and odd noises

Look on the web for jet sizes, see if jet needle has a spacer or clip you can move down to raise the jet needle. Blow out and carb clean all the passages

["Dangerous" Dan K]

If the old piston melted because of detonations then new one in same risk

Never ran better is the
"Famous Last Words of 2 strokes"
as too lean causes heat and detonation but best power.

It also sometimes causes double cycling where there is insufficient fuel for the motor to fire every stroke and starts firing every other stroke rough idle and odd noises

Look on the web for jet sizes, see if jet needle has a spacer or clip you can move down to raise the jet needle. Blow out and carb clean all the passages

Yeah, I wanted to pull the head after some riding to check for detonation anyway. I gave the carb a real serious cleaning, including all passages, when it was off for the rebuild so I'm pretty sure it's plenty clean. Jetting could be off, I have no idea. Will the size be on the jet? I'll see how the plug looks.

edit: Old piston wasn't melted, it was scored with what I was told were detonation marks.


So was the head

[Paul_E_D]

If jetting were lean, it wouldn't have survived southwick. That's about as much load as you can put on a 125! I'd still pull the head to check it. I actually did that after two motos just to verify that I could lean it out a little.

Yes, jets have a number stamped into them.

[KB]

Those are not detonation marks those are marks of bit of metal wallowing around inside the cyclinder whilst it was running. Normally that hit the spark pleg electrode and the bike stops running.

I'd go with what paul said and also check th jetting out.

KB

["Dangerous" Dan K]

I'll check out the jetting for sure, it's an easy enough thing to check (and cheap enough to fix if it's off). All I could really do is check the # on the needle though, and with a built motor w/ aftermarket pipe and silencer I don't know that the jets even SHOULD be stock at this point?

Also, Paul has a point... I beat the hell out of that thing @ Southwick. If it was lean it likely would have grenaded out there.

[KB]

True.......

2 strokes suck when they don't run right.


KB

[Paul_E_D]

That is in fact detonation. A part rolling around in there would leave much more uniform and recognizable pattern. You could likley ID the part from its imprint.

The dets could have been cause by an air leak, but you do need to verify jetting and compare it to stock or commonly known settings.

["Dangerous" Dan K]

I can verify the jet and compare it to stock, but wouldn't the pipe and silencer change what the jetting should be? I'd like to think pulling the plug would tell me something but since it's been bogged some since I put the new plug in I'm guessing it's going to be a bit blackened regardless?

[Paul_E_D]

No, 125 mods don't require fatter jetting. They usually allow you to rune leaner than stock on the mains because combustion is more efficient.

Find out your jetting: pilot, needle, and main.

Pull the head and inspect for any pocking. We're not looking for color necessarily just yet.

["Dangerous" Dan K]

I think I remember my carb only having 2 jets? or maybe there's one inside another? I'll check it out when I open it up.

The head will be pocked because it's the same one. Had a bunch of people and my local shop tell me run it, it won't matter save for a percent or two in power. They were also holding the parts, so I figured they were in a position to make the call, especially when the call was "you don't need to spend $ on this. We'll order you a new one if you want but if it were mind I'd just run this". I will be able to tell if the piston is pocked though, since that's brandy new.

[gregp]

In case you ever get bored, or want to know more than you ever thought there was to know about 2 stroke tuning:
http://www.scribd.com/doc/8568237/Pe...ng-Graham-Bell

[Paul_E_D]

Yes, 2 jets, one needle is what is commonly reffered to as 'jetting'.

Check the piston for marks. Note the jetting settings, including needle and clip position, and get back to us.

["Dangerous" Dan K]

Thanks Paul. Last night ended up being um... interesting, and I never got to the shed. I'll check everything tonight for sure.

[Boston Chuck]

Hey Dan,
If you decide to machine your own piston, I still have the drawings lying around... Haha. Good luck with your bike man.

[richw]

Plug tune

Look at plug now would be indicative of general health

warm up bike
Run some short time like 1 or 2 minutes near wide open look at plug for main jet
(its ok to slow and turn etc but try to keep the bike in the power)

If its very light then too lean.

If its a Mikuni then find Sudco link no work I wonder if they have vanished