Things went downhill abruptly...

[soulnull]

First, I do want to say that it's gotten to the point that I'm googling "motorbicycling [problem]" when I'm trying to find out info, so I figured I should probably sign up for an account on this forum that I'm so regularly harvesting information from..

Anyways, onto the issues.

First kit build, things were excellent for the first week. Thing hauled major butt. Was breaking in nicely. I'm not a motor expert by any stretch of the imagination (yet), but I bought this to learn.. Well, crash course time.

I'd read that cleaning burrs up was generally a good idea. Was not brave enough to try this yet, so I instead went for the lower hanging fruit and recut the poorly cut gaskets for intake and exhaust. Upon reinstalling the exhaust, the bolt snapped.. Great.

Drilled it out and used the heli-coil kit, used some gasket sealant and she's all sealed back up nicely//

Now, here's where the problem really begins... And I have no idea on the timing, whether coincidental or if I messed something else up..

Whereas it was running somewhat rich before, it ran alright. Now, it's running awful. It idles alright, but even wide open, it seems to get "stuck". The engine starts laboring at about 15mph, and she's got nothing left in her after that. Even without load, WOT, she's laboring.

I had the suggestion of checking the piston to see if something was not looking right, and there is evidence of blow-by (once I saw the top of the piston, pulling the cylinder was a must). The engine has maybe 3 hours on it, so this definitely seems excessive. Uploading pictures.


The cylinder doesn't look great, but I honestly have no idea what normal wear looks like. This is all new to me. Including pictures of that as well.


In diagnosing, I found that I can loosen the intake, basically forcing an air leak, and it'll rev better.. Which isn't a shock if it's running that rich. She's drinking gas well beyond what she should be, which, again, isn't a shock.. But I have the needle running as lean as it possibly can now.

So I guess what I'm wondering is, did tightening it up and fixing the gaskets maybe expose an issue with the carburetor? Or is this something more? I really don't know what to try next, I've tried putting everything pretty much as it was before I worked on it, and I can't get it back to how it was.

Thanks again for this extremely excellent resource, I truly appreciate everything I've learned so far, and continue to learn.

 

[allen standley]

First above all Welcome! this is the answer place as you by now know.

Right now you do not have an intake prob. I hate to be bearer of bad news but what you got right there is bad cylinder plating. There is nothing you did that caused the prob. I've seen this many times. These cheap engines are sent from China to us stupid americans without assurance or insurance concerning Quality Control. The Cylinders in these engines are not sleeved or lined, but coated with a chrome plating. What has happened, and I've seen it before, is the chrome plating has flaked off. Was never properly applied or circumstances were not just right and this is the result. This forum has been peppered with stories similar to yours. "Got it going and it ran great for a couple weeks and now NO POWER". What happened? You got a bad one from the start. This whole darn thing is a crap shoot especially from volume vendors, The only assurance you can have is to buy from somebody who takes them apart and inspects for this very reason. If you cannot talk to the person who receives them, inspects them and stands behind them it's a crap shoot. Yes I am disgusted and you should be too. Happens far too often. None the less you need a new cylinder and rings. You may keep your piston but also remember it's best to buy a complete top end that way you get it all. You will need to identify exactly which engine you have. Some are one type then another type, and then a combination of the two. Yet then again you may be better off to buy an engine only. I hate to see this but - tag you're it today. I'll sit back and see how you do. Maybe somebody else can help you with what you got right there but I highly doubt it.

 

[allen standley]

Also lots of info on engine type follow this thread
https://motorbicycling.com/threads/hi-all-two-not-so-simple-questions.59961/#post-624445

 

[soulnull]

So it was just bad timing perhaps getting the gasket opened up a bit gave it just a little more power which aggravated the issue, but either way, wow... Y

I know they're a crapshoot, but still sucks. She ran so good for that brief moment in time.

I went ahead and ordered a cylinder and rings, and if I need a piston too, I'll get that as well. Probably just should have gotten them all together, but I don't know if mine is a high hole or low hole, so taking another gamble I guess.

This would explain why the place It bought it from abruptly stopped responding when I sent pictures and asked for advice... Probably done buying from them now. I get it, manufacturing defect.. that's fine, didn't even expect a free replacement, but their selling point is "we wont leave you hanging".. so that kinda bothers me that he couldn't have just said so. Whatever. Now I'm here, and that's probably better anyways

 

[soulnull]

Also lots of info on engine type follow this thread
https://motorbicycling.com/threads/hi-all-two-not-so-simple-questions.59961/#post-624445

Excellent, thank you. Following.

 

[soulnull]

So I got my new cylinder and rings. Installed and tested. And there's good news.. And bad news.

The good news is the engine runs excellent.. The bad news is I have to turn off the fuel petcock and wait until it's at the end of what's left in the carburetor for it to run excellent. It's running even richer than it was with the other cylinder. However, it is worth noting that when I did the "starve it of gas" trick with the other engine, it didn't make a huge difference. Some, but not nearly as much as this one. This one runs exactly how it's supposed to for about 2 seconds as it's running out of fuel.

Also good, the new cylinder has very very smooth ports and is overall a beautiful cylinder. Almost like it's not some cheap Chinese cylinder.

So I'm on the right track, but now I need to narrow down the rich issue with that carburetor...

Won't idle unless the idle screw is all the way in, wont idle from start (needs revved first), smokes like a chimney, exhaust smells of unburned gas, and choke immediately kills it.. So all the classic rich conditions (and checking choke mostly rules out a stuck choke)

Air intake port is clear, actually removed the filter completely to test, no difference. It's sucking in air, but it doesn't feel like it's sucking enough if I put my hand to it compared to how it was sucking before.. Though obviously this is anecdotal...

Pin is clipped all the way at the top (making the needle the longest it can be.. Which everything I've seen says this is the "leanest" setting)

Am I going to need to rejet, or is there something else I should be looking for?

I sincerely apologize for my newbness, but obviously the sum of all parts is one, and try as I might, I still can't quite narrow down what's causing this. It all went to poo at once it seems. It still runs and is driveable, but very hard to just want to take it out for a spin when I'm so worried about what's going wrong with it.

 

[Greg58]

What oil ratio are you using? 16/1 can cause the problems you are having, I break in mine at 24/1 with good oil designed for air cooled engines. Just to test try removing the muffler end cap and test it, if you or your neighbors don't mine the noise.

 

[soulnull]

What oil ratio are you using? 16/1 can cause the problems you are having, I break in mine at 24/1 with good oil designed for air cooled engines. Just to test try removing the muffler end cap and test it, if you or your neighbors don't mine the noise.

I'm in the boonies, what neighbors? I'll try that suggestion out.
I will try that. I did, however, thin the ratio ever so slightly when I started having the issues, since I knew it was running rich.. Probably about 20:1 now, but I'll try a bit thinner as well and see if it makes any difference.

 

[allen standley]

Clip on needle position determines fuel volume from idle to roughly 3/4 throttle. The jet size determines fuel volume from 3/4 to wide open. Your rich condition is in that idle to 3/4qtr range.
You say when you "shut petcock and as the bike starves for fuel it leans out and runs as it should just a bit as it shuts down. Good runners will do this same thing.Also... Others may argue, But. From day one any engine I buy before first start I simply remove plug then give a healthy dose of oil into cyl. push it around with plug out so I know the oil has worked into the rings and down into the base. I mix 4oz oil 1gal gas that's 32 to 1 mix. Break in mixes --- I don't bother.
I think too much fuel is getting into the carb bowl. I am assuming this is the stock NT carburator.
This sounds to me as if the float needs to be tweaked just a touch. So remove carb from engine, remove the bowl and the donut float. Check the float for leaks by shaking it, if you hear liquid sloshing in it you have a defective float. Next look at the little fork which is attached to the needle valve. Remove it from carb. Remove the needle from the fork and with a pair of needle nose pliers Very carefully bend ever so slightly the little tabs which hold the valve in place. What you want to do is shut the input of fuel going into the bowl sooner / less fuel in the bowl. The goal is to allow only enough fuel in the bowl so as the carb can sip what it needs at any throttle.
Here's a thread to followhttps://motorbicycling.com/threads/gas-leaking-from-nt-carb.61865/#post-644187

 

[allen standley]

Also visit member 2door on this forum he goes through the NT step by step and is very complete.
found this on utub hope it helps

 

[soulnull]

Well, definitely on the right path. Adjusted the float and leaned up the fuel/oil ratio. Idle screw still in all the way and it's still not super stable. If I WOT it, it bogs, but within 1-2 seconds opens right up and sounds like it should. It's 'four stroking' still, but it's a new engine and I'm just gonna have to wait until I get some more hours on it to really mess with it, but this definitely tells me it's the carb. Even though it's four stroking and bogging, it's got a lot of it's former power back.. Not all of it, but enough to where I'm calling it 'its still breaking in' levels of performance.

And thank you for the video Allen, this is exactly what I was looking for!

 

[javy mcdees]

the NT carb is a half rpm carb. pos terrible fuel milage but tuned as best as it gets it has good pickup but top speed is not possible with that pos, the cheapy RT carb will run awesome compared to the NT but you need about 5 of them to keep you running cause the clamp will break no matter what and out of 5 you buy 2 will run right. The RT carb will top speed nice I got 40 mph out of mine but it was zero to 40 mph in about 2 miles, then I bought a genuine Dellorto and even in a bad tune at half throttle that bit ch hauled the mail even with rich jetting and half throttle only commutes. Once I jetted the main and the pilot the engine runs very well now.

 

[soulnull]

the NT carb is a half rpm carb. pos terrible fuel milage but tuned as best as it gets it has good pickup but top speed is not possible with that pos, the cheapy RT carb will run awesome compared to the NT but you need about 5 of them to keep you running cause the clamp will break no matter what and out of 5 you buy 2 will run right. The RT carb will top speed nice I got 40 mph out of mine but it was zero to 40 mph in about 2 miles, then I bought a genuine Dellorto and even in a bad tune at half throttle that bit ch hauled the mail even with rich jetting and half throttle only commutes. Once I jetted the main and the pilot the engine runs very well now.

I was looking at carbs, ended up buying a microdrill kit, I'll try rejetting for now, mostly because while it does hit WOT, it's running itself out of gas now, and unless I richen it back up, that's just how it's going to go.. So I'll do the solder method and see if that gets me any joy. Should at least give me a rough idea if this is the right path.
The Dellorto carbs do seem well regarded, I keep finding "dellorto style" knockoffs, not sure if those are the way to go or if I should hold out for a legitimate one.. Any thoughts on that?

 

[javy mcdees]

I had tinkered and tuned the NT carb then one day I was like close to the right jet and decided to make one more change to get it right and I removed the slide as usual and the slide would never slide back in, after2/3 hours of massaging de-burring I took a brass hammer and 3 swift swings and a toss into the trash bin I fixed the NT carb. all the heat cycles must of warped the body. pofs

 

[javy mcdees]

Mikuni or Dellorto genuine is my only selection, tired of finding issues with knock offs. I used the 19mm Dellorto, have not tried a vm-18 Mikuni yet.

 

[indian22]

Mikuni or Dellorto genuine is my only selection, tired of finding issues with knock offs. I used the 19mm Dellorto, have not tried a vm-18 Mikuni yet.

Javy I agree will you on original Dellorto 19mm on 66cc two strokes and also Mikuni carbs (VM21 Mikuni in my larger 125cc 4 strokes). I use both and they are high quality pieces. I've also used clones of both brands, some worked well, but all clones are not created equal and that's the real problem; some are just terrible! Those went into the trash. I also got fed up with spending time to get them setup close to right. I'm still running two clones (one Mikuni & one Dellorto) that were great out of the box, but will order no more clones in the future...penny wise but dollar foolish....

Rick C.

 

[soulnull]

So I wanted to give an update.. I had already ordered a micro drill bit set so I figured I'd try the solder/drill method. Too a stab at 65, and the results were better... Tried 55, and she's back to her old self now. If I move the clip all the way to the rich setting, she still runs rich, but now at the leanest setting, she's running like she should. If I choke it at idle, it dies... So not too lean, maybe still a touch rich, but I'm done messing with it until it's broken in. Power is back, not excessively smoking, etc.. running almost as good as it was before this happened.

Me being me, can't resist speed tests. Previous setup got me 33 mph, which is nuts since I was running a 16:1 fuel to oil ratio... The new top end feels like it can pull it off, but I'm going to wait until it's got a few hours on it before I try anything crazy.

Thanks guys for your help and suggestions. I'm so glad she's back to normal!

 

[soulnull]

Sorry, apparently my phone and the submit button don't get along too well.

 

[soulnull]

Yep, triple posted... Please delete these two posts if possible. Thanks.

 

[indian22]

So I wanted to give an update.. I had already ordered a micro drill bit set so I figured I'd try the solder/drill method. Too a stab at 65, and the results were better... Tried 55, and she's back to her old self now. If I move the clip all the way to the rich setting, she still runs rich, but now at the leanest setting, she's running like she should. If I choke it at idle, it dies... So not too lean, maybe still a touch rich, but I'm done messing with it until it's broken in. Power is back, not excessively smoking, etc.. running almost as good as it was before this happened.

Me being me, can't resist speed tests. Previous setup got me 33 mph, which is nuts since I was running a 16:1 fuel to oil ratio... The new top end feels like it can pull it off, but I'm going to wait until it's got a few hours on it before I try anything crazy.

Thanks guys for your help and suggestions. I'm so glad she's back to normal!

Your thinking on the problem was and is solid as was the approach to solder and drill, nothing wrong with buying a few jets of various sizes but old school works and you now have a set of drills that you can use as well.

I like to setup a bit to the rich side. A little 4 stroking isn't at a specific rpm isn't necessarily a bad thing either. I run Lucas ash free, semi synthetic in my 2strokes & smoke isn't an issue even running a little heavy on the mix. I tune by feel across the low to upper midrange of a motors capacity, where I spend most of my riding time. Top end is interesting, but not my determining factor in tuning unless it totally sucks on top.

I like the approach you took to getting the motor running as you feel it should.

Rick C.