Weird engine noises?

Oddzball

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May 11, 2011
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Sierra Vista, AZ
So i took my first major road trip today.

34 miles. I know not very far compared to some of you folks. But anyway good for me since im new to motorized bikes.

I do a lot of work on cars so when i heard this noise my mind filled with dread.. it sounded like the engine was "almost" seizing, it would screech/squeek, felt like it was stalling, then resume normal operation.

I pulled everything off the bike that might be rubbing on say the tire, just to make sure i was actually hearing the noise from the engine, sure enough, that is definately where it was coming from.

I am not to familiar with 2 strokes however..

Is the engine toast or would adding more oil to my gas, stop this problem.

I made the engine run leaner by adjusting the carb to the #3 because of my high altitude, (really improved performance so im sure THAT was a good idea) so maybe now that there is less gas, in a 2 stroke that means less lubricant also correct?

Will adding more oil revive the motor/stop this or is it toast?

I was running 32:1 ratio with good quality 2 stroke oil (Not outboard oil either)

Please any advice would be greatly appreciated.

Thanks for your time folks.
 
I betcha you were 4 stroking at WOT.

Eh I dont get the lingo? WOT? Are you saying i wasnt putting enough oil in? Wide open throttle?

I was actually trying to NOT run "WOT" to be honest. i was only going about 20.

SO is it trashed then or...?

Ill add as much more info as i can, engine sounds fine when clutch isnt engaged, and even when it is most of the time it wounds fine, but sometimes, it makes the screech noise...
 
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4 stroking is when the fuel/air ratio is too fat, dumping too rich a charge into the cylinder causing it to be able to fire only on every other stroke... like a four cycle engine.

If you leaned it out and then it came alive, that would indicate the mix was too fat in the first place.

Chances are the factory had it set up rich in an attempt to try and protect the motor during break in.

If you are a competent mechanic, and felt the engine was screeching and squeeling internally, binding up, then breaking free and running better... all in the first 34 miles, my guess would be that you are correct and damage has been done to the engine.

It's only a tiny little popcorn machine.... pull the head and cylinder off and have a look !
I'll bet there is some scarring on the skirts or walls.

IMO, short period warmup and cool downs are a good technique to break in a 2 stroke.
First couple times, the rings are gonna take a real beating, especially on a known low-dollar motor that can not be constructed to the best of tolerances, or even use the best metallurgy for the money they get for them.

...The basket-case I bought from a college student was torn down for two reasons... First on the list was the busted up back wheel... took me a day of robbing parts and truing to get it functional again, but I did. and it had been taco'ed.
Second, the carb was off the manifold and I asked why... the fellow told me he intended to make an adjustment because the engine bogged at higher rpms... My guess is that it was running too fat.

One thing for certain, in a mini-motor basically over taxed, running at a gazillon rpm, things are gonna happen almost instantaneously, especially during break in! Most of em NOT good!

Good luck with it,
rc

I just re-read your OP... It did NOT say this was a break-in run... How many miles do you have on the engine?
How much do you weigh?
What is your altitude?
Do you run a fuel filter?

Obstructions in the fuel delivery system could be causing the mix to lean out on an extended run, where it might not otherwise, during stop and go traffic...
The plug may be a wrong heat range for an extended run.
WOT should not necessarily be bad for a 2 stroke if the carb is set up properly.
Actually, it should perform best at WOT.
Yet smaller the engine, more critical the tuning.
What is the air temp where you made this run?
Was it different than prior short runs?

Again, with these micro power sources, all other systems of the machine must be maintained in acceptable order.
Poor lubrication on a chain, or in a wheel bearing could cause heat build up and increasing drag that would affect the load on the motor over a long run... Heck! a head or tailwind affects all motivators!

Just think of all the hot-rod fun yer havin !
AFAIK, there's no less expensive format to play with performance on.
rc


...is your exhaust pipe sealed tightly at the port?
or
perhaps there's too much back pressure that builds on a longer run????
maybe you could drill a hole in the exhaust to relieve some back pressure? = more noise.
rc
 
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RustyCase,

First thanks very much for the reply.

So I should put the carb back to the stock #2 setting like it came from the factory as?

I assumed it was running to rich due to the performance and smell so I leaned it out. I had already run a tank in it, and the guy before me surely had run at least a tank so I assumed it was broke in already, hence i figured i would be alright.

Well live an learn if i broke it, ill just keep tinkering.

What do you suggest I do, besides check the cylinder for scarring? Run more oil in the mix, and make it more "rich" again?
 
I just re-read your OP... It did NOT say this was a break-in run... How many miles do you have on the engine?

Unknown since it was used, but I have put over 100 miles on it, I started out with little 2 mile trips then just today I did a 8 mile trip, to work, and on the way back was when i noticed the noise.

How much do you weigh?

I weight ~170lbs

What is your altitude?

~5000-6000 Feet

Do you run a fuel filter?

Yes, and its pretty much brand new

Obstructions in the fuel delivery system...

I am pretty sure there isnt an obstruction but i will check.

What is the air temp where you made this run?

~85 Degrees Farenheight

Was it different than prior short runs?

To be honest it RAN great, except when I WASNT running full out throttle then i got the noise, almost like it was engine braking itself(If that makes any sense..)

Again, with these micro power sources, all other systems of the machine must be maintained in acceptable order.
Poor lubrication on a chain, or in a wheel bearing could cause heat build up and increasing drag that would affect the load on the motor over a long run... Heck! a head or tailwind affects all motivators!

I literally tore the whole thing down and lubed all the bearing with high quality bearing grease, chain is well lubed. It was very windy however.

Just think of all the hot-rod fun yer havin !

I DID have a lot of fun. And tinkering with it is part of the fun, what i dont want is to have bought a "bad" motor that died in a week.

AFAIK, there's no less expensive format to play with performance on.
rc

Well, happen to have a good recommendation for where i can get just an engine to replace it if i need to? Some of these dealers seemed shady which is why i bought from a guy used in person

...is your exhaust pipe sealed tightly at the port?

Not perfectly, I wont lie, but it is much better sealed than the original gasket, which leaked like crazy I had to make a gasket, and that seemed fine, was running beautifully for all the short trips.
or
perhaps there's too much back pressure that builds on a longer run????
maybe you could drill a hole in the exhaust to relieve some back pressure? = more noise


AGain thank you VERY much for helping me out. Regular old V8 motors, no prob for me, but these little 2 strokes, they are SO simple its almost hard to diagnose a problem if you get what i mean.
 
Stalling is a symptom of 4 stroking. Regardless of if it was WOT or not, if it was at or nearing the top of the RPM cycle, that would do it. I upjetted and tweaked on the carb needle to solve when mine did that after break in.

Well, first - what is your high altitude?

Next, is it making that sound at a point in the RPM range, or is it all the time? Does it make no difference if it's at WOT or at idle, the sound is still there?

32:1 is optimal for dino oil. 40:1 synthetic is good as well.

True that leaner on the carb needle is less gas and oil to air - but you don't want it set to where it gives you bad performance so don't worry about that.

Worst case scenario is that you've got a blown ring. Honestly, on a used motor like what you've got where you don't know how the previous owner treated it - I'd say match the head, polish your head, jug and piston, and replace the rings. That'll bring it up to "practically/relatively new" status.
 
I was at probably 3/4 throttle. High altitude is 6k feet. Seemed odd. Didn't consistantly have the noise/problem. Was hard to reproduce.
 
@adrian : Semi synthetic isn't bad at all - actually, when you buy off the shelf synthetic oil, it will always say synthetic BLEND. If it doesn't mention what percentage of it is synthetic, you can call the manufacturer and ask them what percentage synthetic their synthetic blend/semi synthetic oil is.


@Oddzball :

In that case, nothing is broken then! :D Or it would be consistent from idle through the RPM range to WOT.

Sounds like it's at a certain RPM range, and that is consistent with 4 stroking on these chinese motors. Keep adjusting the carb, you shouldn't need to downjet due to elevation. Though, an aftermarket air filter and aftermarket expansion chamber exhaust will definitely make a difference. After tuning your carb to intake and exhaust, instead of 4 stroking you'll hit the power curve and really take advantage of what it's got. And if you do go that route - it wouldn't hurt to experiment with all different jets, higher and lower and find what your motor likes it's sweet spot to be at.

Though - I would suggest still what I said earlier about matching, polishing and replacing rings, just because of the used motor aspect of things.
 
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