Could this be my problem?

Cyclin · Oct 16, 2011

For the last few weeks I have been steadily losing tope speed and torque on my 2-stroke engine. The engine sounded strange as well. I had deduced that I may have a vacuum leak or air leak somewhere in the engine and proceeded to order a full gasket set.

I am replacing the gaskets today and when I pulled off the head I noticed some charring on the top of the piston. Could this have been my problem all along? If so, where is the best place to buy a replacement?

killercanuck · Oct 16, 2011

Can that be cleaned up with a wire brush? If not, Bikeberry, Pistonbikes, Gasbike(sale there)[top/bottom/side ads, respectively] can hook you up with a piston. Be careful though, different pistons have a different wrist-pin height.

I suppose an uneven burn could cause power loss, not 100% sure though.

Cyclin · Oct 16, 2011

The wire brush didn't work. I tried that right after I posted. Put the engine back together with the new gaskets and Ill take it for a test run tomorrow. I really, REALLY want to get this engine working at good performance again. Otherwise I am going to have buy a new engine :-||

Wm Holden · Oct 16, 2011

I've seen people use a water mister on the intake side while running the engine at half throttle...it loosens the carbon over time....in a 4 stroke with valves you run the risk of debris under the valve...but with these little guys seems like a quarterly misting would prevent that from happening at all....the build up that is...
JMO

killercanuck · Oct 16, 2011

oh yea, could try seafoam too, not sure about using water oO , er too much water anyway.

http://motorbicycling.com/f46/how-use-seafoam-34398.html

timboellner · Oct 16, 2011

Try this to remove your carbon build-up:

Put a few drops of oil on the top of the piston and spread it around.
Let it sit for about 1/2 hour.

Use a blunt edged scraper and scrape off the carbon. It should be gooey.
Don't use anything sharp that will gouge or scratch the metal.

Get a green Scotch Brite pad and soak it with 2 stroke oil and starting fluid.
Scrub the rest of the residue off. Gasoline will work also.
If you want to you can go further with a piece of 300 grit or finer sandpaper and clean it up further.

I personally take the rings off and clean the ring grooves also. Just be careful getting them off because they are brittle.

TiM

donphantasmo · Oct 16, 2011

OK, This will sound funny, but it might work. Try either kerosene (Usually, ACE Hardware sells it). Soak the piston in it for an hour or two. Try scrapping it off. If it doesn't work, try Marvell's mystery oil. That stuff works great, too.

Hope it works, mate!!

MotorBicycleRacing · Oct 17, 2011

Cyclin said:
I am replacing the gaskets today and when I pulled off the head I noticed some charring on the top of the piston. Could this have been my problem all along? If so, where is the best place to buy a replacement?

How many miles to get that much carbon build up?
How thick is that carbon?

Would have helped to see the head combustion chamber too.

What oil mix are you using and have used?
and what oil?

If you were using Opti 2 you wouldn't have any carbon.

Allen_Wrench · Oct 17, 2011

These nice fellows have pretty good advice on removing that carbon, so I'll let 'em voice their experience. What I was taking a look at: "the last few weeks I have been steadily losing tope speed and torque" that got me thinking. In your photo, that seems like quite a bit of carbon, even for just a few weeks. Now, it might have taken the engine a while to build it up to the point where you'd notice. But still, once the engine is back up and running, I think you should double-check your gas-oil mix, in addition to looking for an air leak, and whatever else might be going on. Otherwise, this won't be the last time you'll need to remove carbon. Just my 2 cents.

Cyclin · Oct 17, 2011

Thanks for all the advice. I've put about 2,000+ miles on the engine so that would probably explain having so much buildup. The carbon is about 1 mm thick.

I am running 32:1 with universal 2/cycle from target and 91 octane gas.

Do you guys think the carbon buildup on my piston is causing the loss in power?

CTripps · Oct 17, 2011

If the difference in the thickness of the gasket(s) in the cylinder can change compression ratios noticably, it stands to reason that a 1 mm thickness on the piston would too. How does the rest of the cylinder look? I've been told brake cleaner is a good degreaser, and very good at cleaning out 2-stroke exhausts, but I don't know if it'll help you, I'd go with what the others recommend first.

Allen_Wrench · Oct 17, 2011

Cyclin said:
Thanks for all the advice. I've put about 2,000+ miles on the engine so that would probably explain having so much buildup. The carbon is about 1 mm thick.

I am running 32:1 with universal 2/cycle from target and 91 octane gas.

Do you guys think the carbon buildup on my piston is causing the loss in power?

Could be. I'm thinking you could try 40:1 and 87 octane. See what that does for you.

Cyclin · Oct 18, 2011

I'll try switching my oiil gas mix when I get my bike running again. I put it all together and replaced the clutch lever and cable last night. Got it down the street and back and then heard a pop and now the engine won't fire. Plus my carb is leaking all over the place now! gahhhhh

double trouble · Oct 18, 2011

2000 miles and losing power usually means your rings are shot. The carbon is a product of cheap 2 stroke oil ,but you have gotten well beyond what is expected so if you get it running , who cares.
The carbon build up can be cleaned with a number of cleaner-softeners. brake cleaner ,g-m carbon cleaner , mopar carbon cleaner, kerosene ,
b-g carbon clean , seafoam , marvel mystery , lucas ucl , all have decent solvents. toluene, acetone , or even kerosene and trans fluid should work.
soak overnight if possible with a rag on top. scotch brite green pad or plastic scraper if you need it.
I would switch to a tc (not-tcw-3) oil or at least one rated jaso fc which is a semi-synthetic.
If you wish to go cheap, get an oil rated for chainsaws not outboards.
I just got done with 2 carb leaks. A tiny bit of permatex blue gasket maker on the float bowl and the intake to carb seal work wonders as does a tie wrap on the fuel line. I also bent my float retainer that hits the needle valve up just a bit so the float closes earlier. That sealed leaks on 2 carbs.

Cyclin · Oct 18, 2011

Thanks double I'm going to go buy some permatex right when I get off work. I love my Dax RT so I would have hated to have to replace it with my stock NT carb.
My gas can is almost out so I will switch to a new oil later this week. How can you tell if the rings are shot? As I was looking at the piston I didn't notice any cracks or breaks on them (since I had heard they are very brittle)

double trouble · Oct 18, 2011

A compression check would tell a lot. rent one from autozone if you don't have one. its free.

If the rings have good tension and sharp edges they may be o.k. I would not count on it . Check the cylinder bore too for glazed areas and scratches..
Without pulling the cylinder off the piston and a visual its almost impossible to know if it is the rings .

if you pull the piston, look under the rings for carbon buildup too .That could cause a lack of power too. The rings are not sealing . Cheap oil can cause it.

camlifter · Oct 18, 2011

i'd bet a dollar that since the piston is carb'ed up, the exhaust is too, probably to the point of being pluged up. try cleaning out the exhaust pipe.

Cyclin · Oct 18, 2011

Well I just ordered new piston rings since they were like $6 after shipping. I will pull apart my engine again when I get home today and clean off whatever leftover carbon I can find. I also ordered a brand-new 80cc slant head engine as well so I can have a spare to alleviate downtime due to shipping. This way if something goes wrong I can swap out the engine until replacement parts arrive.

I love these little 2-strokes but one of these days I am going to have to get myself a 4 for reliability. So today I am going to pick up some permatex for my carb, seal it up, and clean the carbon off the piston and check the rings.

double trouble · Oct 18, 2011

camlifter said:
i'd bet a dollar that since the piston is carb'ed up, the exhaust is too, probably to the point of being pluged up. try cleaning out the exhaust pipe.

very good point! That could explain the loss of power too, but unlikely . A plugged exhaust would normally not run at all or run like crap like a plugged cat. It would still be wise to clean it. .

Cyclin · Oct 18, 2011

Ok I will clean out the exhaust as well. I was thinking about replacing it with an SBP expansion chamber anyway. The muffler is only a month or so old though so I don't know how much it could have clogged up by now.

nightcruiser · Oct 18, 2011

camlifter said:
i'd bet a dollar that since the piston is carb'ed up, the exhaust is too, probably to the point of being pluged up. try cleaning out the exhaust pipe.

Good point about the exhaust.....
On the carbon, I would try scrubbing with some gasoline....

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