4 stroking

F

fischer550

Member
My motor is 4-stroking at the bottom end, but it runs pretty well at mid-full throttle. I have a stock NT carb on with the stock jet, I live at 5,000ft. My needle clip is at the top notch. Any suggestions? Smaller jet? Should I leave it like it is until I'm done breaking the motor in, and then go smaller jet?
 
It probably would be best to ride it for a while, about 250 to 300 miles before changing anything. If its not that bad that's what I would/have done.
 
Attached are photos from my spark plug, I ran it for 10 seconds full throttle then shut her down. Notice the porcelain part and the spark plug tip are pretty dark brown, but the ring has little oil on it (keep in mind I am using Lucas oil semi-synthetic at 24:1 (break in stage) and it is not as dark as other oils
 

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It may be a little rich but that's better than lean, 24/1 mix will darken the plug a bit so it might change when you go to the mix ratio you plan on running. I run a sbp high flow air filter that helps also.
 
Eventually you might want to experiment with a smaller jet size. At your altitude that is to be expected. We have less air up here in Colorful Colorado so we need to adjust the air/fuel mix accordingly.

I'm at 6000' and I solder and redrill all my jets. You might need to do the same. That said, I'd still put some miles on that little engine before worrying too much about performance.
You have a good carburetor in the NT. It can be made to give you all the performance you can expect from a stock engine. It simply needs to be tuned for your altitude.

Tom
 
Tom, what size jet are you running? I just put a 65 in, and she runs so much better. I will keep the 65 in mor 200 miles or so and then experiment with a 60
 
Here's the plug after about 10-15 seconds WOT with the 65. Weird, there is a black buildup (won't just rub off) on the ring that wasn't there when I had the stock NT jet. but it runs way better. thoughts?
 

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I don't use "jet size' because they don't seem to be consistent. Instead I use drill bit size. As I said I solder the jet orifice closed then redrill them to give me the best performance.
My drill set is in one thousands inch increments. Different engines respond differently. I use anywhere from a .024 to a .026 drill size. However I also run Opti-2 oil at 100:1 ratio. That means I must reduce my fuel to air ratio more than if I were running standard 2 stroke oil at 32:1. When you reduce the oil content in your mix you must also reduce the fuel to air mix.
Complicated, I know but it will all make sense eventually.

Tom
 
With a break in ratio of 24:1 that color is to be expected. That ratio is heavy on oil which is great for proper engine break in.
The carbon buildup should not simply rub off with your finger, ever.
10 to 15 seconds really is not a long enough time duration to properly color the spark plug.
Riding in down the road under a load (not down hill, that's cheating yourself) for 1/2 mile is the minimum I hesitantly recommend. 1 mile is better, 2 miles are perfect.
Also, once a spark plug is heavily blackened by a very rich carburetor tune or low gas/ oil ratio the spark plug gets a permanent stain on it and getting a true color imprint becomes nearly impossible.

I recommend burning through 2 gallons of fuel before worrying about fine tuning the engine. So long as it starts without excessive struggle and runs down the road without stalling you are good enough for the break in period.

Here is an abbreviated method I have used very successfully for reading spark plugs and tuning: http://motorbicycling.com/showthread.php?p=541541#post541541
NOTE: this is done after the break in period is done with a common 32:1 fuel mix or similar.
 
Also, it is very hot when I run it. Like it sizzles a lot when I spit on it, not just the header on the pipe but the cylinder too. My old motor never did that
 
Are you riding it down the road or just revving it up while the bike is sitting still?
Spit sizzling hot is too hot. It should evaporate very, very quickly without sounding like frying bacon.
 
ya, just took it for an easy 5 minute ride. 41 degrees farenheit outside, pretty cold. came home, and minutes after the motor was stopped, I spit on it and it sizzles like bacon. The head and the cylinder :(
 
I think you sad you were running a shaved angle plug head so it will run hotter due to higher compression and a lean condition, it's probably not hurt yet but if you keep running it lean it will. That's why we have said several times to run it a little rich till it is broken in. Rich only fouls plugs, lean melts parts.
 
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Other members here have said that the angled plug heads run hotter than the straight plug heads. If it is shaved as well like Greg58 thinks, then it definitely will run hot.
I doubt that you have done any damage yet. You would have seen a silvery deposit on the spark plug which is actually aluminum melting/ burning off from the piston's crown.
Also, extreme heat will eventually warp the cylinder head and cylinder and over time lead to a blown head gasket which you do not have.

A spark plug's temperature has everything to do with it's ability to keep itself clean.
Also, running a spark plug that is too cold will not give a good color imprint as it needs to be self cleaning and a too cold spark plug cannot do that.
A B7HS plug will be able to burn off the oily deposits better as it will run hotter, but not make the engine run noticeably hotter. You may even end up needing a B6HS in the end, but don't jump to that one right away. Change spark plug heat ranges one step at a time.

Adding an extra head gasket will lower the compression ratio and reduce the engine's operating temperature. Also, lowering the needle clip position one notch will add more fuel which will help cool the burn temperature but also increase the tendency for 4 stroking which is the issue at hand. I vote for an extra head gasket.
 
Grab yourself an NGK BPR6HIX Iridium spark plug, sickbikes carries them.
That 6 number will keep your engine just a bit hotter than the 7's I run here in the desert which will help, and the spark in these little 2-strokes and stock mag is the best you can get, I include on every new 2-stroke build as standard equipment.
 
Before I read any of your suggestions, I lowered the needle clip TWO notches down and still like a frying pan. I am going to put a regular slant head on it (mine is milled), and put the original jet back in the nt and see what happens. also, I believe I have an air leak somewhere, but if I do it's very slight. Sometimes when I disengage the clutch, my motor revs up a little bit but not a lot. Could this be the issue?
 
Yes indeed. A fast idle is a symptom of an air (vacuum) leak. The most likely areas are the carburetor to the intake manifold and the intake manifold gasket to the cylinder. The kit gaskets aren't the best and I prefer to seal the carb to the intake and not rely on the metal to metal clamping action. Any good gasoline compatible sealer will work.
I'm not a fan of the 'O' rings because they rely on the carburetor staying tight against them to retain a good seal. If the carb loosens and slides away from the 'O' ring, you have a leak again.

Tom
 
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