Speed Carb or Performance Carb?

S

skinnerman

New Member
At full throttle RPMS fly up then down, up and down.

Hi! I ride my bike to work thrice a week (hour ride there and back) and I noticed that my standard carb SUCKS!

So I was wondering, which is better for my purposes (daily commute), the performance carb or the speed carb?

drn2
 
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What carburetor do you have now?
Don't know what the "performance" carb is. I hope not the infamous CNS.
As far as the "Speed carb" it is essentially the same carburetor as the venerable NT.

As far as performance the NT is your best choice for a stock engine. Unless you have loads of modifications you'll find the NT will provide you with everything you can ask for from a Chinese 2 stroke. Some prefer the RT carb. Personally I've used both and don't see any significant difference in the RT and NT. You'll get other opinions so just be patient.

What problems are you currently having, specifically? It might just be a tuning issue or something else we can offer some advice on.

Tom
 
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I have the standard NT carburetor. I bought everything from bikeberry.com, and they have the

performance carb http://www.bikeberry.com/engine-kit-parts/performance/66-80cc-high-performance-carburetor.html

and they have speed carb http://www.bikeberry.com/engine-kit-parts/performance/2-stroke-speed-carburetor.html

I tried asking my carb problems multiple times but got nowhere. When I let out full throttle the RPMs rev up for a few seconds, then they drastically decrease, then go back up again, and on and on.

Here's what I've already checked.

Fuel flowing well -- Check
Air filter clean - - - Check
Motor mounts tight - Check

Its a new carb!
 
MotorBicycleRacing said:
Air leak where the carb seals on the intake.
how are you sealing it now?
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Ditto: What you describe is the classic symptom of an air (vacuum) leak somewhere in the intake circuit. The carburetor and intake manifold must be sealed so that there is absolutely no air being pulled in downstream of the carburetor.

The kit supplied intake manifold gaskets are poor quality and prone to early failure. If you have the chrome steel manifold it is a good bet that the flange where it attaches to the cylinder is warped from the welding process. That warped, uneven surface will allow leaks even if you overtighten the fasteners. Grind or sand the gasket sealing surface flat then use good grade gasket material to make a new gasket.

Seal the carburetor to the manifold with a gasoline resistant sealer. Most silicone based sealers are not gasoline compatible. Read the label before using.

If the problem persists then you might be looking at crankshaft seals. There are two, one behind the magneto rotor, left side and the other behind the primary gear, right side.
Get the intake side sealed up first then let us know how things go.

Tom
 
Okaydokey thanks for telling me about that. Um, I haven't done anything to seal the case. Is there anything I can do without replace gaskets/seals?

Here's what I was thinking. . .

Lightly sand the intake manifold, apply a generous portion of some type of sealant, but the carb back on and tighten it really hard?


Would that help?


Shouldn't I just get the better carb anyways, so that my engine will last longer?
 
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skinnerman said:
Okaydokey thanks for telling me about that. Um, I haven't done anything to seal the case. Is there anything I can do without replace gaskets/seals?

Here's what I was thinking. . .

Lightly sand the intake manifold, apply a generous portion of some type of sealant, but the carb back on and tighten it really hard?


Would that help?


Shouldn't I just get the better carb anyways, so that my engine will last longer?
Click to expand...
Engine longevity has little to do with your carburetor preference. That will be determined by other factors such as how you ride, oil to fuel ratios, oil quality etc.
The carburetor will have no bearing on how long your engine might last.

As for your 'fix', yes, your method will work just fine. I doubt that the crankcase gaskets are the culprits here. I'm confident that if you get the intake circuit sealed properly you'll be happier with your current carb.

There are tuning changes you can make such as altering main jet size that will give you better performance. Seal things up and do some test riding. Let us know how things go.

One thing we haven't asked is how many miles/gallons of fuel does the engine have on it? If less two hundred miles don't expect the engine to produce maximum performance. They are slow to break in and need time/miles. 300 is even better.

Also what fuel to oil ratio are you using. If the kit recommended 16:1, drop that to at least 24:1. 16:1 is too much oil and the engine won't perform as well as it could with that ratio. There are other drawbacks to the 16:1 ratio. Fouled spark plugs, clogged exhaust, etc.

Tom
 
2door said:
Seal things up and do some test riding. Let us know how things go.

Also what fuel to oil ratio are you using. If the kit recommended 16:1, drop that to at least 24:1. 16:1 is too much oil and the engine won't perform as well as it could with that ratio. There are other drawbacks to the 16:1 ratio. Fouled spark plugs, clogged exhaust, etc.

Tom
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Alright I will! Any suggestion on a sealant?


2door said:
Seal things up and do some test riding. Let us know how things go.

Also what fuel to oil ratio are you using. If the kit recommended 16:1, drop that to at least 24:1.

Tom
Click to expand...

I'm currently using 20:1. Make it 24:1?
 
I like a product called SealAll. Most auto parts stores carry it. It's made for use with gasoline. Permatex also makes a gasoline compatable sealant.

When applying the sealant to the throat of the carb make sure to completely fill the slots. Some will suggest using an 'O' ring instead of a sealant. The problem I have with that method is the carburetor must be tightened against the 'O' ring firmly to get a good seal and it must remain tight against it. If it loosens or slides back you'll get an air leak again. A good sealant will also act as an adhesive to help keep the carb in place.


24:1 is good. Some go as far as 32:1 even during break in. Just make sure the oil you use is formulated for those ratios and it isn't for water cooled outboard engines.

Tom
 
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