Carb problem?

they're probably linked. my bike doesnt four-stroke until its warm. Sounds like you're drowning your motor. Get a smaller jet or (more likely) check your carb float. I could stop the four-stroking without grabbing a new jet by simply lowering the float (bending the tongs for the float bowl AWAY from the carb body).

The float bowl (the cup shaped thing on the bottom of the carb) can be removed by taking out two phillips ('star') screws, and theres a fuel drain on the bottom of it (also a phillips screw with a small gasket... DONT LOSE IT). Just remember to turn your gas line off, then when it comes off (may be full of fuel so be warned) youll see a white plastic donut in the bowl itself, and still attached to the carb is the tongs and needle. Careful when you tilt the carb body on its side, without the bowl on it anymore, the hinge can and most likely will fall out, its just a metal bar that slides in and out. But theres two metal prongs reaching around the main jet, looks kinda like a thin gold toilet seat. Bend the tips of it AWAY from the body to let less gas in, a little at a time. Do plug checks (theres threads on the forum that are easy to find about this) but generally speaking, four stroking (when it sounds throaty and feels almost powerless, it will ONLY do this when riding it, in my experience, just revving it will sound normal.) means your getting tons of gas, and you can bend the tongs down more. Of course theres a limit to where your only option is a new jet, but this is the fastest free way to get it running better. It should sound almost like a chainsaw or lawnmower when its not four stroking. Generally speaking however, the top of the float (white plastic) should stick out 21mm when you set it on the tongs and measure it from the base of the carb (which is obviously upside down right now) , another issue may be your float has a hole in it and is sinking... Just look to see if its full of fuel when you remove it

as far as I'm aware, its still limited to the main jet size, however running it leaner will... run leaner haha, You could try that, but it only affects the mixture from 25-75% throttle, going WOT will still be limited by that

They are pretty crappy, I drilled a 1mm hole to bypass the main jet and improve idle. however there are 3 ways you can adjust the air-fuel mixture (you dont have to buy a new carb). Adjusting the float level, adjusting the needle clip, or buying a new jet (I think they're $2.00 at SBP, you could also just drill them out and/or solder then re-drill them if you have small enough drill bits)

Setting the jet wont really gain you any speed, once its set properly, thats it. Its different for each bike and person though. For example, port matching, expansion chambers, reeds, carbs, etc will increase performance AND your fuel requirements. Basically you just gotta experiment, find where your spark plug turns a nice chocolatey brown, being black is too rich, and white (or normal colors, maybe a lil grey) means way too lean, id rather run rich than lean, means at most id have to clean my motor more and replace the spark plug more often, running lean runs the risk of damaging the motor, up to and including siezing. However you can gain a LOT of top end and speed if your bowl and jet arent set right already. And youll know what im talking about when you take the bowl off, but with the carb sitting upside down, you will be bending the prongs UP, away from the carb

running lean will risk killing the bearings in the motor the "high performance" carb is a lie if its the one with the blue air filter its a EPA carb and its a junker the are fuel mix screw has a plug over it if you pull the plug out you can adjust the air fuel mix also make sure the choke is closed all the way it dumps fuel into the engine

Adjusting the needle clip will not do the same thing as adjusting the float arms.
Adjusting the needle clip position will tune how much fuel is added to the incoming intake air charge from just above idle to 3/4 throttle.
Adjusting the float arms will adjust the fuel level inside the float bowl.
It is hard to damage the float arms unless you try to adjust the bend of the arms with a hammer and bench vice.
You only need your fingertips to bend them and only bend them a teeny bit at a time.

Be sure and check the gas cap vent.

Remove the fuel line from the carb. With the gas cap in place, open the petcock and see that you have good fuel flow.

It's a common problem for the stock gas caps to not be vented properly. The symptom is, it starts fine after rest, then after a short ride, starts running progressively worse till it dies. Then after it sits for a while, will start back up. What's happening is the fuel tank gets a partial vacuum, and stops fuel from flowing.

From PDF File for a high performance Briggs and Stratton Carb... but same idea applies to the theory..... just note it is best to get something specific for your carb for how it is done.

I just liked how they explained theory and that on go cart tracks that vary (I suppose they mean avg speed) then for best performance maybe I think they mean for high or low end power. Fast track mostly forgo the low end acceleration to some degree, and visa versa.

Oh yea see the end of my copy paste from pg 3 where it say to be sure float valve should not going too far out as it could get stuck in out position.

Last not mentioned in the Briggs pdf, but I had once happen with a float valve where on a non-briggs egnine they used a nylon washer that guided the valve. The washer was worn and was catching the valve so it would get stuck. It stuck and was flooding so much that the bowl overflow would drip fuel out of a pressure relief valve. I suppose this was to prevent damage to the carb bowl gaskets ect. Still seemed to be a dangerous thing to be happening where it has gas dripping out, but that was the design of this outboard motor (not a briggs). Oh yea also it had a fuel pump so the out board motor is a different situation where it is not gravity feed. External fuel tank lower than motor necessitated the use of a fuel pump.

Moving a gas tank up or down with relation to the fuel inlet on a bowl carb is also a way to have a change in fuel metering if it is being intended or not!

The link for Briggs:

http://www.briggsandstratton.com/en...ing Guide/~/media/Racing/carbtuningguide.ashx

See pdf on page 3

TUNING
Rich and Lean: An internal combustion
engine needs a specific ratio or mixture
of air and fuel for best performance. This
mixture is delivered by the carburetor.
In the following discussion numerous
references will be made to the air and
fuel mixture (air/fuel ratio) being rich
or lean. Rich refers to a mixture with an
excess of fuel. Lean refers to a mixture
with an excess of air.
Float height
Parts involved:
• Float
• Inlet Needle
The float height controls the fuel level
in the float bowl. This adjustment
determines the point at which the inlet
needle opens as the fuel level drops
in the bowl. Float height is usually
measured with the float bowl removed
and is specified from the carburetor
body to an edge or surface on the
float. The float should be resting on
the inlet needle but not depressing the
spring under the needle stem when
this measurement is taken. To adjust,
carefully bend the tab where it makes
contact with the inlet needle.
The float height should be adjusted
before any other adjustments are
made. A higher fuel level will cause
a richer mixture and possibly excess
overflow from the vents. A lower fuel
level will a cause a leaner mixture and
could lead to an engine miss or cut-out
while cornering. Start at the specified
height and change as needed for best
performance on different type of tracks.
The float drop should also be checked.
The proper adjustment will prevent the
needle from pulling too far out of the
inlet seat and becoming stuck in the
open position.

327ren said:

see that's the problem. I have a high performance carb. The guys at motovelo said this:


"I can tell you though, that the carburetors that come on those kits are junk. by reducing the fuel which is what's happening when you shut off the fuel valve you lean out the carburetor and give it a proper fuel mixture for a moment ... and that's when the engine runs properly..what you need to do is get a good carburetor and that will fix that problem because the 1 that you have is giving the engine way to much gas not enough air and bugging down the entire engine."

So I need to lower the float? I thought that was done by adjusting the clip on the needle? Please advise. When I do this, I wanna know what I am doing.

Click to expand...

What's a performance carb? What kind is it? If it's a CNS you'll never get it to run right.

As far as float level goes, it's not that critical. If the float level is too high, the carb will leak fuel. If the float level is too low, it will starve for fuel at top speed, but will cruise fine at other speeds, like up to about 20 mph.

If you have a CNS you need to get NT, or Speed carb. If you bike is a 50, get the NT.

327ren said:

What does that mean, if my bike is a 50? Why do I get 10 seconds of power when I shut the petcock off? I have a CNS with the blue bowl vent. I described the problem in my original post. If I lower the float, is that the answer? And another thing......

Just before I had this problem, I saw that when I first took the bike for a ride, it would take off like usual. But then I saw that after I paused at a light, the motor would take a long time to accelerate. Then I noticed that top speed was never as high as before, and the top speed gradually diminished. What caused all these problems, and how can I fix them? Is adjusting the float the answer? Remember, my bike only works when I shut the petcock off, and then only for a few seconds. Then I have to wait a half hour before I can get another ten second thrill.

Click to expand...

For a 50, a NT is the best choice. The Speed carb is a great carb, but it's 2mm bigger than a NT. It'll work on a 50, but bottom end throttle response is better with the NT.

It's doubtful your problem is related to the float level. The changes you've noticed are probably related to the motor being new and starting to wear in.

I doubt you'll ever find happiness with a CNS. They're really just crappy carbs. You might, with a lot of effort get it work half way good, but it will never work as well as a NT, or a Speed carb for that matter.

I've bought 2 speed carbs from BGF for $16.95 shipped. You'll spend more than that on jets trying to get your CNS to run half as good. I'm sorry that's probably not what you want to hear, but that's how it goes.