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Motorized Bicycle Trouble Shooting Use this area to post problems that may arise, if you could use some help in figuring out what is wrong with your engine and what needs to be done to achieve top performance.

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  #1  
Old 12-16-2012, 09:46 PM
Shred_cred Shred_cred is offline
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Default Carb jet sitting high, poor/rich mix?

I got a new Carb, the speed carb from zoom bicycles.
My engine was running fine but now it only runs with the choke down. It idles Way too high, and bogs down when i throttle. It dies completely with the choke off. So too much air not enough fuel makes sense right?

The fuel slide sits half way down in the venturi when im idling wih closed throttle.
Is my throttle cable too short? Shouldnt the slide almost close the air intake?
I moved the little pac man clip up and down. Nothing changed. The speed carbs needle was a little bent so i thought that might be restricting fuel and switched back to the old needle, but its about 3mm longer.

Is the needle the likely issue keeping the venturi intake open so wide?



Notice the slide in this diagram is 75% closed, mine sits at halfway at idle.
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Old 12-16-2012, 10:04 PM
crassius crassius is offline
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Default Re: Carb jet sitting high, poor/rich mix?

Were it I, I'd put back the old carb and trash the new one.

If not, start with getting the throttle cable right, then work through your jetting.
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  #3  
Old 12-17-2012, 01:35 AM
Shred_cred Shred_cred is offline
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Default Re: Carb jet sitting high, poor/rich mix?

Its from the same company its obviously supposed to work. Im not just going to trash it
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Old 12-17-2012, 12:19 PM
crassius crassius is offline
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Default Re: Carb jet sitting high, poor/rich mix?

also, I've seen some performance parts that only work with other performance parts, such as carbs that won't work without a modified exhaust
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  #5  
Old 12-21-2012, 06:50 PM
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maniac57 maniac57 is offline
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Default Re: Carb jet sitting high, poor/rich mix?

Be sure the cable is properly seated in the carb slide and the slide works ALL THE WAY up and down. If installed wrong, it will not slide. There is a notch in the slide and a pin inside the body that have to line up to work right.
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Old 12-21-2012, 07:56 PM
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moonerdizzle moonerdizzle is offline
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Default Re: Carb jet sitting high, poor/rich mix?

also, check your idle adjustment.
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  #7  
Old 12-21-2012, 08:42 PM
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dingodog dingodog is offline
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Default Re: Carb jet sitting high, poor/rich mix?

I feel the first and most noticable upgrade on a 2stroker is the spantion header. It does not make sense to get a bigger carb if you have stock porting, exhaust, etc.
In fact, you might degrade the bottom end. As always, just my honest opinion.
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Old 12-21-2012, 08:50 PM
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turkman turkman is offline
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Default Re: Carb jet sitting high, poor/rich mix?

yes if the needles bent it would keep the slide from closing,I'd try the old needle ,but make sure your slide will move open to closed without the needle if it won't it maybe a cable issue. There's realy not much diff from those carbs we're running the dolordo nockoffs and we like them you can get them from Piston Bikes.good luck Later Bob
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Old 12-22-2012, 12:29 AM
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biknut biknut is offline
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Default Re: Carb jet sitting high, poor/rich mix?

I'm running Speed carbs on both my bikes. The Speed carb is superior to the NT, because
it's about 2mm bigger. It's a very simple carb to tune, and trouble shoot.

First, you're going to need a new slide needle. The one in the Speed carb is shorter, and
thicker than the one in a NT, but I don't think it's long enough to hold the slide up.

You need to figure out why the slide won't go down all the way. Do you have any slack
in the throttle cable, with the adjusters shortened all the way? If not then the cable is too short.

If you have slack, then something is binding the slide in the carb body. Are you sure the
slot in the slide is lined up with the post in the carb body? The slot in the slide should be facing the right side of the carb. It sounds like this could be your problem.

Make sure the jet, and jet holder are properly installed and tightened. You can try running
with the NT needle, but I don't think it will work very well like that.
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