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Old 04-12-2011, 01:00 PM   #9193
It's a short cut, really
Ladder106's Avatar
Joined: Jan 2005
Location: Davis, CA
Oddometer: 5,102
My AT is exhibiting the same problems as Thump's. I've had it to the LHD twice and have gotten no relief. I have the carbs off now and one issue discovered is one side of the pilot jet screw is broken where someone tried to remove it. We haven't checked the diaphrams yet. Could this affect performance?
Could the broken pilot affect performance?..........Possibly, if it's partially clogged. However, if the bike idles and runs well at small throttle openings, the pilot jet should be OK.

Whenever you remove the pilots you MUST have a screwdriver that fits the slot perfectly....otherwise they can break. If it were me, I'd try to remove it once but if it doesn't want to turn, I'd leave it alone. Shine a strong light down inside and try to determine if it's blocked or has foreign material in it. It's a very very small this is difficult at best.

Generally, I never stick anything inside a jet - the pilot in particular - because the hole is so small. If you find it blocked I'd try compressed air first. Shoot the air up through the pilot jet hole on the other carb (with the pilot jet removed) so you can see where the pilot bleed hole is on the carb body......then try to shoot air in through THAT hole on the bad carb. What you're trying to do is "backflush" the jet.

Blowing air into the pilot jet in the direction that fuel normally flows just serves to block it further if there is dirt or other material down there. back to the problem. The bike runs fine until 4000 rpm or so at which point it seems like it's running out of fuel, correct.

A few things that will give this symptom:
Water in the fuel.....if there's just a bit, the water will form a bubble at the low point of the bowl. Fuel is not drawn up from this point (through the main and into the needle jet) until higher rpms the water just sits there until it gets sucked up at higher rpm causing problems. Drain the bowls through the drain ports in the bottom of the bowl. Drain into a clear container so and let the fuel sit for a few minutes. If there's any water, it will settle to the bottom.

A dying fuel pump....The bane of the ATs. Your fuel pump may be able to keep up with the flow required at lower loads and rpm but not provide enough fuel at higher rpm and load. You should be able to test this by bypassing the fuel pump with some extra fuel line. The tank will "gravity-feed" for about 2/3 of the tank before the fuel pump is really necessary anyway.

A partially torn carb diaphragm...Description of problem already provided. To examine the diaphragms remove them and gently invert them looking for tears or cracks. They tend to bend and flex at one point at the crusing speed the bike sees most often. This is normally where cracks occur.

Hoping you find this helpful. Pleas post what you discover
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