When turn on petrol and kick bike, petrol is running out of overflow pipe on carb and bike wont start, and bike sounds flooded.

The carb is flooding because of a stuck needle valve in the float chamber. When the bike is running at higher revs, it is probably drawing enough fuel into the engine to run OK, but at low revs, the overflowing petrol will be getting into the engine in far too higher volume and flooding the cylinder, drowning the spark plug.

You will need to remove the float chamber from the carb, take out the pivot pin that the float hinges on in order to release the needle valve and clean it out. 99% of the time simply dropping the needle valve out, giving it a wipe with a lint free cloth and flushing a little clean petol through the inlet pipe to dislodge any obstruction will fix the problem. While the float chamber is off, check that there is no dirt in the bottom and that the entire chamber is clean and free of any muck.

There will probably be a drain valve on the side of the carb (Usually a brass screw set into the base of the carb float chamber at a slight angle). Before you go to the trouble of removing the carb from the bike, try this:

Turn off the fuel supply.
Put a cup under the carb to catch fuel.
Remove the drain plug and allow the fuel in the float chamber to run out.
Now the float is sitting at its lowest possible position inside the float chamber, turn the fuel supply back on and as petrol runs out of the drain hole, tap the carb sharply and repeadedly with the end of a screwdriver as you let about a pint of petrol flush through.
Turn off the fuel supply and replace the drain plug.

The flushing and tapping MAY dislodge the obstruction that is holding the needle valve open and fix the problem without having to remove the carb

i take it the carb isnt the original one? well you can still set it up for the bike take the carb of and remove the bottom and check the floats there shouldnt be petrol flowing out of the overflow pipe when the bike is running when you have done that take the top of the carb apart and remove the needle valve from the top its connected to the throttle cable blow down the jets to clean them out re assemble the carb
there is 2 screws on the side of the carb 1 is the air screw the other is the tick over turn them both in till they are tight then turn them 2 turns out
when you start the bike it might run fast at idle or backfire if it does adjust the top screw for tick over(idle) the bottom screw for running better

hope this helps


John

hi, you dont say what bike this is, however the main reason for this would be at least 1 float valve not closeing, has the bike stood for a while, classic symptom, reason for not starting would be overfueling, normaly you will find a drain screw on each carb with a pipe for fuel to overflow, this would then be oviouse which carb is giving the problem as the fuel flows out of the problem carb overflow, your overflow tubes which are located inside the float chamber may be blocked, i would think that in this case a strip down of the carbs to check and clean as ness would be in order, in the same way the fuel will run out through the airbox it will also run into the engine, causing it not to run

Kinda sounds like your needle valve is sticking in your carb and it is giving it to much fuel

Those bikes can be a pain to start after they've sat awhile. What always worked for me was twist the throttle a bunch. I mean make sure its flooded. Then lay the bike over on its left side until the gas runs out the overflow. Stand it up and lay it down until it stops running out. Then I squeeze the decompression lever and cycle the motor. Now just barely pull on the decompression lever to open the valve just barely. Get it to top dead center and give her a good kick with a twist of the throttle. Becareful it could kick back.
This technique works for when the bike stalls when its hot. Most important part is if you think its flooded lay it over and start the process over. Remember your XR has two carbs and will flood QUICK. After some practice you'll be able to hear it in the exhaust pipe if she's flooded or if she trying to come around. Trust me. I have four of these bikes. Two 83's, one 84 and my beloved 85.

Your float is stuck and allowing fuel to overflow. If the float, floats it checks off the fuel exactly like the tank on your toilet.

plugs/coils/leads breaking down, are you getting a spark and are the plugs wet ? could also be kinked petrol pipe or blocked petrol filter, maybe blocked jets in your carb

You need to get some new float needles, and have the carbs cleaned and the float heights set correctly.

it sounds to me like the carb float levels are out of adjustment and it is overfilling the bowls,or,the needle valve seats are worn and leaking,which will allow fuel to continue filling the bowls even though it looks like they are closed,remove the carbs from the bike,remove the bowls,turn the cabs upside down close the floats(push them right to the top,this simulates full bowls)then blow throgh the fuel inlet pipe,if you can hear air escaping from around the seats they are faulty,also check that the seats themselves are tight in the carb body,i dont know why but gsxr carbs seem to shake the valve seats loose..hope this helps

To me I want to know how old that gas is. If it smells like old paint or stale at all you need to rid the complete system. Then you need to take your carb. off and take it apart and clean it and all the jets, since you said there was sand in the gas tank.