The bike will only start if I put my hand over air intake, then will run rough, what can i do?

when a motor has been cooked ( run with out water ) the rings loose tension , the pistons score the cylinder walls, the head cracks or warps and the head gasket generally blows. In mechanical circles , your best option is a replacement motor either from an engineering rebuilding shop or a good unit from the wreckers.

Are there any valves, vacuum hoses related to or on the air box? Otherwise should not matter but if you need to hold hand over the intake to raise pressure to suck fuel out of a carbureted system need to know more about it. Did it run okay before air box was removed? Try to re-install the air box would possibly be the simplest way to find out because if it then runs okay you have your answer and if not you need to go further into the problem. Has anyone been messing with carbs, as with a carbureted system in contrast to a fuel injected system where fuel pressure would be governing and holding hand over the intake should not affect fuel delivery at all but only fuel rail pressure or injector size or pulse width would. In a carbureted system the float level is the most critical thing. and if it is not correct this could also be your problem and that would be a first thing to correct. What type of carb(s) are on the bike??? CV or otherwise??? Does the bike run at higher rpm's or just not at all unless fuel is being sprayed into the intake or intake covered??? If not at all there could be a myriad of problems. But again, poper float level is critical and should be your first carbureted system check point. Also fuel filter, pinched or otherwise restricted fuel lines etc. Does the bike have a vacuum operated fuel shutoff valve?? If so does it source its vacuum from the air box?? Could there be a massive downstream induction system air leak?? Check for that also BUT the history of the bike's running before the present problem is crucial in diagnosing. ALSO not assuming is important and I have been assuming it is a four stroke engine. If it is 2 stroke there are a myriad of different things to look at right away. SO, give some more information to get some more assistance.

John

Most modern motorcycles don't like to have their air boxes changed. As they are set up at the factory to run with a particular amount of air. Changing from dual to single, you are actually reducing the amount of air to the bike not increasing it. Increasing the jets will only add to the problem, because you are allowing more fuel in to the bike. It already has a fuel issue.

Check there are no air leaks around where the air intake rubbers are at your carburetor. It sounds like your bike is running too lean or weak which means your air/fuel mixture is running on too much air and not enough fuel. This would explain it running smoothly when you put the choke on as the choke "chokes" the majority of the air from the carburetor and allows more fuel to flow through the carburetor creating a richer mixture. There will be a mixture screw somewhere on the carburetor which will allow you to either richen (more fuel and less air) or weaken (more air and less fuel) by turning the screw either in or out. Only adjust this by a small amount (about a quarter turn at most) at a time and try the bike to see how it rides each time. After adjusting the screw each time let the engine idle for about 30 seconds or so to let it settle to the new mixture setting before riding. There will be another screw on the carburetor which is your "idle" or "tick over"speed adjustment screw which adjusts how high your engine revs while the engine is "ticking over". Turn it in to increase idling speed and out to lower the idling speed. This will probably need adjusting as you change the fuel/air mixture. I hope this helps you and good luck :o)

Somewhere between the carbs and the cylinder there are air leaks. Cracks in rubber fittings or seals, clamps on hardened rubber manifold material may no longer seal well, intake manifold to cylinder bolts may be loose. A loose spark plug, bad head gasket and burned exhaust valve can let un-carbureted air into the cylinder as well.

turn the bike on and fuel comes out of a line behind the air filter. Can you tell me where that line is supposed to go

I have the same bike, put fresh gas in it and make sure its high octane. Check your plugs make sure they arn't fouled, make sure the intake boots on the carb are tight. Check air filter.

I bet its the gas, thats what happened to mine.

have checked for air leak @ intake manifold? this is com.prob.

sounds like you may have an intake leak. with the bike running spray a little starting fluid on the intake manifold but make sure you dont spray it into the back of air cleaner as this will give you a false reading. if the idle changes when you spray starting fluid on the intake manifold then you have an intake leak and need to replace the intake manifold gaskets. God luck let me know what you find

If the old spark plugs are real clean you can use them otherwise put in new ones. Put all the plugs back in the engine and connect up all the plug caps to the plugs. Check the air cleaner and air box. Make sure mice or bugs haven't gotten in there and built a nest plugging up everything. Look at the air cleaner. If it's a paper type blow it off and use it until we are sure the bike will run and the gears work. Then get a new one. Paper tends to plug up, as it ages. If it's a foam one, clean it in solvent. As you clean it, rub the foam somewhat roughly. Not too roughly, just a little roughly. If the foam starts to come apart in your hands you will need to get a new air cleaner. A lot of bikes must have that air cleaner in the system. If you leave it out, the engine may run too lean. This, of course, makes you think there is something wrong with the carb. I had an old Suzuki GS750 come in once. If you just took the air cleaner cover off, it would refuse to idle. Put it back on and it idled perfect. The owner put over 60,000 miles on that bike. Ran great, but it had to have that air cleaner on. I've seen a number of different makes and models do the same thing. Sometimes, even a crack in the air box can make them run funny. I've also seen a lot of bikes where having the air cleaner on or off made no difference in their running. If your not sure, leave the air cleaner in place while you work on the engine. ,,,