Question about 1993 Honda CB 750 Nighthawk

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Fuel is coming from under the carbs and pouring over the engine. Spark to all cylinders. Can't see exactly were it's coming from cause there are too many hoses in the way.

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  • bulldogchief
    bulldogchief May 11, 2010

    Can you explain this a little better? You say fuel is coming from under the carbs...exactly what do you mean, is it in drops or a stream? Why would you check spark if you are chasing a fuel leak?

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Your float needles and or seats are probably the cause. Of course check the fuel line itself first, if it is ok, remove the carbs then turn upside down and remove the bowl. (do one carb at a time to keep parts in order) the float will be made of plastic (sometimes brass) and as the fuel level rises in the carb it "floats" up causing the needle to seat and stop fuel flow. Check for dirt and debris on the needles. If none found, then remove the needle seat (a brass plug that the needle goes into) it should have an oring that goes between the seat and carb body. This oring will shrink over time and if it does not seal tightly it will allow fuel to leak. You can get the o rings at a auto parts store if you take an old one for sizing it will be cheap (less than 5 bucks)

Posted on Sep 23, 2009

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I'd check to make sure any fuel shut off valve (often "inline" or located directly under the tank) is open or on. Check or replace any inline fuel filter as well. If your snowblower has a priming bulb, you should hear gasoline spritzing after the second or third full press. More presses will probably cause gas to drip out of the carb to the ground. Next, check the spark plug. Clean or optionally replace it - set / check proper gap. With the plug out (and the spark plug wire away from the spark plug's threaded opening in the engine) pull the starting cord several times, and then check for the smell of gasoline in the cylinder. If no gas odor, you may have a bad float in the carb or other blockage. It will not run until you can get fuel into the cylinder. You can try pouring a few drops of gas into the cylinder of the engine via the spark plug opening or give it a "quick blast" of aerosol starting fluid or ether. Reinstall the spark plug and try again. If you added fuel, starting fluid or ether, the engine should have either attempted to run or sputtered briefly or is actually running. If it did neither, check for spark. Remove the spark plug wire from the spark plug and insert the tip of a screwdriver into the boot on the end of the spark plug wire and position the screwdriver's shaft to within 1/4" of the top of the spark plug. Be sure to only hold the screwdriver by the insulated handle (do not come in contact with the metal shaft of the screw driver) and pull the starting cord again. You should see a spark jump to the spark plug. If none, you may have a bad spark plug wire or magneto - and need to clean or replace it. before trying again. Good luck!

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If the carb is flooding it will fill the cylinder with fuel, this will cause a hydralic lock, making it near impossible to crank the engine, remove the spark pluf, turn the ignition off, crank the engine, if fuel pours out of the plug hole then it is well flooded, you will need to get a pressure test on the carb to check the needle is not leaking, this will be the quickest way to check the carb.

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This can happen if there was fuel left in the carburettor for a few months. The fuel forms a gel in the jets which can block the fuel getting through. You could try the following procedure which might help get it going.

  • Remove the sparkplug.
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Try to start the generator. The fuel that you poured in should ignite. This might be enough to get the engine running. You may have to repeat the procedure 2 to 3 times. Don't be tempted to pour too much fuel in as it will cause the engine to flood.

If the jets are blocked in the carburettor this might be enough to **** the fuel through but if not you'll need to get a mechanic to strip down the carburettor and clean the jets.

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if the gas poured-out of the carb then the cylinder filled with gas when you pull start it the full cylinder will act as if frozen when the valves are closed you can not compress the liquid remove the spark plug and try to turn engine slowly make sure the kill switch is set to OFF so no spark can ignite the gas turn the engine till no more gas comes out then you will need to replace the engine oil to new the carb will need to be dissembled and checked what causes this is a stuck float a brass float can get a pinhole in it and sink then a free flow of gas will enter the cylinder.it it called hydraulicking you can bend valves and con rods trying to turn it hard with no place for the fuel to go.
when you do this squirt some oil in the cylinder to lube the rings and not score the walls reassemble and run the engine after these steps followed. have the water hooked up and it free flowing not to run under a load until your satisfied with the results a carb kit is around $20.00 bucks and a float $6.00 hope this helps

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Coleman Powermate 3000-Will not start.


You may know this already but I'll go over how to troubleshoot a small gasoline engine :-)

To run properly these engines need 3 things a) the right fuel/air mixture into the cylinder, b) compression, and c) spark at the right time. As you check out the engine you prove to yourself that each of these things is there.

First, double check the fuel valve and the run/stop switch. I've forgotten this once or twice and wasted time fixing what wasn't broken.

Next pull the starter rope. Do you feel a fair amount of resistance that gets stronger then weaker as the engine turns over? This is also when I listen for any odd noises.

Double check the fuel level in the tank and the amount of oil in the crankcase. Again, we're systematically proving that the darn thing ought to work.

OK, got fuel in the tank, oil in the crankcase, all controls to "go", and it feels like we have compression - that leaves checking it for spark. Take out the spark plug and look at the end of it. If it isn't nice and clean go get a new one. Lay the spark plug against the cylinder head so that you can see the gap at the business end and gently pull the starter rope, you should see a nice bluish spark jump across the gap. You may need a friend to help by pulling the rope while you watch the gap ;-)
This doesn't check that the plug will spark when it's under compression in the cylinder but it proves that the electrical parts of the engine are working.

If there was any sort of spark at all reinstall the plug (use the new one if you found it dirty). Take the air cleaner off of the engine an inspect it, if it's dusty tap it against your hand to knock the dust out of it, if it's oily and/or wet get a new one. Get yourself a can of carb cleaner, brake cleaner, or other handy starting aid and shoot a 1 second blast of it thru the carb intake. You want to get the brake/carb cleaner past the carb and into the intake manifold. Do Not use ether or gasoline for this at penalty of your eyebrows. Close the choke half way and pull the rope, if the engine starts or tries to start and then stops you probably have carb problems, if there is no detonation at all from the cylinder you may have compression or spark problems.

Carb problems:
Put a catch pan under the carb, I use a cut down 1 gallon oil container. Using a 13mm wrench loosen the bolt on the bottom of the carb bowl and then remove it by hand. You should see fuel start to come out of the hole where the main jet you just took off was. If you don't see fuel come out gently remove the bowl from the carb, be careful of the oring/gasket between the bowl and the carb body. At this point fuel should be pouring out into the catch basin, if it isn't you have to find out what's blocking the fuel supply. Shut off the fuel valve, many fuel valves have a built in filter in the body of the valve. If you've got one of these you can take the bottom of the valve apart with a 10mm wrench and clean/inspect the screen inside, be carefull of the oring here too.. If the filter is OK, remove the float and needle vale from the carb by pulling out the hinge pin in the float, when you turn the fuel valve back on fuel should pour out into the catch pan, if not you need to remove, check, and possibly replace the fuel line.
If you've got fuel to the carb (fuel poured into the catch pan above), you need to remove, clean, service (lube, inspect) and reinstall the carb. There aren't many adjustments on modern small engine carbs.

Spark/Compression problems:
Get a spark tester and check that the engine gets spark with the plug installed. If it does not, you have to determine why starting at the run/stop switch. Find the (usually black) wire at the center of the switch and disconnect it. Check for spark again, if you got spark you may have a bad switch. If you didn't get spark you probably have a bad ignition module which is located under the blower housing and above the flywheel.

The only good way to check compression is to use a compression tester. You should see 50 psi or more of compression for the engine to work. If you don't have good compression, especially if you get very low compression check the valves first then the head gasket.

If everything checks, you have fuel, compression, and spark but the engine still won't run. You may have a broken flywheel key. To check that you have to remove the blower housing, the ignition module, and then the flywheel.

Hope this helps narrow down the problem, feel free to ask me directly if you need more help.

Carl

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