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I own an '82 Yamaha 750 Maxim. I have single air breathers for my four carbs and I removed the carbs to clean out and install air filters. Before I removed the carbs the bike ran fine, however now it won't start.

I do know the carbs are getting gas to the bowls, and the spark plugs have a spark but for reasons beyond me, I can't get the bike to start now. I have tried starter fluid, and putting gas directly into the cylinders, but I still cannot get it to start. Let me also add, since then, I have removed and cleaned the carbs twice more, thinking I might have missed something when cleaning them.

Can anyone suggest why it won't start?

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  • what are the symptoms of it not starting when using starter fluid? does it stutter? or does it not fire at all? did you connect the High Tension leads to the correct plugs?
    – Mauro
    Jul 23, 2013 at 11:31
  • oddlly, no will not even bark, and yes all wires r to the right plugs. all it does is turn over
    – user3454
    Jul 23, 2013 at 17:31
  • Are you getting compression? has anything else been changed? it should at least splutter with starting spray unless something is drastically wrong - timing, ignition, compression. Any fuses blown?
    – Mauro
    Jul 23, 2013 at 17:40
  • yes there is compression, and no, nothing else has been changed, trully mind boggleing, ran fine before i cleaned carbs and added filter, why would the gas not go from carbs to cylinder
    – user3454
    Jul 23, 2013 at 17:46
  • i even removed air filter to see if a vacuum was felt from back of carbs and felt something
    – user3454
    Jul 23, 2013 at 17:48

6 Answers 6

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My guess is you flooded it (possibly stuck needle after the first rebuild). And by putting gas and starting fluid directly in the cylinders, you have privacy made it worse and washed out the rings on the piston and have essentially lost compression. Typically, I would turn off the gas tank petcock so that no gas is getting to the carbs, and crank it for a good ten to twenty seconds (you can usually here compression returning, or it will spit and sputter and nearly run). It may take longer, but give the starter a good thirty seconds rest between the ten to twenty second cranks. Once it spits and sputters, or you can definitively hear compression returning, turn on the gas and try again but do not give it any throttle!

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If the only thing that changed between then (ran fine) and now (won't fire) is carburetors / fuel, and if it now won't fire on ether, then either your ignition timing is suddenly far out of whack for totally coincidental reasons or else your spark plugs are now too wet (with fuel) to fire from flooding. Pull out the plugs, let them air out, let the cylinders air out. When you can no longer smell fuel from the spark plug holes, put the plugs back in & try again to start - this time with no choke at first.

While the plugs are out, clean them up & check their gaps.

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I had a similar thing on a Suzuki. It turned out in the end the coils had got wet inside, causing a short. It just happened to be coincide with me cleaning carbs and sorting a rocker cover leak.

Brilliant spark with the spark plugs out of the machine; no spark under firing conditions. I used an autotune device to see inside the cylinder whilst running.

Solution: new coils, or could try baking them over night at about 110-120 F to force the moisture out.

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Have you checked to make sure you don't have a vacuum leak? This can be caused by any hoses that aren't plugged in but it can also be caused by a bad carb gasket or a carb that isn't tightened to spec. Checking for vacuum leaks is hard without the engine running, but you can do a spot test by simply pulling off a vacuum hose and putting your finger over the hose when you crank the engine. You should be able to feel a little bit of suction.

Another possibility is that your carbs are not choking properly. I am unfamiliar with this particular bike but I would assume the choke is electric. It is possible that the wires for the choke weren't hooked up correctly, or that the choke is stuck open for some reason.

These are my best ideas, but I'm sure someone more familiar with the bike might be able to suggest more specific things to check.

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  • no it does not have an electric choke, it is manual, and as far as vacuum hose, the only vacuum line on the bike, is from the fuel tank to the boot, the only lines that even go to the carb is the throttle cable, the choke cable, and the fuel line, but thank you to takeing the time to reply
    – user3454
    Jul 22, 2013 at 21:18
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Have you check your spark? If you got absolutely nothing with starting fluid your spark plugs probably might not be firing. Pull a spark plug and hold the tip against the engine case with the plug wire attached. Crank the engine and you should see a fat blue spark. If not check the points/ignition coils, CDI or stator.

Make sure to hold the only the spark plug boot and don't touch the spark plug. Maintain constant contact with the engine case or you might damage a good working ignition system.

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I also have a 750 maxim .There is a simple rule when starting this bike.When the engine is COLD,full choke and No throttle until it starts.If the bike has been sitting for a few months then turn the petcock selector to PRIME until it starts.I usually then ride with the Choke on 1/4 for the first 5-10 minutes.If the engine is Warm,No choke and 1/4 to 1/2 throttle.If you give it throttle before it starts when the engine is Cold it will prevent it from starting.I have owned my bike for over 30 yrs and it has always started.GOOD LUCK

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