I just brought this 1982 Yamaha XJ750 Maxim and the first two days it started up well. However today when I tried to start it, the bike wouldn't start. It cranks but never catches.

I think it has to do with the gas because in my haste to start the bike I forgot to turn the gas on and left it off initially. Yet even when I turned it on it is still yet to full start after I have tried cranking it for a good ten minutes. I am completely lost. I just started getting into bikes and don't know where to go. Please help! thank you

  • Have you checked the basics? Is there fuel? Is the battery charged enough (ie does it sound like its turning over at the right speed) Is it parked out in the cold? Motor is a 4 stroke so no oil to mix.
    – Criggie
    Apr 14, 2022 at 6:25

2 Answers 2


I'm not familiar with this particular bike but many from this era have a vacuum operated fuel valve.

These usually have a PRIME or PRI setting to force fuel to flow even without the engine running to pull the vacuum and open the fuel valve.

What happens is that you run out of fuel and the carb bowls are empty and there is nothing to start the engine. Normally there is enough fuel in the bowls to get the engine started and then the vacuum valve will open up and let more fuel in.

Check your fuel valve for the PRIME position and turn it that way and wait about a minute, then try to start the bike normally. You may need to add some choke.

If it started, turn the fuel valve back to the "NORMAL" position so that the fuel delivery will stop when your shut off the engine.

If it doesn't start then there may be a problem with the fuel valve or tubing and you'll want to investigate that further. The PRI position usually has a separate and LOWER fuel pickup screen in the tank and that can become clogged with debris over time. This is an older bike and there may be bits of dirt or rust or other gunk that has accumulated. If needed you may need to drain the tank and remove the fuel valve assembly and clean it and/or replace the screens.


First make sure there's fuel in the first place, and the fuel valve is open. Then quickly twist the throttle to full three or four times before cranking it again. When you crank the throttle quickly it activates an accelerator pump in the carburetor which squirts extra fuel into the throat, the purpose is to keep the engine from stalling after coarse throttle inputs. This may pump enough fuel into the carb to get things started. Don't overdo it though, as too many twists can flood it.

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