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1979 XS750 running great and now won't start.


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So I recently got this beautiful 750, was running great for like a week. I took it on a short spin and it died while I was out. I figured it ran out of gas (tank was super super low) so I put some more in it and then started it up. It started but idled extremely low and would die unless i gave it throttle. When i gave it throttle it revved like it should, but when i rolled off the throttle it would hover for a second and then race up 700-1500 rpms before settling down very low and then dying. I let it sit for a day or two and now it just won't start. Was making a loud pop without starting so I figured it was flooded. I popped the plugs out and turned it over a bunch of times to clear it out then let it sit. Then I popped them back in (after testing for spark) and tried again, to no avail. I've got good compression and the carbs are filling as they should. I have the battery on a battery tender so I know it's fully charged. I can't for the life of me figure out what changed and why it won't start. Any advice would be amazing.

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Just a guess here but are the carb slides moving smoothly? Just need one to bind and it can really spoil your day. Also check the throttle cable for binding, it might need an oil or replacing .

Also you might need to whip them off and clean them, you don't say if it has sat all winter and it might be just old fuel gumming up the works.

This might help, sorry if you know all of this but we have to assume sometimes that folks know nothing:)

https://youtu.be/l6QCYOCYPXM

Once you have done that and it still won't start come back and we can try something else!

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On 6/4/2021 at 1:52 AM, slice said:

Just a guess here but are the carb slides moving smoothly? Just need one to bind and it can really spoil your day. Also check the throttle cable for binding, it might need an oil or replacing .

Also you might need to whip them off and clean them, you don't say if it has sat all winter and it might be just old fuel gumming up the works.

This might help, sorry if you know all of this but we have to assume sometimes that folks know nothing:)

https://youtu.be/l6QCYOCYPXM

Once you have done that and it still won't start come back and we can try something else!

You are amazing! Great call, I went to take a look at the carbs right after you suggested they might be the culprits. I found evidence of leaking or something not right around the float gasket on carb #2 and realized that what the small amount of liquid I witnessed coming out of the airbox after dropping must have been gas leaking backwards into the air filter and box from the carb which would explain why I can't get it started now and maybe why it flooded. Also noticed that one of the vacuum lines to the petcocks was kinked in a bracket which might help explain my idling problems. Anyways, all of this is grand speculation. I'm finally back in town and can start trying to fix this now. I'll let you know how things go. Thank you again!

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