Bogging under load - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 9 (permalink) Old 08-05-2018, 02:59 PM Thread Starter
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Bogging under load

I filled up my tank yesterday and rode about 20 miles. I washed the bike this morning - gentle water, nothing extreme. When I went out for a ride this afternoon I began bogging when under load. It bucks like a bronco! If I gradually roll on throttle it seems fine but if I twist it hard it goes buckety buck. I thought maybe the gas wasn't great so I put in a can of sea foam, and I sprayed carb cleaner down the vent tube under the gas cap. I waited a while, and drove around a bit. No change. Any thoughts?
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post #2 of 9 (permalink) Old 08-05-2018, 09:09 PM
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Drain your carbs through a 3/16" x 18"-24" hose into a glass jar and see if there's water in there. It'll be on the bottom under the fuel. A 3mm Allen wrench fits the drain valve screw.

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post #3 of 9 (permalink) Old 08-06-2018, 07:13 PM Thread Starter
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Thank you for the suggestion. I drained both carb bowls and the fuel was pristine. I'm posting on the engine string so see if anyone thinks it could be mechanical.
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post #4 of 9 (permalink) Old 08-06-2018, 09:06 PM
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if it happened after you washed the bike it's probably water in the carb vent tube. if you have the stock air boxes you can find it plugged into the upper middle section on the right airbox, between the back of the airbox and the bike frame. try and shake it out or let it dry out, that can cause all kinds of issues.

otherwise, very unlikely it's mechanical. probably carb (fuel) or electrical. check coil wires and such, I've had something as simple as the power wire to the front coil being loose cause all kinds of scary problems

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post #5 of 9 (permalink) Old 08-06-2018, 10:05 PM Thread Starter
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Thank you for the reply. The vent tube was fine - I don't go crazy with water when I wash it. I checked the coil wires but they were all tight with no obvious problems.

Last edited by T-Bone; 08-06-2018 at 11:03 PM.
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post #6 of 9 (permalink) Old 08-07-2018, 12:18 PM
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Maybe weak fuel delivery, not enough volume/fuel flow. Like a restriction in the fuel lines, dirty screen on the petcock pickup in the tank, poor flow through the petcock.

Could check your charging volts, mine bucks when the charge volts drop too low, straightens up when the voltage recovers..

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post #7 of 9 (permalink) Old 08-08-2018, 09:34 AM Thread Starter
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I took off the air cleaner tube and manually worked the vacuum slide a few times. On the front cylinder side it had a little resistance and made a "click" when I first moved it, but then it went up and down smoothly with a nice little "woosh" sound. The rear cylinder side was fine. I buttoned it up and took it for a ride and it was perfect. I ride regularly, the gas was clean, and there was no dirt or varnish on the parts, so I don't know what hung up the slide. I guess any repair that costs zero dollars is nothing to complain about!
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post #8 of 9 (permalink) Old 08-08-2018, 12:04 PM
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Quote:
Originally Posted by T-Bone View Post
I took off the air cleaner tube and manually worked the vacuum slide a few times. On the front cylinder side it had a little resistance and made a "click" when I first moved it, but then it went up and down smoothly with a nice little "woosh" sound. The rear cylinder side was fine. I buttoned it up and took it for a ride and it was perfect. I ride regularly, the gas was clean, and there was no dirt or varnish on the parts, so I don't know what hung up the slide. I guess any repair that costs zero dollars is nothing to complain about!
May have had a sticky slide and the testing freed it up.

If the problem returns, you might try hosing the slides with carb cleaner spray. That's something I forgot to do when I cleaned the jets on mine.

Some light polishing of the slides with fine steel wool or fine scotchbrite can help. They get wear patterns from all the up and down. You'll want to polish with the same up/down motion, not side to side, which could make them stick more.

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post #9 of 9 (permalink) Old 08-08-2018, 03:03 PM Thread Starter
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Good advice. Thank you.
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