Any idea what's going on with my '86 Vulcan 750? Major hesitation on low RPM's - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 12 (permalink) Old 05-14-2017, 01:24 PM Thread Starter
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Any idea what's going on with my '86 Vulcan 750? Major hesitation on low RPM's

Title and video below say it all. Some major firing issues. I already did the whole seafoam treatment and sprayed the whole carbs and jets with carb cleaner (no I didn't put the nozzle inside the jets). Seafoam I filled the bowls with 100% overnight then ran in the morning with a 50/50 mix until it ran out.

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post #2 of 12 (permalink) Old 05-14-2017, 04:36 PM
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Thant honestly doesn't sound too hesitant to me, especially if you haven't changed the jetting. Have you checked the air/fuel idle screw settings? Could be turned too far in and making the bike too lean (which would cause the hesitation you seem to be experiencing)

Mine used to be more hesitant until I jetted it up to 142/42. Stock is 138/38, which was sometimes too lean for the stock intake and exhaust, hence the litany of popping/backfiring on decel issues people have posted here.
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post #3 of 12 (permalink) Old 05-14-2017, 04:37 PM
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btw I love that look for this bike. That seat and the classic look fit really well. Handlebars back to the tail light, looks nice.
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post #4 of 12 (permalink) Old 05-14-2017, 06:01 PM Thread Starter
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Thanks, it makes all the hard work over the winter worth it I gotta paint the blue stuff to be black because of that new tank. Other than that I absolutely love the look.

As far as the hesitation, it's a lot more noticeable in person. The RPM's drop way low and it seems like one cylinder isn't firing down low. If I give it some gas both cylinders kick in. I have 140/42 jets in there, I could step the pilot down to 40 need be. My old tank had a bunch of **** in it so it's possible it could've clogged that pilot jet.

'86 VN750
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post #5 of 12 (permalink) Old 05-14-2017, 08:38 PM
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140/42 oughta be good for you, maybe fiddle with the idle mixture screws. I've found about 2.5 turns is good with 42's and open intake, you may need more since it looks like you have a custom exhaust. Probably have to fiddle with turning the rear carb's mixture screw out further then the front cylinder screw in order to reduce/eliminate popping on decel

as for crud in the carb from the gas tank absolutely. That happened to me too, so bad I could see gunk stirring up in the tank when I would gas it up. People like to get these bikes and let them sit forever. My carbs were NEVER clean enough until I pulled and deep cleaned/rebuilt them, even with B12, Seafoam, Techron, Gunk, Lucas, no cleaner would get it quite right because of how much sediment and varnish was in the carbs, gas tank, and petcock from months/years of bad gas
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post #6 of 12 (permalink) Old 05-14-2017, 09:42 PM
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definitely running on one cylinder down low.could be flooding. look into Wolfie's blowback method, it's a sticky in the carb section

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post #7 of 12 (permalink) Old 05-14-2017, 10:12 PM Thread Starter
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No, definitely not flooded Doc. Plugs are dry as a desert and I just fixed it being flooded (oil change, dried cylinders). I'll try fiddling with the mixture screws and see what happens. If that doesn't work it looks like I'll have to rebuild the carbs :/

'86 VN750
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post #8 of 12 (permalink) Old 05-15-2017, 09:29 AM
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Clogged pilot jet would be my guess....

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post #9 of 12 (permalink) Old 05-15-2017, 08:54 PM Thread Starter
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Quote:
Originally Posted by Knifemaker View Post
Clogged pilot jet would be my guess....
Even if I took the jets out and sprayed em with carb cleaner?
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post #10 of 12 (permalink) Old 05-16-2017, 09:00 AM
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Quote:
Originally Posted by snoopyonderdonk View Post
Even if I took the jets out and sprayed em with carb cleaner?
Did you run wire through them? There can be a tiny bit of crap that's not big enough to totally block the hole, but just big enough to alter the flow rate.
I find it easier to replace pilot jets than to clean them on bikes that have sat awhile...
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