Really bad hesitation - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
Carbs and Fuel System
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post #1 of 62 (permalink) Old 03-29-2020, 12:05 AM Thread Starter
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Really bad hesitation

So I just put the bike back together after redoing several items (new agm battery, iridium plugs, new wires, went from 42/142 jets with 2 shims to 40/140 with no shims, new oversized tires front and back, progressive springs, new fork seals, new brakes all around, the whole thing. Last year, before I laid it down, when I got on it, it had a really bad hesitation. When I had the carbs out to rejet them, I noticed that the nipples in the boots were not lined up 100% with the marks on the heads, so I rotated them, hoping this would solve the issue. Tonight was the first time taking the bike out, after the rear spline relube, and it is actually worse now. I will spray some WD40 around the boots, but what else would cause this? If I transition smoothly with the throttle, with the choke on, it is fine. If I hammer it, it stumbles terrible. I also have high flow vance and hines

'08 Road King Classic
'86 VN750:
Ear Shave, K&N Filters, Mean Streak Seat, AGM battery, Blue Wire Mod, Pick-up Coil Mod, Timing Advance Mod, NGK Iridium Plugs and Wire, LEDs, Bed Liner Paint Job, Over-sized Tires, New Brakes, New Fork Seals, Progressive Springs, Kick Stand Mod, Highway Pegs, 40/140 No Shims, Vance & Hines Exhaust, New Grips, Extra Wide Emgo Handle Bars
John 8:44, REV 2:9, REV 3:9 - If you were kicked out of 109 bars, would you think the problem was you, or the 109 bars?
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post #2 of 62 (permalink) Old 03-29-2020, 01:15 PM
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Quote:
Originally Posted by MSattler View Post
So I just put the bike back together after redoing several items (new agm battery, iridium plugs, new wires, went from 42/142 jets with 2 shims to 40/140 with no shims, new oversized tires front and back, progressive springs, new fork seals, new brakes all around, the whole thing. Last year, before I laid it down, when I got on it, it had a really bad hesitation. When I had the carbs out to rejet them, I noticed that the nipples in the boots were not lined up 100% with the marks on the heads, so I rotated them, hoping this would solve the issue. Tonight was the first time taking the bike out, after the rear spline relube, and it is actually worse now. I will spray some WD40 around the boots, but what else would cause this? If I transition smoothly with the throttle, with the choke on, it is fine. If I hammer it, it stumbles terrible. I also have high flow vance and hines
I had this exact symptom when the diaphragms in the carbs weren't seated. Looking all over the carbs for a vacuum leak by spraying carb cleaner/wd-40 is also a good idea.
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post #3 of 62 (permalink) Old 03-29-2020, 05:35 PM Thread Starter
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I’ll check for a leak, but when At any speed (even 4K) if I crack on the throttle, it stumbles terribly before picking up albeit bogged down. I’ve never balanced the carbs... do I need to add a shin?


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'08 Road King Classic
'86 VN750:
Ear Shave, K&N Filters, Mean Streak Seat, AGM battery, Blue Wire Mod, Pick-up Coil Mod, Timing Advance Mod, NGK Iridium Plugs and Wire, LEDs, Bed Liner Paint Job, Over-sized Tires, New Brakes, New Fork Seals, Progressive Springs, Kick Stand Mod, Highway Pegs, 40/140 No Shims, Vance & Hines Exhaust, New Grips, Extra Wide Emgo Handle Bars
John 8:44, REV 2:9, REV 3:9 - If you were kicked out of 109 bars, would you think the problem was you, or the 109 bars?
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post #4 of 62 (permalink) Old 03-30-2020, 07:01 AM Thread Starter
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Okay I sprayed wd40 around the boots, and the rpms did not drop. I had this issue with larger jets, but not as bad, and I reeked of fuel it was so rich. Now the smell isn’t as there.


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'08 Road King Classic
'86 VN750:
Ear Shave, K&N Filters, Mean Streak Seat, AGM battery, Blue Wire Mod, Pick-up Coil Mod, Timing Advance Mod, NGK Iridium Plugs and Wire, LEDs, Bed Liner Paint Job, Over-sized Tires, New Brakes, New Fork Seals, Progressive Springs, Kick Stand Mod, Highway Pegs, 40/140 No Shims, Vance & Hines Exhaust, New Grips, Extra Wide Emgo Handle Bars
John 8:44, REV 2:9, REV 3:9 - If you were kicked out of 109 bars, would you think the problem was you, or the 109 bars?
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post #5 of 62 (permalink) Old 03-30-2020, 07:42 AM
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The diaphragms are the rubbery parts of the slides under the "top" cover of the carbs. If they're not seated the slides can't come up properly. I had to use a bit of vaseline to keep them properly seated while I dropped the top covers down

You can check if they're working right by reaching into the intake side of the carb throat and lifting the slide up, letting it go, and listening for a small "woosh" noise

(You can access the diaphragms and needles to adjust shims withOUT taking the carbs off, just remove the gas tank)

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post #6 of 62 (permalink) Old 03-30-2020, 07:59 AM Thread Starter
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Okay, I’ll give that a check once the tank is empty. It makes the whooshing sound, as I made sure of that before I put it back together. Now this issue was present before and would be better when I used the choke, with the previous 42/142 jets. According to Spockster, it was running rich and lean. From what I’ve read, the 142 on the main is wasting huge amounts of fuel, which explains the rich smell and black plugs, so I don’t think that a lack of fuel is the problem. However, the problem got worse with smaller jets, or less fuel. Also, the left exhaust is louder. I’ve never synced the carbs, could this be the issue?
*edit* since I have had this issue before, could there be a tear in the diaphram? I didn't see one before. Could the diaphram be sticking?

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'08 Road King Classic
'86 VN750:
Ear Shave, K&N Filters, Mean Streak Seat, AGM battery, Blue Wire Mod, Pick-up Coil Mod, Timing Advance Mod, NGK Iridium Plugs and Wire, LEDs, Bed Liner Paint Job, Over-sized Tires, New Brakes, New Fork Seals, Progressive Springs, Kick Stand Mod, Highway Pegs, 40/140 No Shims, Vance & Hines Exhaust, New Grips, Extra Wide Emgo Handle Bars
John 8:44, REV 2:9, REV 3:9 - If you were kicked out of 109 bars, would you think the problem was you, or the 109 bars?

Last edited by MSattler; 03-30-2020 at 09:21 AM.
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post #7 of 62 (permalink) Old 03-30-2020, 08:27 AM
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post #8 of 62 (permalink) Old 03-30-2020, 08:34 AM Thread Starter
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Quote:
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Did you mean to say something?


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'08 Road King Classic
'86 VN750:
Ear Shave, K&N Filters, Mean Streak Seat, AGM battery, Blue Wire Mod, Pick-up Coil Mod, Timing Advance Mod, NGK Iridium Plugs and Wire, LEDs, Bed Liner Paint Job, Over-sized Tires, New Brakes, New Fork Seals, Progressive Springs, Kick Stand Mod, Highway Pegs, 40/140 No Shims, Vance & Hines Exhaust, New Grips, Extra Wide Emgo Handle Bars
John 8:44, REV 2:9, REV 3:9 - If you were kicked out of 109 bars, would you think the problem was you, or the 109 bars?
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post #9 of 62 (permalink) Old 03-30-2020, 12:25 PM
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Quote:
Originally Posted by MSattler View Post
Okay, I’ll give that a check once the tank is empty. It makes the whooshing sound, as I made sure of that before I put it back together. Now this issue was present before and would be better when I used the choke, with the previous 42/142 jets. According to Spockster, it was running rich and lean. From what I’ve read, the 142 on the main is wasting huge amounts of fuel, which explains the rich smell and black plugs, so I don’t think that a lack of fuel is the problem. However, the problem got worse with smaller jets, or less fuel. Also, the left exhaust is louder. I’ve never synced the carbs, could this be the issue?
*edit* since I have had this issue before, could there be a tear in the diaphram? I didn't see one before. Could the diaphram be sticking?

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If it runs better on the choke, it's starving for fuel. I'm not sure how I would've said it's rich and lean at the same time, but I would have to review if I could find it.

The woosh test is kinda just a preliminary check, will show if a diaphragm is blown wide open or not seated correctly. Small cracks can leak under vacuum and cause the slide to be slow to lift when you hit the throttle. Need to flex the rubber in front of bright light to check for cracks.

Where is the carb vent hose located? Re-reading the first post, it does sound like a diaphragm though.

Carb sync would have to be way off to begin causing problems. Visual check is easy when you're earshaved, just look to see if both butterflies (throttle plates) begin to open at the same time. Finger on one plate, eyes on the other.

Modern WD40 doesn't burn, but it will cause a stumble if there's a leak, same as water. If you happen to have a really old can, it should burn.

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post #10 of 62 (permalink) Old 03-30-2020, 01:08 PM Thread Starter
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Quote:
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If it runs better on the choke, it's starving for fuel. I'm not sure how I would've said it's rich and lean at the same time, but I would have to review if I could find it.

The woosh test is kinda just a preliminary check, will show if a diaphragm is blown wide open or not seated correctly. Small cracks can leak under vacuum and cause the slide to be slow to lift when you hit the throttle. Need to flex the rubber in front of bright light to check for cracks.

Where is the carb vent hose located? Re-reading the first post, it does sound like a diaphragm though.

Carb sync would have to be way off to begin causing problems. Visual check is easy when you're earshaved, just look to see if both butterflies (throttle plates) begin to open at the same time. Finger on one plate, eyes on the other.

Modern WD40 doesn't burn, but it will cause a stumble if there's a leak, same as water. If you happen to have a really old can, it should burn.
Not to sound stupid, but is there anything in particular I should be checking for, to make sure the diaphragm is fully seated? I placed it down in it's track, like I've done before and screwed on the cover. I honestly didn't give it much thought. It would make sense if there was a crack in them, because I can hear them open and close. Should I take off the ear pods to make sure they open and close at the same time? It won't hurt anything to run the engine with my finger in the butterfly? The carb hose is located on the nipple on the fuel gauge sending unit's cover. I only have the new WD40, but I have starting fluid... since I can't get a haircut, maybe I can get creative! I can check the parts stores, but are the diaphragms still able to be located?

'08 Road King Classic
'86 VN750:
Ear Shave, K&N Filters, Mean Streak Seat, AGM battery, Blue Wire Mod, Pick-up Coil Mod, Timing Advance Mod, NGK Iridium Plugs and Wire, LEDs, Bed Liner Paint Job, Over-sized Tires, New Brakes, New Fork Seals, Progressive Springs, Kick Stand Mod, Highway Pegs, 40/140 No Shims, Vance & Hines Exhaust, New Grips, Extra Wide Emgo Handle Bars
John 8:44, REV 2:9, REV 3:9 - If you were kicked out of 109 bars, would you think the problem was you, or the 109 bars?
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