Sputting really bad at high RPM. - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 22 (permalink) Old 03-22-2012, 08:45 PM Thread Starter
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Sputting really bad at high RPM.

Hello all,

I am having an odd problem with my bike. It starts up instantly, idles fine, and rides like a dream through all the gears as long as I stay under 4000 RPM.

Right about 4000+ RPM it starts sputtering real bad, and at 5000 plus it gets downright terrible where I can feel it shaking and sputtering if I try to ride on the expressway.

If I give it full throttle, either riding or parked, it will accellerate smoothly and cleanly until it hits around 4000+, no problems at all.

It does have the "ears shaved" as I believe it is called. The stock air boxes are off and there are just some small round filters over the intake ports. The previous owner also punched out the baffles, so it actually sounds great.

After some discussion with the local bike shop, he said it probably needs re-jetting. Does that sound right?

Also, if I return it to the stock air boxes but leave the baffles punched out for sound, do you think that would help or do I need to buy a new stock exhaust pipe?

Thank you for the help.

-Jeff
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post #2 of 22 (permalink) Old 03-22-2012, 10:12 PM
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Quote:
Originally Posted by JRaschke11 View Post
Hello all,

I am having an odd problem with my bike. It starts up instantly, idles fine, and rides like a dream through all the gears as long as I stay under 4000 RPM.

Right about 4000+ RPM it starts sputtering real bad, and at 5000 plus it gets downright terrible where I can feel it shaking and sputtering if I try to ride on the expressway.

If I give it full throttle, either riding or parked, it will accellerate smoothly and cleanly until it hits around 4000+, no problems at all.

It does have the "ears shaved" as I believe it is called. The stock air boxes are off and there are just some small round filters over the intake ports. The previous owner also punched out the baffles, so it actually sounds great.

After some discussion with the local bike shop, he said it probably needs re-jetting. Does that sound right?

Also, if I return it to the stock air boxes but leave the baffles punched out for sound, do you think that would help or do I need to buy a new stock exhaust pipe?

Thank you for the help.

-Jeff
Putting back on the stock air system will restrict air-flow appropriately for the stock jets, and should determine if that's the cause of your issue. The baffles won't affect the pressure THAT much, I don't think.

My 'new' bike is bogging at 4000-5000, but once you push through 5k it runs fine. It's most likely electrical on that one, though.

1986 Kawasaki Vulcan 750
NGK Iridium Plugs #7803/DPR7EIX-9
Duralast Gold ETX15 AGM Battery
Coastered & Shaved
TOC MCCTs
Metzeler ME880 [110/90-19, 170/80-15]
Balance Dampers Replaced
Tuxedo Mod
Rebuilt Forks w/ Progressive Springs
V&H Cruzers
VN750.com Grill Cover
Meanstreak Seat
Emgo 23-92411 Handlebars
MOSFET FH012AA R/R


1990 Kawasaki Vulcan 750

1998 Honda VFR800 FI

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1989 Pontiac Firebird Formula 350
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post #3 of 22 (permalink) Old 03-23-2012, 12:01 AM
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If it sputters when parked, it's likely not your carb vent line but poor jetting. It's possible the PO did not use a big enough... Or maybe too big .... main jet.

If you do a search here on "earshave" you'll find jetting info. Write it down and give it to the shop.... Or tackle the job yourself. If you still have the stock exhaust... But just drilled out baffles, it won't effect your jetting issues.

As a test, try opening the throttle up just past 4000 rpms. When it begins to stutter...pull open the choke. If it seems to help....your main jets are too lean. If it seems to make it worse, your mains are too big. Not conclusive, but good info if you take the bike in to the shop.

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post #4 of 22 (permalink) Old 03-23-2012, 12:11 AM
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Remove the air filters completely and give it a run. If it runs good the filters are the problem. The late Ron our friend and vn guro gave me this advise. He said to use the rc-2340 K&N air filters.

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post #5 of 22 (permalink) Old 03-23-2012, 05:23 PM
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That was just happening to me, the vent hose was off the right ear, and facing out to the side. Once I put it back, the bike ran great again at high speeds. Maybe your vent hose needs to be moved? I know you no longer have ears, but maybe there's something up with the venting? before I covered it like that, my bike was running horribly at high speeds, no power at all...



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Bought 4/2011 28k Miles,
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post #6 of 22 (permalink) Old 03-23-2012, 06:12 PM
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...sounds like fuel starvation...my one cyl was doing similar until I saw one of the fuel lines bent and crimped. Higher RPM requires more fuel...and air accordingly for that matter.
May wanna check the flow from the petcock too. Should be a nice even stream (like after a night of beer at Murphy's).



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post #7 of 22 (permalink) Old 03-24-2012, 04:41 AM
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Could also be a bad coil, or just dirty carbs.

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post #8 of 22 (permalink) Old 03-24-2012, 10:27 PM
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Quote:
Originally Posted by niterider View Post
Remove the air filters completely and give it a run. If it runs good the filters are the problem. The late Ron our friend and vn guro gave me this advise. He said to use the rc-2340 K&N air filters.
I had issues after my ear shave and finally figured out it was the cheap universal filters. Had to order the K&N's.

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EMGO Handlebar, V&H Exhaust, Drop Shocks, Raised/Painted Fork, MeanStreak Seat, Tank Bib, ME880 Oversize Tires, Engine Guard, Custom Mirrors, Chris Products Turn Signals, Ear Shave, 150/42 Jets, PINGEL Fuel Valve, MCCT, Volt Meter, Shendegen R/R, AGM Battery, Coastered, .020 Coils, Relo Gauges & Headlamp, SilverStar Ultra, LED Flashing Brake Light, Center Stand Delete, WOLO Airhorn.
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post #9 of 22 (permalink) Old 03-28-2012, 06:51 PM Thread Starter
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Thanks for all the suggestions. I am going to put the stock air boxes back on and see if that helps and try a few other things. I will report back what I find so I can hopefully help others.
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post #10 of 22 (permalink) Old 04-05-2012, 07:30 PM
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I have similar issues and I just took the tank off and petcock out of the tank to paint the bike, which came out amazing for rattle can!!! but I know I put all the fuel lines on the petcock correctly and it started up fine but it seems to be right around 40mph and any kind of uphill. Im concerned that taking the tank off may hav messed up my air/fuel ratio even tho I have stock ears and adjusted my air/fuel knob after the issues started. I also took a ride for 1 1/2 hrs today and it only happened again at 40mph and uphill...and at that speed in 4th gear our bikes i believe are around 3000-3500rpm and it will do it in 5th as well obviously at lower rpms...I dont want to hav to take it to my local bike shop so anyone's help will be greatly appreciated to solve my issue


2003 VN750
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-VN1600 Meanstreak seat(modified)
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-highway pegs!!!!!
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