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Loss of Power not related to Electrics

8K views 8 replies 6 participants last post by  Jasonjetski 
#1 ·
Searching all Forums here produces some power-loss stories, but not quite like mine, so I’m posting a new thread. The following happens to my 2007 Kawasaki Vulcan 900 Classic, 4300 miles, purchased 1 year ago with 1200 miles on it. It had a sudden single-occurrence event of a 30% power loss within 2 months, took it back to dealer, they cleaned the fuel intake (said there was a little bit of debris, but not unreasonable) and it performed fine for the next 5 months. On the way back of a 600-mile round trip (300 each day, 4 days apart) it happened again at the halfway point back and remained for the rest of the trip. Did nothing, and it was fine for another 4 months, but for the last 3 months has consistently performed as follows:

When I start out, I ride about 2 miles to get to the interstate, then 10 miles on the interstate with absolutely no problem, easily merging, put on the throttle to get to 70mph from 50 merge speed with ease in two seconds. Can go on any hill at 80 and clearly feel that there's still more power should I desire it. At 12 miles of continuous 75-85mph uphill or down (nothing but shallow hills, worst case maybe 4% grade), it starts losing power, to where it gradually decreases to max of 70-75mph, even downhill. It'll do this again at about 20 miles, and again at 30, to the point then that it won't even do 65mph going downhill; range is 50-62mph on the interstate, period. Increasing throttle in 5th gear actually acts as if downshifting: higher whine, loss of power & speed.

Once in this mode, nursing the throttle to eke out a measly 5mph requires 10-15 seconds, and nursing the throttle at around 70% and never more than 75% is necessary to keep it going at its highest possible speed, where at the start of the ride keeping the throttle at around 80-85% coasts beautifully, and kicking it to 100% provides immediately responsive passing power.

Getting off the interstate to take back roads (tired of annoying poor truckers behind me) it'll be sluggish at all gears, but I can at least generally stay at the speed limit (but annoy people behind me when an uphill of more than half a mile appears in a speed limit of 55). If I stop for coffee and give it a rest for half an hour, it'll regain most of its power, but then go back into the power-loss mode soon enough.

No electrical anomalies, and the problem seems to me to be a general motorcycle engine at any CC (i.e., seems to be a general engine mechanics problem, unless there’s something quirky known to exist with a valve or component used only in the VN900, which I sincerely doubt). The bike has backfired only once ever — on a recent ride, when I was trying different throttle levels just as the bike’s predictable first loss of power for the ride occurred at 12 miles.

This behavior holds for any fuel vendor (Shell, BP, Chevron, Exxon), any octane rating (87-93 O+M/2), any fuel octane booster or fuel system cleaner (though haven't tried Sea Foam), any level of tank fill, any weather (55F-95F, overcast, drizzle, sunny), any atmospheric pressure: Atlanta = 700 ft above sea level on up to the North Carolina border (1700 ft).

I've spent about 1000 miles of testing this while putting effort into controlling parameters so as to be precise and cover the bases; and sorry it's so long, but that's to give y’all as much info as possible -- I so dislike it when people post a two-sentence description on any topic and then expect a decent diagnosis ["My car slows down every once in a while. Got any ideas?" How about, "Take your foot off the break?"]

I feel it certainly can’t be fuel filter/injector cleanliness — surely behavior both comparing rides and intra-ride would be somewhat random, correct? There's no way I can do that 600-mile ride again through the Blue Ridge unless my power loss problem is solved.:frown2:
 
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#3 · (Edited)
I would say 'No', in that it still runs utterly smoothly (even though it's sluggish to pick up speed), and even continues to have a smooth, rhythmic purr per normal, both in motion and when idling at a stoplight. Only when increasing the throttle past 75%, does it make the sound somewhat "choppier", but nothing like I'd imagine that a single-piston machine would sound like to make the bike continue to run at 70mph.

I suppose I could be incorrect, but it should become quite a different sound to be hurtling 850 pounds at 65mph on 2 cylinders with all strokes running per normal, to suddenly be doing the exact same speed on exactly half the resources -- the loss in strokes should make it sound unbelievably horrid, like a 2-stroke lawnmower, correct?
 
#4 ·
75-85% throttle to go 65-75mph? when it is running fine? MAYBE Half throttle at the most.
If both cyl. are running, I think the full system would be suspect, Pump/lines/injectors/ECU.

If anyone can help you diagnose it Sfair is THE one.

Good Luck and keep us posted(mine is a 07)
 
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