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post #1 of 8 (permalink) Old 05-02-2011, 02:55 PM Thread Starter
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bike losing power?

At first I thought I was imagining it but it's happened a few times, and I'm at a loss as to how to start to figure out what's going on.

Most of my riding is done at lower in-city commuting speeds - I spend most of my riding time in 2nd or 3rd gear, with only a few stretches of a few minutes at a time in 4th gear. I usually shift up at around 5K RPM. Rarely, like when crossing a bridge that for some reason has no traffic, I can get up to 5th gear.

The last time that happened, a 5th-gear-worthy stretch on the 59th St. bridge, I found that revving my engine up to 5K RPM wasn't moving me as fast as I thought I should be going. Usually 5K in 5th gear gets me to over 65 MPH, close to 70 MPH, and I was barely doing above 60. Hmm.

This past weekend was the first time in a while I got to take an extended highway trip and I found it nigh impossible to get my bike over 70 MPH. I usually cruise at 65-70 MPH anyway, but it was very strange, it felt topped out. And if I hit an uphill incline I could be nearly WOT and the engine wouldn't rev past 5,500 RPM and I'd be doing around 50 MPH.

Something isn't right but what do I check for? I just changed my oil a few weeks ago, along with other routine fluid changes (brakes, coolant, etc.), and nothing seems particularly amiss otherwise. Spark plugs seem OK but they're about 2 years old; would old plugs factor in a situation like this?

I'm a regular user of SeaFoam so I wouldn't suspect my carburetors, or should I?

"Until you have the courage to lose sight of the shore, you will not know the terror of being forever lost at sea." (Despair.com)
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post #2 of 8 (permalink) Old 05-02-2011, 03:08 PM
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Sounds like you've rarely, if ever, opened up the mains on that bike. How long have you been putt-ing around city streets on it ? I wonder if they (the main needles) could be stuck ? Clogged main jets ?

~~C8> Ratt
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Done: Coastered, .020 ign., Iridiums, VM
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Next: LED's
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post #3 of 8 (permalink) Old 05-02-2011, 03:14 PM Thread Starter
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Oh I've definitely done long highway rides on it, enough to feel like something's different/wrong with the bike, just not in a while due to a winter layoff. I commute-ride year round (a 6- or 7-week layoff from December through early Feb was the longest in a while) but put in 3-4 hour rides a few times a month during the warmer months. This was probably the first extended higher-speed ride I've done this year though.

"Until you have the courage to lose sight of the shore, you will not know the terror of being forever lost at sea." (Despair.com)
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post #4 of 8 (permalink) Old 05-02-2011, 03:19 PM
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I'm no expert, but it does have the marks of a fuel delivery issue. If you have any wrenching skills, I'd take a day and do a carb inspection/cleaning. I suppose the vacuum passages to the main needle diaphrams could be blocked somehow.
Maybe someone with more confidence will comment soon.

~~C8> Ratt
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'91 VN750 - Cosmic Splendor/Candy Wine
Done: Coastered, .020 ign., Iridiums, VM
Plexistar II, MCCT's, Relocated MOSFET
Next: LED's
Will Do: Horns, Shave(maybe)
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post #5 of 8 (permalink) Old 05-02-2011, 04:15 PM
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First check your throttle cable adjustment. It just might not be opening all the way. Then check the carb linkage to see if it is opening all the way.

Then check you fuel delivery.

You might also have a bad diaphragm in a carb or your vent line is clogged or broken.

I would look there first.


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post #6 of 8 (permalink) Old 05-02-2011, 04:39 PM Thread Starter
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For my continuing education, what sorts of things contribute to issues like this, and what could I or should I have done to avoid it (even if it turns out to be something else in this particular case)?

For example - if it turns out to be the carbs, would this be attributed to carb gumming in just 6 weeks of non-use (and without fuel stabilizer)? I don't usually winterize my bike because I usually ride it a few times even over the winter during a 2-3 day thaw or warm spell; this past winter was the first time in 5 years that I had gone as long as 6-7 weeks straight without riding it once.

Or if it turns out to be the throttle cable, how does that wear out, just normal aging/wear and tear that I have to budget for every... 2 years, 5 years? (This is a 2004 bike I bought used and I haven't swapped any cables)

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post #7 of 8 (permalink) Old 05-02-2011, 05:05 PM
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Doing more than riding your bike, and learning and performing maintenence on your bike might be kin to sailing a ship past the horizon. You take risk, you conquer, and you reap the rewards of confidence, and money in the pocket. I like your favorite quote, it has meaning.

Get a Clymer's repair manual for the bike. Do your homework by reading the periodic maintenence section. Stay with this awsome forum, and check out "The Vulcan Verses". The time you invest will be returned to you in quality riding time. Get on an open road and open her up every now and then. That's how I keep my bike running great!


~~C8> Ratt
________________________
'91 VN750 - Cosmic Splendor/Candy Wine
Done: Coastered, .020 ign., Iridiums, VM
Plexistar II, MCCT's, Relocated MOSFET
Next: LED's
Will Do: Horns, Shave(maybe)
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post #8 of 8 (permalink) Old 05-02-2011, 05:22 PM
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Quote:
Originally Posted by robardin View Post
Or if it turns out to be the throttle cable, how does that wear out, just normal aging/wear and tear that I have to budget for every... 2 years, 5 years? (This is a 2004 bike I bought used and I haven't swapped any cables)
Cables stretch over time. when you get the point where the adjustment nuts have reached the end...it is time for a new cable. There is no set lifespan that I know of. My dirt bike ate clutch cables fairly quickly. If lubed and adjusted correctly a cable can last the life of the bike....but they can stretch and need adjustment.

I would think if you are using Seafoam , letting the bike sit 7? weeks should present no issue. But I just read somewhere that gasoline with ethenol (10%)
does not store as long as normal fuel.

But If you recently filled the tank I doubt that is the issue.

New plugs (iridiums) would be a good move no matter what.


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