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post #1 of 15 (permalink) Old 03-11-2012, 01:56 AM Thread Starter
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Valve Question:

I'm not sure where this question should go, but hopefully someone will help me out.

I have an '06 vn750a, all stock. I have noticed a problem with the overall acceleration of the bike. I can get it up to about 70 to 75 mph on a fairly flat surface, but if I hit any kind of rise, I would lose speed, very bad on freeways.

So far, I have adjusted the throttle cables, changed out the oil (yuck, sludge), changed over to a higher firing spark plug and a new battery. Each thing seems to help a bit, but still can't get much above 70.

I'm not looking to race, but if I need to get out of the way of something, I would like the option of "punching it" and moving.

A friend told me that the valves might be too tight and that the motor would have to be pulled to address this issue.

Any thoughts????????
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post #2 of 15 (permalink) Old 03-11-2012, 03:13 AM
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Two possible problems. Doubt its your valves. Not sure what you mean by "higher firing spark plugs" though.

One. Carburation- blocked jets, torn diaphragm, improperlly adjusted throttle.
Have you used SeaFoam? Have you checked your airfilters? Are you sure the carb vent hose is not bottomed out in the right airbox or has fallen out?
Are you sure both cylinders are firing?

Then..Can you get the bike to rev higher-- meaning you can only go 70mph but you can rev the motor past 6000 rpms.

Two. Clutch. Your clutch could be slipping. Does the bike sound diffrent when you try and go faster?

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post #3 of 15 (permalink) Old 03-11-2012, 06:17 AM Thread Starter
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Re: My Valve Question:

The clutch works fine in all gears, nice and smooth. In neutral I can rev it all I want. In fifth gear I can get up to 70 and my RPM is around 5k. Unless i'm going down a hill, that is the fatest and the highest RPM.

I need to check the air filters and probably clean them as well. And I will check the carb vent hose at the same time.

As far as the higher (hotter) burning plugs, I used the optional ones listed in the book: NKG-DPR8EA-9.

OH, I forgot, I also put in a bottle of Carb/Fuel System Cleanout when I refilled the gas tank.

The carburators were totally rebuilt by an actual mechanic (not by me).
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post #4 of 15 (permalink) Old 03-11-2012, 10:39 AM
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Quote:
Originally Posted by freebird573 View Post
As far as the higher (hotter) burning plugs, I used the optional ones listed in the book: NKG-DPR8EA-9.
Just for the record, the '8' in the part number indicates that it is a 'colder' plug than the '7' plug recommended for the VN750.

~~C8>
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post #5 of 15 (permalink) Old 03-11-2012, 01:08 PM
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I'd switch back to the stock plugs, or better yet the NGK iridium plugs reccomended by this forum.

Not sure who did your carb work, but they could have messed something up. And your clutch can seem perfectly fine but slip at high loads... But if you can't get it to run over 5000 rpms while moving in top gear, it's not the clutch.

You could be starving for fuel... (improper float height) you can have the wrong jets, the already mentioned torn diaphragm, or a clogged air intake.

If you are not sure about your mechanical ability, you might want to take if to a different shop and have them look at it.

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post #6 of 15 (permalink) Old 03-11-2012, 02:40 PM Thread Starter
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oops, ty for the correction on the plugs
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post #7 of 15 (permalink) Old 03-11-2012, 03:54 PM
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Quote:
I'd switch back to the stock plugs, or better yet the NGK iridium plugs reccomended by this forum.
You want the NGK DPR7EIX-9 Iridium plugs.

Gordon

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post #8 of 15 (permalink) Old 03-11-2012, 05:28 PM
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Agreed with Gordon,,Iridium plugs are a "must". Also KM theory,,"jet size" also sounds a possibility,as does float hight. If it was mine,i would get the carbs looked at,just for piece of mind (second opinion). Good luck.

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post #9 of 15 (permalink) Old 03-11-2012, 08:50 PM
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Be sure to check the petcock vaccuum hose for leaks.

02 honda sabre 1100
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post #10 of 15 (permalink) Old 03-12-2012, 01:08 AM
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Since someone "worked" on your carbs, I strongly suspect that is where the problem is. I am not much of a believer in coincidences. I suspect "messed with" rather than "rebuilt" is probably more accurate in this case. There are a lot of "mechanics" out there who could do a fine job messing up motorcycle carburetors. Also the symptoms point to the carbs, specifically fuel starvation. Unfortunately there can be a lot of causes for this, and pinning it down online can be difficult. How does the bike idle? Does it pop and sputter at higher speeds, or just won't go any faster? Does it just hit a limit, or does it surge at top speed, constantly slowing down and speeding up? Check and make sure the throttle is opening the carbs all the way. With the throttle all the way open, grab a hold of the throttle shaft o the carb (the one with the spring on it) and see if you can turn it further.

I am a motorcyclist, NOT a biker.


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2006 Sportster 1200 Low
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