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freebird573
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Discussion Starter #1
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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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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freebird573
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14 Posts
Discussion Starter #3
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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Member? ... check.
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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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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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Linkmeister Supreme
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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. :smiley_th
 

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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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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.
 

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freebird573
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14 Posts
Discussion Starter #11
I took it for a second opinion and I had two people tell me that due to the following:

1. Ripped foam on the left side air filter
2. Cool to the touch pipe on the left side
3. Too hot to touch pipe on the right side

That only one of my cylinders is firing and that I needed to try and see if a piece of that foam got stuck somewhere bad.

When I got home from that evaluation (which was free), I did notice some pops when I had it in the driveway and both pipes were too hot to touch.

So, I have taken off the airboxes totally and am trying to find a good diagram of how to disassemble the airbox to see if something is blocking and causing one of the cylinders to not fire.

The manual I downloaded from here (and thanks to whoever went thru that work) has kinda fuzzy pictures.
 

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I guess by airbox you mean the surge tank under the gas tank, if so you can't remove that without taking the motor out, also you say that both pipes were hot when you got back which indicates that both cylinders are firing.
 

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Sounds like the main jet is clogged on the carb feeding that missing cylnder. Sitting in your driveway the bike would be running on the idle circuit and that's why the cylinder came back to life.

You can feed s hose connected to a vacuum cleaner down the air intake in hopes of finding the missing chunk of airfilter foam. You really should pull the carbs to make sure it's not stuck in there. Might be possible to remove the top of the carb without having to take the whole carb off the bike. You didnt mention which cylinder was not firing.
 
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