Can't drive 80 ( Sorry, doesn't rhyme :) ) - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 13 (permalink) Old 04-25-2012, 01:26 PM Thread Starter
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Question Can't drive 80 ( Sorry, doesn't rhyme :) )

So today, decided to have a little fun on the highway. Put the hammer down and opened her up to see how fast I could get. Once I hit 80MPH, it seemed like the bike didn't have the power to go beyond that. Motor was not cutting out. Bike seemed perfectly fine, just did not want to accelerate past 80 for some reason.

As far as I know, everything is stock except the pipes.

Any thoughts? I have this odd feeling I gonna find myself tuning the carbs soon. I do want to richen them up some, not fond of lean fuel mixtures. I've seen what that does to R/C nitro motors. They gain huge power momentarily, but overheat rapidly.

Thanks!

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post #2 of 13 (permalink) Old 04-25-2012, 01:48 PM
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You may need bigger jets. I am sure somebody here with more carb experience can give you a more definitive answer.

1986 Kawasaki Vulcan 750
NGK Iridium Plugs #7803/DPR7EIX-9
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Coastered & Shaved
TOC MCCTs
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post #3 of 13 (permalink) Old 04-25-2012, 01:54 PM
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Do you have the stock airfilters?

Not being able to go fast is a horrible problem and should be fixed ASAP...

Check that your throttle does indeed open the butterfly's all the way. Make sure the carb vent hose in the right ear is properly inserted and not bottoming out. (many cut the end at a 45 degree angle to prevent this)

New plugs can't hurt. You are burning regular gas right?

And BTW.....you "ride" a bike, you don't "drive" it....

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Last edited by Knifemaker; 04-25-2012 at 02:02 PM.
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post #4 of 13 (permalink) Old 04-25-2012, 03:05 PM Thread Starter
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Air filters are stock, I am burning 87 octane gas as well. The acceleration really seemed to disappear once I hit 80. Maybe I am expecting something when there is actually nothing. I dunno. Just thought it would be more peppy in the higher rpm range. Not like I make a habit driving above the posted speed limit.

I will check that hose when I can.

Thanks!

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post #5 of 13 (permalink) Old 04-25-2012, 05:08 PM
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80 is too soon to loose acceleration... I hit above 100 mph, never gotten to where it doesn't accelerate any more because after i hit about 110 i get scared and let it go back down to about 80
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post #6 of 13 (permalink) Old 04-26-2012, 01:23 PM Thread Starter
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Still haven't looked at the carb air hose yet.

The bike plows thru the RPM ranges easily in other gears, just 5th seems to take a while once I hit 80. I do believe new plugs are in order as I can hear occasional misses; however, not bad enough to cause the bike to lose power.

I don't go that fast often, so kinda hard to diagnose.

Peace.

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post #7 of 13 (permalink) Old 04-27-2012, 09:26 AM
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There is a vent tube that goes into one of the air filter housings (right side?). It is supposed to fit into a rectangular opening in the rear of the housing. If it falls out or bottoms out against the housing, it will cause high speed missing issues. Check to see if yours is inserted into the opening and cut the end at a 45 degree angle to keep it from bottoming out.

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post #8 of 13 (permalink) Old 04-27-2012, 10:16 AM
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Quote:
Originally Posted by flitecontrol View Post
There is a vent tube that goes into one of the air filter housings (right side?). It is supposed to fit into a rectangular opening in the rear of the housing. If it falls out or bottoms out against the housing, it will cause high speed missing issues. Check to see if yours is inserted into the opening and cut the end at a 45 degree angle to keep it from bottoming out.
Good ideas bare repeatiing? See post # 3. Lol

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post #9 of 13 (permalink) Old 04-27-2012, 02:21 PM Thread Starter
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Alrighty, I replaced spark plugs. Old plugs seemed to be burning fine. In fact, they did not look all that used. I also checked the carb vent tube, it is where it needs to be. The shop gave me plugs DPR8 and the ones I pulled are DPR7. Could not see visually any difference. Could someone chime in on the difference, if any. Thanks.

Drove the bike around the block, trying to reach upper rpm range. I did not notice any missing. Will be a while b4 trying to reach 80+ again.

A side question though, does anyone know what the round cap with a leg pointing to the rear is on the carb? It has two small screws on top and bottom and sits above the reed plate. Just a curiosity. Thanks!

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post #10 of 13 (permalink) Old 04-27-2012, 06:31 PM
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Quote:
Originally Posted by blazblu82 View Post
Alrighty, I replaced spark plugs. Old plugs seemed to be burning fine. In fact, they did not look all that used. I also checked the carb vent tube, it is where it needs to be. The shop gave me plugs DPR8 and the ones I pulled are DPR7. Could not see visually any difference. Could someone chime in on the difference, if any. Thanks.

Drove the bike around the block, trying to reach upper rpm range. I did not notice any missing. Will be a while b4 trying to reach 80+ again.

A side question though, does anyone know what the round cap with a leg pointing to the rear is on the carb? It has two small screws on top and bottom and sits above the reed plate. Just a curiosity. Thanks!
Could you give us some numbers here. This bikes when running right can easily reach up into the red line.
You may consider checking your vaccuum line from the carb to the petcock.

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