doesnt want to rev down when changing gears - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 29 (permalink) Old 09-01-2009, 12:28 AM Thread Starter
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doesnt want to rev down when changing gears

Just got a 1995 VN750A11 and my only complaint so far is that it does not want to rev down quick enough when I'm changing gears. It does rev down eventually, it just seems to take its time doing it. Starts fine, runs fine, idles fine. Throttle is fine, doesnt stick, snaps back when released so I dont initially suspect the cables or adjustment on them but I'm still learning the bike...any suggestions?
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post #2 of 29 (permalink) Old 09-01-2009, 08:05 AM
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Welcome to the group. Is this your first bike? Are you watching the tach, or waiting for the engine to slow down? The tach is going to continue to show high revs during a normal (quick) shift because it takes a little while for the engine to slow down with the clutch engaged, which is fine. Really don't want the engine to loose many revs, at least when upshifting. My procedure is to pretty much simultaneously roll off the throttle, engage the clutch, upshift, release the clutch and roll back on the throttle. When down shifting, I usually let it coast a little between gears.

I'm keepin' all the left over parts. I'm gonna use 'em to build another bike!
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post #3 of 29 (permalink) Old 09-01-2009, 08:59 AM Thread Starter
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Smile

Thanks for the welcome! I am waiting for the engine to slow down and since I noticed the problem I am watching the tach a bit more closely. If, for example, I dont wait long enough for the RPM's to drop down low enough I will get a surge of acceleration from the bike once I shift and let the clutch out. This is understandable since I am for the most part dropping the clutch with the engine at a higher then normal engine speed.

I cleaned and lubed all the cables, linkages and springs for the choke,carb and throttle today and it IS much easier to throttle, but then again it wasnt really binding before either...I'll post again after a test ride. and no, this is not my first bike.
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post #4 of 29 (permalink) Old 09-01-2009, 09:44 AM
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Welcome to the group, you've come to the right place with or without this bike if you like motorcycles. Great bunch of helpful people here.

Now, your problem. This is a better suggestion if you smoke cigars or even cigarettes. With the bike running on the stand, bring some smoke near the rubber intake manifold first on one side then the other and see if there is any suction between the manifold and the cylinder. Sometimes they need tightening or replacement. If there is an air gap there, especially when the engine is hot, that will cause the motor to rev higher with more air coming in with the fuel. This is a simple check and if that's it then it's an easy fix. Hope you find it soon because eventually if this keeps up you will need a clutch replacement and that's a little harder. Good luck.

Ride safe and enjoy the bike.

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post #5 of 29 (permalink) Old 09-01-2009, 10:05 AM
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Adding to the above post, check vacuum lines for cracks that are hard to see. Hairline cracks in vacuum lines will cause the same problem, and if there are any vacuum caps on any ports, like if someone has removed the smog hugger crap from your bike and capped the vacuum port on the rear carb, those caps are notorious for cracking all to heck and still looking like bran new! But they'll let the intake suck just enough more air to keep your revs up and drive you nutty. Plus, in the long run, you are heating up your upper end with all that added air and your engine ain't gona like it very long!

Fergy
Kyle, TX VN750.com member #707 VROC#19556
2002 VN1500 Classic
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post #6 of 29 (permalink) Old 09-01-2009, 02:19 PM
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Welcome to the Vulcan madness RH. I can`t offer any help over what has already been said. I usually shift my bike or truck "by ear", ie. when it sounds right, as opposed to using the tach.

Fill out your profile and tell us where you`re from. Maybe there is another member close enough to lend a hand with diagnoses and repair. Enjoy the ride and keep the shiny side up.

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post #7 of 29 (permalink) Old 09-01-2009, 10:07 PM Thread Starter
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quick update...found that performing maintenance on the cables did'nt fix the issue but did make it work easier for me. I am working on an inspection of all the vacuum lines and checking for vacuum leaks. I did notice the back rubber grommet clamp that holds the back carb to the cylinder wall is loose. I tightened what I could as the screws are a pain to get to and didnt notice an improvement after a test ride. Do you have to take the tank off to tighten these 4 clamps correctly and securely?
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post #8 of 29 (permalink) Old 09-03-2009, 09:15 AM Thread Starter
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still stumped. Does not appear to be vacuum related as I have checked for vacuum leaks and so far appear to have none. One thing noticed on yesterdays ride to work...the bike acted totally normal for the first 5-10 min of the ride while still fairly cold...the symptom appeared after the bike was warmed up well. I have checked the choke over very well and did not have it on or half on or anything else...
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post #9 of 29 (permalink) Old 09-03-2009, 09:52 AM
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I know this is frustrating! I had a very similar problem on my kz1000. I even bought new manifolds (the black rubber grommet clamp you referred to) and replaced the old ones and sprayed wd40 on stuff and couldn't figure it out for a while. It would run fine until it was warmed up then would rev too high and just wouldn't back off the throttle like it was supposed to. It turned out to be the rubber vacuum caps that were cracked on mine that once replaced it solved the problem. Each manifold had a vacuum port on it that I capped because I switched to an ON/OFF petcock and ditched the vacuum operated one, so the ports weren't used anymore. I guess when things heat up, even rubber expands and contracts so my thoughts would be to get yourself a bunch of vacuum hose and start replacing it all and see if you find the leak. The manifolds have to be installed correctly, oriented correctly, and there is a front and a back, not interchangeable. They will cause you trouble if not right. I don't remember if you said if the bike had the smog stuff still on it, or if it had been removed and plugged? Hang in there, you'll find it!

Fergy
Kyle, TX VN750.com member #707 VROC#19556
2002 VN1500 Classic
Spline Lube Procedure, with photos, R/R Relocation and Coil Mod
Rusty Tank Cleaning!
Electrical Fault Finding Flowchart
SEAFOAM JUNKIE!


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post #10 of 29 (permalink) Old 09-03-2009, 10:04 AM
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Have you checked the air cut valve diaphrams on the carbs?


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