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Discussion Starter #1 (Edited)
Need some help with an '05 Vinson I just picked up.

Someone dumped gas down the side of the tank and toasted the harness. I was able to piece it back together and get it to somewhat fire up and barely idle. After going through a valve lap and rebuilding the carb I can get it to start and idle real nice. Just can't get it to accelerate past the idle.

Here is a video of the bike idling and what it does when i try to accelerate:

some general observations:
*previous owner replaced the CDI with a new one
*I have replaced the wiring harness with a used one
*I rebuilt the carb with a kit off ebay
*I have tried the OEM fuel tank and a different one I had laying around just in case that was cause the issue

I am starting to think I have the timing one tooth off or something is way off in the carburetor that i'm missing. (not sure if it could be the wrong CDI)

Struggling to find a solution, does anyone have some ideas?

Thanks!
 

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Hi,
I suspect the problem is with the carb and may be an easy one to fix.

I am assuming your carb is the stock Keihin CVK36 and you used the Shindy rebuild kit.

-Remove the cover on the right side of the carb to reveal the area where the thumb throttle cable connects to the throttle, and the idle cable adjustment screw butts up against the idle.

-Completely back off the idle adjustment so the screw cannot make contract with the throttle.

-Disconnect the throttle cable from the throttle.

-By hand turn the throttle clockwise to ensure it moves freely. It should snap back into place when released.
If it does not do either of the above you will need to remove and disassemble the carb to further troubleshoot.

-If the throttle did move clockwise freely and snap back when released, carefully reconnect the throttle cable. If necessary adjust the Throttle Cable Play to be between 3-5 mm. Use the thumb throttle control to ensure the throttle is moving freely and snaps back when released.

-Do not reconnect or adjust the idle yet.

-Start the engine and use the thumb throttle control to maintain engine idle and gradually increase idle speed (do not over-rev!) Visually make sure the throttle is able to freely move freely clockwise and counterclockwise while gently adjusting engine idle with the thumb throttle control.

-Use the idle adjustment knob (left side of carb) and turn it clockwise until the screw makes contact with the throttle and then set the idle to 1300 RPM (plus or minus 100 RPM)

-If the above steps did not work then you should remove the carb and go back over everything. Start by removing the top cover to reinspect the diaphragm assembly and ensure the slider makes a solid "aspirating sound". (Did you replace the diaphragm when you did the carb rebuild?) When replacing the cover ensure the diaphragm is not pinched and that it's lip makes solid contract with the cover all the way around. (IMHO this is the hardest part of a carb rebuild!)

-If the above did not work then I would take apart the carb and go over everything again.

Please let me know if this information worked, or if you need additional info for rebuilding a Keihin carb. A guy on YouTube has an excellent set of videos for rebuilding this carb.
 

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Discussion Starter #3
DesertRider,

thanks for replying!

I agree with you...I do believe it is the carb....

I was given the same advise as you did with adjusting the throttle cable and tried to follow the procedure very carefully. The throttle seems to be free and snaps back in place very easily. Low end idle settings seem to be responsive and work well when adjusted.

As for assembling the diaphragm, yes, this appears to be the most difficult and frustrating part of the reassembly, to ensure it is not getting pinched but sealing all the way around properly. I did not replace the diaphragm and am highly suspect of it. However, the standard tests of holding it up to light to determine a hole or tear, I am not able to determine any failure. It appears to be in good condition. Makes the 'aspirating sound' as you have pointed out. (as far as my novice ear can determine)

Do you have any idea if a failing diaphragm will cause this type of response in the engine?
 

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Hi Elektro21,

Question: Does this problem exist whether the fuel stopcock is set to "ON" or "PRIME"?

Because the CVK carburetor uses engine vacuum to raise the slide valve and maintain the throttle opening angle in proportion to the engine vacuum, I am very inclined to focus on the diaphragm, slider, jet needle, and vacuum hose.

- Ensure the vacuum hose is in good condition and secure fit onto the carb.

- Remove the top cover and ensure the diaphragm, jet needle, spring retainer, and spring are installed in the correct order.

- The plastic spring retainer is installed "feet" first. Look down the hole to see if there are little indentations that the "feet" should set into. (some Keihin carbs have this, others don't).

- I know this is silly but make sure the Jet Needle is correct. Compare it's length and diameter to the old one.

- The diaphragm should be very flexible, not brittle, no holes or cracks, and lips easily stretch for a good tight "gasket" fit when you reinstall the cover.

If the above doesn't solve the problem then you will need to take apart the carb and start going over everything.

Here is the link to Shane Conley's outstanding video series on CVK carb rebuilds. It is worth setting aside a few hours to watch the full series on carbs (I think there are 3 or 4 videos). He provides far more information that what is in my Suzuki Vinson Shop Manual.

 

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I have this exact same problem except for I tried a brand new carb and still doing the same thing I’m thinking I got a bad CDI even though I just replaced it with a new one and it’s not advancing the timing or I had to get a different one harness also but I just cut the end off for the CDI in attach the wires and hooked it up because they were afraid I’m worried about if I hooked it up wrong by going with the colors instead of looking at the port I’m working with the 2005
 

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Discussion Starter #6
I still have not figured mine out. Although I've been very busy lately and not had time to do a whole lot more troubleshooting. I have talked to many so called 'experts' and/or tinkerers with powersport vehicles. The answers I normally receive are carburetor or CDI issues (pickup and stator appear to be fine electrically, I used my meter to check resistance per factory manual). I wish I could find another Vinson 500 owner that I could borrow a 'known good' carburetor to see if there is something messed up with mine. (carbs are ~$200 even used for these vinson's)

I have also attempted to replace my CDI with a brand new aftermarket CDI...no change. Still will idle perfectly and stumbles then falls flat and dies when cracking the throttle.

I am going to pop the timing inspection plug and double check all timing etc.... I might end up ordering a used carb online to see if that will fix the mystery issue.

Last course of action will be taking the entire ATV to one of our local gurus and see if they can figure out what is going on. getting frustrating....from a technical/troubleshooting standpoint.
 

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Discussion Starter #7
DesertRider -

Thanks for posting the info on the CV carb rebuild stuffs...I actually watched shane's video before and during my attempts at rebuilding my carb....he is an excellent resource for CV carbs and rebuilding!!
 

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Have you checked the voltage at the battery while running at idle and revved up?
 

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Discussion Starter #10
Just tested the other day at idle...was like 11.x volts (battery was low as well from me running it). Seemed low to me. I went ahead and ordered a rectifier. I am unable to increase RPMs or Rev the ATV as it instantly cuts out.
 
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