Some Carb stuff- after carb kit and Vacuum lid

[vl5150]

I wasn't sure exactly how a Vision was supposed to run since mine was pretty much shot when I got it.  The 1st thing I did was get a few used carbs from ebay and Keyster kits. 

So that being a baseline and messing with the carbs for a while without the vacuum lid, I'm pretty sure that the keyster accl pump diaphram really pumps out the petrol compared to stock.  I didn't have anything to measure it with, but after I got my vacuum airbox lid, the stumble went away and drivability at 4-55K rpms is great, but 7K and above got really rich and was burbling badly under full throttle at hight RPM.  Rolling on between shifts was not really clean either since it was dumping fuel it couldn't use.

I have a few irons in the fire on this one.  I have a shortened accelerator pump arm on the workbench, but I decided to lower down the main jets to see what that would do since that's quick and painless to do.  Anyway starting with stock I started decreasing a few jet sizes at a time until I could get a clean pull.  As I went a size lower, it started to get better and better.  Burbling stopped at 115F/120R main jet.  So I'm going with it since that's what it likes and I'm not going to fight it.  I had nothing to lose anyway.

If it stays an issue, I can play with the arm.  I was also looking at some sort of limiter in the accl circuit and hose to lower the volume and increase pressure.  Anyway I saw some old posts here on that keyster pump issue and I can see I've experienced it as well.

[Rikugun]

Normally I don't argue with results but I can't help but wonder if you "jetted" away a problem that wasn't caused by improper jetting. I've not heard any other reports of Keyster carb kits causing rich burbling under high RPM acceleration. Doesn't mean it never happens, I just don't recall reading about it.

What kind of air filter are you running and how clean is it?  Is it possible float level is off a bit making it rich? Measuring fuel level is more accurate than setting float height.

I'm not sure if the Keyster accell diaphragm is any better than the stock one was when it was new. At their current age they can be very inflexible. Often times the initial throttle movement isn't even moving it but rather just pushing the over-travel spring. Replacing it makes such a huge difference because now it's actually responding to throttle linkage movement. Additionally, when the throttle is closed the pliable diaphragm quickly responds moving back into position ready for the next shot.

What is purportedly different about the Keyster diaphragm is the central pin that the actuating cam pushes against. It may be shorter than the stock one so the accell linkage has to be adjusted up to get you to the "stock" setting. Additionally, some opt to shorten the adjustment a few more turns for good measure. This often reduces stumble.

Just my 2 cents...   :)

When in use the diaphragm only moves so far. My guess is it runs out of travel before the throttle plates are at WFO. At some point you've used the entire stroke of the pump and further throttle opening is just compressing the over-travel spring.

[vl5150]

I agree--it's the strangest thing.  I checked the floats when I first got the bike and did the carbs and it was OK.  I knew something was up with the stock air lid when it ran worse when I made the accl pump rod longer.  It was still slightly rich when at it's shortest setting so I had no where to go with the acc pump adjustment and since I had the jets I thought "what the hell!"

I re-did the whole thing from the MAC exhaust to getting perfect carbs to restore, keyster kits.  Brand new uni filter oiled correctly- no expense spared (unfortunately, lol).  As hard as it is to get these carbs worked out, I think I just got lucky so I need to buy a lottery ticket.  I was hesitant to get another set of carbs with the vaccuum nipple to not put a $ more into it.  I found a set on ebay for $40 so I picked it up to go with the airbox lid I already hoarded away.  I do have an Innovate LC-1 Wide band O2 sensor so I'm tempted, but it's a PITA to set up and it's in my car now.

But I can't complain.  I have probably $2200 into the bike with the body work and it just passed 3000 miles.  Where else can you get a unique bike that looks that cool for that cheap.  Now mine is running as good as it looks so I'm just going to relax and enjoy it.

[Rikugun]

Now mine is running as good as it looks so I'm just going to relax and enjoy it.

That about sums it up   :)  Some Visions out there unfortunately don't end up satisfying their owners so this is a success story. Glad you get the bike running well.