Author Topic: My jetting story  (Read 964 times)

vl5150

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My jetting story
« on: June 18, 2014, 05:08:26 PM »
My jetting story..

I picked up my Vision a few weeks ago and it looked like the PO just gave up on it...

I'm not that hard to be defeated.  Mine needed a new air filter (replaced with UNI), a carb rebuild, and dunk.  Yics is leaking and is disabled, no intake leaks.  After that was done, I couldn't get it to really rev.  Anyway long story short, mine is running lean on the pilot and really, really rich on the main/acc pump.  Acc pump is set for less throw and 115 mains on both.  135's up top seem to be better.  Mine has the regular airbox flap the the pilot plugs were still there.  So it still wouldn't rev so I removed the flap all together and it's working much better.  I can hit redline no problem and took it on a road trip today for 90 miles on the highway.  I get the stumble, but I think I can cure it with the next size up pilot since my screws are a bit over 4 turns out.  I have .7 drill bits on the way and will use my spare jets for the mod.  I also have 140 air jets and will try them as well.  I think it has a tough time on the transition from the pilot with the butterfly partially opened to the main at around 5k RPM.  If I roll on harder there's no stumble.  So with every change it's responding.  I know some of this is nutty, but it's what this bike likes and I'm not fighting it.

vl5150

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Re: My jetting story
« Reply #1 on: June 20, 2014, 11:35:52 PM »
Update..Since I took the flapper off it ran much better and started pulling so I refined things a bit.  I upped the 130's up top to 140's tonight and with the 115 mains below there was a stumble at 4500rpm.  I upped both mains to 122.5's and the stumble is 99% gone.   On an aside note, mine doesn't like the acc pump with any more than the minimum throw.  The new diaphragm must really squirt the gas.

In my experience on my bike, the flapper was not necessary at all and actually caused tuning issues because the intake condition changed when the flapper moved.  In my estimation meeting the US-EPA standards in the US was the reason for the flapper.  The pilot screws were blocked off so no tuning was possible on an important circuit.  Also the 60 pilot is too small for the carb and that's the largest size in that form factor.  My flapper had the coins on it and it ran like crap.

I'll do some more riding and tweak from there.

One more thing--The clutch action on mine sucks.  Weird short throw to the clutch. I replaced the lever and perch with one from a 1981 Maxim 550 and readjusted.  It actually the same switch as well.  Problem solved and standard dirt bike levers will work now.

**UPDATE**  I concluded that the bike won't run as good as it can be with out the vacuum operated flap.  Mine had the regular flap and it was broken so this was an attempt to jet around it- a tall order with downdrafts.  I've since added the vacuum operated flap and posted on the results in 4/2015.
« Last Edit: April 28, 2015, 09:04:21 AM by vl5150 »