Bucking and Stuttering, Take two  By  rcq92130 (Read 4,826 times)

Holy CRAP !!!!!!!!!!!!!!!!
SIXTY BUCKS

Wow.  You are one rich dude!  

I got an electric pump last week, thinking exactly what you said.  Tried it last week with the old (and I think no good) carb, but it didn't fix the problem so I never installed it.

Will see what alley, GEH, etc say .... thinking maybe i just have too lean a mixture ... but if not will try the elec. pump again!

Yeah, I have a BMS.  Looks pretty similar to yours (incl the stainless floor boards)!

So --- you are going to raise the carb up so the pipe to the air filter goes OVER the cross brace, huh?

That means you will sacrifice your under-seat cargo box ... right?

Thanks, Alley.  Had no ideas that was an unusual Uni.

I'll first open the diaphragm cap and see if the needle valve is adjustable (that way don't have to take the carb out, which is a pain with this carb).  Maybe, if it's adjustable, I can raise the needle enough.

If not, I'll try a 125 main jet.

Thanks again.

>>"That is a pumper carb which does not have an ACV valve to help when the throttle is suddenly closed and coming down to idle to feed it some fuel so it doesn't run lean on de-cel.


so, the popping is "normal" with a pumper carb?

OK, will screw out the mixture screw a bit.

Idle is at about 1800 RPM (see video), so I guess it's a mixture problem.

Yes, it's a "Red" uni - I removed the "red" dust sleeve so it would be easier to put the latex glove on.

Yeah these scoots are sold under several different brand names. I can always tell them by the seat config, the floor boards, and the chrome accent on the front all match up. 

Yes I plan to raise the carb up so that the air intake goes over that dang cross brace. The 30mm carb I bought hs that pumper thing on the side of it and it won't sit on the head except in a very very odd angle. I hadn't really thought about my underseat storage, but since you bring it up. Worst case I will just cut a channel length wise in the sub floor of the compartment and flip it upside down and reattach it. Making a tunnel in the bottom of the compartment for the carb and intake.

I really don't keep much under there as it gets really hot. The body style on the vintage isn't very nice to air cooled engines in Florida heat. I think my rear side panels come down a bit further than yours. The airbox over the CVT was completely covered by the body. So things tend to get pretty warm under there. Before I added a cooling scoop it would get so hot under there you could literally heat your lunch in that compartment.

This heat was what I thought to be the source of the cutting out. I was thinking that the heat was causing a vapor lock situation. Then it was pointed out that I was running lean. Then When I still thought it might be lean it was explained that the pump is the source of my problem. 

What Ally is saying makes perfect sense and is more than worth trying. But just so you know I was having this problem  with the stock airbox and still have it running a 125 main jet on the stock carb. Rocky has also fought this problem with his lance vintage and said it.. well here easier to just quote him..hope u don't mind rocky.

"The cutting out is usually the fuel pump not being able to keep up with refilling the fuel bowl at speed. Lance was pretty good at putting the correct jets in the carb in 2007 but...



Once verified that you have a leak free intake and a clean fuel system, properly adjusted valves are really the next must to maintain a good fuel pump action at high speed.



Changing the intake or the porting of the airbox can also have a detrimental effect on vacuum pulse which is required to maintain fuel flow with a vacuum fuel pump.



I did try a Hydrogen/Brown Gas system on the Lance and that did help a bit with maintaining higher speeds and over time decarbonized the piston and cylinder. Clean piston rings are more free in their grooves and give a better seal for a better intake pulse.
"

You might want to take one last look at fitting this.

You have a GY6 - and I'm guessing the exact same crankcase casting.  It's the engine mount tabs (and the mounting bolt) that cause interference.

What I found was if I REMOVED the rubber boot that connects the carb to the (metal) intake manifold I could just barely get the carb in --- with the metal output of the carb more or less touching the metal of the input manifold.

I then looked at the rubber boot (sleeve) that came with the intake manifold and saw it had a molded ridge inside intended to separate the manifold and carb.  The width of the ridge was "just" wide enough the carb would not fit.

So, I got a piece of radiator hose the right diameter (no ridge inside, of course), and am using it.  This way I can get the carb and manifold essentially together, and the carb more or less fits.  The pumper casting still hits the right side mounting ear cast into the crankcase, but rotating the carb about 5 degrees from upright fixes this.  I think this small rotation will no lead to a problem with the fuel height in the carb bowl.

Anyway - something to check.