[stickyfox]

Just sharing an experience this time wondering if anyone else has seen this.

The piston was not sliding smoothly from about 1/2 to full throttle. I haven't really cleaned the carb out but I did wipe the bore clean. I noticed that the piston didn't really fit very well in its intended orientation, but rotated 90° was fine. So I drew all over it with a sharpie and worked it up and down for a while.

All the ink rubbed off on one side, and I found a shiny spot in the carb housing. Polishing the interior of the carb did no good, but I got a wacky idea and squeezed the carb body as hard as I could with my fingers; the piston dropped right into place.

So I put the carb in a vise and worked on it .. very slowly.. and now the piston is still a tiny bit sticky, but drops in with no hesitation when the spring's installed.

Anyone else ever see this?

[mrunderhill1975a]

This has never happened to me, but I believe it was Pete that said the out of round condition can be caused by tightening the carburettor "screw cap" too tight using a channel-lock pliers, for example.  The screw cap should just be "hand tight".

[enfield freddy]

this is/was a common problem with amal concentric carbs (2 bolt fixing) and to a lesser degree the vm24 fitted to the 350 model , if you overtightened the flange bolts , it pulled the carb out of shape,

now presumably yours is a vm28 with a rubber stub mtg? , this should not happen , just put it down to carp inyun mfg tollerances


if you have had to "file" the slide , or pollish the bore of the carb , it is probably trash now , as air will be escaping , and you might/will get a crap tickover etc

[The Garbone]

They make carbs out of some cheap metal these days.. My 30mm flatside had a gas weep through the side of the float bowl when it was brand new out of the box..  Instead of returning it I put a dab of JB weld on it and its all good.. I guess its the state of metallurgy these days.

[dogbone]

I found a brake cylinder hone works well, doesn't take much.

[stickyfox]

I didn't figure it was a crisis, just kind of a curiosity. By polish, I meant run a felt wheel and some rouge over it, not enough metal was removed to affect anything. Not in this carb anyway. As it turned out, not enough metal was removed to make a dang bit of difference, but I tried it because there were some little granules of oxide growing in and around the carb, and I was hoping that some oxidation had gotten in the way of the piston.

[Vince]

      You can distort a carb body by over torquing the cap or flange. You can have oxidation or dirt in the slide bore. Polishing the bore is the fix. Just be careful to not damage the guide pin for the slide. If you take that out with a hone or vigorous sanding, the slide will rotate in the bore. The cut-away must be in a fixed orientation to the intake side of the carb.

[clamp]

There is a definite front and back --you can not rotate it 90 degrees.

      There is a slot that it slides up and down on.

    I can not imagine what you have done.

    Anything with a knurled edge to it is finger tight only.

[Ice]

 Many assume that carburettors are made from aluminum but such is not the case
they are made from a mostly Zinc alloy.

[stickyfox]

The pin only keeps it aligned when it's in its normal operating range. The piston can go about an inch and a half into the bore before hitting that pin, so if you back it out just beyond full throttle, it spins. Or at least it should spin. In my carb it kind of lurches.

There is a definite front and back --you can not rotate it 90 degrees.

      There is a slot that it slides up and down on.

    I can not imagine what you have done.

    Anything with a knurled edge to it is finger tight only.

[bullethead63]

I've found the best carb cleaner to be denatured alcohol on a rag,and Q-Tips...after cleaning and drying,I lube the slide with a few drops of Royal Purple synthetic oil,and 2 OZ  of Marvel Mystery Oil per tankful of gas...I also use the synthetic oil as cable lube,and with the MMO,I rarely have to clean the inside of my carb...I only do it when I have to change a broken cable (WTF,it's already apart),or if it's sluggish...but that's just me...Happy Motoring,Bullethead63/Matt Law~

[clamp]

The slide does not rotate or lurch round.It has a positive front and back with a cut out that it needs facing the front to suck fuel from the needle jet.

     You must have the wrong slide, how can you be sure the slide will relocate its peg.

    You have some thing very wrong with that carb.

 

[stickyfox]

Just to clarify, for posterity, this carb is off of a bike with 20 miles on it. I am 99% certain that, aside from "inyun manufacturing" (now one of my favorite terms), this carb is exactly as it was designed.

If the cap is screwed on, there is no way the slide piston can rotate. The guide pin prevents it from rotating. If, however, you remove the cap, you can see that at full throttle the slide piston protrudes about a cm out of the body of the carb.

If you lift the piston just a little bit higher, it will clear the guide pin; it can now be rotated freely, and a good 3-4 cm of the piston will still be inside the bore of the carb body. This is what I'm talking about. The piston can rotate, but will only drop back to the bottom if it is aligned once again with the pin. Ordinarily the cap prevents the piston from ever lifting high enough to clear the pin.

On my carb, the guide pin is very low in the body. If you have a variant in which the pin is placed higher up, then I can see where it's impossible to install the piston in any but the correct orientation, but with this carb, it can indeed be done.

Bullethead63: I think adequate lubrication in the spring and cable area is going to be the key here. With my "modifications," I am pretty sure that I will not have any binding problems as long as the added drag of the cable doesn't compound the problem.

[bullethead63]

When I bought my first Bullet,it only had 166 miles on it...HOWEVER...it had been sitting for seven years,and the slide in the carb would stick......lubing the cable,having the carb tilted and turned into the "sweet spot",cable routing,slide lubrication,throttle lubrication,how tight the top of the carb was,and just plain dumb luck all came into play...keep us posted!

[baird4444]

do you run WFO? 
  I'm think'n that yer spring has been shortened... not enuff  down pressure
 to keep it on the pin...   am i think'n too simple here???
            Mike