venturi L&L m-74b

[chuck58pan]

disassembled and cleaned carb for inspection and general understanding of it,s condition. observed one small shiny brass spot where the butterfly hit the bore. my question is I couldn't move the venturi, at least without some force which i am unwilling to do without a tried and true technique.I don't know if it even has to come out although from my perspective it looks a little worn. in the event that a replacement is needed how do you locate the hole for the shaft ;which i think is supposed to be .001 or .003 Idon,t have my info it felt pretty tight without appreciable rock , don,t have a dial indicator . thanks for the time.
cL

[Cotten]

Chuck!

The venturi must come out for one fundamental reason: You can't clean the insides any other way.

Try gentle heat with a penetrant, and gentle persuasion using a 1 9/16" wooden dowel. (Don't forget to remove the nozzle first!)

Chances are that once you have cleaned it, it will slip back in rather easily.
With luck, it won't be so loose as to rattle.

Finding the spigot hole is easy when it is loose, of course. When a proper light press-fit, however, a probe is inserted up the nozzle well with an offset 'tit' on the end. Turning it centers the hole.

....Cotten

[chuck58pan]

Cotten, thanks for the scoop;hope things are in order at your end. Will be needing your float at least. Is shellac an appropriate sealant for the screw.

[FlatHeadSix]

Chuck,
Like Cotten said; don't forget to remove the nozzle first. Its a Chinese puzzle, one piece holds the other in. If you don't drop the nozzle out you will never be able to slide the venturi out of the carb body.

Some of the period shop manuals have detailed instructions for removing "crust" from the carburetor bodies. The crust is usually the only thing holding the venturi in. Once everything is clean, the venturi will usually rattle in the body, it is no longer a light press fit.

mike

[FlatHeadSix]

Cotten,
while we're on the subject, have you ever evaluated the position of the nozzle when you assemble a Linkert?

I've always wondered if it makes any difference how you orient the nozzle when you stick it back in. Holes forward?, holes toward the rear?, holes sideways? I have never documented any results or taken any notice of subsequent tear downs to see if the nozzle rotated in the body after initial installation and running the carb on the bike for any length of time.

signed,

curious in Arkansas

[59Panman]

Mine fell out as well after cotten rebuilt it.

Orientation does not matter.


ozwick

Cotten,
while we're on the subject, have you ever evaluated the position of the nozzle when you assemble a Linkert?

I've always wondered if it makes any difference how you orient the nozzle when you stick it back in. Holes forward?, holes toward the rear?, holes sideways? I have never documented any results or taken any notice of subsequent tear downs to see if the nozzle rotated in the body after initial installation and running the carb on the bike for any length of time.

signed,

curious in Arkansas

[Cotten]

RE: Locking the float screw
Today's fuels are getting more and more digestive, limiting the kinds of sealers or 'dopes' that can be used. J-B Weld (used sparingly) or an isocyanate urethane paint will still work in the worst Midwestern P4gas.
One of my associates managed to soft solder his, but beware of added weight!
I have commissioned screw and pivotnut sets where the screw will extend through the pivotnut far enough for the exposed threads can then be clipped or "upset" to prevent the screw from backing out, but intend this as a last resort for when the fuels get worse....if that's possible!

Re: Nozzle orientation
Only the Indian Model 741 literature cites anything about orientation, and they have a slot in the venturi to aim at.

If perhaps you felt that there might be an advantage, the slot would have to be aimed at the vent hole on the side of the body for most HD carbs.
(Note that most late units such as the M74B have no slot, but are completely turned around their midsections to provide the most volume possible for an 'accellerator pump' effect.)

I have encountered bologna-cut spigots on nozzles that were then indexed with a set screw....but who knows if it was worth it!

And back to venturies...
It would be ideal to have each venturi a light press-fit to seal absolutely all air from passing around it, and to prevent rattle wear upon the spigot. (A loose fit of the spigot into the venturi can hinder the 'accellerator pump' effect.)
However nearly all potmetal venturis have shrank over the years.
I regularly swage them back out and cut for a precise press,...but they shrink back to loose in about a year!

There are aluminum venturies available from at least two sources (USA and Left-Coast USA) that were made pre-shrunk. (Duh.)

Since aluminum doesn't swage nicely, our hopes for quality venturies would be 45PartsDepot (I haven't tried one yet), or private commissions to have them done right..

....Cotten

[chuck58pan]

thanks for the info. i was thinking it had something to do with the venturi body itself ,took aquick look at 58thru68 parts book and the nozzle i see coming thru the bowl i had fortunately removed already. i am a pretty good taker- aparter just not always agood finisher. the venturi itself looks to be potmetal and well worn ,nothing even resembling a new part. not to change the subject but i was to see the guy doing my motor tonite i am psyched it has been most of my adult life sitting around. i do plan sending my heads off to Don Sullivan it only seems prudent to preserve when possible. thanks again , chuck

[kevsett]

I didn't see a M-74B linkert venturi listed on 45partsdepot's website.

[Cotten]

45PartsDepot has now added Colony's line of products, so we are back where we started with our venturies.

...Cotten