Carburetor and Fuel System
Title: Linkert
M74-B venturi
Can someone advise how tight a fit the venturi should be in an M74B? It doesn't rattle around but with the main nozzle removed it pretty much falls out.
Excellent forum.
Post by Cotten on Jan 19, 2007, 4:03pm
As tight as you can install it.
Potmetal venturies have a habit of shrinking with heat and age, allowing undesirable airflow around them. Most carbs have carbon'd up this slow-growing gap, but upon cleaning you will suddenly see daylight.
My approach is to swage the venturi oversize and then cut it back to a light press fit, as the potmetal will continue to shrink in the future.
(Freshly-swaged venturies can collapse .001" in a years time just sitting on the shelf.)
Colony now offers venturis, but they copied shrunken originals!
Please inspect for wear at the mainnozzle spigot hole, or matching wear upon the spigot itself, as this is a common result of running with a loose venturi. .
Originally there was a phenolic seal there, although it is hard to find in any parts books.
....Cotten
Post by 59ozpan on Jan 22, 2007, 5:49am
Thanks Cotten - that'll teach me to clean things!
Post by 56panman on Jan 22, 2007, 1:14pm
Man am I glad I read this thread today. I was going to dis-assemble my M88 this evening and give it a good cleaning. Guess I'll just throw the new float in it and call it good.
Like the old saying goes. "If sh*t don't stink don't stir it." ;D
Post by Cotten on Jan 22, 2007, 2:13pm
Liberty makes no endorsement expressed or implied for the incomplete or partial service of any functional part of any machine.
However,...
"If you take something apart, it's broke."
...Cotten
Post by 59ozpan on Jan 23, 2007, 6:04am
Cotten,
Not having "swaged" before, am I looking to spread just the suction (air cleaner) end of the venturi?
Thanks for the help.
Post by Cotten on Jan 23, 2007, 3:30pm
59ozpan!
Actually, it is the manifold end of the venturi that is critical for a seal, although you want the venturi secure at both, lest it 'rock' with vibration.
Many Linkert (and Scheblers, mostly for Indians) models actually have a slot at the front to vent air to the nozzle. Your M74B vents through the side of the body.
Swageing is more art than science; I still ruin a venturi every now and then.
Modern aluminum venturies are very difficult, even to gain a few thousandths.
....Cotten
Post by 59ozpan on Jan 24, 2007, 7:55am
Thanks Cotten - I'll proceed with caution. I just bought another carb on ebay so I might see how that one shapes up before I do anything too drastic.
Thanks for your assistance.
Post by Rich on Jan 24, 2007, 8:52am
If the old one has shrunk, swaging it wont take it back to size in the bore of the venturi. I would have thought that using the Colony repro gives the same result (both shrunk in the middle, both fit tight in the carb)....plus of course the Colony one will have no wear on the nozzle hole.
Just a thought.
Post by Cotten on Jan 24, 2007, 3:26pm
Ten thousandths of a inch of bore diameter is pretty negligeable.
But you could always polish it out if it bothers you.
I'm glad to hear Colony has finally sold all of their loose inventory and started making tight ones.
....Cotten
Post by Rich on Jan 24, 2007, 3:46pm
I didn't realise that some of the Colony venturis fitted loose.
It seems that parts take time to reach stockists in Europe, so maybe they use you guys as R&D !
I can only vouch for the fact that the Colony Venturi supplied to me by J W Boon (Holland) fitted tight to the point of being difficult to align with the nozzle.
I also fitted a Venturi to my M88 supplied by Kurt at 45 parts depot...this also fitted tight.
Cotten....glad to hear that the bore you consider to be of minor effect....I had assumed as much taking into account production tolerances, but its nice to hear it from another source.
Post by Cotten on Jan 25, 2007, 2:05am
If a 1.3125" venturi bore shrinks .010",... that's about three-quarters of one percent.
....Cotten
