Board index Flathead Power-Technical Questions, Answers, and Suggestions 45 Flatties Bombsight Venturi

Bombsight Venturi

Moderators: Curt!, Pa

Post Sat Jun 25, 2011 7:00 am

Posts: 28
Location: Texas

Hey guys! First time posting here but I've enjoyed reading some of the excellent threads. Anyhoo, I'm tryin' to get information about this 1-1/4" bombsight venturi I picked up the other day. My good friend Greg sent me this flyer that appears to describe it. OD is 1.370. Your comments are appreciated.

Image

Image

Post Sat Jun 25, 2011 4:12 pm

Posts: 3134
Location: Central Illinois, USA
Mr. Big!

Your advertisement says it all.

One can only wonder how long until the single vane suspending the secondary venturi might crystallize and break.

There are other variations, but the market never accepted them.
BRASBOMB.jpg

The irony is that the "spit" was probably only a vacuum leak.

....Cotten
PS: At 1.370", it is five thou undersize from a perfect fit.
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Post Sun Jun 26, 2011 6:02 am

Posts: 28
Location: Texas

Nice looking example you have there and thanks for the info. Good thing the nozzle holds it on the bottom as it probably wouldn't hang very long on it's own although it looks very well made and brazed in nicely.

Interested to see what it does on my 45 just for giggles.

I noted that the ad offers notched and unnotched venturi's in both sizes? Wasn't the notch for internally vented bowls like on an M88?

Post Sun Jun 26, 2011 10:47 am

Posts: 3134
Location: Central Illinois, USA
Mr. Big!

Yes, the notched venturies were for the many models that were internally vented, mostly Indian.

Althought the spigot of the nozzle is captured within the secondary venturi of the "Frisco", it could only dampen stresses from the pulse and reversion of the running motor. Soft solder would help.

Here is the typical spigot wear of a vibrating ordinary potmetal venturi.
NZLWEAR.jpg
Brass venturies found in Scheblers wear extremely, even producing grooves into the carb body itself. I would predict that the Frisco would eventually wear a second ring as well.

This is only one reason why you want as snug of a slip-fit for a brass venturi (or aluminum), or a mild press-fit for a potmetal. (Potmetal venturies continue to shrink over time.)

...Cotten
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Post Sun Jun 26, 2011 4:16 pm

Posts: 28
Location: Texas

Great info and thanks so much. I tend to forget about Injuns as I don't know much about Linkerts setup for them.

Good point about the vibration and need for a snug fit. Havent' squeezed into a body yet but tried a nozzle and it requires a little nudge on the little venturi to get it lined up which appears to put pressure on the brazed fin. Can't be good long term.

Do plan to drop it in my M51 and give it a spin.

Post Mon Jun 27, 2011 6:50 am

Posts: 3134
Location: Central Illinois, USA
Mr. Big!

I would imagine the fin or vane is silver-soldered, although it looks like soft solder in your pic.

If it is indeed a full five thou undersize, then it may suffer leakage at the rear of the venturi, confusing the transition from the idle circuit to the power circuit, and defeating the nozzle's "accellerator sump" effect.
After you install it, hold it up to the light and look for "daylight":
CLNYVENT.jpg

This ordinarily can be remedied by swaging, but your secondary venturi is in the way.

....Cotten
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Post Mon Jun 27, 2011 6:14 pm

Posts: 28
Location: Texas

No worries about it leaking because it's tighter than Dick's hatband. I test fit it a tad on a couple bodies I have and it will go but will take some patience to get it lined up with the nozzle. My abilities with a caliper are suspect so I'm sure it's a bit bigger than I stated.

Maybe this weekend I'll pull my carb and install it for the curiosity test. I will report my findings......
Last edited by Mr. Big on Mon Jun 27, 2011 8:55 pm, edited 1 time in total.

Post Mon Jun 27, 2011 6:55 pm

Posts: 336
Location: Kirksville Missouri United States
Mr. Big,

Welcome to the forum it's one of a few I've spent the last decade reading.To all that haven't met Mark from other forums he's a true friend and pretty good with linkerts too.I figured he'd mention his WL with same year goulding sidecar and his extra parts including another engine,a nice set of cases,etc. It was great chatting on the phone today my friend...........

Post Mon Jun 27, 2011 9:30 pm

Posts: 28
Location: Texas

Thanks for the welcome Greg. I don't know crap from crisco about Linkerts but I sure dig learnin' about 'em..... :D

Post Wed Jun 29, 2011 7:00 am

Posts: 304
Location: Jonesville, Louisiana, USA
Mr. Big wrote:
Thanks for the welcome Greg. I don't know crap from crisco about Linkerts but I sure dig learnin' about 'em..... :D


Me too, Mr. Big !

Post Wed Jun 29, 2011 2:28 pm

Posts: 336
Location: Kirksville Missouri United States
I know this vintage bombsite is the best thing since bottle soda in my opinion .I suggested what has been proven over and over by myself and fellow employees at the shop ,Since Mark has the good fortune of both linkert brass bodies and this unique venturi being brass I feel my best proven method to securely locate the ventura in bore with no chance it will vibrate in turn damaging his fuel nozzle.Install ventura as well as fuel nozzle to be sure of perfect fit of nozzle installed in ventura.Lastly from choke end of carb pass a proper length ,for job,of silver solder through length of bore.Then use small professional grade solder pen to flow aproxx I/8" line of sliver solder smoothy between brass ventura and brass linkert body,duplicate exact process center of linkert bore roof smoothly flowing in minor amount of silver solder.

I will say even give the information that every member of this forum silver solders items together on a daily basis my first hand experience (not just reading about possibility method may work)has proven numerous times over the last 3 decades silver soldering brass to brass foolproof at least for 30+ years using method.If any forum members is a professional plumber or alternately has enough experience it's pretty easy especially with brass to flow your silver solder into pieces needing connected.And with no attempt of brag meant I can flow silversolder that with closed eyes you could easily pass over flowed solder with a finger and not identify location.

Post Wed Jun 29, 2011 8:47 pm

Posts: 976
Location: Markt Einersheim, Germany

:evil:
Last edited by George Greer on Wed Jul 13, 2011 9:11 pm, edited 1 time in total.

Post Wed Jun 29, 2011 10:07 pm

Posts: 336
Location: Kirksville Missouri United States
*
Last edited by greg1 on Sat Jul 02, 2011 4:20 pm, edited 1 time in total.

Post Thu Jun 30, 2011 11:26 am

Posts: 976
Location: Markt Einersheim, Germany

:shock:

I think that I am finished here.

Post Thu Jun 30, 2011 1:53 pm

Posts: 28
Location: Texas

Whut?

Post Thu Jun 30, 2011 10:57 pm

Posts: 976
Location: Markt Einersheim, Germany

:evil:
Last edited by George Greer on Wed Jul 13, 2011 9:12 pm, edited 1 time in total.

Post Fri Jul 01, 2011 9:00 am

Posts: 304
Location: Jonesville, Louisiana, USA
I have enjoyed your posts for years, George. Please, don't leave over a personal difference with another member.

Post Fri Jul 01, 2011 9:46 am

Posts: 976
Location: Markt Einersheim, Germany

:evil:
Last edited by George Greer on Wed Jul 13, 2011 9:12 pm, edited 1 time in total.

Post Sun Jul 03, 2011 3:54 pm

Posts: 28
Location: Texas

As I mentioned on the "Parts" thread, it is hotter than heck around here but I was determined to get something done with the bombsight. Earlier I went out and took about a 45 minute spin on the hack to get a feel for how she ran in her current stock configuration. Installation was fairly easy and I was able to get the nozzle in both holes and the fit was perfect. I could move it with my fingers but definitely fit well enough that no light was coming through.

Image

I did notice that it seemed to sit a little further back in the carb then the stock venturi. Anyhoo, took a quick spin and, as expected, the reduced airflow made it a litte fat. Unfortunately, it was 104 today and I didn't want to attempt any tuning in that heat so I am going to try again in the morning.

Post Mon Jul 04, 2011 8:58 am

Posts: 28
Location: Texas

Took another 45 minute ride this morning and did a little tweakin' by leaning out the power needle about 3 clicks and it cleaned right up. Obviously my results here are fairly unscientific and just "seat of the pants" but I could see a tad more pull on the low end but surprisingly, it was the big end of 2nd gear where the improvement was really noticeable.

Odd I guess because what I've read indicates that a booster is more likely to improve low end performance. And the better 2nd gear could have been due to just the leaner setting. Who knows. Do think I need to raise my bowl level a bit.

Anyhoo, it's a very nice period piece and I've really enjoyed tinkerin' with it. Happy Trails and Happy 4th!


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