Vacuum

[pd]

Gary Wollard wrote in his Tech Tips that our motors need , at least , 3.5 inches of vacuum .

 With which gauge and where would it be attached ?

I'm thinking the gauge would have to be fit flat against the carb inlet . But , I don't know which gauge would be used .


 Pete .

[Ricks]

Gary Wollard wrote in his Tech Tips that our motors need , at least , 3.5 inches of vacuum .

 With which gauge and where would it be attached ?

I'm thinking the gauge would have to be fit flat against the carb inlet . But , I don't know which gauge would be used .


 Pete .

I would make a flat plate that bolts to the carb flange and then a hose to the gauge.

[pd]

I wonder if the screw at the bottom of the case carb mount was used for vacuum testing .
It seems pretty small for that , but

Pete .

[Ricks]

I wonder if the screw at the bottom of the case carb mount was used for vacuum testing .
It seems pretty small for that , but

Pete .

Pete, I have never met anyone who could tell me what that screw is for!

[pd]

I noticed that the M parts page offers no part # for that screw .
I haven't checked other models .

Anyway , other than that screw , there doesn't seem to be any vacuum port , dedicated or otherwise .
That seems strange for something so critical to operation .
That and the fact that none of the manuals even mention vacuum , that I've seen .

Maybe they left that part out for the sake of keeping it simple ?

Pete .

[Ricks]

Pete, as these were cheap bikes, I don't think Simplex believed that they would last long enough that they would wear out the cases in the rotary valve area.  Treen would probably be surprised at the number of bikes being restored.

[pd]

You're probably right , Rick .

I'm just glad we can make J Paul happy , even if it's from the 'other side' .

Pete .

[Ricks]

Pete, check out this thread.  There is a drawing with the tools Gary made for checking vacuum.  Let me know if you can figure out where tool 14a attaches to.


http://www.simplexservi-cycle.com/index.php?topic=301.0

[kartjockey]

I read down through the link you posted here.  Mike M. seems to remember #14A being for different carb bolt flange.  I wonder what kind of motor he would have been working on.

[pd]

Rick ,

I'd have to think that 14A is used at the carb inlet . It seems to resemble the mount plate of the M air filter housing .
14B would also fit at the inlet of an MT carb . I don't recall seeing the inlet of an MS carb . Maybe there is a difference ?

Pete .

[kartjockey]

MT replacement and MS on the right.  Flanges are the same.

[pd]

Tom ,

That makes sense as the mount surfaces on the cases are pretty much the same .
How about the carb inlets / intakes ? Are they the same as well ?
I wouldn't think they would be very different .

The inlet side of the MT carbs is simply a circle with single screw holes on the east and on the west edges .
I don't know why the odd shaped air filter mount plate was necessary or why 14A needed a similar shape .

For easy reference :



And , the M Air Filter Housing



And , a shot of my MT carb inlets .



Pete .

[kartjockey]

Other End!   On the MS carb that is the low needle valve screw at about the 2 o'clock position.  The star wheel is the high speed needle valve.   (review in the 1947 manual Rick posted)

[pd]

Thanks for the pics , Tom .

The mystery remains . To add to that , I noticed that 14A seems to be drawn about twice as thick as 14B . Why the extra thickness ?

I'm speculating that 14A may have the odd shape to accommodate access to the adjusting screws on the MS carb . But , why so thick ?

Something else to consider : was Gary testing vacuum with the intake channel drain hole intact or did he have it plugged ? I'd imagine that would make , at least , some difference in readings .

Pete .

[pd]

Ha. Half a thought after I left that^ last post and my laptop , I realized that access to the adjusting screws wouldn't be necessary as only vacuum would be tested . I suppose that if the screws were to be totally closed , there might be a very slight difference in final vacuum readings , but ...

Anyone know a decent medium that could call Gary up so he could answer a few questions ?

Pete .