MPS question

[mike_the_man]

Hi all,

This maybe a silly question, but here it goes: I have heard that to test the diaphragm you can suck or blow into it? Which is it, I assume suck. Then what do you look for? I would imagine that there should be no suction coming from the two little vents in the back, but can you hear if it is leaking? What is the best way to tell if the diaphragm is deffective. Any help would be great!

Thanks,

[Bleyseng]

Take a standard vacuum auto pump and attach the hose to the MPS. Pump the vacuum up to 15hg on the gauge and if the MPS holds the 15hg for say 5 min or so without much leakdown (2-4lbs) then the diaphram is good.
The diaphram could be good but other reasons the MPS leaks are:
1. The case halfs o ring is bad
2. The paper gasket that the diaphram seats to is bad.
3. Someone has adjusted the MPS out too far so the mix screws are leaking. (rare)

[bowlsby]

Get trhe pump with a gauge as Geoff says. A suck test is not reliable becasue it does not tell you if it leaks down.

[norustscott]

IT does if you keep your tongue on the end..

[bowlsby]

The tongue test is not reliable and it is a myth Scott.

I have lost count of how many MPS units sent to me that I have evaluated that were 'known good' where the suck test was used to determine that the MPS was good, and the problem is that it cannot reliably indicate leakdown. It s just plain false. Only a vacuum pump with a guage can tell you what you need to know.

[tmp914]

like this

[chrisreale]

Yup, I "suck tested" two of mine, and they passed. used a vacuum gauge, and both leaked at the diaphram....bummer

[norustscott]

ok ok ok, MPS and jokes don't mix I see...I guess @ 400 bucks each nothing is funny...

[Bleyseng]

The problem is unless you can suck a golf ball though a garden hose you can't produce enough vacuum like the pump. The cracks inthe diaphram are small to start and seal themselves at low vacuum. At 15hg they leak like crazy! That's why a leaky MPS will run fine but the idle is goofy and hard to set right. Its amazing to just switch a leaky one for a good one and see the difference in the idle right away.
Geoff

[Pritchard]

I used the "suck" test and my MPS seemed OK. I could not get the engine to idle properly at all. I borrowed a vac. guage and it would not even hold 5 hg. My unit was leaking at two places: around the plastic that goes into the unit (the wires plug in here), and by the adjustment screw. Yes, I had been fooling with the adjustment trying to get it to idle. I used a little sealant around the plastic and resealed the adjustment screw and all is well. Now it will hold 15 hg for more than the required time.

Good luck

Pritchard

[Dave at Pelican Parts]

Originally posted by norustscott
ok ok ok, MPS and jokes don't mix I see...I guess @ 400 bucks each nothing is funny...

Dude, where are you getting MPSes for $400 each? Let me know, and we can make a mint!!

I think list is now in the 600s... AAAAAGHHHH!!!!!!

--DD

[jamcleod]

guess i'll have to pull out those 6 i've been stock-piling in my parts bin!

[norustscott]

I bought one from the TheBusDepot.com two years ago for $279.00...