International Engine type m compensating valve 3hp

[@PackratsFabrications]

Good job explaining the mixer body. What's that compensating valve do? Would the wimpy spring let too much air through?

[@paulclithero1822]

Let me preface by saying I have found no literature on the subject. I believe that the purpose of the compensating vale is to provide a spike in the vacuum levels at the beginning of the intake stroke in order to draw the fuel through the needle valves, followed by the compensating valve opening to allow a air to more freely move through the venturi, then past the throttle plate. As to why the kerosene compensating valve has more holes in it, my only supposition is that the higher viscosity of the fuel leads to it having higher inertia, and thus not as great of a tendency to cease moving in the needle valve assembly. As I said, this is all supposition, I’m still looking for literature on the subject. I do know that every liquid fueled, throttle governed, engine I’ve paid attention to it on seemed to have some form of compensating valve on it, and hit and miss engines do not, possibly due to the air volume being reduced in the throttle engines, and not in the hit and miss.

[@PackratsFabrications]

@@paulclithero1822 Thanks for the reply. So this is all because a mixer doesn't have an idle circuit. When the throttle plate closes, there's not enough air flow through the mixer so no fuel flows. The compensating valve acts as a choke to create a vacuum to suck fuel out of the needle valve when there's not enough air flow to make the venturi create that vacuum. So maybe you could say the compensating valve compensates for lack of air flow. When somebody invented the carburetor with an idle circuit the fuel could get past the restriction of the throttle plate. I learned on modern carburetors so I had to think about that one. I don't understand more holes for kerosene, seems like that would make less vacuum below the venturi and a leaner mixture, I expected you'd want to go richer for kerosene.

[@paulclithero1822]

@@PackratsFabrications Kerosene has a higher energy density than gasoline, though a lower effective octane rating. Which is where the water needle would come in, to prevent pre-ignition under load. Mixtures are controlled in use, though. You “tune” as the load and cylinder temperature change. It is also possible that all of this parts development was purely empirical, and the theory of “why it works” was developed afterwards. I’m taking some WAGs on this. It’s possible (probable!) our host has access to literature on the subject that we don’t, and I’m hoping he’ll chime in if we’ve gone way off into the weeds.

[@steviemote670]

Sam you stated you were putting permatex on the rest of the mixer. What number did you use ? Thanks

[@Danjr948]

I have never understood the water needle valve on these engines. There is no passage from the water hopper and no other water reservoir on the mixer. Where does the water come from? Was this just a useless sales gimmick to sell more engines?

[@paulclithero1822]

The water needle is connected to the coolant reservoir via a tube running from a fitting directly above the drain valve to another fitting on the left hand underside of the upper boss of the throttle body. If you find a shot in Sam’s videos with the lower plane of the mixer body visible, you will see a large slotted screw, this is a fitting which holds the check valve for the water circuit. All of this allowed the water needle to draw from the cooling reservoir when the needle valve was opened. Since the purpose of the water circuit was to cut down on pre-ignition when running on kerosene under heavy loads and high temperatures, and 90%+ of these engines today are just run at idle, many owners either do not cut the hole in the lower gasket for the water feed, omit the water feed line line entirely, or, (as ShopDog did in one of his videos, crimp the water feed line closed), as the engine will never need it. This also reduces the chances of freezing damage to the mixer from water being left in the chamber below the needle. The factory book devotes several lines to the process of clearing any water from the circuit during engine shutdown specifically to avoid freezing/corrosion damage to it. Hope this helps.