Just Looking for Some Input

[James Combs]

I have a small problem, just thought I would get some other input.
Background:
I have two rider mowers, an old 73 vintage Craftsman that I use as a tractor and a 6-8yr old Troy-Built Bronco which I do the mowing with. Both have Briggs engines and both have carburetors that leak and will fill the crankcase with gasoline if I don’t turn the gas off to the carb someway. Have installed manual shutoffs on both machines which has worked well except when I forget to turn the valve off. Given my sometimes forgetfulness I have purchased a couple 12volt fuel rated solenoid valves to do the for me automatically since I seem to be loosing my memory functions. Adding valve will not be a problem on the Troy-Built because there is a 12volt anti-after-fire circuit going to the carb which I can tap into. The anti-after-fire circuit is supposed to keep the engine from doing that big backfire like noise when you turn it off, it has 12volts available anytime the ignition is on. However, the old Craftsman does not so I needed a new ignition switch with additional contacts to do the same thing.
The Problem:
I purchased a “MaxPower 9623 Ignition Switch” which should have done the job, however, while checking it to verify that continuity through the contacts was compatible with my old Craftsman switch which should have been the case, I discovered what I think is a problem/defect with the switch. If you research lawn mower ignition switches you will find that “most” have the same IDs on the connector terminal lugs on the back of the switch. For example, most will have a “G” for ground, “B”-battery, “M”-magneto, “L”-lights and “S”-start stamped next to the appropriate terminal. Others may add “A”-auxiliary1 and “Y”-auxiliary2 or they may be A1 and A2. By hooking up my ohm meter to various combinations of these terminal lugs I can verify continuity between any two given terminals depending on the position of the switch key. I have included a copy of a graphic representation of the internal connections of a switch I found on line which for the most part matches the new switch except in one area. I have added dashed red lines to the “Start” position graphic which shows the difference and the problem. In my experience G and M should never be connected together except in the off position. Any time M is connected to G or ground the magneto is in “Killed” or off status which kills the engine, that’s exactly how the engine is shut down when the key is turned to the off position. The engine will never start with this switch?? Unless there is something I am missing in the design of more modern mower ignition systems this switch is defective. I have also included a short video of me testing the G and M terminals.
Question:
Is there anyone out there that can confirm for me that this is a defective switch or that it is correct and just works differently in today’s more modern ignition systems? If it is correct I would sure love to see a circuit diagram or schematic showing how it is used.

This pic is a graphical representation of the internal connections of the switch. All positions are ok and match my old switch except the last position, "Start", the dotted red should not be there, also my old switch does not have A&Y.
9623-Con-Chart.jpg

I appreciate any and all comments and feedback.

As it turns out I could use the L circuit on my old switch except it is ~40yrs old or so. My old Craftsman uses a separate light switch and not the L circuit. I will be using a new switch in any case but it doesn't look like it will be this one.

Just bought another switch, a Stens 430-674 which according to cross-differences should be the same as the MP 9623. When I get it I will post what I find out about the Stens' start position circuits. Oh and BTW, truth tables, graphics like the above and other contact info for compatible switches that I have been able to find do not show the G to M connection. For example this circuit for a Murray mower uses a similar compatible switch.

The 95226 switch shown in the lower corner crosses to the Stens 430-674 and to the MP 9623. My MP would not work in this circuit.
Note the terminal truth table below the switch.
2011-02-13_182813_murray.gif

[Dan Hunkele]

You are making it too complicated. All you need is a terminal on the switch that is putting out 12V when it is in the run position. The 12V will open the valve and let the fuel through and will close when you take the 12V away. The valve will need grounded if it is put inline in the hose. Hope this helps.

[Nike Nihiser]

Wouldn't it be better to rebuild the carburetors to fix the real problem?

[John K Jordan]

Wouldn't it be better to rebuild the carburetors to fix the real problem?

I wondered the same thing. I've never had a carburetor that leaked except once on a motorcycle and I fixed it right away. But I don't think I have any Briggs & St. engines.

[Lee Schierer]

I've had several B&S engines and never had a leaky carburetor. I also owned a Craftsman lawn mower for many years with a B&S engine and it didn't leak either. I have rebuilt one or two carburetors with rebuild kits and never had one leak. Parts for most B&S engines are readily available so fixing a leak should be pretty straight forward.

[James Combs]

All great advice folks, but... ;-)

You are making it too complicated. All you need is a terminal on the switch that is putting out 12V when it is in the run position. The 12V will open the valve and let the fuel through and will close when you take the 12V away. The valve will need grounded if it is put inline in the hose. Hope this helps.

Hi Dan, yeah, I get a little wordy in my old age but I am having fun. Really appreciate the look and comments. I am x-Navy electronics and electrically trained, 24yrs & 9mths experience. I actually could do what I want with the old switch but the real issue for me was the quality of the new switch and wondering if I was miss understanding the use of it's terminals in maybe some new ignition scenario/circuit that I had not seen as yet but I have since determined it was just a bad "new" switch.

Wouldn't it be better to rebuild the carburetors to fix the real problem?

I wondered the same thing. I've never had a carburetor that leaked except once on a motorcycle and I fixed it right away. But I don't think I have any Briggs & St. engines.

I've had several B&S engines and never had a leaky carburetor. I also owned a Craftsman lawn mower for many years with a B&S engine and it didn't leak either. I have rebuilt one or two carburetors with rebuild kits and never had one leak. Parts for most B&S engines are readily available so fixing a leak should be pretty straight forward.

Thanks for looking Nike, John, Lee and as always I like and appreciate any and all comments. As for carb kits, I have done that a few times with different machines but in the case of these two Briggs I seem to get only a few years out of a rebuild. Would be using the machine a few years latter and go out to start it up for a new mowing and the crank is locked due to gasoline in the cylinder bore so I solved the problem by putting in a manual valve in the fuel line and it works great, if I remember it. LOL That was a few years ago and now I just want to take the memory issue out of the equation. Besides I am keeping my hands busy at the same time chatting with some great folks on SMC .

[James Combs]

Someplace in my "wordy" original post I think I said something about getting another switch. I did get another and this time I got a Stens 430-674, except for markings it looks identical to the MaxPower 9623 and they both appear on many compatibility lists I have seen in my research. It arrived this morning, long story short, the Stens does not have the issue and was even cheaper. The MaxPower is on it's way back to the seller.

BTW, I did have a lot of fun in researching the problem and actually learned several things about Lawn/Garden tractor ignition circuits. Thanks to all who read or at least attempted to read my OP and especially thanks to those who commented.

[Tom M King]

Replacement carbs are cheap on the auction site. They're almost as cheap as a carb kit. I keep a spare carb for a generator that only gets used for the, fortunately rare, large hurricanes. If a carb is leaking, it probably has other issues as well-like hard to start, poor idle, or pulsing.

I do think a simple manual cutoff switch should come on any machine to start with though. Our bought new, 1980 Troybilt tiller has one, and I've never been in that carburetor.

When a carb does need rebuilding, the best helper I've found is a white dish pan.

Since running non-ethanol in all the small equipment, including the newer stuff that's supposedly made for it, we haven't had a carburetor issue in years, and have too much stuff to start every month. It wouldn't surprise me a bit if ethanol was the cause of the leaking to start with.

Even with the auto cutoff circuit, I'd still replace the carbs, since they probably have leaking floats, or some other issue, and the needle valves are probably close to end of life anyway, regardless of their age. If the float is corroded, the needle valves, and or seats, probably are too

[Bruce Wrenn]

Another option, after switching to alcohol free gas is to run some "Mechanic in a Bottle" thru mower. I don't how this stuff works, only that it does. One of the local places that fixes commercial mowers turned me on to it. It will soften rubber in needle seat, so it seals. Available at Walmart and HD, with Walmart being cheaper.