642B Carburetor and fuel pump

[DAW]

I have a Melroe 642B. I think it needs the carb rebuilt and new mechanical fuel pump. Any advice on where to get the carb kit and fuel pump for this motor (not the $800. dollar one from Bobcat). I think the motor is a 4G32 and the Carb is 28-32 DIDSA. I can find the kit for 28-32 DIDTA but not SA.

 

[brdgbldr]

"3) For the carb, you can use a rebuild kit for a MIKUNI SOLEX Model 28-32DID - Many of the parts found in kits like the Walker Products KIT #15581B intended for auto market also fit this industrial carb. Very important that the float valve is works well, and you have a fuel shutoff solenoid (often people remove it)."

I found that under the post "742B Sputters"

I have a brand new Mikuni-Solex carb. But it is worth its weight in gold it seems. So I doubt you want to buy it.
The 742B also has the Mitsubishi 4G32 engine. You may want to search the posts for the 742B to answer engine questions.

As for the fuel pump, I just used the brand new one I had lying around. I think your best bet is to go with an electric fuel pump. This is one I was looking at years ago for my 742B because someone on here suggested it to me.

Beck Arnley 152-0576Fuel Pump - Universal Electric

Amazon product ASIN B000CB32U2
You may be able to take your old fuel pump into a good parts shop and maybe they can find a replacement. I've been told that the 4G32 is based off of an old Mitsubishi Lancer engine but who knows.

 

[Kalbiking]

"3) For the carb, you can use a rebuild kit for a MIKUNI SOLEX Model 28-32DID - Many of the parts found in kits like the Walker Products KIT #15581B intended for auto market also fit this industrial carb. Very important that the float valve is works well, and you have a fuel shutoff solenoid (often people remove it)."

I found that under the post "742B Sputters"

I have a brand new Mikuni-Solex carb. But it is worth its weight in gold it seems. So I doubt you want to buy it.
The 742B also has the Mitsubishi 4G32 engine. You may want to search the posts for the 742B to answer engine questions.

As for the fuel pump, I just used the brand new one I had lying around. I think your best bet is to go with an electric fuel pump. This is one I was looking at years ago for my 742B because someone on here suggested it to me.

Beck Arnley 152-0576Fuel Pump - Universal Electric

Amazon product ASIN B000CB32U2
You may be able to take your old fuel pump into a good parts shop and maybe they can find a replacement. I've been told that the 4G32 is based off of an old Mitsubishi Lancer engine but who knows.

Why it so important to have fuel shutoff?

 

[brdgbldr]

Why it so important to have fuel shutoff?

The fuel tank is above the carb. That means that there is always fuel pressure, from gravity, pushing into the carb.

When my fuel shutoff failed, and the machine sat idle for a couple of weeks, I noticed, when checking the oil, that the level had risen. Upon closer inspection there was fuel in the engine oil. If I had not noticed this before starting the machine, at best I would have killed the engine, at worst a fire would have destroyed the machine.

 

[Kalbiking]

The fuel tank is above the carb. That means that there is always fuel pressure, from gravity, pushing into the carb.

When my fuel shutoff failed, and the machine sat idle for a couple of weeks, I noticed, when checking the oil, that the level had risen. Upon closer inspection there was fuel in the engine oil. If I had not noticed this before starting the machine, at best I would have killed the engine, at worst a fire would have destroyed the machine.

Thats not the reason.Fuel in your oil isnt good but it wont kill your engine. My machine has tank below carb from factory Bobcat. Main reason is to stop pre ignition backfire.

 

[dfb]

Thats not the reason.Fuel in your oil isnt good but it wont kill your engine. My machine has tank below carb from factory Bobcat. Main reason is to stop pre ignition backfire.

Brdgbldr is correct on both the need for a fual shut off and the damage that can result from leaking gasoline washing the oil of the cylinder walls or diluting the engine oil enough to cause bearing damage

I just changed the engine oil in my 742B that is in need of the fuel shut off, there is absolutely more gasoline present in the oil than there should be.The machine runs great but sitting inside over night in the shop it will stink the place up with a strong smell of gas. I will be installing another shutoff to replace the one that no longer works in the carb{it was disabled years ago when I had stalling problems.

 

[Kalbiking]

Thats your float needle not sealong against the seat and can happwn with any carbed engine. Yes diluted engine will eventually cause bearing failure but not the first time you run it.

 

[Tango-Charlie]

When I bought my 742B years ago the previous individual put in a manual shut off valve between the fuel tank and carb line. It came out just below the right lift arm. I always had to remember to turn it on or more importantly turn it off. I found that in the winter when I had it in my house heated garage ready to move snow I would find out that I forgot to turn it off by the heavy smell of gasoline because it was still gravity feeding from the tank. So, I did a lot of research and found the electric gas shutoff valve that my 742B called for. I was floored at the price that Bobcat wanted and dug deeper into my research. I was able to find the exact manufacturer for the bobcat part from the tag on another bobcat shutoff. Long story short I ordered a couple directly from the manufacturer at 1/3 the price that Bobcat was charging. On my 742B the wiring harness already had the connector above where the fuel shutoff was originally installed. I think I mentioned the manufacturer and where to get one of them in my other posts. Brdgbldr and dfb are correct that you want some type of fuel shut off either manual valve or electronic. I'm an older wrencher and was taught to smell transmission oil to see if its burned back in the day. I also sniff the oil dip stick which one might be able to smell a hint of gas if it's getting into your oil.

 

[Kalbiking]

Well cars have tank below carburetor. Why does mitsu car carb have shut off solenoid? Also it has a mechanical.fuel pump. Fuel going travel from.tank up to mechanical.fuel pump and up to carb? Photo is 1979 colt carb.

 

[UnexpectedBill]

The fuel shutoff solenoid prevents deiseling when you turn it off by stopping any fuel from being drawn in after the ignition system is off.

 

[dfb]

UnexpectedBill is correct, service information for those cars refers to it as an anti dieseling solenoid. It kills fuel flow through the idle circuit.

 

[Kalbiking]

The fuel shutoff solenoid prevents deiseling when you turn it off by stopping any fuel from being drawn in after the ignition system is off.

Yes 100% . most here think it's to stop flooding.

 

[brdgbldr]

The fuel shutoff on the 642s and 742s with Mitsubishi engines was not enough to stop the dieseling. They have a separate anti-dieseling solenoid hooked up separate from the carb.

It is actually an air valve that is connected from the horn to the intake bypassing the carb. This would keep the fuel from being sucked out of the carb while the engine was stopping despite the fuel shutoff.

It is part number 31 in the attached schematic.

 

[Kalbiking]

I got a bobcat trencher with the mitsubishi. Doesnt have that

 

[brdgbldr]

I got a bobcat trencher with the mitsubishi. Doesnt have that

I'm sure not all equipment had them.

My 742B had one but it was not working so it was removed and I just dealt with the dieseling.

The photo you posted wouldn't show it if it did have one because they were on the intake side of the engine, not the exhaust.

 

[UnexpectedBill]

The solenoid on the carb only shuts off the idle circuit. Unlike cars skids have fixed throttles, not spring return. If the throttle isn't closed when its turned off, there's still fuel being drawn through the main circuit venturi booster and a hot engine could still diesel. I'm guessing the air valve opens to create a big vacuum leak to stop that.