742B sputters

[Fitz]

I have an older742B with a Mitsubishi. It started missing on higher rpm and is getting worse. Thinking lack of fuel I've replaced fuel pump with electric, all fuel lines to the tank pick up filter. I did a cylinder compression check and all were the same at 145#. I noticed the number 2 and 4 plugs were very light in color, 1&3 were as they should look, why??? Also I adjusted the timing a bit while running and when I put hand pressure on the cap the missing stopped, rotor??? I've been chasing my tail for a week on this. Anyone have an idea? One more thing , since this has gotten worse the last month the governor wants to pull the rpms down from high to mid range at max.

 

[SkidRoe]

How old are the distributor cap, rotor and plug wires? That would be my next step. Does it have points? If it does, points and condenser would be on my list too.

 

[Fitz]

That makes sense. I replaced the points and rotor a few years ago along with new plug wires last summer. I couldn't find a cap or condenser at the dealer or NAPA. I pulled the cap and noticed a bit of grey fine dust in it. Rotor arcing ? Any other resources I could try for a cap/condenser?

 

[SkidRoe]

Shot in the dark - The Dodge Colt of the 1970's was a rebadged Mitsubishi and used the 4G32 engine. RockAuto lists ignition parts for these cars...

 

[brdgbldr]

That makes sense. I replaced the points and rotor a few years ago along with new plug wires last summer. I couldn't find a cap or condenser at the dealer or NAPA. I pulled the cap and noticed a bit of grey fine dust in it. Rotor arcing ? Any other resources I could try for a cap/condenser?

You can still get a cap and rotor through https://shop.bobcat.com.
I actually just bought a couple of caps and rotors for my 742B which I am now in the process of selling. As for the points, I would suggest swapping to a magnetic pickup. This also gets rid of the resistor and the condenser but you also have to upgrade the coil.
I just had a problem with my 742B and bought the extra caps rotors, and another magnetic pickup and coil since I thought I was chasing an ignition problem, It was not the ignition. Contact me if you would be interested in buying them from me.

 

[keesling1]

as far as the points and condenser go, google "transdesor 2" a electronic ignition switch, very simple. i have used on every thing from
lawn tractor to farm tractor. works great. make Shure your coil pos. resistance is ONLY 4 to 6 ohms.
those old mitsubishi engines, some had a JET valve that the o rings would crack and load up the effected cyl. with oil.
if yours has them, screw them out and clean them up, replace o ring seals, don't replace them .

 

[Fitz]

as far as the points and condenser go, google "transdesor 2" a electronic ignition switch, very simple. i have used on every thing from
lawn tractor to farm tractor. works great. make Shure your coil pos. resistance is ONLY 4 to 6 ohms.
those old mitsubishi engines, some had a JET valve that the o rings would crack and load up the effected cyl. with oil.
if yours has them, screw them out and clean them up, replace o ring seals, don't replace them .

Thanks for the advise but I did find a cap and ignition kit including condenser. I just came in from the garage after installing new plugs, points, condenser, rotor and cap. It runs smooth now with no sputtering at all. I don't know what exactly was the problem but thanks SkidRow for the suggestion. It still gets throttled back by the governor when I tried to bring the rpms way up, any thoughts on that??

 

[Wayne440]

...It still gets throttled back by the governor when I tried to bring the rpms way up, any thoughts on that??

Define "way up", one function of the governor is to limit the RPM. I think maximum governed RPM is 2800.

 

[Fitz]

Define "way up", one function of the governor is to limit the RPM. I think maximum governed RPM is 2800.

I can't really say since there's no tach, When working it under load I would go full throttle then back off a bit so as not to starve the pumps. Being a gas engine it's not exactly a powerhouse but it plows snow. I never noticed the governor even doing anything till lately dropping the rpms down. What are the other functions of it??

 

[Wayne440]

The governor limits engine RPM, and controls the carburetor throttle plate position to maintain reasonably constant engine speed.

Using a car as an example, you go up a hill in a car, step harder on the accelerator to maintain speed- but when you push into a pile of snow, you do not have to change your 742b throttle, the governor does that. The governor is like auto "cruise control" it keeps the engine speed fairly constant until you run out of power. Without the governor, you would have to manually adjust the throttle when the load changes.

IF this was my machine, I would consider hooking up a tach, timing light or other means to see what the governed RPM actually is, and change the governor oil and check the belt tension. Many people fail to realize that the governor has its own oil which should be checked and changed as needed.

 

[Tango-Charlie]

Hey Fitz,
I also have been the happy owner of a 742B gasser with the Mitsubishi 4G32. I've put a few bucks into it as problems developed but for the past few years, I've had no problems and love the machine. Below is a copy of the common tune up parts that I've made over the years. Reference your original problem I cured mine by changing out the points and coil with a Pertronix electronic ignition and coil. I want to also say that I'm no way affiliated with Pertronix.

After the swap over to electronic ignition I got rid of the miss problem, and it runs sweet. I also replaced cap and rotor which I searched the internet for the below listed part numbers. I think I may have also order something from Rockauto but be careful that they don't swap something out for what you originally ordered. I try to stay away from the dealer as their prices are so high compared to searching on the internet. But at times I've had to get parts from the dealer too.

All in all after the swap over this machine runs great but is a little cold blooded in winter below freezing for starting. But using the blocked heater or keeping it inside overnight cured that issue. I love my 742B so much that I actually found a brand-new original in cab heater that I installed.

As a side note another smaller issue snuck up on me and I started getting a gas smell in the garage. I found someone had removed the original electronic gas shut off solenoid. I did some searching and found the original manufacturer of the solenoid and purchased it through them even though the Dealer said no longer available.

I even rebuilt one of the lift cylinders when it started dripping. By the way I'm only a backyard mechanic so I've ventured into some unknown territory with hydraulics but happy with my outcome. I also finally broke down and purchased a new governor as one of the side seals was dripping on the old one and I couldn't find a seal replacement.

Regarding your latest dropping out of high RPM. Have you checked the oil level in the governor?
I know it sounds stupid because when I got my 742B I didn't know the governor had a separate oil reservoir. It's easy to check. If the governor is pulling the RPM's down, then I'd agree with the other comment that the governor is probably doing its job. But I'd still check the oil. If it was running fine in the past, I wouldn't mess with the governor linkage to carb or stops on the governor. I borrowed an older tach/dwell meter from a friend's shop in order to set the high and low RPM's.

If I can help with anything just ask because I'm a happy 742B gasser owner.

Mitsubishi 4G32 Gas Engine

Distributor Number T3T05772 C

Coil – Manufacturer – Pertronix - Flame Thrower II Part # 45111

Electronic Ignition – Manufacturer - Pertronix Ignitor II Part # 91943

Distributor Cap - Manufacturer – Standard – Part # JH67

Distributor Rotor - Manufacturer – Intermotor SMP – Part # JR80

Spark Plugs – Manufacturer – Champion – 405 RN14YC

Denso – W14EX-U

Spark Plug Gap .028 - .031 – Set at .030 for Electronic Ignition

Timing 5 degrees BTDC @ 600-650 RPM w/Vacuum Hose Disconnected

2800 RPM/Vacuum disconnected the timing should advance 10 degrees

 

[Fitz]

Great info guys, thanks. Wayne440, the governor explanation was perfect and I did see that it was low on oil so I added a 90wt gear lube. I have a timing light with a tach so I'll be able to check the rpms as suggested. Knowing what it's function is now I can understand how it's working. 63012753, thanks for the parts list and Petronix info. The parts guy at the dealer also suggested going that direction instead of paying $130 for the cap and ignition kit. I'll be picking your brain on the lift cylinder rebuild, I just noticed a leak in one.

 

[Wayne440]

90wt is certainly better than running dry, but the governor should have engine oil in it. Also do not tighten the belt too much, the governor bearing will not stand much tension.

 

[Tango-Charlie]

Great info guys, thanks. Wayne440, the governor explanation was perfect and I did see that it was low on oil so I added a 90wt gear lube. I have a timing light with a tach so I'll be able to check the rpms as suggested. Knowing what it's function is now I can understand how it's working. 63012753, thanks for the parts list and Petronix info. The parts guy at the dealer also suggested going that direction instead of paying $130 for the cap and ignition kit. I'll be picking your brain on the lift cylinder rebuild, I just noticed a leak in one.

Great info guys, thanks. Wayne440, the governor explanation was perfect and I did see that it was low on oil so I added a 90wt gear lube. I have a timing light with a tach so I'll be able to check the rpms as suggested. Knowing what it's function is now I can understand how it's working. 63012753, thanks for the parts list and Petronix info. The parts guy at the dealer also suggested going that direction instead of paying $130 for the cap and ignition kit. I'll be picking your brain on the lift cylinder rebuild, I just noticed a leak in one.

Hey Fitz,

My 742B 4G32 gasser manual says to use the same oil that you use in the engine for the governor. I think mine was 10W30. The 90wt gear lube may be way to thick especially in the winter. I would drain the 90wt in the governor and put what the manual calls for which I believe mine was 10w30. You surely don't want to have to replace the governor because the oil weight was too heavy and blew a seal. I had to replace my governor because I couldn't find the side shaft seal and the governor was $1200 ouch. But I kept the old governor and going to take my time to see if I can find a suitable seal replacement from a seal manufacturer. If I recall right when adding oil to the governor remove the back and top plugs and fill via the top plug until you have oil coming out the back plug. Then replace both plugs. I think I read a caution in the manual that said you don't want to overfill the governor because it will create too much pressure inside the governor and possibly blow out a seal.

When I ordered my Pertronix electronic ignition I sent Pertronix my distributor number from the side of the distributor shaft to ensure they matched up the new module to my distributor. Just a little wiring and eliminating the resistor and putting in the new coil and it fired right up. Been running perfectly for years.

Hope this helps.

 

[brdgbldr]

Here are the electronic ignition parts for the 742B.
Pertronix 1941 Mitsubishi 4 Cylinder Ignitor

PerTronix 40511 Flame-Thrower 40,000 Volt 3.0 ohm Coil

You can currently buy these on Amazon for about $115 together.
I have a brand new set that I can't use, and depending on how much shipping would be, I'd be willing you give you a deal on them If you're interested. Otherwise, Amazon has been the cheapest place that I've been able to find them. I'm trying to get rid of all the extra parts I have lying around for my 742B.

 

[Fitz]

I'm glad you caught that 90wt oil in the governor mistake of mine, I sure don't need another issue to fix right now. I drained it and added the 10w/30 to the top of the overflow plug. Thanks brgdbldr but after spending $130 on ignition parts that seemed to solve the problem I think I'll leave it as is for now… "if it ain't broke don't fix it", I may be kicking myself if the problem comes back for not buying it. Thanks everyone for the help. I'm a happy 742B gasser now, not a frustrated one

 

[dfb]

Hey Fitz,
I also have been the happy owner of a 742B gasser with the Mitsubishi 4G32. I've put a few bucks into it as problems developed but for the past few years, I've had no problems and love the machine. Below is a copy of the common tune up parts that I've made over the years. Reference your original problem I cured mine by changing out the points and coil with a Pertronix electronic ignition and coil. I want to also say that I'm no way affiliated with Pertronix.

After the swap over to electronic ignition I got rid of the miss problem, and it runs sweet. I also replaced cap and rotor which I searched the internet for the below listed part numbers. I think I may have also order something from Rockauto but be careful that they don't swap something out for what you originally ordered. I try to stay away from the dealer as their prices are so high compared to searching on the internet. But at times I've had to get parts from the dealer too.

All in all after the swap over this machine runs great but is a little cold blooded in winter below freezing for starting. But using the blocked heater or keeping it inside overnight cured that issue. I love my 742B so much that I actually found a brand-new original in cab heater that I installed.

As a side note another smaller issue snuck up on me and I started getting a gas smell in the garage. I found someone had removed the original electronic gas shut off solenoid. I did some searching and found the original manufacturer of the solenoid and purchased it through them even though the Dealer said no longer available.

I even rebuilt one of the lift cylinders when it started dripping. By the way I'm only a backyard mechanic so I've ventured into some unknown territory with hydraulics but happy with my outcome. I also finally broke down and purchased a new governor as one of the side seals was dripping on the old one and I couldn't find a seal replacement.

Regarding your latest dropping out of high RPM. Have you checked the oil level in the governor?
I know it sounds stupid because when I got my 742B I didn't know the governor had a separate oil reservoir. It's easy to check. If the governor is pulling the RPM's down, then I'd agree with the other comment that the governor is probably doing its job. But I'd still check the oil. If it was running fine in the past, I wouldn't mess with the governor linkage to carb or stops on the governor. I borrowed an older tach/dwell meter from a friend's shop in order to set the high and low RPM's.

If I can help with anything just ask because I'm a happy 742B gasser owner.

Mitsubishi 4G32 Gas Engine

Distributor Number T3T05772 C

Coil – Manufacturer – Pertronix - Flame Thrower II Part # 45111

Electronic Ignition – Manufacturer - Pertronix Ignitor II Part # 91943

Distributor Cap - Manufacturer – Standard – Part # JH67

Distributor Rotor - Manufacturer – Intermotor SMP – Part # JR80

Spark Plugs – Manufacturer – Champion – 405 RN14YC

Denso – W14EX-U

Spark Plug Gap .028 - .031 – Set at .030 for Electronic Ignition

Timing 5 degrees BTDC @ 600-650 RPM w/Vacuum Hose Disconnected

2800 RPM/Vacuum disconnected the timing should advance 10 degrees

I am having a similar problem with the gas smell and think my solenoid has been removed also. Can you share the info on where you found the replacement, please. Much appreciated!

 

[brdgbldr]

The fuel shutoff solenoid on my carb quit working and I figured it out because the oil level was getting higher and smelled like gas. The solenoid had failed open and all the fuel was being gravity fed into the engine. I was lucky that I found it before there was a fire.
I ended up installing an electric fuel shutoff solenoid after the filter and hooked it up to the ignition. Fixed the problem.

On a side note, I have a brand new Mikuni-Solex 2bbl carburetor, in a sealed package, for a Mitsubishi 4G32 industrial engine. It is the same carburetor for the 742B but the linkage is different ( easily swapped over ). Anybody know what these are actually worth? I found a couple places that wanted between $1100 and $2000 for one. I'm thinking about selling it and while I don't want to gouge someone I also don't want to give it away.

 

[tjacobson01]

A few points regarding 742B Mitsubishi 4G32 engine from my experience..., FYI:

1) I spent days trying to figure out why mine would not run well... even tore it down and checked timing belt etc.! Drove me nuts. Had a nice bright blue spark... everything else was also correct, rebuilt a spare carb I had, no luck, would sort of run if I put ether in it. Finally ended up being the coil... it made a nice bright spark, but was delayed/out of time due to failing insulation or something in the coil, put in a different coil, and it fixed it....

2) These engines are known for spinning big end rod bearings.... I strongly suggest one should change oil frequently, and keep it topped up, and use correct weight oil. It might be worth it to change to synthetic oil....

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).

If I had it to do over again, I might be temped to re-engine my 742B... s/b easy since all you have to do adapt the coupling U joint. Then you would have a nice modern engine with electronic governor...

 

[Ktmadventure450]

The fuel shutoff solenoid on my carb quit working and I figured it out because the oil level was getting higher and smelled like gas. The solenoid had failed open and all the fuel was being gravity fed into the engine. I was lucky that I found it before there was a fire.
I ended up installing an electric fuel shutoff solenoid after the filter and hooked it up to the ignition. Fixed the problem.

On a side note, I have a brand new Mikuni-Solex 2bbl carburetor, in a sealed package, for a Mitsubishi 4G32 industrial engine. It is the same carburetor for the 742B but the linkage is different ( easily swapped over ). Anybody know what these are actually worth? I found a couple places that wanted between $1100 and $2000 for one. I'm thinking about selling it and while I don't want to gouge someone I also don't want to give it away.

Did you just leave the mechanical fuel pump mounted to the engine block and maybe block off ingoing and outgoing fuel line pump ends?
Thanks