642B Carburetor Needle and Seat

[henryc97232]

Hello! This is my first post. It appears that my 642B fuel system (Mitsubishi 4G32 engine) has been damaged by the use of gas containing ethanol. All parts from the fuel tank uptake hose and screen back to the carburetor have been recently replaced. I removed the top of the carburetor and found the fuel intake screen caked with fine red dirt/rust - much of it also got onto the needle's seat and even on the seat's threads - it appears that the last person to work on it installed the screen off-center, which twisted the screen and kept it from doing its job well. A mess. I cleaned everything up and put it all back together, only to find the fuel level overflowing in the float bowl when I tried to start the engine. I had noticed some VERY shallow scratches and pitting on the needle, possibly from contact with the debris-encrusted seat. So it is probably a good idea to replace the needle and seat - and these are no longer available from Bobcat. I have looked at a few dozen carb kit photos online for 4G32 and related engines, and I don't see any pictures that have a needle and seat that appear to match what I have. Does anyone have suggestions on how to find this part? I may even purchase a new/refurbished carburetor, if such a thing exists. Thanks in advance for your help!

 

[henryc97232]

I was looking through some old posts and noticed that some people have had trouble with the carb needle valve not closing properly with the engine off, when the fuel shutoff solenoid in the fuel line between the fuel filter and pump has been removed. I do NOT have that solenoid, and I suspect that the debris in the carburetor intake has been building up for quite awhile. Could the absence of that solenoid be at least part of my problem, now that the carb intake has been cleaned up? Thanks again!

 

[alchemysa]

I cant help much with your problem but I do have a comment regarding the 'red dirt/rust.'
I recently had the same issue in a small Honda engine. The source of the rust was entirely from the fuel tank. It was rusted on the inside and constantly produced a very fine dust that eventually clogged the fine mesh filter in the gas tank.
So whatever you do you may find that rust from the tank is a constant problem. I was able to easily remove the tank and coat the inside with 2 part polyurethane. (I actually used Estapol floor finish). A Bobcat tank is somewhat harder to clean. I don't know if you can do much more than keep a good supply of disposable filters on hand.

 

[henryc97232]

I cant help much with your problem but I do have a comment regarding the 'red dirt/rust.'
I recently had the same issue in a small Honda engine. The source of the rust was entirely from the fuel tank. It was rusted on the inside and constantly produced a very fine dust that eventually clogged the fine mesh filter in the gas tank.
So whatever you do you may find that rust from the tank is a constant problem. I was able to easily remove the tank and coat the inside with 2 part polyurethane. (I actually used Estapol floor finish). A Bobcat tank is somewhat harder to clean. I don't know if you can do much more than keep a good supply of disposable filters on hand.

Thanks for the advice! I tested the fuel tank with a magnet, and it's not made of steel (except for a few metal inserts for installing parts). I am hopeful that replacing most of the fuel system got rid of most of the rust.

 

[henryc97232]

I was able to find a needle and seat kit through a dealer, though it was VERY expensive - $144! Scarce parts for this machine are definitely getting expensive....

 

[Lowe.Buuck]

I was able to find a needle and seat kit through a dealer, though it was VERY expensive - $144! Scarce parts for this machine are definitely getting expensive....

You probably didn't want to hear the cost of a replacement carb even if it was available.
I have reconditioned a number of carb seats when replacement carbs were no longer available. Many small engine carbs are $250 and up if even available at all. Most of the damage I see is from gasoline with ethanol. Brass seats will have grooves eroded across the seating surface. Lots of lawn equipment gets scrapped because carb or needle/seat are no longer available.
I did a carb for a friend last week. 1980's yard tractor with Kohler opposed 2 cylinder, but carb no longer available. Took about 45min to fix and test the seat.
$144 sounds bad until you consider you probably could not rent a machine for half a day for that amount. What is the value of the machine if you can't use it?
Fire it up, smile and get back to work. &nbsp

 

[flyerdan]

You probably didn't want to hear the cost of a replacement carb even if it was available.
I have reconditioned a number of carb seats when replacement carbs were no longer available. Many small engine carbs are $250 and up if even available at all. Most of the damage I see is from gasoline with ethanol. Brass seats will have grooves eroded across the seating surface. Lots of lawn equipment gets scrapped because carb or needle/seat are no longer available.
I did a carb for a friend last week. 1980's yard tractor with Kohler opposed 2 cylinder, but carb no longer available. Took about 45min to fix and test the seat.
$144 sounds bad until you consider you probably could not rent a machine for half a day for that amount. What is the value of the machine if you can't use it?
Fire it up, smile and get back to work. &nbsp

A bit of Google sleuthing indicates that this engine was used in the 76 and 77 Dodge Colt, and Rockauto.com has a complete carb rebuild kit for under $33. There were 2 engines used, but if you have the model number of the carb you can match it up to the listing. All new repair kits should have materials and compounds that are impervious to the corn gas that the green energy crooks have foisted upon us.

 

[henryc97232]

A bit of Google sleuthing indicates that this engine was used in the 76 and 77 Dodge Colt, and Rockauto.com has a complete carb rebuild kit for under $33. There were 2 engines used, but if you have the model number of the carb you can match it up to the listing. All new repair kits should have materials and compounds that are impervious to the corn gas that the green energy crooks have foisted upon us.

I did a lot of digging looking at carb kits. The engine itself is the same, but the carburetor on the Colt does not look the same as the carb on the 642B. I have seen posts online over the past several years by people who tried and tried to get kits that fit - it does not appear that any of the cars that use the same engine as the 642B actually have the same carb. I didn't see any way to get the model number for the carb - it's not stamped on the carb anywhere that I can find, even though "Mikuni Solex" is plainly visible on the top. I will not use gas with ethanol in this machine again - I have easy access to non-ethanol gas, though it's a bit spendy.

 

[henryc97232]

You probably didn't want to hear the cost of a replacement carb even if it was available.
I have reconditioned a number of carb seats when replacement carbs were no longer available. Many small engine carbs are $250 and up if even available at all. Most of the damage I see is from gasoline with ethanol. Brass seats will have grooves eroded across the seating surface. Lots of lawn equipment gets scrapped because carb or needle/seat are no longer available.
I did a carb for a friend last week. 1980's yard tractor with Kohler opposed 2 cylinder, but carb no longer available. Took about 45min to fix and test the seat.
$144 sounds bad until you consider you probably could not rent a machine for half a day for that amount. What is the value of the machine if you can't use it?
Fire it up, smile and get back to work. &nbsp

Lowe.Buuck, I did see a listing for a carb for $500 (I forget whether new or reconditioned), but the source didn't look trustworthy. I hadn't looked into rental prices yet, but I have thought about the option. The problem I'm facing is that the machine, even with low hours, is not in the best of shape, and many parts are becoming scarce and/or very expensive. I hope to keep it running for awhile, but at some point I may be faced with a part need that can't be filled, as the lawn equipment owners you mention are discovering. Thanks for the info!