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Long on-going problem with Tecumseh Engine Model: OHH50-68023J. Carb leaking. OEM carb part # 640340. After many years of service the carb suddenly started leaking. Motor is part of a Cyclone Rake tow behind vac. I'm stumped. I have rebuilt my share of carbs but this problem which SEEMS like a common one, cannot be fixed. I have tried "everything".

Rebuilt the orignal carb about 7 years ago. Worked fine until just last year.
Rebuilt original again but this time the carb started leaking after 5 to 10 minutes of being pulled around the yard picking up leaves.

Rebuilt carb again. Same problem. Runs while stationary and all is fine .. then start driving around yard and within 5 to 6 minutes engine floods and stalls and gas starts pouring out of carb mouth.

So I bought a new carb. Replace the NEW carb. And same thing. after towing it around the yard for five minutes engine stalls and gas pours out of brand new carb.
So I took the brand new carb apart carefully, check float level, checked float for leaks etc. examined the needle and seat and all looked fine. Put it back on the engine and same problem.

Checked everything. Finally bought a 2nd new carb. Same thing. Check fuel tank all hoses, and everything is fine. Unfortunately I when I bought the first new carb I tossed my orginal one. The first and 2nd replacement carbs were cheap China made things and both had different needle setups. One had the float needle with a normal press in place seat. Then next new version they got rid of the seat and instead manufactured the needle with a rubber tip on it that made it's seal directly with the metal of the carb. That one also poured gas out like an open faucet after 7 minutes.

So I then decided I needed to find an original OEM carb and found someone with some NOS units for sale for about 4 times what I was paying for the China units. I bought one. It was an OEM product made in US, and was exactly like the 11 year old one I had thrown away. I installed that and STILL had the same problem.

Engine always starts on first pull. Runs properly and correct but only for 5 to 6 minutes. This has me stumped. Once the engine stalls and the fuel starts pouring out of the carb mouth, it does not stop. It's like I opened up a faucet.

The Cyclone Rake I'm using is in perfect condition and my problem is they no longer make engines for my model and a new engine would require a change to their newer Briggs line which has different mounts and would require I also purchase a new blower impeller and housing. It would be cheaper for me to buy a whole new unit. Anyone have a clue why the carbs keep doing this?

When it stops pull the fuel line off
If it blows out like a fire hose then you are getting a pressure build up in the fuel tank

Rich A said:

So I took the brand new carb apart carefully, check float level, checked float for leaks etc. examined the needle and seat and all looked fine.

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Noting but a visual test. Now you need a functional test on it. New doesn't mean new these days.

As Bert is hitting on - Try removing the fuel cap. Possible tank over pressure condition after a few minutes of the fuel sloshing around. This tank cap might not be venting. Listen for a soda can pressure sound when opening the cap.

If this is the plastic fuel tank mounted on the engine with the thick cap threads, people are bad at overtightening the cap. On those the cap vents through the thread gaps, and if tightened down beyond a light seat will seal off the thread passage and cause overpressure and/or venting issues.

Ah thanks guys. I thought about that, and DID notice once in a while while the thing was stored for a while with some gas in the tank that when the temperature changed over night from very cold to hot (been having extreme weird weather here lately) when I cracked the gas cap to add gas I could hear the sound of air escaping from pressure built up in the tank. I examined the cap carefully and could not see any type of vent hole or other way of releasing the pressure. The cap is the original (about 12 years old). I think the comments from others, especially ILENGINE might be exactly what is happening.

I've tried a LOT of things .. and I THINK one or two of the many dozens of times I tested, I did try running it with the cap just loosely screwed on. But my memory on that is suspect <grin> Not seeing any kind of vent hole or other signs of venting on the cap, I dismissed that as a problem. Never heard of the "thread" vent thing? I'll try again today and leave the cap loose, but I have to ask if I can find a proper new cap do you think that will work? I wonder if I can try drilling a very small vent hole in the cap? I ask because I'm worried leaving the cap too loose will cause it to loosen too much and start leaking fuel. Should I try to locate a new cap ??

Rich A said:

Ah thanks guys. I thought about that, and DID notice once in a while while the thing was stored for a while with some gas in the tank that when the temperature changed over night from very cold to hot (been having extreme weird weather here lately) when I cracked the gas cap to add gas I could hear the sound of air escaping from pressure built up in the tank. I examined the cap carefully and could not see any type of vent hole or other way of releasing the pressure. The cap is the original (about 12 years old). I think the comments from others, especially ILENGINE might be exactly what is happening.

I've tried a LOT of things .. and I THINK one or two of the many dozens of times I tested, I did try running it with the cap just loosely screwed on. But my memory on that is suspect <grin> Not seeing any kind of vent hole or other signs of venting on the cap, I dismissed that as a problem. Never heard of the "thread" vent thing? I'll try again today and leave the cap loose, but I have to ask if I can find a proper new cap do you think that will work? I wonder if I can try drilling a very small vent hole in the cap? I ask because I'm worried leaving the cap too loose will cause it to loosen too much and start leaking fuel. Should I try to locate a new cap ??

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From my Tecumseh school training the proper tightness is to start the threads on the tank and then grab the cap and then flick your wrist to spin the cap down on the threads, and when it stops don't touch it.

Stop turning the cap when the cap stops turning. Gentle snug is all you need.

If you have to make a vent hole, take a small paperclip. Use a propane torch to heat the tip. Shove the hot clip into the cap. Don't need a big hole. Course now your tank is vented. Fuel will deteriorate faster and possibly leak out of the cap. Best to get a new OEM cap.

Yeah, I do regular maint. on all my stuff. Cars, trucks, tractors, appliances etc. Enjoying retired life on a mountain top in the middle of a forest where I do daily battle with chipmonks, mice and squirrels. They get into everything so keeping the machinery clear of acorns etc. is part of my normal routine.

This leaking carb is really strange. Update: I made a nice clean hole (about 1/16") in the gas cap. Note this old orignal cap and this problem with the leaking carb. only started a year ago. I've been tightening the cap normally (as I have always done) for many years. I know how it works. Had an old Techumseh powered snow blower that also had a similar cap that HAD to be tightened only loosely or it wouldn't run correctly. This cap I'm dealing with has a concave curve metal plate and small loose fitting rubber flap that is press fit into the cap. This is the way it came as delivered and I've not touched it. However yesterday I examined it carefully and thought it may not be working correctly and might be the problem. (I forget exactly but I think this engine is close to 12 or more years old). The rubber looks pretty bad and maybe it's no longer allowing air to escape. The thing looks like it's designed to be loosely tightened to the point where the thing keeps the gas from splashing out, but still allows air to equalize in the fuel tank so as to not build up pressure. So yesterday I removed it, and made a vent hole in the cap. So it is now just a plain old gas cap with an added vent hole. And then tried it. It "sorta" worked. Normally it runs for 5 minutes or so and then engine stalls and gas starts pouring out. This time I ran for a full 1/2 hour at which time while it was still running (and NOT leaking) I had to shut it off so I could dump the clippings.

I was emptying the several bushels of clippings, and while the thing was sitting there not running, the carb. started pouring gas out. I'm doing a few acres so I was only about half finished. And I had shut off the engine and then drove a few minutes out to the place where I unload the debris. It didn't start leaking until I started unloading several minutes after I shut the engine off. Looks like the vent hole I made in the cap only increased the amount of time it runs before it starts leaking. And I did examine the hole carefully and it was NOT plugged .. completely clear.

So I'm looking to find an original OEM gas cap for this thing, but still don't know why the vent hole in the cap only "delayed" the leaking and gave me an additional 20 minutes more of "non-leaking" time, but didn't stop it.

Rich A said:

Long on-going problem with Tecumseh Engine Model: OHH50-68023J. Carb leaking. OEM carb part # 640340. After many years of service the carb suddenly started leaking. Motor is part of a Cyclone Rake tow behind vac. I'm stumped. I have rebuilt my share of carbs but this problem which SEEMS like a common one, cannot be fixed. I have tried "everything".

Rebuilt the orignal carb about 7 years ago. Worked fine until just last year.
Rebuilt original again but this time the carb started leaking after 5 to 10 minutes of being pulled around the yard picking up leaves.

Rebuilt carb again. Same problem. Runs while stationary and all is fine .. then start driving around yard and within 5 to 6 minutes engine floods and stalls and gas starts pouring out of carb mouth.

So I bought a new carb. Replace the NEW carb. And same thing. after towing it around the yard for five minutes engine stalls and gas pours out of brand new carb.
So I took the brand new carb apart carefully, check float level, checked float for leaks etc. examined the needle and seat and all looked fine. Put it back on the engine and same problem.

Checked everything. Finally bought a 2nd new carb. Same thing. Check fuel tank all hoses, and everything is fine. Unfortunately I when I bought the first new carb I tossed my orginal one. The first and 2nd replacement carbs were cheap China made things and both had different needle setups. One had the float needle with a normal press in place seat. Then next new version they got rid of the seat and instead manufactured the needle with a rubber tip on it that made it's seal directly with the metal of the carb. That one also poured gas out like an open faucet after 7 minutes.

So I then decided I needed to find an original OEM carb and found someone with some NOS units for sale for about 4 times what I was paying for the China units. I bought one. It was an OEM product made in US, and was exactly like the 11 year old one I had thrown away. I installed that and STILL had the same problem.

Engine always starts on first pull. Runs properly and correct but only for 5 to 6 minutes. This has me stumped. Once the engine stalls and the fuel starts pouring out of the carb mouth, it does not stop. It's like I opened up a faucet.

The Cyclone Rake I'm using is in perfect condition and my problem is they no longer make engines for my model and a new engine would require a change to their newer Briggs line which has different mounts and would require I also purchase a new blower impeller and housing. It would be cheaper for me to buy a whole new unit. Anyone have a clue why the carbs keep doing this?

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Welcome to aftermarket parts which are being supplied by the oem Tecumseh. Also, welcome to our world of Ethanol damage. Even NON-Ethanol is allowed ethanol in it by law. I have had 7 brand new carb floats fail to seal. We have gone to adding marvs Mystery oil into the gas to lubricate the needle and seat, helping very much the problem at least to get out of the shop and run till new fuel is added.

If the fuel tank is located close to the engine, or above it, heat can radiate from the engine to the fuel in the tank when the air flow from movement is stopped. Still, I would think a 1/16" hole should sufficiently vent enough vapor to prevent pressure buildup. Have you tried removing the cap while fuel is coming out of the carb mouth to see if it stops?

lbrac said:

If the fuel tank is located close to the engine, or above it, heat can radiate from the engine to the fuel in the tank when the air flow from movement is stopped. Still, I would think a 1/16" hole should sufficiently vent enough vapor to prevent pressure buildup. Have you tried removing the cap while fuel is coming out of the carb mouth to see if it stops?

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Makes no difference. Once it stalls and fuel starts flowing out profusely, it doesn't stop. It flows whether or not the cap is loose or removed during or after it starts leaking, with or without the original unmodified cap or with with cap with the hole. And as I said this last time I did examine the cap and the new hole was clean. And when I removed the cap to examine it, the gas continued to leak. The many dozens of times I've been thru the leaking scenario, I usually have to hurry to get the remaining gas out of the tank while the carb is leaking profusely because once it starts, it drains quickly and doesn't stop.

Once the tank is drained I have on several occassions very carefully removed the carb bowl thinking I would find the needle in the bottom of the bowl, but that never happens. The needle is always in place and moving the float up and down manually shows it's not sticking etc. and float is sealed and has no fluid in it. Remember, I have installed three different brand new carbs the last which was an exact OEM NOS unit that is exactly like the original one that came with this engine. The problem exists no matter which type of carb is used. (knock off with old style needle / seat, knock off with new system with rubber tipped needle and bare metal seat .. and OEM with old style needle and removable seat. One would think the problem is NOT the carb.

The addition of the small vent hole to the cap seems to have only increased the number of minutes of run time before the leaks starts and what is truly bizzare is this last time I got about 20 -30 minutes without leaking and shut off the engine at which point it was still NOT leaking only to have the carb start to pour gas out of it's mouth while the engine was off and I was emptying the clippings. I estimate the leak STARTED about 2 minutes AFTER I shut the engine off. Figure that one out! Maybe the only solution is an exorcism? <grin>

Tomorrow after the holiday I'm going to try to find an oem gas cap for this engine. Frankly I don't think that will help and if that doesn't work, I guess I'll have to invest into a new lawn vac. Anything that does NOT have a Tehcumseh engine .. too bad cuz over a year ago just before this leak problem started, I had spent a good amount of money to replace the 12 plus year old canvas bag and a few other repairs to the vac chassis and blower. So I got a like new unit .. with a weird leaking carb. Oh well, I got most of the 2 plus acres of lawn cleared .. I'll put another 1/4 tank of gas in the tank and try to finish the rest.

BTW, many thanks for all the attempts at help here. I really appreciate it.

How does the carb. vent? Had one years ago that did a similar thing and it turned out to be the carb bowl vent.

What you are describing is not possible. That carb is gravity fed. These are the only causes I can see possible.

* failed needle float assembly
* over pressurized tank since it does not have a fuel pump
* fuel line accidentally hooked up to breather port on carb
* Engine gets so hot it is boiling the gasoline

hlw49 said:

How does the carb. vent? Had one years ago that did a similar thing and it turned out to be the carb bowl vent.

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Rare but I have been wondering the same thing. Is a gasket blocking the bowl vent causing a siphoning effect.