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?
Tecumseh OHH50-68023J w/ 640340 carb problem.
- Thread starter Rich A
- Start date
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.
sgkent
Lawn Addict
- Joined
- Sep 27, 2017
- Threads
- 33
- Messages
- 1,695
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
* 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
Last edited:
Rare but I have been wondering the same thing. Is a gasket blocking the bowl vent causing a siphoning effect.