Tecumseh carb leaking out the side vent hole

copyman

Well-Known Member
#1
Hi, I read some good posts on this forum about this same issue but had a few questions about carbs leaking. Can anything with the engine cause carbs to leak or spew gas from side vent hole? 1974 HS-50 Engine I rebuilt had the original carb which I cleaned in ultrasonic cleaner and rebuilt with genuine TEC carb kit like I've done many times. It ran like crap and couldn't get carb to adjust at all with slight gas leaking from choke side not vent hole. I had 2 new chinese carbs that were from same company I've used many times with decent results. Both shooting gas out of vent hole, not leaking but like pulsating gas out of hole. I find it hard to believe the genuine and 2 new chinese carbs would all leak and why I ask if engine can cause this. It doesn't seem logical to me but didn't know if something like back pressure, etc from engine?
Not sure if it matters but running engine with air cleaner off? Use only 4 cycle fuel from Home Depot / Lowes in my engines.

Thanks in advance
 
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Bird Brain

Active Member
#2
How did it perform before the carb repair? Any chance the points driver cam was removed and then re-installed backwards? I made that mistake 40 years ago and seems i recall the same symptoms.
 

copyman

Well-Known Member
#3
Thanks for reply Bird.

Will check out the cam but didn't think it could go in backwards.

I never ran the engine before the rebuild but the person I bought it from had video of it running and it was ok. Attached is pic of engine before rebuild.
 

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copyman

Well-Known Member
#4
Update, put on a new "genuine" tecumseh carb and engine started right up and ran great. After engine ran for about 5 mins it started to spew gas from vent hole. What I noticed is the converted work table I use to test engines has excessive vibration which I think is causing the float / needle to bounce up and down and flooding bowl. It's the only thing I can think of after 4 different carbs including this new genuine doing same thing. But if my theory is correct what about when riding a mini bike, lawn mower, etc with vibration and up and down hills, wouldn't the carb leak as well under those circumstances?
Can excessive vibration cause carb to leak? Think I will have to make a better test bench, in mean time will have to take an engine off one of my bikes and mount this engine to test.
Thanks for any input
 

Bird Brain

Active Member
#5
That is odd, you wouldn't think vibration and bumps would over come a needle and float. Highly unlikely. Seems that problem always stems from positive pressure in a system(carb)designed for vacuum only. Wonder what condition your intake valve and seat are in? If the ignition system is correct it could be low intake valve spring pressure that would get even less as the engine warms up and the spring gets worked a zillion times a minute or worn valve sealing areas or the combination of both. Could be the camshaft off a tooth internally last time it was reassembled. Alot of them will run like that. Just some other ideas for you to rule out. Im sure somebody else might have some interesting things to suggest checking for you soon.
 

copyman

Well-Known Member
#6
That is odd, you wouldn't think vibration and bumps would over come a needle and float. Highly unlikely. Seems that problem always stems from positive pressure in a system(carb)designed for vacuum only. Wonder what condition your intake valve and seat are in? If the ignition system is correct it could be low intake valve spring pressure that would get even less as the engine warms up and the spring gets worked a zillion times a minute or worn valve sealing areas or the combination of both. Could be the camshaft off a tooth internally last time it was reassembled. Alot of them will run like that. Just some other ideas for you to rule out. Im sure somebody else might have some interesting things to suggest checking for you soon.
Thanks for the reply, yes thought it was odd and looking like I have to tear this engine down again and check valves etc. At least engine isn't fully painted yet. Pics of engine and bench I've been using to test engines.
 

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#7
Usually a carb inlet needle is not sealing in the intake seat or the float level is incorrect.

I like to explain carb fuel intake like a toilet. Gas is added to the bowl thru the needle seat which allow the float to raise until the float reaches a pre-determined height which you can adjust as described below and the needle closes off the fuel intake . If the needle is not set correctly to close off the fuel at the correct level in the bowl or the needle leaks when in the closed position you will have the problem you are describing which is a over filling of the float bowl. Look in your toilet, as the water rises the float comes up and at a predetermined height the float closes the water valve, same principal in a carb. If you float is set in the wrong place it does not shut off the water valve in your toilet and you be experiencing overfill or overflow just like you have in your carb.

If your carb has a brass float you can bend the tab that rests on the needle to get the needle to close sooner [do not bend too much] this will allow less fuel in the bowl before the needle seats which stops excess fuel from entering the bowl or a new needle and sometimes the little rubber o-ring in the bottom of the seat may be required because your needle leaks even in the closed position. Don't worry if you bend the tab on the needle the wrong way, if the carb still spills out gas try bending the tab the other way.

Best thing to do if you have a good running engine is go to your local lawn mower shop and buy a complete carb rebuild kit. Carb kits are fairly inexpensive and easy to install.

Hope this helps.

O.J.
 
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