1968 3.5 hp Briggs & Stratton

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  #1  
Old 10-13-04, 05:24 PM
Kushballz
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1968 3.5 hp Briggs & Stratton

I have a 1968 3.5 hp B&S engine that likes to leak gas out of the carburetor after I turn it off. It drips from the carburetor barrel at a rate of 1 drip per 2 seconds. I have thought of the many things that could lead to the leakage, but after all the work I did it still leaks while cooling off. These are the things I did:

1. Cleaned: carburetor, air filter, fuel pickup tubes, gas tank, breather, and the muffler.
2. Replaced: diaphram, gas cap, and rubber breather tube things.
3. Made: gaskets for breather, and carburetor.

Any Ideas?
Thanks,


Kushballz
 
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  #2  
Old 10-13-04, 05:37 PM
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Kushballz
Can you give me the model and type of the motor so I may look at the reference drawing?

snoman
 
  #3  
Old 10-14-04, 04:14 PM
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I've got an engine of about the same age on a tiller. I think the needle or seat in the bowl is shot. Even when the float holds the needle in place a small amount of fuel drips past. When the engine is running this fuel is consumed and there is no dripping. When I turn it off the bowl eventuall fills up and gas leaks out around the top of the bowl (yes, that gasket is shot as well). I just turn off the fuel shut off valve when I'm done and I forget about fixing it until next spring.
 
  #4  
Old 10-14-04, 05:00 PM
Kushballz
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ya never know....

The flywheel casing is not the original one, but it has 5.12.1968 punched into the crankcase on the inside. I not sure if this is the date of manufacturing, but that is most likely to be. I bought this engine off ebay, and I don't know about its usage history, but anyways, its a horizontal shaft. It has a pulsa-jet carb, and the gas tank is screwed on under the carb. I have a picture of it on my motorized bike. The webpage is http://www.geocities.com/toobadudunn...4/newbike.html

Yea I know its kinda long, but im trying to keep the bandwith limit in the green. So tell me if you know anything to fix the problem...

Thanks,


Kushballz
 
  #5  
Old 10-14-04, 08:28 PM
sceptre
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try this when you stop the engine loosen the fuel cap,for the tank may be building up pressure, forcing the fuel through the fuel pipe into the carb
throat. (this is just a theory)
 
  #6  
Old 10-15-04, 07:46 PM
Kushballz
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Cool

I've already tried to do that and it didn't make any difference. I also tried releasing the pressure in the diaphragm (which was actually holding the gas in from pouring out), but just pours gas out of the ports coutinously. Keep in mind that the engine is on a level surface too, so I am thinking that the pressure is somehow kept in the fuel intake... Well as I said before, I"M STUMPED! ;( This is actually the first time I have ever had this happen to me, with all of the engine repairs and all the rebuilding I have done.

Comments greatly appreciated!

Thanks,
Kushballz
 
  #7  
Old 10-15-04, 08:04 PM
sceptre
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does this engine have the very vertically short fuel tank? i stumped also
i've never seen this problem.i'm sorry, it beats me.
 
  #8  
Old 10-16-04, 02:01 AM
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Very strange problem to have with that carb. Where does the leak originate from? Is it leaking inside the tube, and dripping from the end, or does it originate at the end? I have a carb like that in the shop, and I'll take a look to see what might be able to cause the leak. I can't think of anything other than pressure buildup right off the top of my head, but looking at it might reveal something.
 
  #9  
Old 10-16-04, 11:12 AM
Kushballz
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The tank is short vertically, only about 2-3 inches high. As for the gas leak location, i'm not sure. As soon as the engine stopped I unscrewed the air filter and looked down the tube, it already had fuel in there, I believe that leaks in the tube, then leaks out the end, where the choke is. I just posted a few pictures of the engine at:

www.geocities.com/toobadudunno/pic01.JPG
www.geocities.com/toobadudunno/pic02.JPG
www.geocities.com/toobadudunno/pic03.JPG

Thanks for all your attempts to help,

Kushballz
 
  #10  
Old 10-16-04, 07:52 PM
cando
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Smile Stumped

I have this engine on an ancient reel mower and after long runs it tends to overheat the gas tank and spit gas out the gas cap. I wonder if yours is overheating and causing a pressure build-up into the carb. Does it do the leaking no matter how short the run period, i.e. before it can overheat or does it have to have run 5-10 min full throttle before it happens? Have you modified the blower section or air-flow so that it doesn't get enough cooling? Could it be overloaded in your current application and overheating? Keep peeling the onion, the answer is in there somewhere. If you can see it through your tears!
 
  #11  
Old 10-16-04, 09:00 PM
Azis
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Have you checked for cracks in the carb or intake...gas will find cracks even other mediums such as water will not. Rig some gaskets and plugs and fill it with gas. I have found cracks in car engine heads this way.
 
  #12  
Old 10-16-04, 09:13 PM
sceptre
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i know one more thing you can try, start the engine without the breather assy. see if you can see fuel puddled up in the carb throat, while it's running.
 
  #13  
Old 10-17-04, 05:37 PM
Kushballz
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I tried starting the engine as sceptre stated, but the same thing happened when I turned it off. I took apart the carb, looked for cracks and checked it with gas, and everything checked out okay. As for the overheating, it runs fairly cool for what it is being used for. It stays a lot cooler than lawn mowers do. The engine has to run for about 1-2 minutes then it'll leak. You don't even have to let it warm up.
 
  #14  
Old 10-17-04, 07:00 PM
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Kushballz
Well I am also stumped but after reading all the sugestions that the others here have said, alot of them make sense to look a little further into. First off, you said that you made gaskets, replace them with factory ones because if they don't make a perfect fit you can possibly have a leak. Another thing that may work is the overheating as Cando said....what I'm referring to is maybe the muffler is getting too hot and causing the carb to start to overheat. I had a mower that ran great for about 5 minutes but then it would die out and wouldn't start for about 45 minutes. It seemed the muffler baffle would shift over to point at the carb bowl and cause it to get so hot that the gas would either vaporize or boil causing a major air lock. I replaced and redirected the baffle and it ran great. In your case, maybe the insides of the muffler have been corroded enough that the insulating factor of the carb/muffler area has been jeprodised.
Just something else to look into.

snoman
 
  #15  
Old 10-17-04, 08:34 PM
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Is the tank completely full when the leaking occurrs, or does it do it regardless of fuel level? I see no place for fuel to leak from this carb without internal pressure from the tank. Does it leak until the tank is dry, or just until the fuel in the throat is gone? Here's my take on what is happening from the info so far: I think your valves are in need of adjustment, especially considering the age of the engine. I think the engine is puffing out the carburetor a little while running, causing the tube to puddle with gas, especially when the ignition is turned off and the engine sputters to a halt. Then, the puddled fuel is leaking past the choke barrell until the carb tube is drained. The addition of heated fuel in the tank causing pressure in it may be contributing to the problem.

Place your hand over the carb intake when the engine is running...close to it, but not closing it off. Then, remove your hand and smell it. Does it smell like gas? If so, the valves probably do need adjustment.
 
  #16  
Old 10-18-04, 12:05 PM
Kushballz
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OK. Got factory gaskets, and it prevailed no change. The muffler will get hot, but not red hot like my riding mower did. Also, the muffler is still good, strong, and unrusted. The muffler is a straight output; directly blowing exhaust away from the carb. I have some electrical tape right next to the muffler (if you didn't see it in the picture) for a throttle control return spring, and it doesn't melt, so I would have to say the muffler isn't the problem. When it leaks, it does so regardless of how much gas is left in the tank. Then engine won't run if the tank is less than 1/6 of a tank of gas. (about 1/2" from empty.) I think cheese is probally correct about the valves needing adjusting. I replaced the camshaft, valves and the oil dipper, when the engine decided to break a camshaft into 2 pieces, make an oil dipper disappear, and put a hole in the crankcase. Also, the engine kept on running after that incident until I turned it off, which is kinda weird. But anyways, back to the subject, the engine has been rebuilt since 1968... When I got it, it had a new piston, set of rings, crankshaft, and a head. About the sputtering, this engine does knock while at a low idle speed (around 2500 rpm). I put my hand over the air intake, my hand came back dry.

Thanks for all your suggestions,

Kushballz
 

Last edited by Kushballz; 10-26-04 at 09:08 PM.
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