Fuel dumping out exhaust

[tnyankee82]

Gents,
This is my first post so please bare with me. I am working on an all original M725 that is perfect shape! The only issue I am having is while the engine runs, it is dripping fuel out of the exhaust tail pipe and running very rich. Do I just need a carb rebuild or adjust my valves? Sometimes it smokes and sometimes it doesn't. Besides this it runs very well and idles smooth. Thanks for the help!

Tony DiMaiolo

[Don Cavey]

First of all, welcome to the forum. I am sure you will find much useful information here.

OK, fuel out of the exhaust is an issue. Are you sure it is fuel and not oil? What color is the smoke, is it blue or black? Or is it white?

The Holley 1920 is a a very simple carburetor and is easy to rebuild. (Listen to me, like I am an expert... NOT!) But seriously, I have mine disassembled and in soak. They have rebuild kits for the carburetors and depending on whether you buy a Jeep kit or a Military kit, the one (military) has more parts and in my case was from 1978 so it is not ancient.

Is the engine misfiring; shaking? If you have a fouled plug from either excessive oil consumption or a rich mixture, you may foul a plug. When I was in the army in 1970, my M715 would foul plugs if I didn't run it hard. Valve seals no doubt. What I did was to take the dipstick, put a drop of oil on each runner of the exhaust manifold near the head and start the engine. The plug that was fouled would not burn off the oil immediately as would the running cylinders.

So, I guess if you are experiencing fuel running out of the exhaust, it should be puffing black smoke and fouling plugs.

Other members, please jump in here with your suggestions...

[jeeper]

Fuel out the exhaust would mean that the fuel going into the cylinders is not burning right? Would a weak spark or low compression cause fuel to not burn?

The other possibility I can think of is a stuck float in the carb. If the float can't stop the fuel from entering the carb the excess gas could drain into the engine. I have a quad that has a sticky float and if I forget to turn the gas off at the tank the carb will leak into the cylinder and eventually into the crank which then means it's time for an oil change.

Do you smell gas when you pop the hood? Have you checked the oil? Is it over full and thin?

[randyscycle]

If you have liquid fuel coming out of the tailpipe (meaning the back of the truck) then there is a major issue. The valve adjustment would have nothing to do with that.

If the carburetor needle valve or float is stuck, then it would allow a huge amount of liquid fuel into the combustion chambers. Liquid fuel is a bad thing, because fuel needs to be vaporized and mixed with air to actually burn correctly and efficiently. If the fuel pump were over-delivering, this could also do the same thing. If it were leaking internally, it would most likely fill the crankcase with gasoline, diluting the crankcase oil, and causing other problems.

If gasoline is in fact coming from the tailpipe, I'd be surprised that the truck is actually running at all. A flooding carburetor that is leaking that badly, will usually soak the spark plugs and kill the engine long before fuel could ever get that far downstream.

Are you sure that it isn't condensation dripping from the exhaust?

[97XJSP]

I'd also recommend checking to make sure it's not water, my truck drips quite a bit until it's warmed up!

[brute4c]

I would bet on condensation too...drive it around, if you can, for like 10-15 minutes and see if anything is coming out then...running it without driving will do it too...

Some mufflers come with little tiny weep holes in them for relieving condensation...you can drill a tiny hole in the low point of the muffler to drain it out...like a 1/16ths hole or so...beats having the condensation sit in there and rot the thing out from the inside.

[militarypotts]

My bet is on condensation also. The most common cause of having to replace a muffler or exhaust system?...Condensation! Mt tailpipe drips like crazy when I just let the truck idle. An awful lot of rae fuel would have to run through the motor to make it all the way back to the tail pipe. Give it a closer look, take it for a ride, come back and see if things have dried up. Good luck.

[tnyankee82]

The engine has a bit of a vibration, but nothing I would consider excessive. It drips a black liquid that smells very strong of fuel. It does blow out some pretty black smoke. The oil looks great and not thinned at all. I already rebuilt the carb once not too long ago after a very good cleaning, and yes they are very simple carbs. THe plugs were fouled when I first started it this season, so I replaced them and just put in some new ones anyway. Thanks for all the replies already! I have found this forum very useful so far and will surely comtinue to use it once I start on my 715!

Tony DiMaiolo

[militarypotts]

Tony, maybe let some of that liquid drip into a can or jar. My tail pipe dripping is also black in color, and in fact has sprayed the cabinet along the wall in the garage. I can't say that it has a real strong odor of raw fuel, but their is a exhaust smell naturally. If your truck idles relatively smooth, then I'll still go with heavy condensation.

[Don Cavey]

I didn't think about condensation when I responded. Being the ultimate pessimist, I always figure for the worst-case-scenario. I would bet it is condensation. As for the black spray, condensation picks up the carbon in the exhaust system and shoots it all over the wall. Remember that these vehicles have just about zero emissions controls so they run rich and don't have a catalytic converter so the exhaust will smell different than what we are now use to. Old guys like me can smell a classic vehicle on the road immediately by the flavor of the exhaust__

You should be able to capture some of that moisture on a piece of paper or whatever. You could try to SAFELY ignite it with a match, outdoors of course and see if it flares or does not light. If it is water, it won't light. If it is raw gas, it will light rather quickly and flare up.

So if it is just condensate, no problem. Just a thought.