OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Engines Questions On Briggs & Stratton Engines Fuel squirting out of carby

Hi, I have a Briggs 16 HP Vanguard engine 280777 fitted to a MTD 42" ride on. It has been out of action until the wet hit this year. I pulled it out, changed the oil, refuelled and tried to start it. I took the filter off when it wouldn't start and turned it over. As soon as it started, fuel started squirting out of the carby up about a metre in the air. It was running even with the fuel squirting out and I had trouble getting to the key to turn it off. I have been told it was because of the breather so have replaced that, the filters and the fuel pump diaphragm. It still did it. Today I took the OHV cover of and fuel poured out. Does any one have any idea what could cause it?

Gazza,

Does the motor sound as loud as it used to or slightly muffled down?

Hi Bruce, I only had it running long enough to get in under the raining fuel and kill the ignition but I think it may have been slightly muffled. I think my heart beat was a bit louder.
Gazza

Gazza,

Ok try removing the muffler and try running the mower to see if the fuel comes out of the carby.

Thanks Bruce, will give it a go as soon as I get home from work tomorrow.

Hmmmmmm Do you smoke?

If you do, it's probably a great time to quit.

Yes smoking can be bad for your health especially with the problem.

I gave up smoking 3 days ago, I can be very moody at the moment.

Maybe I'm missing something, but it sounds to me as if the carburetor float is stuck in the fully-down position, due to the fuel drying out over the summer and leaving a bunch of gum behind. With the needle right down and a car-type fuel pump, you could just about estimate the fuel pump outlet pressure from how high the fuel squirts up from the floatbowl vent. Hmm, a metre would mean a fuel pressure of 2.2 p.s.i. at the seat (which should be blocked by the needle, but isn't if the needle or float is stuck down). Sounds about right - it's within the normal range for a car fuel pump anyway.

The float could be part of the problem but I am looking for back pressure causing the fuel pushing back through the carby.

Hi Grumpy, you are missing something, I didn't leave fuel in it to dry out and leave gum behind. I ran it dry.
Looks like Bruce has hit the nail on the head. I took the muffler off, refitted everything else, hooked up the jumper leads and hit the key. After a few seconds it started to fire and then it caught and ran like a charm. I disconnected the leads and jumped on it and mowed for about 5 minutes without missing a beat. Will pick up a new muffler in the morning.
I don't understand why it did it because it doesn't appear to be blocked but it works. Thanks heaps for the advice Bruce. I have sent a little something through Paypal, enjoy a beer or two!
Gazza

Gazza,

You might not need to replace the muffer as I think you might have a wasp nest in it just clean out the outlet (in the muffler) first before you waste any money paying for a new muffler.

Hi Bruce, I had a good look at the muffler and couldn't find anything in it. Blew through it with a vacuum cleaner that has a blower outlet and felt the air coming out reasonably strong.
The muffler is quite large, approx 20x10x10cm and the outlet is a series of holes in a circular pattern punched in one end of the front. It has a plate that bolts over that with a pipe attached at about a 30 degree angle. There is nothing in the pipe. While it was running, I noticed a lot of sparks shooting out of the exhaust port. Could it just be a carbon build up in the muffler?
Gazza

Well done Bruce, you went straight to it as usual. I thought he was talking about a solid stream of liquid fuel rising into the air, not a spray/mist caused by exhaust backpressure. You've pointed out before that there is an art to reading the fault descriptions that are posted.

Gazza, depending on what baffles are in the muffler itself, you might be able to poke a curved rod in through the muffler's inlet port and loosen up the crud, which you could then pour out through the inlet port. If that isn't possible you might be able to cook the stuff until it turns to loose powder. Seems a pity to throw away a good muffler just because it has crud in it. I'd probably cut it in half, clean it out, and weld it back up but I'm a cheapskate.

Gazza,

Have you had the head off the cylinder as it could also have a carbon build up if you are getting sparks coming from the exhaust port.

Yes you could have carbon build up in the muffler as well as the exhaust port.

The steps that I would do are:

1. Decoke the cylinder head.

2. Check around the exhaust valve for carbon and clean.

3. Check the valve and seat for pitting or flat spots.

4. If pitted or burnt valve reface the valve and seat then lap back in.

5. If refacing the valve then check clearance and reset.

6. Check exhaust port for build up of carbon and clean.

7. If the mower has the same problem with the fuel coming back out of the carby then you will have to replace the muffler with a new one.

Hope that this is of some help to you. I have had in the past when a machine comes from a farm or country area the mufflers being blocked by a wasp nest as it is hard to see and you go through hell try to work out what the problem is because the muffler looks new and you think nothing can be wrong with it.

I have been caught many time with this happening in the past.

Hi Bruce, had a couple of heavy days so haven't got back to it yet. I had a quick play with the muffler and did manage to get a bit of muck dropping out so will hold off buying until I check it out properly on the weekend. I was in the process of pulling the head off when I logged on and you performed your magic so I didn't finish taking it off.
If a good clean and decoke of the reachable areas doesn't do it, I will drop the head off and do that and the valves too. Might even do what Grumpy suggested so I can get some practice with my new TIG.
I can relate to what you say about wasps because I had a Ryobi edger that wouldn't start and eventually found that it had a wasp nest in the muffler. Didn't even consider it with this one though.
Again, Many thanks and hope you enjoy a beer or 3 with a bit of the donation. Gazza

Gazza,

After reading what grumpy was saying I realised that what I used to do and still do to clean the carbon build up is cook the mufflers.

In the old days I used to cook them on the stove but these days I use the oxy by heating the muffler to a bright red all over. This makes it easy to clear the carbon as all you need to do it tap the muffler in order for the carbon fall off.

Not many people do this procedure as it is common sense and easier to just replace the muffler.

Hi Bruce, I thought I would let you know that you were spot on with the muffler. I soaked it in brake fluid at the advice of my brother (mechanic) and then used the blow torch to burn the carbon off. I have cleaned up around the exhaust port and all and finally got it all back together about lunch time today, after taking mum and the kids to Maccas for Mums Day brekky. Started it up and for 10 minutes it ran beautiful and then started backfiring and spitting out debris, obviously carbon. Once that cleared it settled down and ran for a few hours while I caught up with the mowing. Would have finished the whole block but rolled the deck belt when it got clogged in the long grass.
Off to Mt Isa tomorrow (driving) so will fit a new belt next weekend and finish off. Thanks again for the quick diagnosis and have a great week. Gazza

Gazza,

Glad to be of some help with your problem. What I have never used is brake fluid to release the carbon from a muffler.

I know that brake fluid is usually good for rusty bolts but I suppose you learn something every day, that's why I like the forum as it can be a wealth of knowledge.