OutdoorKing Repair Forum Forums Restoring, Customising and Modifying Tech Talk carby leaking fuel - mechanically challenged :-)

I have been told that it's a good one and I should keep it as it will last forever. I do want to learn this stuff, I appreciate all the assistance!!!!

I checked the needle and seat. was a tiny bit of stuff there and got that out. all looked OK from what I could see.

Think the float bowl gasket might need replacing though, see pic. only $5.59 anyway.

Also not sure about the thread tape that has been used on the fuel tap. I think bits of that might have been getting in the way of the needle/seat. what should be used rather than tape? is there a threadseal type product that can be used?

when upside down the float seems to be in the right spot. No sign of a hole in the float.

Can't seem to clean the rust out of the float bowl so perhaps a new one of those would be a good idea??? Not sure how much they are, the search function on the store seems to be having problems when I try and search for the part number 221995.

The gasket needs to have a continuous surface all the way around the float bowl. In the picture it looks either dirty or discontinuous. Teflon tape is usually pretty harmless, because if you put in on properly it does not project past the front of the thread. However yours seems to have been very badly applied. You could use liquid thread-sealer, or nothing - it shouldn't really need sealant, but if you want to end up with the tap horizontal or on any non-random angle, you will need to do something to help it slip. I think I'd try liquid thread-sealer, which you should be able to get from an automotive shop.

There is no need to remove all the rust from the inside of the float-bowl, you just have to make sure there is no loose rust. I'd give it a scrape, wipe it clean, and forget it unless it's badly pitted. No need to replace it.

Can you confirm that the engine was running well at the beginning of this process? If it wasn't, you need to clean out the carburetor - remove jets, blow air through the drillings, reinstall jets. I prefer not to disturb such things if they are already clean, but in this case there could be loose bits of teflon tape all over the place. Your mower guy seems to be more of a plumber than a motor mechanic. If you want to strip the carburetor, you have to note the initial setting of the adjustable idle mixture screw so you can put it back in the same position.

the engine was running OK before I had this leaking fuel issue which was leaking from the where the breather tube had come off.

then last time I tried to start it, after putting in new battery, there was a small puff of smoke, I assumed it was some wiring insulation given the length of time I was trying to start it. But will see what happens....

if you look at the photo using this link you can zoom in
http://picasaweb.google.com/lh/photo/UuLaEu1xljU9rhHSud2y8A?feat=directlink

part of the gasket is protruding on the outside and some on the inside, if that makes sense. I am not sure how it should look when seated correctly. I am keep an eye on it, if it is not sealing then I expect i would see fuel leaking around there.

so i will put the carby back on the mower and get the tank and fuel line hooked up. I'll remove that red tape off the fuel tap and use some new tape and no go past the end of the thread...

might as well give it a burl and see what happens.... might check the exhaust and make sure I am not providing a cosy location for a wasp nest.

Nathan

The top gasket around the float bowl does not have to hold pressure - it is there to keep fuel from slopping out when you run over bumps or work on a slope. It looks more squished than torn or chopped. However it mustn't leak - loose fuel around a running engine is dangerous, especially when it's right under your backside. The safe way to go is to reassemble the carburetor, fill it with fuel, and try a bit of shaking and tilting to see if liquid fuel leaks out. Then, either before or after putting the carburetor back on the mower, turn the fuel on with the carburetor the right distance below the fuel tank, and fuel in the tank. Wait ten minutes and see if it floods, drips, leaks etc. If it doesn't emit any fuel, it's time to crank up the engine.

Do you have the owner's manual, to find the correct way to start the engine (use of choke, etc.)? Old Briggs engines are very easy to start if everything is working and if you follow the manual. Does it crank at a sensible speed? Some of the larger Briggs engines have automatic decompressors, and if they don't work the engines are difficult to crank, overheat the starters, ruin the batteries, and sometimes cook the wiring.

hmmm a manual, no don't have that. I am the 3rd owner apparently or maybe the 4th. before I had it, it was used to tow small helicopters around a little airport, so I have a orange flashing light on the bonnet (but like the other lights it doesn't work)

I will try the fuel into the carby trick. so no fuel should leak out anywhere correct, not even the end that connects to the engine?

Nathan

When you are doing the swishing-and-tilting test (technical term) you should put your finger over the fuel hose connection on the carburetor. Don't tilt it beyond a normal tilt-angle for safe operation of the mower. In that test you are only looking for wetness on the outside of the float bowl, due to fuel passing between the carburetor body and the top of the float bowl.

When you do the static fuel pressure test (fuel hose connected, fuel on, carburetor level, watch for ten minutes) there should not be any fuel comes out of anything. The float bowl should fill, the float should shut off the needle-and-seat, and then nothing should happen except the grass keeps growing.

Now that you have found the model numbers and codes, you should follow Bruce's advice from early in this process and check in the parts and manuals section of this site. There may be an owner manual there - I don't know. Because your engine has a manual choke (mine is automatic - <<smug mode on>>) you can easily prevent it from starting, or running decently, just by not choking it when you should, or choking it when you shouldn't. As Joe said at the beginning, you might even get it to leak petrol from the breather tube if you over-choked it then stopped it.

I think my mower has the wrong muffler fitted to it. The one on there is this one https://www.outdoorking-forum.com.au/index.p...ath=193_195_375_526&products_id=2268

But from according to the parts list I downloaded when my subscription was valid I should have this one which seems a lot bigger https://www.outdoorking-forum.com.au/index.p...ath=193_195_375_526&products_id=2262

Not sure of the differences between these two mufflers other than the physical size, just wondering if the smaller one is providing too much resistance that could be causing a problem??

Nathan

A moderately smaller muffler will only slightly reduce the maximum power (perhaps by one hp or a little more), it won't affect the way the engine starts or runs. When you get everything else working properly, a muffler upgrade might make you feel better (I admit it would make me feel better if it were mine) but you seem to have more important things to do first, in my opinion. Meanwhile I'm wondering how you control the choke - is it done with a control rod reaching outside the engine compartment? Does it open fully and close fully? Is your carburetor now leakproof? Have you checked the intensity of the spark?

ran out of time today. I will try and do the carby "slosh" test tomorrow and post the results. Once the carby is back on I will take a video of the choke operation :-)

Nathan

I'm still here :-) just been busy with work (a good thing)

OK, so the swishing and tilting test has passed. no leaks at the bowl gasket. although fuel does run down to the air intake end inside the carby body and a little bit is noticeable towards the engine end as well.

I'm not happy with the length of the fuel line, I want another 10mm so that it completely covers the barb fittings, there's a small leak at the fuel tap as the hose dose not go all the way on.

Looks like this is what I will need https://www.outdoorking-forum.com.au/index.p...p;cPath=193_195_307&products_id=2336
I have a couple of hose clamps that use screws and nuts. I noticed in the store that the B&S ones are just spring clamps, what is the best to use?

I'll wait until I have the fuel line sorted out before progressing any further, last thing I need is for the fuel line to come off and then have a flame roasted mower

Good thinking: secure fuel lines are kind of fundamental. The only advantages of those spring clamps that I have noticed, are first that they are much easier to assemble in the factory, and second, are less likely to be overtightened or undertightened by insufficiently skilled repairers. I get a bit annoyed with the spring ones twisting out of the pliers at the crucial moment, but once they are on they are one less thing to worry about, which I wouldn't really say about the screw-clamp ones because of possible improper tightening at some point in time. Sounds like your hose is either incorrectly routed or too short. I bet it was long enough when the mower was new, so if it is wrong, either it has been shortened or somebody has messed up the routing. Don't get inventive with fuel hose routing: putting the hose too close to something hot is both dangerous, and prone to causing vapour lock, so following the original design is best.

You could do your ten minute flooding test while you are waiting for your new fuel line to arrive. Once you have done that successfully, you know that the original problem is fixed: when you started, fuel was coming out of the carburetor. Don't be too surprised if some fuel came out of the main jet during your swishing and tilting test: there is nothing to prevent it, if the fuel level momentarily rises above normal due to tsunami effects inside the float bowl.

I'll try and pickup the fuel line tomorrow or Tuesday. i suspect the end(s) have been cut off at some stage and now the hose is just too short. to make it connect properly I feel there would be too much tension on the hose.

easier to do the flooding test while the carby is attached to the mower. will have the right level below the tank then.

Fuel lines should not have any tension whatever, so you have to do something differently to make it work with even a basic level of safety. Be careful with the routing of your new line - don't let it wave around or it will get its finger in the wringer sooner or later, and don't run it within say 5 cm of anything warm like a cylinder or cylinder head, and not within 10 to 15 cm of the exhaust pipe. Try not to run it down-then-up, or it will collect crud at the low point. It's best by far to follow the original routing.

funnily enought originally on some of the brggs motors the fuel line is clamped onto the cylinder head!

Maybe they just don't worry about warm climates, Joe. The block and head don't get nearly hot enough to damage the hose (unlike the exhaust pipe) but if you need your farm's fire pump to work in Katharine (northern N.T.) in the middle of summer, you might get pretty unhappy if it had a vapour lock problem. Or then again, you might not have enough time to get unhappy.

Part of the problem is that some equipment is only used occasionally, and is therefore likely to still have winter petrol in it during the summer. That's why I try to be mildly conservative in what I suggest to people.

I'll upload a pic of where the fuel line currently is. No idea if that is where it was when it came out of the factory or not.. local mower place has fuel line in bulk so will go grab a couple of feet and a couple of new clamps tomorrow.

Nathan

I know about the warm climates grumpy, had a vapourlock problem the other day, day in day out I drive my beloved datsun ute to work but it would not fire on one particular afternoon a week or so back when it was 45 degrees, In the end it must have had the lock somewhere on the fuel inlet to the carby as after i tapped around the metal fuel line pretty hard it coughed into life.


Moral? I will park it in the shade for summer and walk a bit further to work :P

With a carburetor engine there is usually a fuel pump on the side of the block, operated by the camshaft. Vapour lock nearly always originates in the last foot of fuel line before the pump, because the fuel is being sucked up-hill in that section. Being subjected to less than atmospheric pressure makes the fuel especially likely to generate vapour. However under slightly more severe conditions you will get vapour lock even if you have an electric pump in the top of the fuel tank, as the last of the carburetor cars often did. By the way, in the good old days we used to be able to get home despite vapour lock by wrapping a wet rag around that last bit of fuel line before the pump: the evaporation of the water cooled it enough to get us going for a while, until the rag dried and we had to soak it in water again.

In the days of the carburetor engines, car manufacturers used to fit 'vapour return lines' when necessary, to remove petrol vapor from the fuel line just before the carburetor. If you want to see how this works look at any carburetor-engine Commodore or full-sized Holden and compare the air-conditioned model (which always had a vapour return system) with the non-air-conditioned model (which didn't, because it had lower under-hood temperatures). Nowadays, fuel injected cars nearly always have a recirculating fuel system, with a swirl pot in the top of the fuel tank to separate the vapour from the returned fuel, so vapour lock has almost disappeared as a problem. My own car happens to be the only port-fuel-injected design I have ever encountered that does not have either recirculating fuel, or a vapour return line, so it suffers from vapour lock in summer.

You could remove the vapour lock from your Datsun by bleeding the fuel line at the carburetor intake fitting, like bleeding a diesel fuel line, or a brake system. However to keep it from happening again in a few seconds, you might need to do the wet rag trick.