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.
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.
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.
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.
It seems to be clamped to the cylinder head, like the examples Joe mentioned - that looks like an original equipment retaining bracket to me. At least the hose is restrained so it can't flop around. If the hose has not gone hard where it is hottest (around the retaining bracket) over the last 21 years since 1988, it sounds like it will be OK unless you eventually find you have vapour lock problems on days when it's way too hot to mow grass anyway.
aarrhhhggg!! the hose line I bought has a slightly smaller OD (7/16 rather than 1/2) and the clamps I have don't fit. the place I got the hose from didn't have clamps to suit.. should have just bought it from Bruce but thought I would buy local to try and get this thing going a bit quicker.. always the way!
OK, I have finally got the fuel hose sorted out and left it to see if the fuel leaks out. and it does!
from around the bowl gasket and look like also from where the air filter "tie down" rod comes down through the air intake into the bottom of the carby body.
now when I look in to the air in take I can see fuel in there so I guess that means that the whole needle/float thing isn't doing it's thing.
With your flo-jet carburetor, if the mower is on level ground fuel can't come out from the float bowl gasket (i.e. the gasket at the top of the float bowl, not the one at the bottom of the float bowl) unless the carburetor is flooding. That can only happen if the needle-and-seat are leaking. If fuel is entering the carburetor body, the fuel level has to be up above where the main jet passage enters the body - which is way too high. So, you have to attend to the needle and seat.
Remove the carburetor, dismantle the float bowl, and look at the needle and seat again. If the sealing surface at the end of the needle is perfect you probably have one of two things: misalignment of needle with seat; or a damaged seat. Check that the spring-clip attaching the needle to the float arm will slide along the arm to allow the needle to align itself properly. Assemble the float without the needle and make sure the float will lift up freely past the needle-closed position. If those points are OK, try to get a magnified view of the seat. It may be a bit rough, which would make it leak. If so, there are two possible cures: replacing the seat, and trying to lap the old one in-situ. Quote from manual: "Replacing Pressed in Float Valve Seat Use a #93029 self-threading screw or remove one selfthreading screw from a #19069 flywheel puller and clamp head of screw in a vise. Turn carburetor body to thread screw into seat. Fig. 80. Continue turning carburetor body drawing seat out. Leave seat fastened to screw. Insert new seat #230996 into carburetor body. (Seat has starting lead.)" This is difficult stuff for a beginner, and it is perhaps best done by a local motor mechanic. I've attached the diagram from the manual.
Thanks again. I have a friend of a friend that I am hoping will be able to help with this one. going to try and take the mower over to him next weekend and see if we can get it sorted.
I will take the carby off again and try and get a picture of the seat. Is there a picture that shows what it should look like?
If you look at the illustration above, you will see that the seat is a hollow cylinder: the seating takes place on the inner corner of its end-surface, so it should be a perfectly square corner (see just below the note 'press flush'). With normal wear a small conical surface would develop on that inner corner due to contact with the needle's conical sealing surface. The worn, conical part of the seat should be even all the way around. The simplest way to fix the leak would be to lap a clean conical surface, but if it were the least bit out of square, it wouldn't work. Similarly it must be quite narrow: the force applied to the needle by the float may not be enough to seal over a large area. I guess that is why B&S just say replace the seat. However if you damage that square inner corner of the seat the slightest bit while installing it, you've wrecked it. Hence the screw that goes through the inside of the old seat must be retracted so it does not protrude at all before you start pressing in the new one. It is the kind of job that is pretty easy for someone experienced, and pretty difficult for anyone else.
You said you've examined the conical sealing surface of the needle, and it is good. The slightest wear on that conical part of the needle has the same effect as wear on the seat. Unless it is pristine, replace both needle and seat at the same time.
There is an old-guy's trick that you could try. Once upon a time I bought an old 850 Mini in lousy condition. It very slowly flooded its SU carburetor at idle, but was fine (for a tired old Mini) when in motion. I fitted a new needle and seat, with no effect on the problem. I therefore swallowed my pride and went to see an old guy who ran a carburetor repair shop. He took the carburetor top, turned it upside down, slurped on the fuel-line connection, then blocked it with his tongue, waiting to see how long it took to lose the vacuum by leakage. It lost the vacuum fairly quickly, and seeing that it was a new needle and seat, he unscrewed the seat from the body and reinstalled it with liquid sealant on the thread. After that it would hold vacuum properly. Didn't flood either.
My point in this long story is that you could make the same test, and find out whether your needle and seat will hold vacuum. If it doesn't you can probably find out why by doing other tricks, such as sealing each possible leakage path in turn with a drop of oil.
No, but it screws into the body on most automotive carburetors (which are more complex and expensive devices). My point was, you may be able to pinpoint the leakage path by using the same process the old carb guy used. Once you prove that the needle and seat won't hold vacuum, you can try temporarily sealing off various possible leak-points. The only leakage paths that occur to me are between the needle and seat, or around the outside of the seat. Your seat is pressed in, not screwed in. If you can temporarily seal one of the two leakage paths and do a vacuum test, if it still leaks, it must be the other path. Then you can verify this by opening the first path and sealing the second.
The bit one row below, and one column to the left, of the needle looks like it may be the seat - hard to tell from that angle. Be sure you are getting the right kit for your engine, with the mixture adjustment screw running through the middle of the float bowl retention nut. If it doesn't have that it is for a small flo-jet. Check that your engine type number is one of those listed.
The self-threading screw has to be just the right size (p/n 93029), and it is an American size that may be hard to get here. (Post-Edit: The screw required is an ordinary 1/4" UNC, available from any hardware store, but in Australia you are unlikely to find a self-threading one, so you would have to buy a 1/4" UNC tap and create a thread inside the seat, before inserting the screw and removing the seat.) A competent mower repair shop that deals with B&S engines should have it or be able to get it though. Don't let them try to use a randomly-selected self-tapper, or they'll ruin your carburetor body. Self-threading screws are quite different from self-tappers, even though the two terms mean the same thing - look at the picture of the screw.
Last edited by grumpy; 25/11/1209:09 AM. Reason: Add post-edit
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