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Hello all. Gaz here from UK.
My Flymo XL500 fitted with Honda GCV160 is running terrible. It'll start easy but after a few moments will cut out. When left a short spell, it will start and do the same so I'm convinced it's a fueling issue. There is a hose that is off at the minute, it must have popped off at some point. It comes from the pump. It appears to be the vacuum hose as when I suck on it with a pulsing technique, fuel flows rapidly from the fuel supply to carburettor line.
My dilemma is that I have no idea where this hose is supposed to connect engine side. Obviously it will have to be either downwind of the throttle butterfly on the carburettor or on the crankcase side under the piston to sense crankcase vacuum.
Does anyone know where this hose should connect? Inside the end of the hose is a small brass ferrule that looks like it should be pushed in to something.
All the images I have found online show the pump, the hose etc but nothing is giving me a clue as to where it should be fitted on the engine to sense the vacuum to actually make the pump work.
At the moment, I have bypassed the pump and fuel valve just to get the grass cut but certain angles cause the mower to cut out. Any help much appreciated.

tomocr said:

Hello all. Gaz here from UK.
My Flymo XL500 fitted with Honda GCV160 is running terrible. It'll start easy but after a few moments will cut out. When left a short spell, it will start and do the same so I'm convinced it's a fueling issue. There is a hose that is off at the minute, it must have popped off at some point. It comes from the pump. It appears to be the vacuum hose as when I suck on it with a pulsing technique, fuel flows rapidly from the fuel supply to carburettor line.
My dilemma is that I have no idea where this hose is supposed to connect engine side. Obviously it will have to be either downwind of the throttle butterfly on the carburettor or on the crankcase side under the piston to sense crankcase vacuum.
Does anyone know where this hose should connect? Inside the end of the hose is a small brass ferrule that looks like it should be pushed in to something.
All the images I have found online show the pump, the hose etc but nothing is giving me a clue as to where it should be fitted on the engine to sense the vacuum to actually make the pump work.
At the moment, I have bypassed the pump and fuel valve just to get the grass cut but certain angles cause the mower to cut out. Any help much appreciated.

Click to expand...

Fuel Pump ??????
GCV 160's are gravity fed.
There is a fuel filter inside the tank which is most likely clogged
Or the vent in the fuel cap is clogged

The tube is the crankcase vent and should go from a spigot behind the controls to a spigot behind the air filter housing

The crankcase breather hose is connected fine. The fuel filter in the tank is clear, I'm getting fuel flow from the tank fine. The tap is also clear although bypassed just now


The first photo is what appears in the manual as called a fuel pump.
So. On this pump, there is a hose to the tank, a hose to the fuel tap and the third hose??? I have no clue where that is supposed to be.
The second photo is showing the hose that is off with the brass ferrule. If I take the fuel line to the carb off and suck and blow on this ferruled hose (mimicking an engine cycle vacuum), the fuel flow starts. As soon as I stop sucking and blowing, the fuel flow stops. I see a few US versions on YouTube don't have this fuel pump fitted. Maybe it's a legal thing but without this connected up, gravity isn't cutting it (pun definitely intended)

Interesting.
None of the parts lists for GVC series shows a fuel pump so this must be UK Flymo specific engine
This is why I thought it was a breather line
It should be easy to find if you can keep the engine running as it will be blowing & sucking from the hole so there should be lots of wooshings and some oil to lead you to it.
You might like to clamp off the breather tube with a pair of lockjaws or similar, remove the plug, tip the mower and spin the blade to spin the engine
With the breather blocked off you should be getting 1600 cc of gas vented through the hole where ever it is
As there is no obvious retainer on that spigot it might have originally been a shrink fit into the crank case so when you find the hole you might need to freeze the fitting & heat the cases then us some loktite bearing retainer

When you do please post a pickie of where it is

We get the japanese Honda engines down here in the colonies not the USA ones.

I've blanked off the breather and also put my thumb over the carb intake so I can get a good ear on it. Can't hear any wooshing. This hose has been off since the day I bought it 2nd hand. Going by photos of XL500s on eBay, this hose disappears somewhere between the cowling and the carburettor. Now. Here's where it gets weird. There is an item listed on some parts lists online called a carburettor insulator. This is the black piece that sits between the carb and the head, obviously to insulate the heat from the carb. There are 2 numbers for this. One number is the insulator that I have fitted. The other number shows the same insulator but with a brass hose fitting. My insulator definitely doesn't have this, neither does it have a hole where it may have been fitted. As this insulator is after the carb throttle butterfly, this would sense a vacuum right? Is it possible that over the years, someone has fitted an incorrect insulator to my particular mower? If this is a possibility, I may well have trouble finding the correct insulator as a UK websearch has so far brought no listings up, just USA ones.
I'll wait and see what you guys reckon before I take my drill to the insulator to adapt it.
My biggest concern is that this side of the engine would sense purely vacuum during running and I would have thought it would need to see vacuum and pressure on a constant cycle to allow the diaphragm in the pump to do its thing.
Looking forward to your thoughts chaps.
Gaz.

Yes it would under vacuum with the engine running but no it would not pulsate to power the pump.
The pump impulse line is plugged into the crank case or the rocker cover.
Some times even the dip stick tube.
It has to be high to avoid filling up with oil
It will not work plumbed into the inlet tract because it needs a blow suck blow suck pressure pulse.
There is a return spring inside the pump but it is very weak.

Great. That's that theory out the window then. I'm away in to town just now and there's a hardware store that sells them new. I'm gonna have to swallow my pride and go look at it to find out where it's supposed to be. I honestly cannot see anywhere on this engine that could feed it. Good shout Berts on the rocker cover but alas, nowhere for it to fit to.
This is going to be something really silly isn't it? Either way I'll keep you updated.

Well. I've just had a look at a brand new XL500 and that hose does indeed for to the carburettor insulator plate. If it's purely a vacuum from there, I can only deduce that it is utilised as a safety device to stop fuel flow when the engine is off.
The problem I face now is that I can't source a part in the UK, even though there is a brand new one sat in town with it fitted and the only spares they do are "the ones on the shelf", ie spark plugs and blades.
Is it worth drilling the isolator plate to effect a makeshift fitting to attach the hose? I can only imagine that this plate has been changed out at some point for a non pump version.

Just a shot in the dark here. This may have been jury-rigged before you got the mower. If they unhooked the hose, then the spot where the hose connects may have broken off and been tapped and a bolt placed in it. Take the engine shrouds off and use hose as a distance guess and see if there is a bolt going into engine for no apparent reason. Also check very carefully for other holes if this isnt the case. If this isnt found it will allow dirt and sand in the engine that will kill it in short order.

dfbroxy, in the radius that the hose naturally draws, there is no blanking plug or bolt or hole. The whole carburettor has been off as has the control linkage plate. Nothing amiss. I can only assume right now that the plate has been replaced at some point with the wrong part, the previous owner has realised that it runs without the hose fitted and left it at that.
I picked the whole mower up for £80 as spares/repairs as it was "hunting". When I viewed the mower, I could see that the gasket was hanging out at the heat deflection plate. Got the mower home, made a gasket, fitted it and it ran sweet.
The engine has only just started doing this (cutting out after a period but then restarting after being left for a bit). I'm tempted to drill in to the insulator plate and fit/epoxy this hose in place.
Before doing this, I may connect this hose to my mityvac and see if allows the engine to run without cutting out. I could try sucking on it but I doubt I'll have any eyebrows left if I try this with the engine running ???

Ordered the insulator I require so once the rain goes, I'll get it fitted and update

That's a vacuum hose and it powers the fuel pump. It's called a "pulse pump" because it is powered by pulses of vacuum from the engine that turn/power the pump. If you don't have the vacuum line connected to the pump, the only thing moving fuel from your tank to the bowl in your carburetor is gravity, and if the carburetor is at or above the level of the fuel tank you're likely getting little to no flow. I believe the vacuum hose is 1/8in or 3mm ID. You can use fuel hose if it's the same ID, but on some GC/GCV engines the nipple on the engine is at a right angle to the nipple on the pump, and you may have difficulty bending the stiffer fuel line to fit.