OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Trimmers and Brushcutters Two Stroke Trimmers & Brushcutters Stihl FS 56 fuel problem

Hey Guys,
First post on the forum, looks like a great site.

I've got an old FS56 bent shaft whipper snipper and I'm not getting fuel to the carby.

I was starting reasonably easily but then idiling really rough and stalling. Tinkered with it for a bit and now it doesn't start at all.

I replaced the fuel hose as it looked a bit perished, got a new fuel filter aswell and can now see through the new clear fuel hose that fuel isn't being sucked up into the carby.

What should I try next?

Cheers, Sam

This is a bit of a mystery - I replied to this an hour ago, and now no answer is present, so I'd better start again. The first test is to disconnect the fuel hose at the carburetor end, put a cup under it, turn the whipper snipper so the tank is higher than the open end of the hose, and see if fuel runs out of the hose. If not, remove the fuel tank cap and repeat the test. If no fuel comes out even then, try blowing into the tank. If no fuel comes out when the hose is lower than the tank, you have a blockage in the hose either inside or outside the tank. If fuel only comes out when you remove the tank cap, you have a blocked fuel tank vent.

If fuel runs out even with the cap on the tank, all is well up to the point where fuel goes into the carburetor. Before we go beyond that point, it would be a good idea to check that nothing else has gone wrong. You do that by removing the spark plug, squirting a small amount (a small spoonful) of fuel into the cylinder, and trying to start it. It should start and run for a couple of seconds until it's used up the fuel. If it won't start even when primed in that way, the problem probably isn't fuel.

To illustrate why you need to make that last check, I once knew a guy who rode a motor scooter. One day he tried to start it and failed, despite a long session of kicking the pedal. He happened to live downhill from where we were at the time so he asked me to push him to the top of his street. I did this easily, by applying my right foot to the back of his pillion seat, and riding my own scooter. Before we even got to the top of his street he tried to start his engine, in first gear, which would have dislocated my hip if I hadn't removed my foot very quickly, so I let him coast over the crest and abandoned him to his fate. (He'd taken a drink or two, so it was my own fault for trying to help him get the scooter home.) I later learned that he coasted home, and walked up to the scooter the next morning to try to fix it. He immediately noticed that his first kick of the starter the previous day had neatly dislodged the spark plug lead from the spark plug.

ok tests completed.

fuel comes out of the fuel line when disconnected from the carby with the fuel cap on. Fuel hose and fuel filter are brand new so this is a good result.

Motor runs for a second or so when a teaspoon of fuel is dropped in the chamber so idicates that the motor will run, just doesn't get any fuel from carby?


I just watched a youtube video posted on here about rebuilding carburetors, and it occured to me that maybe the fuel pump diaphram needs replacing?

what should i try next? how do i know if the diaphram is stuffed?

cheers.

It has to be the carburetor, or an air leak between the carburetor and cylinder. On those small engines with chainsaw carburetors, the main suspects are the intake filter, and the pump diaphragm, but many other things can go wrong as well. What kind of carburetor is it? If we can find the carburetor manual, we can work from that, making life quite a bit easier. It is probably Walbro, Tillotson or Zama. Find out which, and which model, please.

Ok its a Walbro, numbers on the side are as follows: WT 45A K9. I assume this is the model number?

The main point is that it is a Walbro WT. Here is the service manual:
http://wem.walbro.com/distributors/servicemanuals/WTseries.pdf

The first thing you need to do is look at the gauze filter in the intake chamber. The second thing is to set the adjustments to the initial settings shown in the manual, and try to start the engine. If you can't get a satisfactory result with a clean filter and following the manufacturer's tuning process, you will have to go further. Usually the next step after that is a new diaphragm and a clean, following the manual throughout.

My concern is that you might have started out with a clogged filter, then compounded the problem by tweaking the adjustments without cleaning the filter first. That is why I suggest the approach I've described.

While browsing I found this tune up guide for Walbro carby's.
It may come in handy.
Click HERE

Thanks for the manual and the tips, they are great resources.
I removed the fuel pump diaphragm to see the gauze filter only had a couple of specs in it, cleaned them out anyway but didn't seem like it was the issue.

I took the cover with the 4 screws off to get into the metering area and the metering diaphragm seemed to have a tiny tear in it. Hard to tell as it was quite rigid and hard to pull away from the metal surface. I assume this is meant to be air tight?

I put it all back together and tried to start it and i've definetly got an air leak somewhere still. I can see bits of fuel coming up the fuel hose but there's still air getting in somewhere so no suction.

Should I replace the metering diaphragm? Should I do the fuel pump diaphragm while I'm at it? Where else am I likely to be getting an air leak?

cheers

There are at least two ways you can get air flowing back into the fuel hose from the carburetor. One is if there is a blockage in the fuel hose or fuel tank vent: when a vacuum forms upstream of the fuel pump, it doesn't perform well as a vacuum pump and there will be an air leakage into the pump, one way or another. The other way is a defect in the carburetor that lets air in - such as a perforated diaphragm or a leaky gasket. And yes, the diaphragms can only work if they are air-tight.

I suggest you get a kit for the carburetor, which will include gaskets and diaphragms. Then follow the process in the manual as far as possible (you may not be able to access some special tools), cleaning, clearing, adjusting and putting it back together with the wearing parts replaced. I wouldn't recommend that approach with a bigger carburetor for a B&S or similar engine - I'd normally just find and fix the problem - but those little carburetors are fairly complicated and rather sensitive. A blind, largely mindless overhaul seems better than having to acquire watchmaking/forensic skills that might be fairly useless afterward. Of course if I weren't a bit on the heavy-handed side myself I might see this differently. If fixing watches is your game, working through a diagnostic process might work. However it seems to be cheaper to buy a kit than to chase individual bits as you belatedly find defects in them.

Sounds like good advice. I thought that might be where this was going. I'm definetly no watchmaker so sounds like a kit is the way to go. Should I get an entire kit with new needle valve and seat and leaver and all that stuff? Or just get a diaphragm and gasket kit? I'm thinking a kit with diaphragms and gaskets is all I need.

Do you guys sell such things on here or know of any good online stores? Or should I go into my local stihl shop and get them to order me one in?

thanks

I can't tell how much work it has done, Sam, or how heavy-handed the previous owner was, so I can't say whether the basic kit will be sufficient. From my limited experience with whipper snippers I'd guess that it won't need more than diaphragms and gaskets unless it has been used by a farmer or contractor. You will have to adjust the needle valves of course - the manual tells you how. They would only need replacement if someone has messed them up by ham-handed adjustment (screwing them all the way in, hard, or bending them). Your problem is most likely diaphagms, gaskets, maladjustment, or dirt.

I think the right kit will be available in the on-line store here.

I'll just try a gasket kit for now. If that doesn't work i'll look at other options. Hopefully it doesn't come to that.

I've looked at the online store and there are lots of gasket kits for a WT walbro. How do I tell which one is suitable for me as none of them seem to match my model number? Or do all of them fit simply because its a WT model?

Mine is a WT 45A K9, i don't seem to be able to find a K9 WT kit?


Thanks very much for you help. Its much appreciated.
Cheers Sam

That sounds like a question for Bruce - he may come in and set us straight. I did see one explanation of the difference between K9 and K10 here:


There is a PDF download file called "Carby Kit Information" from Outdoorking that seems to be saying that the D10 WA&T kit is the only correct one, as far as genuine ones go. However I've never had much success interpreting documents like that - I think Bruce is the man.

hmm, that youtube clip is about tanks...?

I do agree that carby kit info pdf seems to indicate that the D10 WA&T kit is the go.

Bruce?

Sorry Sam, my sense of humour appeals to me, but not to most people.

Bruce is the site owner, and actually understands the online store.

haha, thats cool, I get it now. I just thought it was a mistake

Click HERE for the carby kit which you should start with first and also replace the fuel filter in the tank.

Once you have replaced the diaphragms and fuel filter remove the muffler and try running the trimmer (make sure that you are wearing ear muffs). Then if it runs ok put the muffler back on to see if it will run with it on, if it won't then your muffler is blocked.

Try this to start with and let us know what happens.

dropped into the local stihl shop today as its on my way home, they had the gasket kit on the shelf, so I grabbed it and a new NGK spark plug while I was at it.

Fitted the gaskets and diaphragms with a new tank of fuel and I could see with the first pull after it was all back together that fuel was sucked straight up the fuel hose and it started on the next pull.

Ran through the tuning methods from a previous post and got it running pretty well. Thanks for the tips guys, seems like the gaskets and diaphragms were the main problem.

Cheers
Sam

Good to see you got her running, its fairly common to have the old gaskets/diaphragms go stiff and perish.

As this topic is now complete I will lock the thread. If you have any further trouble please feel free to start a new topic.

Cheers Joe.