Maico490

Straight off I'm no expert on these but valve lifting twice may be an auto decompression device.

And so the fun with this new stuff starts.

Spray on stove or BBQ paint for the exhaust.

Did the magic involve JB Weld in a certain pump?

Some of these premium fuels have ethanol in them to help raise the octane rating. They are therefore more likely to absorb water if not used quickly enough. This isn't usually a problem in cars but for 2-strokes it can equal an early death. Just take a look at the US chainsaw sites to see how many problems they have with ethanol and you will see that it is a blessing that the Government went off making it's inclusion in all our petrol compulsory due to rising cereal prices. Just use fresh ordinary unleaded with good oil and don't mix more than you will use in a few weeks.

RangerMatt If you are struggling with brambles you want one of these wonderful bits of kit:

Was it the one on ebay the other day? I've got some parts for the 045/056 range but no handle/top covers. There are plenty on the US ebay but shipping would be quite a bit. Good luck with it as those saws make a wonderful noise when working hard.

She was trying to make skip chain to impress the "real" chainsawers

Thanks for that Megatron I'll try some. Now I think about it the alkaline cleaners we used to use on dairy equipment would eat an aluminium milk churn through in no time.

I've come across lots of people who are none too happy with work done by dealers. Trouble is it costs nearly as much to put someone to work on a small engine as it does on a £20k car. As a result most try to convince their customers to buy new where there is a known margin and the warranty slopey shoulders the responsibility back to the manufacturer.

I use a cheap bike pump with the seal flipped over so it sucks instead of blowing. The proper Stihl tool resembles a large syringe but the ones I've tried from agricultural suppliers are a bit sticky when working dry. You only need a couple of pumps to get 7psi of vacuum on most small saws. I've got exactly the same Draper gauge you show in the earlier pics which seems to work well. For a non return I "doctored" the spring on a screw in type tractor valve but always clamp the pipe close to the tee to take readings.As you stated pressure is quickest to find major problems but apparently some dodgy crank seals only show up under vacuum.

So Megatron what is this patented cocktail or would you have to kill anyone you told. I have had little luck in getting hold of decent strength hydrochloric acid. Most of the patio cleaner sold wouldn't hurt you if you put in on your fish and chips. I've been using some industial toilet cleaner which has a reasonable HCl concentration but some other things added.However the label has faded too much to be able to read. I normally heat the cylinders first on top of the Rayburn then take them outdoors to treat. The heat definitely helps with these weaker acids. Note to anyone who hasn't cleaned cylinders like this before. WEAR GOGGLES (Full face shield better) plus rubber gloves and make sure any other skin is covered up. Also have some weak bicarbonate of soda solution to hand and a bucket of clean water. Don't rely on getting them after it goes wrong as you could well be in too much pain or lacking the ability to see well enough to do much.Other than that enjoy saving lots of money on a new cylinder. PS Excellent case splitting pics

Spud, I got called away to the phone just as I posted and didn't notice that I had pretty much repeated what you said. Hopefully it may solve the problem but then again there are also those million and one other little things that come along to try you. My favorite lately was pressing a front wheel bearing in the wrong way round and then having the ABS light come on. Sensor gets it's signal from a little magnetic strip on the bearing. First bearing was £42 from the interweb. Second one £78 because it was a Bank Holiday Sunday. Happy Days

With the Tillotsons very similar carbs sometimes have the diaphragm that hooks over the metering lever and some have the more normal type that just presses on it. The bloke at Rowena Motors is a real mine of info for these sort of probs and seems to carry every carb kit made since the earth cooled.

As no one else has chipped in. First off I'm no expert on the 4-Mixes but have picked up a few things on other forums. It sounds like it is flooding so check that the metering needle isn't leaking. Should hold 5psi on the inlet pipe. Don't over do the pressure though. The valve clearances need checking every 100hrs or so and the early ones had issues. Also there were problems with the ignitions. From memory they still spark but fail to full advance and are hard to start. They have a lifetime warranty to the original owner in the US but not sure over here. Hope this is some help.

+1 on the last post. Drive link gauge has nothing much to do with chain strength as the actual links are all the same with just the lower part ground down. The biggest difference will be between brands. Also 0.050" 3/8 chain isn't easy to find over here. Go to the West coast of the US and they hardly use anything else.

Black smoke indicates they have not yet decided. Only white smoke means there is a new Pope. Could also be your turbo has blown it's seals.

Could you post who the UK agents are please.

You'll take forever to blow it up with an attitude like that!

I also always try to use OEM clips and prefer the "earless" ones. They are only a few pence so not worth the risk. Also ditto on reusing the original wrist pin as they are generally lighter and have less of a chamfer on the end to ride over the circlip. Whilst on the subject of clips it is worth installing them with the gap at either 6 or 12 o clock as the predominantly vertical forces then squeeze them tighter into the grooves. At 3 or 9 o clock they can flutter especially the eared type. Although I've used plenty of aftermarket pistons without any failures yet, these little details are worrying. Just a pity OEM ones are so bloody expensive.

I initially thought that you had a problem with "Spooge". That however looks like unburnt spooge most likely linked to the fuel leak you mentioned. I would hazard a guess that the inlet needle on the 450 carb is leaking, possibly the 400 as well. Should hold 5psi on the inlet pipe for a fair while, if not swap for a new one. Are both sides of the cylinder wet with oil or just the exhaust side? Replacing the exhaust gasket should in theory be easy enough but I have had several exhaust screws twist off on these bigger Stihls and yours have been there for a year or two. Out of interest what attachment are you running. If ours are on blade work they will put oil out of the exhaust as you can't load them up. 3.3mm Stihl black cord will soon burn it off after though.

Thanks for that Spud. Must admit the problem had me at my wits end and took ages to work out. As there was little information on it anywhere, other than "Buy a new carb" I did the post. Although like you I've been playing with small engines for years these little probs still come along to catch you out. The Zama website is well worth a look even for old hands. The Maico was a German MX bike. 490cc piston ported with no trickery at all but put 50 horses to the back wheel when the Japs struggled to get much over 40 with pipes, wires and gizmos everywhere. I took MX up again for a few years and on a long start it certainly made the youngsters on their "powerfull" 4-strokes a shock. Only thing was they soon got by again on the rough stuff. The one thing I really kick myself for selling.

Sorry about the delay but didn't finish work too early this evening. This is a cut and paste job from a posting I made on another site as it would take me ages to re-type: This has been my first experience with the notorious check valves found on newer carbs. I've been chasing this problem on a FS450 trimmer for a while but luckily it has been between cuts on Water Authority sites. Searching here didn't throw up much but these carbs are used on lots of blowers, trimmers and smaller saws. The carb is a Zama C1Q-S34H which is fixed jet with only what appears to be an air screw (reverse thread) for idle adjustment.Symptoms were hard starting, inconsistant idle which couldn't be adjusted and would run out of fuel with an inch still left in the tank. When operating the primer bulb you could keep pumping without it becoming full and air bubbles were visible in the bulb. At full throttle everything was fine but as soon as you let off it would often stop dead. New lines, primer bulb,fuel filter and a rebuild kit did nothing. The answer was eventually found on Zama's excellent website: USA Zama : Service Tips. Before you do anything to a Zama carb I would recommend reading all the Service Tips. Especially DO NOT BLOW COMPRESSED AIR THROUGH A CARB WITH CHECK VALVES. It seems you also have to be careful with aerosol carb cleaner if directed straight into the valve with an extension tube. The jet at the bottom of the metering chamber is the main jet which Zama call the "Nozzle Assembly Check Valve". Stihl call it the "Valve Jet". The hole in the middle, which is normally hidden by the metering lever leads to the idle circuit. To test both circuits use a piece of square ended hose pressed against the jet and blow with your mouth. If clear then try to suck back. If you can the check valve is defective. In general if it is working you can hear a faint click. If you can suck back it is bad news on the idle circuit as it means a new carb but the main jet can be replaced. Zama do a special tool but I managed to use a cheap drill press and one of my extensive collection of broken drill bits. This is clamped in the chuck upside down. If you have adjusting screws remove the H before starting. It took a fair bit of fiddling to get everthing lined up and more force than I expected to get the nozzle to move. It pushes straight through into the bore of the carb. The chuck is stationary throughout. Here it is out and the new one: The new nozzle pushed in quite easily with a bit of oil on it to the same level as the old one. Zama say you can punch them in and out but I wasn't too keen on hitting a carb with a hammer. A few minutes of reassembly and it fired right up. Ticks over fine now and is responsive to the LA screw. Hope this helps. The size of the jet is in the IPL and stamped (microscopically) on the jet. Any probs getting the jets PM me as supplier is not a sponsor. Edit: Sorry about the duplicate photos. Haven't got the hang of them on here yet.

Had one just the same and replaced all the same bits as you to no avail. Started to run out of hair to tear out. Ended up being the main jet check valve. Will dig out pics tomorrow and post. Good news is only a few quid to mend.

Not totally sure about the 250 but it isn't a good idea to go too rash with the airline on a carb that has check valves.The high speed one can be replaced but if you muck up the low speed ones it's Game Over.