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Post by dpress on Jul 3, 2020 10:53:12 GMT -5
I am hoping that someone can help me with a frustrating issue I am having with the Walbro WT6 carb on my 240. The saw is a recent addition to me and was in poor shape when I got it, but the fundamentals are good - decent compression, and even the oiler works!
I was using it at work yesterday doing some branch lopping, and although it had started about 4th pull and was running fine, a couple of times it began to die on me (recovering once out of wood and by blipping the throttle) until at one stage near the end of the job it died completely as if it had run out of fuel. This was not the case - I had filled the empty tank before starting work, and although it would start and run at idle, touching the throttle caused it to die immediately.
I did wonder if there was a drop of water that had got into the high speed circuit blocking it, but on stripping the carb today I could not really find anything amiss - there did appear to be a bubble of something under the fuel screen, but all passages seemed to be clear when spraying WD40 into the various orifices, and the diaphragms are really flexible and good (I have not changed them).
On reassembly the saw fired and ran, revving up freely for a few seconds on half choke until starting to splutter and die when the throttle was used. A second strip down did not find anything apparently wrong, and neither did the 3rd strip half an hour later! Each time the machine will fire but not run with any throttle.
Prior to this issue starting yesterday, the saw was running great, and I can't think for the life of me what has changed to cause this problem. On disassembly of the carb there is fuel under both diaphragms, so the metering needle assembly must be working. I just can't understand it.....
I would add that I did drain the fuel tank to look for contaminants, but there were none - it was fresh 50:1 mix.
Any help would be gratefully received.
Thanks Steve.
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Post by edju1958 on Jul 3, 2020 12:57:30 GMT -5
A fresh fuel filter would be a good start.Also a new spark plug wouldn't hurt.I don't know much about the 240.I did look it up & found that it has an electronic ignition,so that doesn't really leave much.You might want to check to make sure that the ignition module is clean & grounded properly.Sometimes the ignition system can mimick a fuel problem.
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Post by onlyhomelites on Jul 4, 2020 10:08:38 GMT -5
I agree with Ed, check the fuel filter and while you are at it, pressure test the fuel line if you can.
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Post by dpress on Jul 4, 2020 13:08:43 GMT -5
I had another go today - new fuel filter, carb gaskets and pump diaphragm (didn't have the metering one to hand). All back together and exactly the same result - it will fire and run, but only for a few seconds before dying out. I have ordered a metering diaphragm and will test it again once I have installed that. When removing the carb there is a decent pulse of fuel that comes out of the line, so I don't think that is an issue, but I will change it if the new diaphragm doesn't work. I am pretty sure it is not spark related - when I had the saw apart originally I fully cleaned all surfaces of the ignition system and it has a good spark.
Steve
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Post by onlyhomelites on Jul 6, 2020 8:56:01 GMT -5
While you are in there, check the height of the fuel inlet lever and the condition of the inlet needle. Ethanol can swell the rubber tip, which of course throws off the adjustment on the lever! Also check the metal screen passage between the metal screen and inlet lever for obstructions (shouldn't be any, but it's worth a quick look).
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Post by dpress on Jul 8, 2020 10:23:37 GMT -5
The repair kit arrived today and I put in a new metering diaphragm. Needless to say, exactly the same result - machine will fire and run on half choke for a few seconds and then die. Blipping the throttle will cause it to die immediately, but when you release the throttle it will fire and run again albeit briefly. This ties in with the original start of the problem when the machine was good and hot - it would restart and idle but the second you gave it any throttle it would die, as if there was no fuel getting through the high speed circuit. I have looked again at the Walbro WT service document, and I wonder if I am missing something. The diagrams indicate that there is a check valve in the high speed nozzle - the circled item in the attached screenshot. Have I got a check valve that has gone bad I wonder? And if I have, how on earth do I get to it - the high speed nozzle seems to be just a solid piece of brass! I have now taken the saw completely apart - more in frustration than anything else, and will be changing the fuel line, but I am sure that is okay because fuel was pouring out of it while I was taking the saw apart - of course with the 240 you have to take it all to bits just to get the engine out, and gain access to the fuel/oil tank. Give me a little XL any day.... Steve  |
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Post by dpress on Jul 8, 2020 14:29:36 GMT -5
A quick update - nozzle assembly check valve removed simply by driving it into the carb. Having removed the microscopic metal spider that holds the check valve disc I could see nothing wrong, although prior to removing the spider the valve disc did not seem able to move up or down at all, with the retaining spider being rather concave. Perhaps for some reason there was insufficient room for the check valve disc to move up and down and release fuel? It is impossible to reassemble the disc and spider so I am going to put the carb back together without the disc in place, simply to see if I can get the saw to run, and prove that this part was actually to blame. Walbro part number 86-540-1 apparently, but heaven knows where I will get one in the UK....
I don't really understand why there would be a check valve in what is the main jet, as at idle it should not draw fuel, and at speed you don't want any impediment to the flow, but there we are!
Steve
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Post by onlyhomelites on Jul 8, 2020 21:22:24 GMT -5
The check valve is prevent any engine pulses that make it past the reed valve from disrupting the flow of fuel. A bad check valve usually results in erratic running, not a blip & die, but each saw is different. Let us know how it runs without the valve!
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Post by dpress on Jul 13, 2020 14:29:08 GMT -5
Time for an update. I did not in the end run the saw with the check valve removed as much to my surprise I was able to locate a new part in the UK from the Walbro distributor who sent it next day delivery for the equivalent of $5, so there was no need. The cleaned saw has been reassembled complete with a new spark plug thread (thanks for that video Leon) and was test fired tonight. I eventually got it to run, but only after completely altering the needle settings from what they had been. Originally when the machine was running well, the Lo was 3/4 turn out, and the Hi 1 turn out - both are now at about 1 1/2 turns out. I have no idea why the settings should have changed so much, but all the internals of the carb are new now. I do need to buy one of the Walbro 'W' style measurement tools just to make sure the inlet needle is at the correct position - I have not changed it at all so far. So to sum up, it must have been the check valve despite the fact that the new one looks no different from the old one I took out! I think that there is a possibility that some crud had got to the jet and blocked the orifice under the check valve - there is no secondary filter screen like there is on HDC carbs, and because there is the small disc in situ you can't see if the jet is actually clear. I expect me blasting it with WD40 might not have helped, as although fluid was forced through, the jet may still not have been completely free and I probably knackered the check valve in doing so.... Anyway another lesson learned, and the saw is better for a clean and polish! Now I must find some paint for that bar.... Steve   Workbench could use a little tidy I think.... |
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