Service & Maintenance Question
I have a Husqvarna 450 Rancher that will not restart hot....
Service & Maintenance Question posted July 9, 2017 by Ray Shapinas
195 Views, 7 Comments
Question:
I have a Husqvarna 450 Rancher that will not restart hot. Always used non-ethonol gas. Primer button will not fill with gas when hot. Primer button, fuel filter and spark plug are new. Button will prime fine when cold, but just whistles empty when hot. Will not restart without priming the button. I can sometimes get it to start for a half second, then nothing. Starts easy when cold. Runs excellent all day if I keep adding fuel and bar oil without shutting the saw off. Otherwise it takes 2-3 hours to cool off and the primer button will pull and pump gas again, and the saw will restart. I though maybe the fuel tank vent was plugged, but most posts say that's rarely the case. If I open the fuel cap with some gas in the tank after running (and saw shut off), I will get a little gas blowing out around the seal, so it seems the tank is pressurized somewhat. I was told by two Husky shops that the carb diaphragm might be bad, making the bulb stay empty. But, the saw starts fine cold and runs great hot. How can it be a bad carb diaphragm if the saw runs great? Any suggestions?
Answer
First I would try replacing the remote primer as I have seen a lot where the internal check valves gets stuck open. If this does not resolve the problem then I would think the main nozzle [non replaceable, require complete carburetor replacement] of the carburetor is sticking open when hot or the screws holding the metering diaphragm cover is slightly loose allowing to be pull in when hot. Also check for loose fuel line between the carburetor and the primer.
The main nozzle and primer being bad is some I have seen several times in the last few years. Due to my shop's workload it has primary Stihl saws but can happen to any.
Also give you saw a good cleaning as sawdust can be blocking air flow over the cylinder fins.
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The remote primer button was replaced by a Husqvarna dealer last week. They are ready to order a carb tomorrow, but I'm reluctant to let them do it. The saw starts cold and runs like a bear all day if I add gas without shutting it off. Also, if I do get it restarted hot, it will run great again. If the main nozzle was stuck open, or diaphragm cover loose, would the saw run great hot?
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Very possible the nozzle is sticking as the result of super heating during shutdown. And yes all air cooled engines goes through the super heating phase after shutdown.
Now I would have thought the dealer would have spare carburetor to test with. Now I don't normally but it is because I am a small independent dealer but I could in this case as I personally own a 450 myself. I also make sure a problem like this resolved before it leaves my shop as I would test the saw here cookie cutting trying to reproduce the problem after repairs.
Now in City/Town shops just don't have an area to test chainsaws or other equipment. A shame in a way as many hard feelings could be resolved before they happen if the testing is done.
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Yes, I understand the super heating after shut down. That makes the most sense. I'm not thrilled with the dealer / shop. The counter person suspected it was not the primer bulb, and told me to take the saw and try it over the weekend. The mechanic was an ***, more concerned with my chain and bar than with the hot restart problem. I told the counter man all the stupid things he said over 2 phone calls. That's why I'm not happy to take it back for a carb tomorrow. I told the counter man I wanted a different mechanic for the carb. And yes, they do have a wood pile to test saws in, but you see what I got back...
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Also, the hot restart has gotten progressively worse. I used to be able to restart hot standing up, with the saw on my left thigh. One pull restart hot. Now it's a struggle. The saw will run great all day if I don't shut it down. It will sit on the ground at idle while we ready another log, then take off and rev / cut with no lag or "clearing out" at all.
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The remote primer button was replaced by a Husqvarna dealer last week. They are ready to order a carb tomorrow, but I'm reluctant to let them do it. The saw starts cold and runs like a bear all day if I add gas without shutting it off. Also, if I do get it restarted hot, it will run great again. If the main nozzle was stuck open, or diaphragm cover loose, would the saw run great hot?
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Also, the hot restart has gotten progressively worse. I used to be able to restart hot standing up, with the saw on my left thigh. One pull restart hot. Now it's a struggle. The saw will run great all day if I don't shut it down. It will sit on the ground at idle while we ready another log, then take off and rev / cut with no lag or "clearing out" at all.
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