Spice Cat Posted September 7, 2015 Share Posted September 7, 2015 Evening everyone, Today at the strip I had a problem starting my Chipmunk with its Laser 70 engine. I then decided to give the fuel system a bit of help by gently blowing into one of the two vents with a spare piece of fuel tube. Well the engine started fine then went to full throttle ignoring whatever setting the throttle was set to. At first I thought it was a problem with the servo and with a full tank I faced the prospect of an overheating engine. Pinching off the two breather tubes I managed to get the engine to shut down and after an inspection found that the throttle servo was fine and the throttle arm moving on the carb. The barrel was also ok moving to close as required. Back home I started her again without the 'wind' assistance this time and she ran fine up and down the rev range. Obviously by blowing in the breather I had caused this to happen but why no response from the throttle and why did it run so long, over two minutes?? Any ideas??? Quote Link to comment Share on other sites More sharing options...
clive orchard. Posted September 7, 2015 Share Posted September 7, 2015 Filled the crank up with fuel, did this to my bsa bantam,ran like hell for a few minutes. 😨 Quote Link to comment Share on other sites More sharing options...
Spice Cat Posted September 7, 2015 Author Share Posted September 7, 2015 Cheers. Hope to fly tomorrow Quote Link to comment Share on other sites More sharing options...
Martin Whybrow Posted September 7, 2015 Share Posted September 7, 2015 I doubt he filled the crankase with fuel, it's a four stroke! To run at full pelt like that there must be an air leak, otherwise it would just be very rich from excess fuel in the inlet tract. Quote Link to comment Share on other sites More sharing options...
will -0 Posted September 7, 2015 Share Posted September 7, 2015 Oh I dunno, I got very confused fueling an OS26surpass installation last year and only realised I'd connected the pump to the crankcase breather tube instead of the filler when fuel started coming out of the front bearing. Whoops. Quote Link to comment Share on other sites More sharing options...
Jon H Posted September 7, 2015 Share Posted September 7, 2015 Sounds like either a momentary obstruction of the throttle or the carb barrel has come adrift. I would suggest checking the carb carefully to make sure the barrel screw has not fallen out or come loose. If the engine has an Irvine carb and has had exceptional amounts of use the barrel screw could have worn through but this is unlikely. Quote Link to comment Share on other sites More sharing options...
clive orchard. Posted September 8, 2015 Share Posted September 8, 2015 Agree Martin, forgot its a 4 stroke 😕 Quote Link to comment Share on other sites More sharing options...
John Privett Posted September 8, 2015 Share Posted September 8, 2015 Sounds odd. To run at any sort of speed, air - and a lot of air - has to be getting in somewhere! Quote Link to comment Share on other sites More sharing options...
cymaz Posted September 8, 2015 Share Posted September 8, 2015 Is the O ring and clamp for the carb ok...that could be the biggest source of air leak. Quote Link to comment Share on other sites More sharing options...
Spice Cat Posted September 8, 2015 Author Share Posted September 8, 2015 Cheers. The carb may be the culprit but it's running a treat now. Gremlins! Quote Link to comment Share on other sites More sharing options...
Engine Doctor Posted September 15, 2015 Share Posted September 15, 2015 Hi. Was it running backwards ? If the tank is full and the exhaust vent/pressure pipe is submerged in the fuel they can draw fuel in via the exhaust,effectively now an open throttle and run with no control until the fuel runs out. The carb will only slow it down a little as this is now effectively the exhaust . Quote Link to comment Share on other sites More sharing options...
Spice Cat Posted September 16, 2015 Author Share Posted September 16, 2015 No, it ran forward but you may be on the right track as I had blown up one of the vents. Quote Link to comment Share on other sites More sharing options...
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