treehopper Posted April 22, 2012 Share Posted April 22, 2012 Hi all. Anyone know what the top 80 should rev to, I have found a figure of 9000 rpm ! I'm guessing that is not spinning a prop but I don't like to rev an engine unloaded. I'm spinning a 125 cm Helix carbon prop with a 3.8/1 reduction and revving out at 4950 rpm any ideas, just seems a bit low. Thanks J Quote Link to comment Share on other sites More sharing options...
pete_b Posted April 22, 2012 Share Posted April 22, 2012 9200-9700 some go to 10000 but thats a bit too much. Where did you get the prop? if the motor revved ok before then the prop is over pitched for the motor, ie the wrong one. Pete (with no motor) Quote Link to comment Share on other sites More sharing options...
treehopper Posted April 23, 2012 Author Share Posted April 23, 2012 Hi Pete, it's the prop that was on it when I bought it, (unlike yours lol ) the machine seems to have fairly good thrust but I don't think the engine is giving quite as much as it was, just sounds a bit flat at top end. Plug looks good so I don't think it's running rich. Do you know if those rpm figures are with or without prop, coz I don't think I'll get anywhere that. Quote Link to comment Share on other sites More sharing options...
pete_b Posted April 23, 2012 Share Posted April 23, 2012 Hi Pete, it's the prop that was on it when I bought it, (unlike yours lol ) the machine seems to have fairly good thrust but I don't think the engine is giving quite as much as it was, just sounds a bit flat at top end. Plug looks good so I don't think it's running rich. Do you know if those rpm figures are with or without prop, coz I don't think I'll get anywhere that. With prop, dont rev it with out as you could over rev it and blow it Check the pop off pressure, when was the carb last cleaned and new membranes fitted? Quote Link to comment Share on other sites More sharing options...
treehopper Posted April 23, 2012 Author Share Posted April 23, 2012 Got a full service kit for carb so will give that a try. Will ask FAF Col to look at the pop off pressure as I think it's surposed to be higher than we set it last time, so maybe it is a bit rich. Quote Link to comment Share on other sites More sharing options...
treehopper Posted April 23, 2012 Author Share Posted April 23, 2012 RAF Col, sorry mate Quote Link to comment Share on other sites More sharing options...
Farmer_Dave Posted April 23, 2012 Share Posted April 23, 2012 Hi Treehopper Is the thrust good enough to fly a good sized bloke.? If yes....have you got a rev counter for a 4 stroke engine? Just a thought Dave Quote Link to comment Share on other sites More sharing options...
treehopper Posted April 24, 2012 Author Share Posted April 24, 2012 Hi Dave Yeah the thrust isn't too bad at all but the engine just seems a bit flat at top end, it may well be fine and it could be the rev counter at fault, it's set for one fire per rev but I will double check. Many thanks Jamie Quote Link to comment Share on other sites More sharing options...
pauldeakin Posted April 25, 2012 Share Posted April 25, 2012 Do you have TinyTach rev counter? I have a TinyTach that shows a reading of half the actual revs, even though it is set to one ignition per revolution, it seems to think that I have 2 sparks per rev so always shows half of the true revs, it doesn't really matter because I know it is doing this, so always know the true revs. Quote Link to comment Share on other sites More sharing options...
treehopper Posted April 25, 2012 Author Share Posted April 25, 2012 It's an eBay Jap tiny tach lookalike so it may well have the same problem. Thanks for pointing out that posibility. Jamie Quote Link to comment Share on other sites More sharing options...
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