Phil Taylor Posted February 27, 2017 Share Posted February 27, 2017 Can anybody help me with my Saito 17 Petrol engine. I have run it in as per instructions using 20:1 fully synthethic 2T oil and it performed great. I flew it in my Seagull DH60 Moth and again it performed great. I have now put it in my H9 Hellcat and it runs great up to about 75% throttle - thereafter it seems to run out of power - it even feels like it is losing power. I have checked it on the ground and all seems fine - the mixture is not to lean and it does not appear to be over heating (using 3:1 ratio air in/out holes and louvres). Does anyone have any ideas? By the way I am running it on Aspen fuel (straight with me mixing in 2T fully syn oil at 20:1).. Quote Link to comment Share on other sites More sharing options...
Gary Manuel Posted February 27, 2017 Share Posted February 27, 2017 Have you checked the valve clearances? Quote Link to comment Share on other sites More sharing options...
flight1 Posted February 27, 2017 Share Posted February 27, 2017 Welll if it is not overheating and you got baffels directing the air around the cylinders then check the fuel lines for any kinks /restrictions preventing full supply of fuel as is needed over 75% throttle. also what prop you are using as to big a prop could cause the same also thats a high oil content for a petrol engine in my opinion but thats what Saito say to use? Quote Link to comment Share on other sites More sharing options...
Phil Taylor Posted February 27, 2017 Author Share Posted February 27, 2017 I have not checked the valve clearences since I ran the engine in - I doubt I have done more than 2 or 3 hours run time after that. I think the book says check every four hours running time so I doubt its the valves - buty I will check! Fuel lines are OK - but I do use a 'T' feed to fill and drain the tank - could this cause issues? I can't see any bubbles in the line so assume (!) its OK. Prop is 15x8 (as recommended) and oil raito is again as recommended. I think I need to check the valves and go back to a 3 line system for the tank! Quote Link to comment Share on other sites More sharing options...
Phil Taylor Posted February 27, 2017 Author Share Posted February 27, 2017 Oh - and try a smaller prop!! Quote Link to comment Share on other sites More sharing options...
Phil Taylor Posted February 27, 2017 Author Share Posted February 27, 2017 Thanks for the quick replies by the way! Quote Link to comment Share on other sites More sharing options...
Engine Doctor Posted February 27, 2017 Share Posted February 27, 2017 Have you vented the Tank ? If air cant get in then fuel cant get out and engine starves. Quote Link to comment Share on other sites More sharing options...
Jon H Posted February 27, 2017 Share Posted February 27, 2017 I agree with the other guys suggesting some baffles for the cowling as overheating is the most likely issue. Remember that the Hellcat is a different beast and may need a different prop to get good performance as its performance profile is very different to the moth. Also which brand of prop are you using and what rpm are you seeing at max power? Quote Link to comment Share on other sites More sharing options...
Phil Taylor Posted February 27, 2017 Author Share Posted February 27, 2017 Posted by Engine Doctor on 27/02/2017 13:29:23: Have you vented the Tank ? If air cant get in then fuel cant get out and engine starves. Hi Engine Doctor, Yes the tank is vented - there is no pressure feed from the exhaust so it just vents to air (below cowl). Quote Link to comment Share on other sites More sharing options...
Phil Taylor Posted February 27, 2017 Author Share Posted February 27, 2017 Posted by Jon Harper - Laser Engines on 27/02/2017 13:45:43: I agree with the other guys suggesting some baffles for the cowling as overheating is the most likely issue. Remember that the Hellcat is a different beast and may need a different prop to get good performance as its performance profile is very different to the moth. Also which brand of prop are you using and what rpm are you seeing at max power? Hi Jon, The prop is a wooden 15x8 job from HK - I have balanced it. I don't have a tacho to check max RPM - maybe I should invest it one! Over heating could be an issue - although it seems to run well in the air at all other throttle settings - just not on full power. It sounds (and feels..??) like it is leaning out but even running over rich on the ground it still happens. Maybe I need to look at air flow around the carb? By the way the recently bought 100 is in the Moth and running beautifully - but then it is a Laser!! Phil Quote Link to comment Share on other sites More sharing options...
Jon H Posted February 27, 2017 Share Posted February 27, 2017 Hi Phil, good to hear our 100 is working well! As for the saito, you are right to be suspicious of airflow around the carb as the carb is regulated and a change in pressure on the cowl could be causing an issue. perhaps a test flight without the cowling may reveal if this is the case. Quote Link to comment Share on other sites More sharing options...
Phil Taylor Posted February 27, 2017 Author Share Posted February 27, 2017 Posted by Jon Harper - Laser Engines on 27/02/2017 16:50:46: Hi Phil, good to hear our 100 is working well! As for the saito, you are right to be suspicious of airflow around the carb as the carb is regulated and a change in pressure on the cowl could be causing an issue. perhaps a test flight without the cowling may reveal if this is the case. Hi Jon, Yes that is probably the most sensible thing to try - I have to ask myself why I haven't done so already! Just need to wait for some reasonable flying weather... Could be a long wait looking at the forecast! Quote Link to comment Share on other sites More sharing options...
flight1 Posted February 27, 2017 Share Posted February 27, 2017 Posted by Phil Taylor on 27/02/2017 16:26:32: Posted by Engine Doctor on 27/02/2017 13:29:23: Have you vented the Tank ? If air cant get in then fuel cant get out and engine starves. Hi Engine Doctor, Yes the tank is vented - there is no pressure feed from the exhaust so it just vents to air (below cowl). If air vent does not point into the air flow you may be getting a venturi effect so you have a negative pressure effect to the tank. also you could have warm air being drawn into the carb from the enclosed cowl situation and the two together will certainly reduce the ability of the engine to run at w.o.t Quote Link to comment Share on other sites More sharing options...
Gordon Whitehead 1 Posted February 27, 2017 Share Posted February 27, 2017 If a petrol engine starts misbehaving, the first thing to check is the plug - certainly before fiddling with the carb and well before faffing with the valves. Clean the plug and check the gap is as recommended.. Regarding tank venting, the carb has a pump so whichever way the vent points is unimportant. My old Saito FG36 petrol started losing top end power, and eventually and in desperation I rotated the ignition pickup to advance the ignition and for some reason that cured it. Maybe an electronic component in the ignition circuit had aged and retarded the timing. It ended up with the ignition advanced as far as it would go. That might be worth a try if all else has failed. Gordon Quote Link to comment Share on other sites More sharing options...
Phil Taylor Posted February 28, 2017 Author Share Posted February 28, 2017 Posted by flight1 on 27/02/2017 19:10:24: Posted by Phil Taylor on 27/02/2017 16:26:32: Posted by Engine Doctor on 27/02/2017 13:29:23: Have you vented the Tank ? If air cant get in then fuel cant get out and engine starves. Hi Engine Doctor, Yes the tank is vented - there is no pressure feed from the exhaust so it just vents to air (below cowl). If air vent does not point into the air flow you may be getting a venturi effect so you have a negative pressure effect to the tank. also you could have warm air being drawn into the carb from the enclosed cowl situation and the two together will certainly reduce the ability of the engine to run at w.o.t Hi Flight 1 - yes the vent is open to the air flow below the cowl. Could be that the carb is being staved of air at to end Quote Link to comment Share on other sites More sharing options...
Phil Taylor Posted February 28, 2017 Author Share Posted February 28, 2017 Posted by Gordon Whitehead 1 on 27/02/2017 19:44:51: If a petrol engine starts misbehaving, the first thing to check is the plug - certainly before fiddling with the carb and well before faffing with the valves. Clean the plug and check the gap is as recommended.. Regarding tank venting, the carb has a pump so whichever way the vent points is unimportant. My old Saito FG36 petrol started losing top end power, and eventually and in desperation I rotated the ignition pickup to advance the ignition and for some reason that cured it. Maybe an electronic component in the ignition circuit had aged and retarded the timing. It ended up with the ignition advanced as far as it would go. That might be worth a try if all else has failed. Gordon Thanks Gordon - I hadn't thought about the timing point. The manual does say that advancing the timing improves top end and retarding helps starting. I think overall I need to check the plug, valves, timing and air cooling (not necessarily in that order) - maybe one thing at a time...! Quote Link to comment Share on other sites More sharing options...
Brian Cooper Posted February 28, 2017 Share Posted February 28, 2017 I am with the "air into the carb" solution. Engine cowls do seem to restrict the air which can reach a rear mounted carb. I had (have) two Spitfires which suffered the same symptoms as described in the original post. Both have petrol engines with rear carbs and both were cured by making a scoop which channels fresh, cold air to blow directly into the carb. . The faster the prop went - or the faster the aeroplane flew - the more air was blasted into the carb. One Spitfire is fitted with a DLE35RA. . This has a rear exhaust and when the engine is mounted inverted, the heat from the exhaust rises a very short distance to the carburettor, and this was affecting the performance. . I installed a heat shield between the silencer and the carb, and made better exiting for the heat, plus a channel to get cold air into the carb. The improvement was stunning. Problems solved. The engines are happier across the entire rev range. . . and sound very crisp at full bore. B.C. Quote Link to comment Share on other sites More sharing options...
Phil Taylor Posted February 28, 2017 Author Share Posted February 28, 2017 Posted by Brian Cooper on 28/02/2017 08:07:06: I am with the "air into the carb" solution. Engine cowls do seem to restrict the air which can reach a rear mounted carb. I had (have) two Spitfires which suffered the same symptoms as described in the original post. Both have petrol engines with rear carbs and both were cured by making a scoop which channels fresh, cold air to blow directly into the carb. . The faster the prop went - or the faster the aeroplane flew - the more air was blasted into the carb. One Spitfire is fitted with a DLE35RA. . This has a rear exhaust and when the engine is mounted inverted, the heat from the exhaust rises a very short distance to the carburettor, and this was affecting the performance. . I installed a heat shield between the silencer and the carb, and made better exiting for the heat, plus a channel to get cold air into the carb. The improvement was stunning. Problems solved. The engines are happier across the entire rev range. . . and sound very crisp at full bore. B.C. Hi Brian - I think you have a good point. I have lots to go at. Thanks for your input Quote Link to comment Share on other sites More sharing options...
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