gordon_dunn Posted April 15, 2009 Share Posted April 15, 2009 Are there any commecially available systems out there- or are these generally home made systems? I'm getting some bubbles in my fuel line during operation and not sure where theyre coming from- perhaps it may be down to cavitation- ie actually petrol vapour bubbles as opposed to air bubbles. Would a header tank be any benefit in reducing this? GD Quote Link to comment Share on other sites More sharing options...
pete_b Posted April 15, 2009 Share Posted April 15, 2009 Hi Gordon You would be better off trying to find and cure the problem rather than adding more pipe and other bits that can give you more problems than you have now. double check all joints including any on/in the tank. Pete b Quote Link to comment Share on other sites More sharing options...
Phil_P Posted April 15, 2009 Share Posted April 15, 2009 Gordon, up till recently I have been having the devil's own job with air bubbles. It would seem that most of them were arising from joints, specifically where I had used a zip tie to secure the pipe. Zip ties exert a very uneven pressure round the pipe, and can if anything actually cause an air leak rather than prevent one. I have found the situation to be massively improved since using proper fuel line clamps that have a full circumference of metal, on every joint. Also, if you use any quick connects in your fuel line, these I have found also can allow in an astonishing amount of air. Replacement 'O' rings sometimes help, as they are prone to getting nicked, and a smear of thick grease can provide a short term (ie flight by flight) solution. The use of a header tank will only help for as long as it contains fuel. Once sufficient air has got into the system to displace the volume of the header, you are back at square one. Just my thoughts, hope they help a little. Phil Quote Link to comment Share on other sites More sharing options...
gordon_dunn Posted April 15, 2009 Author Share Posted April 15, 2009 Pete.. I agree...... I have tried everything- well checked everything and cant seem to find a definite cause. Basically the machine (H&E R120) idles and runs perfectly, with the odd bubble or two... but it just dosent like full throttle. I suspect that the priming bulb may be the offending article- i noticed that when i was priming it, a small amount of fuel came out of the seal at the top of the bulb, so if fuel can get out then i suspect air can get in. I thought it would be a good idea to temporarily bypass the fuel system and priming bulb to confirm the case (not flying of course). Another possible cause may be the membranes in the Walbro carb- i've checked them and they seem OK, but theve been in a year now and done 80 hours. The air in the fuel system is bound to be effecting the needle settings- so i'm not going to mess with them until i get the bubble sorted. GD Quote Link to comment Share on other sites More sharing options...
pete_b Posted April 15, 2009 Share Posted April 15, 2009 Change the primer bulb ,It sounds like thats your problem. Pete b Quote Link to comment Share on other sites More sharing options...
gordon_dunn Posted April 15, 2009 Author Share Posted April 15, 2009 OK I think I'll try this first... but also maybe take the opportunity to change the mebranes too. I noticed that a local automotive shop sell primer bulbs- they were marked 'diesel' though-- are these compatible with petrol? Also for the record- what would be the recommended system for a header tank- i've got 3 sketches - see below- the first one is a 'competition' bottle setup... The second one has a clunk inside the header tank too- i used to have a header tank like this one on my model helicopter. The thrid sketch has the carb connection to the bottom of the header tank- would the engine be more prone to flooding this way? Note- in the second and third sketches- the header tank is closed. On the first there is a vent on top. Quote Link to comment Share on other sites More sharing options...
pete_b Posted April 15, 2009 Share Posted April 15, 2009 Try the third one it should not flood as the membrain in the carb will take care of that. If you have the top of the bottle level with the carb it will not gravity feed any way. Pete b Quote Link to comment Share on other sites More sharing options...
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