Rusty C Posted December 10, 2012 Share Posted December 10, 2012 I have been trying to instal an SC .70 fs to my seagull AT-6 and it has been nothing short of a nightmare!! The engine it self was running sweet on the test bed good idle and throttling after some head scratching. Got it bolted to the airframe and got it started warmed up and re-checked the high needle, seems ok, So I then shut it down to idle which was sounding good for a whole 5 seconds So started to tweak the low to try find the sweet spot again but no matter what I did no joy. After some chosen words I noticed bubbles in the fuel line and thought "well that wont be helping matters" As a result of all the needle turning in a some what confused state I have no idea where the low needle is!! help there would be good, I have been trying this pin and fuel line blowing thing but It depends on how hard I am blowing determines the needle position, which is a fairly dramatic difference. The bubbles in the fuel I suspect is a vibrating tank as it is a tight fitting tank thinking about it. Although any more thoughts on this are very welcome? Very close to throwing in the towel and heading to the safety of the 2 stroke or worse still my motors ! Thanks for any help rusty Quote Link to comment Share on other sites More sharing options...
CARPERFECT Posted December 10, 2012 Share Posted December 10, 2012 While holding the carburetor fully open turn the low end screw out until it stops. now turn screw 4 full turns back in while keeping the barrel open. This is the factory setting. You should not have to turn it more than half a turn either way. if you do it`s not the low end where the problem is. Quote Link to comment Share on other sites More sharing options...
Paul Marsh Posted December 10, 2012 Share Posted December 10, 2012 I'm looking for a 70 4S. Would you sell it? Cheap??? Quote Link to comment Share on other sites More sharing options...
Kev Bamber Posted December 10, 2012 Share Posted December 10, 2012 I recently had bubbles in a fuel line from a leaking remote filler valve. I'd be inclined to look for air leaks in your fuel line, all my i/c planes have fairly rigid mounting of their tanks with no bubbling problems. Quote Link to comment Share on other sites More sharing options...
Dean B Posted December 10, 2012 Share Posted December 10, 2012 Hi Rusty, you do not state which way up you have your SC70. I have had terrible trouble with my SC70 as it was inverted on the model. Glowplug pointing down. I eventually got the model flying but after a great deal of messing around with settings, plugs and fuel. Dean Quote Link to comment Share on other sites More sharing options...
Rusty C Posted December 10, 2012 Author Share Posted December 10, 2012 Thanks for the factory setting Carperfect, I thinking of changing the plug it has an OS F in it just now should I get the same again just in case my one has gone bad or maybe a different plug? Cheers kev I am in the middle of removing the tank AGAIN ! to check the plumbing out, I was also going to trim round the tank mount in order to get some foam around it, Is this a good idea ? Rusty Quote Link to comment Share on other sites More sharing options...
Rusty C Posted December 10, 2012 Author Share Posted December 10, 2012 Dean It is not totally inverted probably around 120 degrees, Dont like the sound of this much is this an SC thing or a four stroke thing ? Quote Link to comment Share on other sites More sharing options...
CARPERFECT Posted December 10, 2012 Share Posted December 10, 2012 I have the same Engine but branded Magnum. I have mine at 90 degrees and it runs perfect, i use a os f type plug Quote Link to comment Share on other sites More sharing options...
Rusty C Posted December 10, 2012 Author Share Posted December 10, 2012 Should an inverted engine run different ? I cant see why it should but my ears are open. rusty Quote Link to comment Share on other sites More sharing options...
Hogster Posted December 10, 2012 Share Posted December 10, 2012 I have an sc70fs in a Seagull AT6. Its fully inverted and I had a lot of trouble getting a reliable idle. I fiddled and fettled but it turned out the main problem was fuel syphoning. I have since put a large loop in the fuel line which has stopped the syphoning. I still need to revisit the low end settings but its a lot better than it was. Quote Link to comment Share on other sites More sharing options...
Kev Bamber Posted December 10, 2012 Share Posted December 10, 2012 I'd be surprised if foam mounting your tank cures the problem you describe, but worth a try if straight forward. Have you ensured you have brimmed the tank by actually looking at it after filling. I ask for two reasons: firstly it will be even less likely to create bubbles from vibration if full, and secondly your clunk should be able to pick up fuel fine no-matter where it's sitting. Oh which reminds me, have you checked your clunk is sitting correctly and not got jammed high against the back of the tank cos too long. As you can see, my thoughts are still on the lines of leaks or poor pick-up based upon the air bubbles. Your installation & engine/angle is very similar to my ASP80 in a Weston Hype, my tank is solid mounted (jammed in!), I use an OS-F plug and this works well so the install as you describe is fundamentally sound. Quote Link to comment Share on other sites More sharing options...
Rusty C Posted December 10, 2012 Author Share Posted December 10, 2012 Hogster That would explain the firewall being soaked after every shot at it. How was that happening anyway? My tank centre is slightly below the carb so it would need to run up hill. Maybe I should try the loop too worth a shot iI guess rusty Quote Link to comment Share on other sites More sharing options...
Rusty C Posted December 10, 2012 Author Share Posted December 10, 2012 Kev I have just had the tank out and check the clunk and it is good, the only thing that was a bit wrong was the the vent pipe had straighten out some how could this be the cause? I think your right about the instal I cant see why it wouldnt work, I just got lost with the low needle when i didnt notice the bubbles. As for checking the tank I dont as it means taking the wing off but I just pump till its back through the vent pipe. rusty Quote Link to comment Share on other sites More sharing options...
Kev Bamber Posted December 10, 2012 Share Posted December 10, 2012 Real dumb long shot; you haven't by chance installed your tank upside down so the vents are at the bottom? I did that once after taking it out, and couldn't see the problem until took the wing off and watched when filling. That's partly why I asked have you actually looked. Kev Quote Link to comment Share on other sites More sharing options...
Rusty C Posted December 10, 2012 Author Share Posted December 10, 2012 Kev I did cross my mind that I might have inserted the bung the wrong way up as the tank will only fit one way up, It may be a touch silly but as you know anything is possible, no offence meant in that. The tanks bung pipes are plastic I might change them to the metal type, Is it possible the exhaust pressure is hot enough to straighten the pipe in the tank. And if so would this be bubbling up the fuel? thanks Guys rusty Quote Link to comment Share on other sites More sharing options...
Ian Jones Posted December 10, 2012 Share Posted December 10, 2012 Syphoning, unhappy memories during the setup of mt inverted SC180. My problem was caused by having the fuel tank too high and nowhere else to put it. The fuel line loop worked to an extent but for me once I'd primed the engine then the syphoning was set up flow too A perry pump would have helped me when the engine was running but not when stopped or trying to start it The engine sounded different because of the excessive fuel giving a rich more thumpy sound. That also caused more vibration which when it was really bad did tend to foam the fuel. The fix was a Cline Regulator. They are expensive, hard to get in the UK and very good. I got one of Ebay for £11.00, expect to pay around £60.00 for a new one.It involves running a pressurised tank system so that the diaphragm in the regulator can give a proportional fuel flow only when the engine runs. I would try everything else first just in case it solves the problem but as a last resort the Cline regulator will fix it. Do plenty of research first though. Quote Link to comment Share on other sites More sharing options...
Kev Bamber Posted December 10, 2012 Share Posted December 10, 2012 Again I'd be surprised if the exhaust gases are affecting the plastic pipe and bubbling cos you don't have a significant exhaust gas flow as such, just a small amount of gas enters to pressurise the tank. Can only try and rule it out. Back to the basic problem, you can run full throttle, holds okay? But can't find the low end/transition?. These bubbles, did you see them as it was running or after the engine cut? Quote Link to comment Share on other sites More sharing options...
Dean B Posted December 10, 2012 Share Posted December 10, 2012 Rusty. I ended up using a Taylor 4 stroke plug. model tech irving fuel at 10% nitro. the one with only 2% castor in it. The rest is synthetic oil I too had syphoning problems, I moved the fuel tank as low as it would go. Slow running is still lumpy but it does not stall. i was told about an on board glow igniter that supplied power to the plug at a preset level on the throttle but I never got that far. Dean Quote Link to comment Share on other sites More sharing options...
Ian Jones Posted December 10, 2012 Share Posted December 10, 2012 Oops sorry, meant to include a few links: Cline regulator ironbay regulator (Just cancel any requests to log in for ftp) Quote Link to comment Share on other sites More sharing options...
Rusty C Posted December 10, 2012 Author Share Posted December 10, 2012 Kev it runs well at full throttle with the odd lean out as bubbles appear, And yes the idle and transition is horrible. To star with it was dying as I removed the glow suggesting a rich low end right? so i leaned out an 8th no response 8th more not much to report. and in the confusion I completely lost where is was. One other thing Kev how far open should the throttle be open for idle, This was about 1/4 open before it would start be the end of my long road to nowhere rusty Quote Link to comment Share on other sites More sharing options...
Rusty C Posted December 10, 2012 Author Share Posted December 10, 2012 Dean I am using model tech contest 10 and a OS F which everyone at the club suggests. I dont really want to go down the on board route. Thanks for all your input, as you have first hand in head ache lol rusty Quote Link to comment Share on other sites More sharing options...
Rusty C Posted December 10, 2012 Author Share Posted December 10, 2012 Ian Thats a clever bit of kit that ay! Its a touch pricey for a small seagull model though, So hopefully will solve it some other way. If I dont manage it by Friday I think I will need to get Mick Henderson on the case, And see what else he can suggest. Rusty Quote Link to comment Share on other sites More sharing options...
Dean B Posted December 10, 2012 Share Posted December 10, 2012 Rusty Thats the stuff. couldn't remember the name off the top of my head. Looks like its the syphoning that is causing your grief. I have a harmon rocket with an SC70 in it but its mounted at 90 degrees. it runs great and has never been a problem. Seems as soon as you start to invert the engine the carburator suddenly becomes higher than the tank. Dean Quote Link to comment Share on other sites More sharing options...
BOB GADD Posted December 11, 2012 Share Posted December 11, 2012 Hi Rusty. Did you do a leak check on the tank before you fitted it? Put the three pipes on the tank, blank two of them off, blow through the other one with the tank in a bowl of water and see if there are any bubbles coming from the tank, just the same as you would do for checking for a puncture in a bicycle tyre tube. BOB. Quote Link to comment Share on other sites More sharing options...
Dean B Posted December 11, 2012 Share Posted December 11, 2012 oops that should read "lower than the tank" not higher Quote Link to comment Share on other sites More sharing options...
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