Are you using gasoline mixed with oil? (I'm assuming that you are, as the engine won't last long without it) I noticed that the web site you referenced says "the Super Tiger _90 and larger_ glow engines can be operated with gasoline and still use their standard carburetor". Since they qualify their answer, I'm wondering if engine size has any significance. You said, in an earlier post, that you were *not* using a muffler. If so, then how are you pressure feeding the fuel to the carburetor? Glow fuel seems to be slightly more viscous than gasoline/oil mixture, perhaps the engine is worn to the point that piston blow-by is causing the back-firing. Do you have access to an electric starter? These do wonders for starting engines that don't want to run. I have a .40 model that can't be started any other way (cheap, ringless engine that has had many gallons of fuel run through it). The electric starter spins the engine much faster than you could possibly turn it by hand, plus it overcomes kick-back. Not to mention the safety issue. This may help you to establish your base timing as you can tell when it starts firing correctly by ear. You would also be able to seat the needle valve initially and then slowly open it. Since the gasoline is supposed to be used more efficiently, then setting the needle to where it ran good on glow fuel would be too rich of a setting for a gasoline mixture. Michael Brown Instant Net Solutions www.KillerPCs.net "In the land of the blind, he who has one eye is king" ----- Original Message ----- From: "Alan Gorham" To: Sent: Tuesday, May 21, 2002 7:41 AM Subject: [EE]: Update 2 - Spark ignition for model engines HI to everyone who has contributed to this. There seems to be some differences of opinion as to my next step here. Eion, Alan and Michael are advocating moving my sensor to give a firing point closer to but still after TDC. Peter is advocating keeping the firing point at 5 degrees after TDC and maybe thinning the fuel. Let me clarify exactly what I have been trying to do and see if we can get a consensus: I want to end up with a unit that retro-fits to a model glowplug engine for spark ignition. I have seen commercial units that do this and they seem to be fit and forget. Look at: http://www.nelsonhobby.com/ignition/samples/samples.htm for an example that uses a single Hall sensor. I will need a unit that does automatic advance and retard eventually and I plan on using the trusty PIC for this. However, I want to prove my ignition system to myself first. I have been working on the assumption that a fixed speed engine where the ignition is retarded for starting and the advanced for running would be the way to prove the ignition system. This assumption stems from the fact that this is the way model spark ignition engines started out. The engine I am using is a 1960's Merco (English) 0.29 cu. in. two stroke. This is an R/C engine (i.e. with throttle) but I have fixed the throttle at idle speed for testing. I think this may be a problem area - do you think I should actually try to start with the throttle open and the ignition retarded? I had intended trying to start with the throttle open at first, but old habits die hard and I always start my glow engines at idle. Presumably a retarded ignition point for full throttle is not necessarily retarded the same amount at idle speed? Peter - the above might explain why I did not see your 'solid column of flame' when I saw a backfire? I'll be trying the pipette method in future, but tell me - this is only to prevent a big backfire, right? I won't be totally sure that the engine will continue to run at an ignition setting that does not cause a bang? Anyway, thanks for all the input, people! Alan Embedded Systems Engineer Microtima Ltd Ouseburn Mews 3-7 Stepney Bank Newcastle upon Tyne NE1 2PW Tel: 0191 2304411 Fax: 0191 2304422 -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu