Alan Blackett

Try B&Q Homebase etc,i buy polythene sheet sold as dust covers for when you are decorating.Comes folded in a small packet and you just unfold and cut off what you require.

Hi Steve i think as you more or less state i need to do my experimenting a little more scientifically i shall see what i can come up with later this week.On my Zen 260pum power boats we remove the intake stack which helps to get the rpms up a bit,but i do need to try this on the TT91.Regards Alan

Well i have today run the TT91fs on glowfuel with the spark unit and with a glow plug.Interestingly i found that combustion seemed to be more complete with a glowplug than with the spark unit,alot more smoke(unburned fuel)was produced with the spark unit.Starting was also easier with a glowplug than with the spark unit.This is hand starting only and NOT changing any needle settings on the carb while swapping ignition systems.Both ways the engine felt that it was running more strongly with glow fuel as opposed to running petroil previously.There was also approx 200rpm increase in top speed with the spark unit as opposed to the glow plug.Thinks maybe the extra rpm and the carb spit while running on the petroil could be caused by the variable timing of the cdi unit?While running on spark or glow plug the engine i think ran better than on the petroil mix.The engine also feels alot nicer to turn over and compression is up to what it was before.From the limited feedback on the just engines site it would appear that all the modified engines have been previously run in or run on glowfuel.Should i have run this new engine in on conventional glow before trying to convert?Experiments to continue but i shall have to decide soon as this engine is destined for the model on the building board now.

Reading peoples responses makes me think that maybe the running on petroil requires some more experimentation.Ken the Saito engine also comes with a walbro type carb does it not,this would help with the spit experienced at idle being a more sophisticated carb.I shall read the Saito review with intererest.Perhaps RCME could do a review of the CDI unit from Just engines .AlanEdited By Alan Blackett on 26/08/2009 01:23:22

Sorry guys am trying to add the utube link to this guy running his os 120 on spark and glow fuel but these computory things dont seem to work right with me on the end.perhaps someone else could add the link to eulboyington .If not i shall have my son do it later

Hi Ken,what you state is a very valid point,at the start of this i did wish to run on petroil mix for the reduced fuel costs and the ease of being able to run the same fuel as my Zen 260's.I just felt that the petroil was causing alot of wear to the conrod bushes very quickly but wished to retain the spark unit for its other good running characteristics.Maybe all that is required is a different oil ratio,maybe my choice of engine to convert was the wrong one.This is just what i have found out myself to date,like i said there is a big lack of information about these conversions so we have to just experiment at our own expense?It is nice to be able to just swing the prop and have it start and tick over so slowly without the need for hanging a glowlead on or carting the model back to the flight box.

I have fitted one of these cdi units to a brand new TT91 fourstroke and my findings so far are as follows; The unit is a superb piece of kit but i did have to dismantle the engine to drill the front bearing housing to tap to hold the hall sensor,there is a fair amount of carb spit at idle which i feel could be a fire hazard if a backfire were to occure in a wooden cowl.The idle speed on spark is incredible and reliable as is the transition to full throttle.Using petrol and a 25 to 1 oil ratio i feel is far to low a oil content on a bushed conrod and i stopped running when i felt there was a possibility of damage to this when the engine was hot.What am i going to do now?Well i am going to run with the spark unit using glow fuel.This has been done a few times over the years when converting glow engines and one guy on utube is doing this with all his 4stroke motors calls himself eulboyington,there is a short vid of him running a 120 surpass sp.I shall be buying another spark unit from just engines but running on glowfuel.(all those old engines from the past,pre the invention of the glow plug,ran spark,did they run petrol or methanol fuels?Did they have needle bearings or were they just plain bushed?There is a lack of feedback on this spark convertion.)

Would make anice change from plan building