ORIGINAL: oldtyme
Hi all,
I was just in the Scale Aircraft forum and someone there mentioned that the newer SuperTigre G75 engines were having problems with mid-range fuel problems in that they ran rich in the mid-range band which could make the engine un-reliable in the event you have to throttle up to do a go-around or other maneuvers after you have throttled back. I have purchased 4 new G75's for various projects because the kit manufacturer suggested that these would be a good fit for the
planes using in-cowl headers and mufflers. Of course in warbirds such as the TF P47 and AT6 and the H9 P47, I wanted realism so I went with a substantial investment here. I'm hoping that this is
not a chronic problem and can be dealt with.
I am not new to the hobby, I have been flying since 1980 but have never owned anything except K&B and OS............and I have a lot of engines.
All input is welcomed and appreciated. I'm commited to these engines now so just wanted to know if there is any basis for this statement and if so how have you dealt with it........I'm not going to sell them so I need to know...........can't afford to buy anything else either.......getting ready to retire and I thought I was set.
Thanks in advance,
Andy
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Was the person that posted about the rich midrange problem running a pump? That could cause the engines to run rich in the midrange if the pump pressure was turned up too high and the high and low speed mixture needles were adjusted to compensate for the condition.
Proper glow plug selection can also influence how the engine runs. The high and low speed needles do influence the mixture strength of the midrange in most two needle carbs. If the glow plug is too hot, the operator will adjust the high speed mixture too rich in order to retard the timing and cool down the engine. This rich high speed mixture will influence the midrange and will show up as a rich condition.
Too much nitro in the fuel will also cause the operator to try to retard the timing by running a rich high speed mixture, again, richening the midrange.
There are a lot of factors, such as prop size, engine cooling, fuel tank height, etc. that will influence the midrange mixture. Don't be discouraged by just one or two folks having some difficulty.
Lately, the trend has been for everyone to run too much nitro. This is probably a spill over from 3D flyers running high nitro in their four-strokes and not knowing any better than trying to run the same fuel in high compression two-strokes.
Those modelers that cut their teeth running OS engines have been spoiled. The ST carbs are a little more ticklish to adjust. Small changes in needle settings can make a big difference. Change any other factor, such as prop size or type of glow plug, while trying to find the right needle settings and you have to start all over again.
Another thing is that ST ringed engines take a while to break-in properly. Before that break-in point is reached sufficiently, they can be a bare to adjust for civil behavior. Do yourself a favor, if you don't have one already, and build a portable engine test stand on which to run a gallon or more of fuel through each engine before even attempting to set the low speed needle for perfect performance. You will be far ahead of the game if you do. You will also have four of the sweetest running two-strokes ever made. Good luck.