Jezmo

I have been experimenting with running it on E85 with a glow plug so I figured why not try spark ignition with gasoline. I already had the CH ignition module and spark coil and making the sensor adaptor was easy. I put a small 1/8" magnet in the prop drive adapter and set the timing at 28 deg. I left the carb set just like it had last run on E85 and when I hit it with the starter she fired right up. It was just a little too rich on both top end and idle so after setting the needles I took her up to full throttle and held it for about 1 minute. Looking at the temp on the thermal probe I was surprised at how cool it was running. It was at 265 which is about 25 or 30 deg. hotter than on 10% glow fuel. I was also surprised at how long it runs on 6 oz of gas/oil. I am running the gas/oil ratio at 20:1 and I am planning on checking the rod and crank for distress later tonight. It has two tanks through it now and that should be enough to give some idea on how the crank and rod will hold up. The plug was tan on the insulator so the mixture and plug heat range are close. Not that I have much choice on plug heat ranges with the Rimfire but at least it is close. If the 40 holds up well I am going to put all my parts on a ST51 and run it on my SuperSportster in place of the 40. Cheap fuel at 3 dollars a gallon and it runs twice as long as 10% glow fuel. The 51 will make up for the power loss from going to gasoline and it should be a very good combo.

buck1856

My Feedback: (49)

Good news.I have an ASP 91 that had a little accident and now the base of carb is broke so im thinking about making an adapter and putting a walbro on it and run it with gas.I too am curious about the crank pin.I dont know why the crankpin wouldnt hold up with gas instead of glow unless its the heat factor.I could just try it.A new carb is 40 dollars at least and its only worth about that in running shape on ebay.I already have a carb and my lathe.

Jezmo

I just tore mine down and looked at the crank pin and rod bushings. All look good. Without bearings it takes quite a bit of oil to keep the bushings properly lubed. I had read that 20:1 was enough for bushings but wasn't sure. Looks like it's off to the LHS to get a new ST51 to run on Gas/Oil in the Sportster. The glow carb is more sensitive than on glow fuel but it is usable. ST's have very fine threads on the needle anyway.

captinjohn

Did the old time spark engines that ran on gas have needle bearings on rod? You know like the old Olsen& Rice .60 engine. It seems like they did use a real grade of oil! Texico 60 weight??? Capt,n

mapnet

The old time ignition engines used a three to one mixture of gas to #70 weight motor oil.

Maurice

pe reivers

Big Supertigres run methanol fuel with 10% oil, and so do many competition pilots. Since gasoline lubricates better than methanol, I would use 10% with gas and plain bushings. The reason for more oil is, that a gas engine uses less fuel as compared to a methanol burner, and a little extra oil will not hurt, if the carb is tuned right.

Jezmo

Thanks for advice pe. I am just experimenting with this and any advice can help. The little ST was turning a 10x6 14,900 and now on gas it is turning 14,000. I have not tried to optimize the timing, it is set at 28 deg. which should be close but a slight change could get me just a wee bit more power. I know I am going to lose some power over methanol/nitro, maybe 15% or so. It runs really well and idles great. The CH has syncro spark which should help the idle some. I am going to switch the ignition over to a G51, break it in and see how it fly's. More to come.

aero nut

I have a Magnum 180 running on Gas/Glow and the oil content for my fuel is between 8 and 10 % it runs great, if you want to gain power on your gasoline conversion try to mix a 1/3 15% nitro glow fuel and 2/3 gasoline this will give you a 6% oil content fuel then make up the 4% oil needed to bring oil content to 10%.

pe reivers

With 28 degree advance in a small engine you may be too early still. Go back to about 20 degrees, and see what happens. If need arises, advance in 4 degrees steps. Fine tune in 1 degree steps.

Jezmo

Thanks pe, I am going to switch over to a brand new ST51 this evening and I will move the timing back to 20 when I switch. This is turning out to be a fun project since everything seems to be working so well. Again, all input is welcome as I certainly don't have infinite knowledge. A day that I don't learn something new is a day out of my life that I have wasted. Thanks again.

P.S. I orderd a couple of extra RimFire plugs from Bill at CH just in case I foul or break one. Those are some very nice and helpful folks at CH.

Jezmo

I decided to run the ST40 one last time before I switched the ignition to the 51. I wanted to get some numbers so I could compare them more accurately. Also, the carb seemed to be acting a little odd the last run. I took it apart and cleaned it out and when I reassembled it and put it back on the engine was back to being very consistent. I assume the new tank I bought to run it on gasoline had a bit of trash in it. I always blow them out with the air compressor but that's not perfect. Could have been a little piece of flash broke off from the vibration. At any rate, the CHT today was steady at 245. The rpm's were 14,200 full throttle and at 12,100 which was about 3/4 throttle, it ran 15 mins on 6 oz of 87 octane mixed 16:1 with Zenoah full synth oil and still had almost exactly 1/4 tank left. All my testing today was with an APC 9X7 sport prop. The timing is still at 28 deg.

I broke the ST51 in on glow fuel today as well. I've owned several 51's and none transitioned as good as this one. It also idled better and lower than any of my others from the first minute it fired. I wanted to get numbers from it on glow fuel so I can see how the spark and gasoline affect it. 11X6 prop 15% nitro Omega fuel. The CHT was steady at 210. The rpm's at peak were 14,100. Now I am off to do the switch.

pe reivers

With all fuels, I normally use tree filters so fuel flow passages stay clean:
one in my fuel fill bottle
one in the fuel fill line of the plane
one in the fuel line to the carb

This prevents any debris from upsetting my mixtures, be it glow ar gas engines.

On the combat starting grid, I seem to be the only one that starts his engine, rev's up, shuts down and then waits for the others to finish their needle adjusting, and waits, and waits.
Before I used triple filters, I often noticed a small lump of fibers inside the spray bar, or a fiber mat in the internai walbro fuel filter. These now are things of the past.

Jezmo

Yeah pe, I have filters on all my planes and my pump, but the gasoline test setup got shortchanged because I was in too big a hurry to go get a filter for it. I should have pulled one off a plane but we all know how shoulda's wind up. I cut a corner and got caught. I am in the process of switching everything over to the 51 and hope to run it tomorrow on gasoline. You can bet I went and bought a filter for the test rig today. Not going to have that problem again.

buck1856

My Feedback: (49)

well,im going to make my adaptor and put a walbro on my ASP 91 and see what happens with gas.Ill start at 16-1 using echo brand oil first then go to 20-1.

pe reivers

keep posting the results please. This kind of fuel change is interesting in view of longevity. If the engine holds out well it should provide much better all weather operating conditions, to which glow engines are so sensitive.

Jezmo

Will do. The weather here in Houston TX is horrible today (steady rain) so I am stuck indoors. It's supposed to be raining and cold again tomorrow as well so testing is going to be just a bit slower. I am anxious to see the results on the 51 so it won't take much of a break in the weather for me to get some testing done.

Jezmo

I got a chance to run the ST51 this evening after work. I started off with the timing at 20 deg total advance. It idled very good but would only turn 11600 with the same prop it had turned 14100 on glow fuel. Not good. I shut it down and moved the timing to 24 and fired it back up. The rpm's picked up to 12600. I shut it down and moved the timing to 28 and fired it back up. It was now turning 13,300 rpm's. The CHT was running steady at 305F. (Quite a bit hotter than the ST 40) The temp was measured with a fluke meter (I can't remember the exact model but I will look tomorrow) and two thermocouple probes one on the head at the spark plug and the other on the back plate. The back plate at WOT was running 109F. It still idled good but not as smooth as it did with the timing at 20 deg. I then moved the timing to 32 and gained nothing on the top but lost nothing either. The idle was worse and unsteady so I moved it back to 28. That seems to be about as good as I am going get until I have time to move it in smaller increments. I ran two tanks through it (6 oz) and timed the fuel burn on the last. It runs 10 mins on exactly 3 oz at just about 3/4 throttle. It was getting too dark to get any more rpm measurements so I closed up shop for the night. I think it's ready to install in the plane and fly. My plan is to fly it for about 1 1/2 hrs. of run time and then check rod bushings etc. It's looking pretty usable to me. I saw no sign of distress tonight and that was about 35 mins of run time. I will post back when it's flying. [8D][8D]

Jezmo

First flight for the S.T. 51 Gasoline Conversion was this morning. The flight went flawless and I was very impressed with the power. I took the ST 40 off that I have been flying on it for years and I thought it was fast with that motor. I am swinging an 11" prop on it now so takeoffs are effortless and it climbs like a rocket. It sounded like it was turning more rpm's on the last flight so I tached it before calling it a day. It was up, but only 100 to 13,400. I can't complain as this engine only has about an hour and a half on it now and is probably still breaking in. I know I said in my last post I was going to tear it down for inspection at 1 1/2 hrs but it is running so good I think I will wait. I can't feel any slack in the rod when I move the crank back and forth so tear down and inspection will come later. I pulled one stupid move this morning. I bought a new fuel filter for it and forgot it at home so I flew without it. On my second flight it started sagging at full throttle and wouldn't go above idle by the time I got it on the ground. I cleaned the carb and all was well again so I flew without incident the rest of the morning. It is absolutely amazing how little gas it burns. On the test stand it was burning 3 oz in 10 mins at 3/4 throttle. I flew for over 30 mins this morning on the last tank. When I defueled, I got almost 5 1/2 oz. back out of a 10 oz. tank. Some of that time was doing touch and go's but still that is great on fuel economy. The temps were around 65 when I started flying and warmed up into the mid 70's by noon. I never touched the idle needle and after cleaning the carb the high would stay set OK for about 10 or 12 mins and then I would land and richen it up by about 1 click. It was running good at lower throttle settings but would lean out too much at full throttle. Ten minutes before having to readjust is OK for me. I know glow is better but I spent about 30 cents flying this morning as compared to 1/3 gallon of $16.00 a gallon 15% glow fuel in my other ship. I am running the oil at 16:1 until it gets broken in a little more then I plan to drop it down to 20:1. It is spitting little black specks on my plane now although it is one heck of a lot less mess than when on glow. More to follow.

Edited to add: The ST 51 Gas is in my SuperSportster 40 for testing. Also, I switched to mixing Synthetic with Pennzoil air cooled two cycle oil 50/50. The Pennz is what I am running in my Giant SpaceWalker with the G26 Zenoah and that way I can just add the appropriate amount of Synthetic to that mix (32:1) instead of mixing up a whole new batch just for the ST51.

Jezmo

I flew three more flights yesterday and the SuperTigre 51 is still getting stronger. I do have the fuel filter on it now and had no trouble with mixture at all. No more JUNK in the carb. It's also getting better about staying more consistent through a tank. Probably because it is getting more broken in. Starting was easy yesterday as well, I flipped it 3 times while choking it after fuel was in the line at the carb. I turned on the ign. switch and it started on the second flip. I start it bare handed, flipping it in the direction of normal rotation, and it hasn't smacked me yet. When it first fires it doesn't have that hard pop like it did as a glow so I don't think it will get my fingers. It starts much like my EI G26. I ran it full throttle for about 6 or 7 mins to see how it would react to the abuse. It still seems to be in perfect shape so no teardown yet. I am thinking I will just run it until I get a feeling something isn't right. I pulled the plug yesterday after flying and it looks good with a dark tan center porcelain. The piston is still like new aluminum on top, no discoloration at all. The Sportster is many years old so I am thinking of giving the SuperTigre a Christmas present and put it on a brand new Super Sportster ARF. [8D][8D]

Jezmo

The weather in Houston/Spring was absolutely beautiful today. I flew the Sportster 4 times each lasting about 11 or 12 minutes. It ran perfect and the only adjustment was one click in on the main needle as the temp warmed up. It was 44F when I left the house and in the 70's by 1:00. The last run was around noon and I leaned it slightly for that flight. That was the only time I touched it. I did learn it is a little cold natured when the temps are that cool. It took 8 flips with my finger on the carb to choke before it would even burp. Two more with the ignition on and choking and it fired. It died almost immediately and rechoking it got it going again. This time every couple of seconds it would start slowing down like it was wanting to die so I would place my finger over the exhaust for just a second and it would pick back up. Two or three times of that and it stayed running and I slowly increased the throttle to about mid and let it warm for about 10 secs. After that it throttled nicely and started easily and ran great the rest of the day. If it sat less than 10 mins between runs I didn't have to choke it to restart. It is running very strong and not making any unusual noises so I think the teardown and inspection will come later. It's hard to justify when nothing appears out of order. I ran it wide open almost the entire flight each time and running this way it uses more fuel than the earlier flights but still very little compared to 15% glow. All total today I burned 14 oz. The plug still looks great and is apparently in good shape since I have easy starting and no misfiring at high rpm's. With the recent increase in glow fuel prices this is not going to take long to pay for the cost of the ignition system. Gas and oil have cost less than a dollar so far (I have burned less than a quarter gallon at 2.75 per) and on 15% glow I would have burned close to a gallon by now costing about 20 dollars.

Pe, if you are still following this thread, it requires adjustment when the temp., baro pressure, or humidity changes significantly. It's not as consistant in that respect as a good walbro or zama (such as on my G26) but it's certainly no worse than when it was on glow.

mrbigg

My Feedback: (21)

Do you think the .90 ST's carb would work or does it need a Walbro? I have a .51 that would be nice to convert also. I'm heading to CH's site now.

Jezmo

I have been flying glow models for about 40 yrs. Gas for about 20 with just a smidge of diesel time thrown in for good measure. Tuning my 51's glow carb on gas is not hard but I can't say for sure that it would be OK for everyone. Once I got the low end set I haven't moved it. The high end is sensitive but I can live with it. Since the carb on the 90 has the same thread pitch as the little motors I can't see why it would be any worse. I know that CH and others sell the adapter to put a walbro on your engine and they're not that expensive. If you already have the walbro maybe that would be the way to go although I would try the glow carb first and see how it works out for you. Some say the ST carbs are hard to adjust even on glow and I have never found that to be the case so that is why I hesitate to say it work well for you on gas. I have shown some of the people at our field my tricks on adjusting the mag carb (ST) and now they adjust them with no problems. Seems most people don't know about the ability to turn the spray bar to help the mid-range. I run my low end quite lean on gas in order to keep the mid-range in check but the only problem is it's a little cold natured that way. Once warmed up it runs very well. Most who see it run are quite fascinated that it runs that good on gasoline. Let us know if you decide to convert yours and how it turns out.

Jezmo

For the latest update on the ST 51 on my SuperSportster, it is running absolutely flawless. I did try some Mobil 2T full synthetic and I won't be running that anymore. It leaves a very hard black carbon on the tip of the plug. The carbon is almost as hard as glass. The top of the piston was as clean as brand new before the Mobil and now it has three areas that are black with carbon as well. Back to the Pennz/Zenoah oils for me. Either works very good in my engine and with either one the piston was staying as clean as new. It now has about 5 hrs on it and runs just as strong as ever. No unusual noises or anything. I don't think I will tear it down until I see something going wrong. I kinda believe in the old saying "If it ain't broke don't fix it."

Edited to correct the number of hours. My math is getting old with me.

profgigawatt

My Feedback: (6)

My ST 51 on gas uses the stock carb and one click either way makes a noticable difference. The 28 degree advance seems good for my engine. The idle is rough so I have the CH module to retard the spark at idle. I made an adapter for my 61 Evolution for a Walbro and later removed it to try the stock carb both worked well. I put the ST 51 carb on a weedeater with only a 1/2" aluminum adapter and that worked very well. The Walbro seems to be a little big to get between the prop and cylinder on less than a 61. I had to use a 1/4" or better washer on the prop drive to clear the prop/carb. I use gas and 18% synthetic but have not run the 51 enough for a positive evaluation of the con rod. Prof G.

Jezmo

profgigawatt,

Thanks for posting your results. Yes, the carb is sensitive but not impossible IMHO. Mine is flying on the SuperSportster weekly and so far has performed flawless. I am still on the original plug although the Mobil 2T made a bit of a mess on it. Until that it was looking very good and I could no reason the plug wouldn't last for awhile. I hope that little oil experiment didn't cost me a plug although it is still running good and if needed I have spares.

If you check your rod after more running let us know how it looks. I just can't bring myself to take the engine off because it's running so good. OK, I have been doing volunteer work at our church on my time off so I have been a little tired and that's the real reason my rod hasn't been checked.

Good luck with yours, keep us posted.
Butch