Running a Gnome 100

[snj5]

As many know, I have gone completely Bonkers and am ponying up for a new build Gnome 100 from CAMS in New Zealand. There is about a two year or so lead time, so good to get the Camel replica up to the Ohio Aerodrome and finish tweaking the bugs out while flying on the Rotec.

I've gotten the English Gnome 100 manual and am memorizing it, but I thought a small thread to discuss with current Gnome and other experienced rotary operators would be good before I saddle up to have this thing waft me into the air.

Topic one. Reduced power?

Tom Kozura (Omega) and I were talking about the section in the manual which describes "throttling the engine" to 85% cruise with the mixture (the only vernier control, as there is no proper carb). It was my previous understanding that this engine was "on" or "off", once the mixture was adjusted to best obtained rpm. Hmmm. I am a little anxious thinking this may cause a pretty hot CHT as the mixture leans out. Any experience or advice out there about reduced power settings on a rotary without a throttle carb?
N.B.: there is also no ignition sequencing mag on the Gnome 100 as there is on a 160.

Thanks

[franzkait]

the best advice I can give you , do not even think about it , to buy a 100 Gnome . And if it must be a Gnome , a Goebler - Gnome .

[Chill31]

Assuming the fuel and oil are delivered to the engine independently, running "lean of peak" should be possible. I do this on my IO-360 all the time, BUT I make sure that I am below 75% power in order to provide a safe margin from detonation.

If you run 100LL avgas in the 100gnome with a compression ratio less 5, my unscientific guess is that you will be ok. Search for LOP operations in google and read as much as you can to decide if its right for you.

My experience in the IO360 is that EVERYTHING runs cooler. CHT, EGT, Oil temp. My plugs are very clean and dry with almost no carbon buildup or fowling.

[franzkait]

you also have in your IO 360 the intake valve in the piston ?
you also adjust the top RPM with leaf springs in the piston ?
and if the intake valve jams up , the fire shots thru the carb in direction pilot ?

I didn't know that a IO360 is so similar to a 100 Gnome .:cool:

[US95Damiani]

Hi Russ,

I don't think I'd recommend running 100LL in this engine. I think the 100LL wouldn't burn completely. I'm not sure about lean of peak especially on a design that old.

[Chill31]

you also have in your IO 360 the intake valve in the piston ?
you also adjust the top RPM with leaf springs in the piston ?
and if the intake valve jams up , the fire shots thru the carb in direction pilot ?

I didn't know that a IO360 is so similar to a 100 Gnome .:cool:

Would you run this engine rich of peak? If so, why?

What are the effects of running it lean of peak?

[Chill31]

Hi Russ,

I don't think I'd recommend running 100LL in this engine. I think the 100LL wouldn't burn completely. I'm not sure about lean of peak especially on a design that old.

Thats interesting! What do you mean by burn "completely?" Right now I'm imagining running Rich of peak EGT and that implies incomplete burn doesnt it? Some of the fuel at that point doesnt have enough air for combustion and is expelled with the exhaust gasses right?

[US95Damiani]

Hi Chris,

100LL is much less volatile for lack of a better description than the fuels that were standard back in WW1. To run something with that much energy with a slow burn in such a low compression slow turning engine may cause heat issues. Also the lead would be detrimental to the spark. There was no such thing as Tetra Ethyl lead in the teens. We're running the 80 LeRhone 9C on 87 auto fuel with no ethanol and it runs just perfectly. The engine really only likes a certain mixture to run.

[Chill31]

Hi Chris,

100LL is much less volatile for lack of a better description than the fuels that were standard back in WW1. To run something with that much energy with a slow burn in such a low compression slow turning engine may cause heat issues. Also the lead would be detrimental to the spark. There was no such thing as Tetra Ethyl lead in the teens. We're running the 80 LeRhone 9C on 87 auto fuel with no ethanol and it runs just perfectly. The engine really only likes a certain mixture to run.

Hijacking his thread a little, but this all seems relevent to his question, so I'll keep asking mine too :)

When you say it only likes a certain mixture to run, do you mean run period dot? or do you mean run smoothly?

While I understand that there are significant mechanical differences between rotaries and opposed engines, they do operate in the same way at a very basic level. add fuel, add air, compress, ignite. Provided you can get fuel distributed to the cylinder, it seems that it should be possible to run with either a rich or lean mixture and not exceed temperature limits.

Lots of learning for me! Thanks for the explaining!

[snj5]

Thank you all for your input.

A lot of this will be worked out on the prototype.

To answer Udo's question, the decision to go with this engine was that I could not find another rotary (I looked for a year for a 110 LeRhone), at least not in my price range. When Graeham O. called about Tony's production run on the Gnome 100, Tony's immense experience and reputation - and frankly the delivered price - seemed to say this would be my best opportunity for my meager means. The 100 Gnome was fitted to the Camel originally, a plus as there are performance figures. The 100 Gnome was a fairly widely used engine, and there are current operators (e.g. Avro 504). I spoke with several people who have flown behind the 100 Gnome, and they said if the new engine could be delivered (and solving the habit of throwing cylinders) it would be a wonderful opportunity. I saw a chance, and I took it. The increased delivery time helps me spread out the cash flow as well.

I do agree about the 100 LL. I seriously doubt I will skyhook this thing, keeping to only a couple thousand feet AGL. The lower compression should easily allow lower octane gas.

To review, the 100 Gnome did not have the intake valve in the piston as previous Gnome models, but rather a series of ports at the bottom of the cylinder to draw in a very rich fuel air mixture, diluted with air drawn in the single top valve after the exhaust stroke. To help prevent pressurizing the crankcase through these ports, the exhaust valve opened BBDC to exit the combusted gases.

The 100 Gnome also did not have a carb. It had a fuel sprayer controlled by a Tampier valve that injected fuel into the crancase. The air entering from behing the crankcase was not throttleable - so there was a preset of calculated air, a sum of that drawn in with fuel from below and that admitted through the top cylinder valve. To reduce power, the pilot(me) can 1. turn the fuel off 2. control the amount of fuel flow to the nozzle ( and thus this discussion) or 3. turn off (blip) the ignition.

The lean of peak thing is intrigueing, as I never studied it much. I certainly have read how dangerous running rich is as the engine is hard to get restarted if it quits. I am familiar with burnt valves in automobiles from lean mixtures under load. I think the secret is 'under load', as I read many internal combustion engines can tolerate slightly lean of stoichiometric if not under full load, perhaps up to an A/F of 15. Having most of my motor modification and tuning experience on high rev Italian car engines, the low compression, low rpm Gnome is new to me and I have a lot to learn. But, that is what is fun.

I can assure you I am going to fart around with this engine a long time on the ground before we ever try to slip the surly bonds of earth.

[franzkait]

if you runn it lean , have a good fire extinguisher . This engine is dangerous .

[snj5]

if you runn it lean , have a good fire extinguisher . This engine is dangerous .

This is what I think as well!!!

[Chill31]

This is what I think as well!!!

Haha, i am curious then, why would you want to put such an engine in the front of your plane and leave the ground with it? Rotec sounding good to me right now...

[snj5]

Haha, i am curious then, why would you want to put such an engine in the front of your plane and leave the ground with it? Rotec sounding good to me right now...

Why even get in a WW1 plane? If I wanted safe and efficient there's none better than an RV. But, what fun is that?

I do believe that, like most engines, if you run them well within their design parameters they are pretty safe. I ran a Wright R-1300 radial that everyone told me was a crap design. I followed the operating instructions to the letter, and it was perfectly reliable and ran great. Likewise, I believe if the engine is built well, set up properly, and operated within safe parameters, it will add immeasurably to the WW1 flying experience of my dear little plane. :)

[franzkait]

investigate the Goebel - Gnome . This one is much better . There are many Gnomes like the Oberursel - Siemens - Schwade - Stahlherz and so on .

[snj5]

investigate the Goebel - Gnome . This one is much better . There are many Gnomes like the Oberursel - Siemens - Schwade - Stahlherz and so on .

Thanks - working it now.
:) Of course, I have to avoid all the porcelein figurines by Goebel as well in my search!! :)

Goebel Goe III ?

[Chill31]

Why even get in a WW1 plane?...it will add immeasurably to the WW1 flying experience of my dear little plane. :)

Agreed! but the manual says lean it to 85% via the mixture...just thinking out loud for discussion purposes...I've been there low, slow, no engine, and no where to go. Was probably the most excitement I've had in an airplane, but not the most fun.

[franzkait]

do you know the main different from the Goebel Gnome to the normal Gnome ?

[snj5]

do you know the main different from the Goebel Gnome to the normal Gnome ?

From what I have read in the past 10 minutes, it seems that Goebel retained the valve in the piston, while Gnome had moved away from that in the 100 and 160 hp Gnomes using the ports at the bottom of the cylinder head.

Also, it looks like the case was different with the Goebel having a one piece case with cylinders held by a collar - this looks like a better design as the split case Gnomes used to be known for throwing cylinders.

[franzkait]

Yes , but this is not the important difference . Let's see if anybody in the Forum knows about it ?

[baldeagle]

I watched (from the ground) a 100 Gnome throw a cylinder in flight once. The fire spinning around inside the cowl was quite impressive, even from the ground, and the vibration in the airplane was apparently quite an experience also.
http://www.oldrhinebeck.org/media/k2/items/cache/af2ef6a0e2c9c528b09655df79f3b312_XL.jpg
What have they done to cure this problem?
Used to happen in the DH-2s and could take out a boom, I think McCudden almost got killed that way, or one of the British aces...



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[snj5]

I watched (from the ground) a 100 Gnome throw a cylinder in flight once. The fire spinning around inside the cowl was quite impressive, even from the ground, and the vibration in the airplane was apparently quite an experience also.
What have they done to cure this problem?
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I relayed this exact problem to Tony a couple of months ago and I know he was looking into this. Andrew, did they say the cause of the accident you saw was metal fatigue or something else? This I could imagine might be due to running the engine too lean and overheating.

thanks

[snj5]

Another thing is matching the prop to the motor, so as not to over prop it leading to a dangerous BMEP (perhaps evidenced by a low static rpm) which perhaps could lead to throwing a cylinder.

Sometimes I think some type of carburetor might still work a bit on this engine giving some control over the amount of air admitted as well as the amout of fuel.

[j ferguson]

"Stationary" cam gear and tricky mechanism to allow tappet to miss cam every other stroke?

[baldeagle]

I thought the problem was that the cylinder walls were just too thin, that's what I always heard anyway. The engine above was in Cole's Fokker Triplane for years, and one day he was (fortunately)coming in for a pass, and at the approach end of the field there was a "Woof!" and something black flew up over the wing and fell into the trees at the north end of the runway. The Triplane shook violently and he pushed the blip switch to ease up the shaking, then let it up once just to see if it still shook, and yup it was bad. Fortunately he was lined up for landing already, and as he came in we could see the flames going around inside the cowl. He bounced hard, and in mid-bounce what was left of the connecting rod got inside the case and the engine locked instantly and stopped rotating. He bounced a couple more times and came to a stop, and somebody got a fire extinguisher and put out the fire. There was a hole in the cowling big enough to crawl through, at about the 1 o'clock position as viewed from the front. Somebody went and searched the woods later that evening and found the cylinder, and it was presented to Cole at the end of the year banquet. He's quoted on the ORA web site as saying that it was the worst experience he ever had in an airplane-

Cole used to say that the rotaries would run on just about anything, so I don't think 100LL would be a problem. My 160 Gnome starts and runs fine on it. I don't think I would try to alter the rpm much with the Tampier though, despite what the manual says.



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[snj5]

Excellent post, Andrew - thanks.
I know Tony is using some modern metallurgy in the motor components. Perhaps this will help. Will pass this story on. Many thanks.

Just out of curiosity, has anyone successfully used any lubricating oil (e.g. 2 stroke oil, Marvel Mystery Oil, etc.) other than castor oil in rotaries?

[j ferguson]

This isn't a direct answer to your question about alternative lubricants for your Gnome. I use Marvel Mystery Oil in our diesel propulsion engine mixed with the fuel on the advice of the fellow who designed the marinization of this industrial Ford engine. A while back, another user sent me an analysis which showed that MMO was not a lubricity enhancer. It is also expensive.

I would have thought that now that you have bought the farm (so to speak) you would be planting Castor Oil plants (which have been grown successfully as far north as Toronto) so that you might be as politically correct as possible - biofuel don't you know.

But I would also think since you are going to be using a LOT of it, you would be looking for a less expensive alternative.

The Wiki page on the Castor Oil Plant suggests that castor oil's use in engines, particularly model airplane engines, has been supplanted by synthetic alternatives which are less TOXIC!! :blink:

Of course there is the possibility that the use of castor oil as a lubricant in WW1 airplanes many not have been what made them toxic. ;)

[Brad]

I would think that perhaps some of the synthetic lubricants used in model fuel would be both less expensive and better... but I'm not positive about that. I don't know if VP (the racing fuel guys) would sell you any oils or not... but they now do model fuel as well. That might be worth exploring.

[Bookmaker]

As an avid modeler using fuels with and without synthetic oils, I find that there is more of a rust potential problem with the synthetic oils vs. the castor. Ths castor gums up more though. There is also a difference with heat dissipation

Also keep in mind the model fuel you are referring to is alcohol based not gas. So those synthetic oils may not mix with gas. The model engines that use gasoline use normal 2 cycle oil of one type or another. Including synthetics for gas. I don't think any model gas engines use castor oil.

Dale

[baldeagle]

I've heard rumors of people using modern oils in rotaries, without success, but don't remember details or whether they were credible stories. AA Castor Oil is the old standard, and Fred Murrin told me that he uses AA, and I think that's what they run in the New Zealand aircraft.

I use de-gummed castor oil in my Gnome, and I believe that Shuttleworth uses something similar. www.blendzall.com (http://www.blendzall.com/) , look at the #465 4-cycle stuff. A lot of the classic Porsche guys use it, it's supposed to be good for the older engines with ball bearing mains, and isn't supposed to gum up like the AA.

Do some googling and you'll find lots of food for thought.


And, just for fun-
https://www.youtube.com/watch?v=CYc-H8Wg-MQ



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[ONEALM]

I thought besides the issue BaldEagle pointed out with the thin cylinder skirts, that the intake pin holes were aligned like the perforations in paper.... once one started to go, they just zipped along.

The solution was to offset them to make the "un-zipping" less likely.

[Brad]

I've heard rumors of people using modern oils in rotaries, without success, but don't remember details or whether they were credible stories. AA Castor Oil is the old standard, and Fred Murrin told me that he uses AA, and I think that's what they run in the New Zealand aircraft.

I use de-gummed castor oil in my Gnome, and I believe that Shuttleworth uses something similar. www.blendzall.com (http://www.blendzall.com/) , look at the #465 4-cycle stuff. A lot of the classic Porsche guys use it, it's supposed to be good for the older engines with ball bearing mains, and isn't supposed to gum up like the AA.

Do some googling and you'll find lots of food for thought.


And, just for fun-
https://www.youtube.com/watch?v=CYc-H8Wg-MQ



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Sounds pretty! And they sure swing a big freakin' stick! :blink:

[snj5]

Another problem with the 100 Gnomes is that they were built by the British under license -- and we all know with the exception of the Bentley the Brit engines were not quite as good as the French (or New Zealanders?) (ducks for cover here :) :) )

Spoke with Fred Murrin today about the issue of running lean on the Gnome. He knows what it says in the manual as well, but thinks it is a bad idea. He believes that pulling the Tampier back that far will result in pretty hot running which may promote early failure. Fred's main take-away was: You just have to get used to controlling speed with the blip. He also talked a bit about fuels, saying he always used 80 unleaded. The specs state that the 100 Gnome compression ratio was 4.85:1 and required 40 - 50 octane gas. Some Gnome did have a mechanical advance/retard of the cam gear to help control speed, but that was dropped.

One of the main applications on the Gnome 100 was on training aircraft, so I hope that is an indication of ease of use for plebes.

Another interesting number is the 100 Gnome weight is about 23 pounds more than the Rotec, so with the shorter moment arm w&b should hopefully not be a big problem. As for torque, the 100 gnome put out a lot less than the more common Clerget or Bentley engines. The 100 Gnome at power put out about 437 ft-lbs of torque, while the 130 Clerget about 570. As a comparison, the 150 Rotec I am running now develops about 341 ft-lbs at take off. The 160 Gnome, described as a 'real handful' in the NZ Camel flown by Gene DeMarco, is up around 650 ft-lbs of torque.

Thanks to everyone for the great discussion.

[j ferguson]

What follows could be nuts.

Few of us have direct experience with an engine which burns so much fuel for what it does. A bit over 1 lb of fuel/horsepower/hour is more than twice what one would expect to see on a more modern engine. you could suppose that all of this fuel would keep temperatures down simply because some of it would absorb heat as it evaporated but did not burn. And there's all that oil too, a couple of gallons an hour - something else to subtract heat from the combustion process.

Where I'm going with this, is the possibility that leaning the engine out would not only reduce the amount of unburned fuel passing through the engine, thus heating it up, but might also produce more power possibly in a way which might produce higher cylinder pressures AND more rpm a bit more than with the less efficient mixture - and maybe too much for a design with a few shaky details?

Did Cole Palen ever reveal what he did with the mixture? Did the departing jug leave more or less intact or did it sheer off outside the crankcase. What failed?

I think if I were planning to fly behind one of these things, i would do a little testing. One test would be to build enough of a section of the case to secure one cylinder, assemble it with a cylinder and piston, secure the whole assembly behind a wall with a thick lexan viewport, block the piston, then pump up the pressure in the cylinder until something fails. If the pressure reached is 3 times more than anything the actual engine is ever likely to see in service, I'd relax a little - just a little.

Maybe someone with experience in these sorts of things can provide better guidance here.

[Maxim08]

Russ,

Sort of missed this thread. Good God man! What are you doing??!!!??!?!?!?!

Anyway, congratulations on this endeavour.

Never got an engine but...

http://i109.photobucket.com/albums/n55/maxim08-15/cgnutz/Aerodrome/photo_zps29c8e930.jpg

I did get the hat.

Regards
John

[Chill31]

I'm really enjoying reading all of the great information in this thread. My level of knowledge on the way WWI engines work is certainly below where you guys are, so I hope you will bear with me as I do some learning here...

I'm trying to grasp the differences between WWI engines fuel mixture and modern engines fuel mixture. Is there anyone following this thread who is well read in operating engines lean of peak egt and/or experienced in these types of operations with either modern or WWI era engines?

My experience with LOP involves modern IO360 with full engine instrumentation on each cylinder. When leaning the engine from full rich, you find that egt and cht rise to a peak where the engine is working the hardest and producing the most heat. In FP propeller airplanes, this is equivalent to leaning to max RPM. Leaning further beyond that peak results in falling cht and egt (and rpm in fp props) due to the fact that the engine is producing significantly less power. Instead of cooling with fuel, we are essentially cooling with excess air and much smaller levels of combustion. The real risk with this type of operation is detonation which can result from too lean fuel mixtures with too high power setting (high internal cyl pressures). On engines where you cannot verify the CHT or EGT of an individual cylinder, you have no way of knowing exaclty how lean and at what level every portion of the engine is running. This creates a risk if one cylinder is running richer than the rest and subsequently generates enough heat to detonate/preignite or burn a hole in the piston/cyl.

From the standpoint of not being able to monitor each cylinder on a rotary, it would certainly be a risky proposition to run such old tech with out cutting edge monitoring systems, and I can see why people would advise against it.

From the standpoint of "increasing temps" due to lean operations, this is not what the science and real world experience shows on modern engines. My expectation would be that the old engines respond to lean mixtures in the same way. Is there a reason they would not?

Thanks for all of the info!

[franzkait]

I use in engines from 1903 modern fuel with 95 Oktan . And this old engines love this modern fuel .

Number one problem with Gnome engines . Backfire in the crankcase . And sometimes a cylinder flies off about this problem .

[snj5]

I use in engines from 1903 modern fuel with 95 Oktan . And this old engines love this modern fuel .

Number one problem with Gnome engines . Backfire in the crankcase . And sometimes a cylinder flies off about this problem .

Do you believe that is specific to valve-in-piston Gnomes or the ported cylinder skirt Gnomes as well?

Great info.

[franzkait]

all Gnomes . But most time valve-in-piston Gnomes . Look what kind of magnetos this Gnomes use . With a selector to switch off the problem cylinder . In case the pilot had the time to do it .;)

Still nobody know the different to a Goebel - Gnome ?

[j ferguson]

all Gnomes . But most time valve-in-piston Gnomes . Look what kind of magnetos this Gnomes use . With a selector to switch off the problem cylinder . In case the pilot had the time to do it .;)

Still nobody know the different to a Goebel - Gnome ?

something other than the Goebel stationary cam for the exhaust valves?

[baldeagle]

I don't think the 160s are as prone to backfiring, but the 100 would sometimes blow flames back out the intake pipes almost to the wingtip. It would wake you up if you were standing there ready to pull the chocks. The engine would stop firing for several seconds, and then would pick up again. It happened to Cole once in the air that I remember, he was pretty low over the trees, and we held our breath till the engine picked up just in time.

The 160s will happily catch fire on starting, we almost burned up Kermit's Avro 504 the one time we forgot to bring a fire extinguisher out while we started it. Kermit called "contact" and I swung the prop, the engine went about a turn and a half, stopped, and burst into flames. I stepped back and said "Oh $@#t, it's on fire." You should've seen the expression on the face of the passenger in the front seat. He was some fancy theme park designer who was helping Kermit design Fantasy of Flight, drove up in a Porsche, and wore a suit that probably cost more than I made in a week. Wasn't happy. Anyway, I applied faulty logic to the situation, thinking about how on a normal radial you keep cranking to start it and suck the fire in. I said "still hot?" and swung the prop again, and it did start, but of course couldn't suck the fire in. The flames filled the cowl and whirled around for a few seconds, then finally blew themselves out, and Kermit taxied off and gave the guy his ride. He never came back.


I think it was a few weeks later that he was giving somebody a ride in his Grumman TBM and a fuel drain came out on landing, causing fuel to come pouring out of the bomb bay as they taxied in. There was some more apprehension for pilot and passenger as they watched us running towards them with fire extinguishers. Fortunately nothing untoward happened.

Fire bad.



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[Chill31]

What was causing the backfires? Was it blipping?

[franzkait]

All rotarys with a selector switch at the magneto have a backfire problem . The 160 has a selector switch .
The 100 Gnome has a backfire problem about a gummed up intake valve .
The Goebel has on top of the con rod a nose to close the intake valve mechanical in case there is a problem .

[Chill31]

With regard to lean/rich mixtures, this is my understanding of the cause of backfires....

In a stoichiometric combustion, the rate at which fuel/air burns is fairlly rapid. As you go rich or lean of that mixture, you slow down the combustion rate and either ignite fuel in the intake/exhaust when you are too lean or ignite fuel in the exhaust if you are too rich.

[j ferguson]

The vision of our hero standing there during the start of Kermit's bird and reacting to the sudden burst of flame out the intake port is priceless. :D:D:D

Something that should be considered in the discussion of backfires is that there is a combustible mixture in the crankcase of these engines, not unlike that in most 2-cycle engines now in use. But with thousands of hours of 2 cycle operation, motorcycles and outboards, I've never had a backfire. And at idle, at least, most of them turned over below 1,000 rpm - albeit with much less fuel consumption than we seem to be talking about here. So there must be something different.

I keep wondering about the excessive fuel pumped through the Gnomes and wonder if it was done to keep the engine cool to avoid the development of spots inside the combustion chamber hot enough to ignite on the intake stroke which would certainly cause a backfire. What about spark plugs designed to not foul in all the fuel and oil? They would need to run pretty hot.

[franzkait]

but how many engines have the intake valve in the piston ?

We better wait this 2 or 20 or 50 years , he will get his engine , and we will see how it runns .:cool:

[Brad]

While not strictly authentic, I wonder if the "selective" ignition from the 160 could be applied to the 100? ;)

[RAF56_Ball]

Haha, i am curious then, why would you want to put such an engine in the front of your plane and leave the ground with it? Rotec sounding good to me right now...
Shush, Chili! Don't say that! He is set on this fine engine, we should encourage him.




And then maybe one of us can buy his Rotec from him for a "song", muhahahahaha! ;)

Gotta admit, it will be very cool to have this kind of replica with an authentic rotary in front of it!!

[snj5]

While not strictly authentic, I wonder if the "selective" ignition from the 160 could be applied to the 100? ;)

I had thought of this earlier, but would rather stay fairly true. That said, the possibility of dual ignitions (as on a 160) has some appeal.An important issue is that this motor will be used for flying me around, not just a perfect replica display engine. So much like with the airframe, I am content with some compromises to the originality for sake of safety. Each of us pays our money, and draws our own line in the sand*. :)




*apologies to Col. William B. Travis

[Chill31]

but how many engines have the intake valve in the piston ?

We better wait this 2 or 20 or 50 years , he will get his engine , and we will see how it runns .:cool:

I was thinking about this, and the intake valve location might be the real kicker here. If the combustion is slowed down enough through leaning or enriching the mixture (or maybe even different octane?), you could still have some flame present when the valve opened, and depending on the way that is timed in the engine, that might be why these have a propensity for backfire at other than ideal mixtures.

Like FK said though, I'll be waiting to hear how it goes since I will likely never have a Gnome of my own to play with so to speak.