caiman

My Feedback: (1)

I have an almost new US-41 installed "Inverted" (spark plug down) on a 1/4 Decathlon. The problem is that since the engine needs some fuel priming on the carb before it can get started, the spark plug gets wet with fuel and a spark is not generated, therefore the engine does not start. I always have to remove the spark plug to dry it and after that, the engine starts more easily.

My questions are:

1)- Could this problem be caused by improper spark plug gap or improper magneto gap? if so, what should be the correct gap spacing for each?
2)- Is there an easy way to add a prime bulb or choke instead of having to add fuel to the air intake? (on another plane, I had no starting problems using a Zenoah 38 with a choke)
3)- Should a Sullivan Dynatron Super Starter (Torque= 340 @12V) be able to turn the prop or should I used a belt driven starter? I tried this starter but it didn't turn the prop, maybe because of the battery or because I have no spinner installed? any suggestions?

Thanks.

Phil Heller

My Feedback: (9)

caiman
I have a US41 inverted in my G-Shark. The only way I can start it is with my Dynatron on a Miller Geared starter with 24 V! You would have to convert to CH or similar ignition to hand start this little beast. It does run very well once started. I took off the spring starter because it did not always start the engine and I felt it was just added weight, the engine runs better without it.
The ignition and the starter cost about the same - so your choice is a toss-up.

Check out http://www.quiknet.com/~pheller

Phil

P.S. I do have an extra Magneto coil If you think that would help - although I doubt it! it's yours for $25 plus postage.

Vince

My Feedback: (1)

The US engine is equipped with a magneto. A magneto delivers a spark relative in strength to the rpm that the flywheel is spinning. The faster it spins the stronger it's spark, to a point.

Vince

w8ye

My Feedback: (16)

The spacing of the coil off the flywheel is the thickness of a business card. With the magnets under the coil, Raise the coil up and place the business card under it. While holding the coil down against the magnets on the flywheel, tighten the coil retainer screws.

The spark plug gap is .020"

Good luck,

Jim

caiman

My Feedback: (1)

Thank you very much for the information.

caiman

My Feedback: (1)

Thank you for the info Phil. I already have a Dynatron starter but wasn't sure if I needed a geared reduction in order for it to start the engine. Could you tell me where you bought your Miller geared adapter? is it the one advertised on some magazines with a belt reduuction? what is the gear ratio on yours? do you absolutely need to used 24V instead of 12V?

Also, would you please tell me more about the CH ignition, where can I get more information about it? where could I buy it?

Phil Heller

My Feedback: (9)

caiman,

I tried the Dynatron alone on 12V - could hardly turn it over! The Miller geared unit would not spin it fast enough on 12V, but on 24V it kicks it right over!

Yes, it is the Miller belt drive unit advertised in many of the Mags. I purchased mine at RC Country in Sacramento (My LHS!)

Tom Perry can set you up with ignition for your US41 - Do a search for him in RCU - He goes by Tom Perry

Good Luck,

Phil

Did the search for you! [email protected]

Phil

WreckRman2

My Feedback: (5)

This is not entirely true. In order for a magento to spark it does require the magnet on the flywheel to pass by the coils on the coil fast enough to produce the spark however once that point is reached and you do have spark then a spark is a spark. Faster the rpm's makes for easier starting but it does not make the spark stronger.

Like w8ye said a business card is a good tool to use for setting the gap providing you don't have a gap gauge.

Does this engine have a choke? If it does then prime the engine by choking it with the spark on. Flip it until you hear the engine pop or fire once. Then remove the choke and flip again until it starts. By doing it this way you won't have raw fuel sitting in the plug. If it doesn't have a choke you could easily make one with a piece of tin that you can slide over the end of the carb for priming.

The choice is yours, a 1-2 hundred dollar starter or a piece of tin from your coke can that your gonna throw away anyway...

Phil Heller

My Feedback: (9)

David,

That system works well with an engine that has electronic ignition, but the US41 has a magneto and is practically impossible to start by hand. Mine would start with the spring starter after it had been started with the Miller for the first start of the day, but hand flipping? - never saw it happen, choke or no choke. Maybe after several gallons of run time and it has loosened up considerably.

The choke, pop, and start work fine with my Q52 and Tartan twin on CH ignition, but the US41 magneto still needs the Big'un!

Phil

P.S. Good looking Website! I bookmarked it , so I'll be watching you! What are you running in your Extra?

Phil http://www.quiknet.com/~pheller

Flypaper 2

The magneto DOES put out more voltage with RPM like any generator.

Vince

My Feedback: (1)

David, I respectfully disagree with your comments relative to mine. The magneto ignition does in fact put out a stronger spark as rpm increases (up to a point). I learned this many years ago messing with drag cars.

I also agree that magneto equipped engines are next to impossible to hand start. I literally worked my self silly trying to start a new G62. I tried everything that everybody in this forum suggested to get it to start. I did get a few starts by hand flipping, but they were far and few between. Only after I added the B&B spring starter was I able to get it running when I wanted it to.

Thanks Flypaper

Vince

caiman

My Feedback: (1)

Thank you all for your comments. In fact, the voltage developed by a magneto is proportional to mainly three variables:

1)- The magnetic field strength (which is proportional to the magneto gap).
2)- The rate of change of the magnetic field over the magneto coil (which is proportional to the prop RPM).
3)- The number of wire winding turns inside the magneto coil.

There is a saturation point above which no increase in voltage is produce. The other thing to consider, is that you might have a very large voltage, but if the magneto coil is wind with a very thin conductor, then it's internal resistence wiuld be so large that it would not be able to produce enough "current" and the spark would be weak. In general the greater the voltage, the lower the current for a certain amount of power. I think the magneto on this engine produces weaker spark than that of Zenoahs for instance,

I used to have a Zenoah engine and it started very well using the choke as previously mentioned and the spring starter. I am being able to start the US-41 with the spring starter, but I definitely have to dry the spark plug after I manually prime the engine, otherwise it won't start.

Could you explain in more detail your choke design using a piece of tin?

Thanks.

WreckRman2

My Feedback: (5)

Not trying to sound harse here but if you guys are having that many problems with engines that use a mag ignition system and then spending the money on starters just to run them then why not just buy a better engine that has an electronic ignition such as the BME.

Flypaper 2

The old Quadra's that had points would easily hand start. Since they went to an electronic trigger they were hard to start.A company makes a small device to make any points mag into breakerless that works well. The first ones would hand start well. If you didn't pull the cord fast enough on a chainsaw it would kick back and break the rope so they modified it so you had to pull it faster to trigger a spark. Bummer!!!

caiman

My Feedback: (1)

Good point WreckRman. In my case, the reason is that I already own two US-41 and its hard to import gas engines into México, why? don´t ask I have absolutely no idea!

Vince

My Feedback: (1)

A relatively low cost solution is the Jump Start made by C&H.

Vince

caiman

My Feedback: (1)

Where can I get more information about the jump start that you mentioned, is there any website?

Thanks.

WreckRman2

My Feedback: (5)

http://www.ch-ignitions.com

John B

My Feedback: (1)

I just prime it till good and wet and it takes off on the first try, i use the spring start when cold, just slap the prop after. I checked my coil gap and its set at .014 I get 7800 on a 18/10 at sea level and 7100 on a 20/8 Im happy with the way mine runs and starts.
wish it was lighter though.

caiman

My Feedback: (1)

John,

Do you have your engine mounted inverted (spark plug down) as I do?

John B

My Feedback: (1)

great runner no complaints, I have flooded it but its pretty hard to do on mine. I just choke it till my finger gets wet then fire it off.

sagacity

Buy the Sullivan Model 4. Run it on two 500 amp batteries. It comes stock with the MillerRC 3" reversible silicone insert, and runs the US 41 at 2400rpm. You don't choke, flip or any of that. You place teh cup of the starter on the spinner and touch the trigger. The US 41 starts in less than a second, with no priming, as the carb's diaphragm is activated by the starter and fuel flows fast. I do flip a few times until I feel the gasoline start to loosen things up, but that's it. My cowl has no cheat hole for priming or thumb-choking, and the velocity stack is bigger than my thumb any way.

As well, you will never buy another starter again. I have a friend at the field who uses it on his
DA 100, and with the sweet ignition that engine has, it's a dream.

greg