Gas engine tuning for newbies....

[Billa]

Oil in use is Amsoil Sabre Pro 100:1 Pre mix mixed at 80:1 and it is a brand spanking new carb. With my own DA 50 I normally only open up the top plate to inspect the screen and take the needles out and flush what ever possible. I have never taken off the diaphragm side in about 8 gallons of fuel - and I am using Amsoil Dominator 50:1 premix mixed at 40:1. We have a very hot climate but our elevation is only about 700 feet above sea level. Thanks in advance for all advice.

Aamer

[mfuess]

You have a base carb air leak. On DA-50's it's imparative that the carb NOT be over tightened. The leak is at the pulse signal hole. Remove the carb, replace the gasket, and re-install the carb. But snug the carb down then add about 1/3rd turn to tighten.

[Mithrandir]

Great reading Mark... your web site is great too!!!

[bob_nj]

Nice work, and good thread!

My questions are these;

The article says that the method of tuning is for a Walbro.
Does it, or will it work with other brands as well?

What if any, is the rule of thumb for weather changes and gasser needle settings?
My thoughts are that going from cooler to warmer temps there is less air available to the previous needle setting. Less air means there is more fuel in the mixture now and the needle may need to close a little.
After tuning an engine in this way, can I expect a cold engine to bog/hesitate when cold and first started up? I've noticed that sometimes a cold engine will bog when the throttle is blipped until it warms up.Last question is, when the meter arm is adjusted/altered, does it change the pop off pressure setting?
Set me straight!

Thanks
Bob

[mfuess]

	Quote: Originally Posted by bob_nj
	Nice work, and good thread! My questions are these; The article says that the method of tuning is for a Walbro. Does it, or will it work with other brands as well? What if any, is the rule of thumb for weather changes and gasser needle settings? My thoughts are that going from cooler to warmer temps there is less air available to the previous needle setting. Less air means there is more fuel in the mixture now and the needle may need to close a little. After tuning an engine in this way, can I expect a cold engine to bog/hesitate when cold and first started up? I've noticed that sometimes a cold engine will bog when the throttle is blipped until it warms up.Last question is, when the meter arm is adjusted/altered, does it change the pop off pressure setting? Set me straight! Thanks Bob

Greetings Bob,

Generally speaking, your needle setting won't need to be changed as the weather changes. Small gas engines are very tollerant to weather variations but there are exeptions though. Extreme heat, and extreme cold may warrant a little fine tune. Assuming your carb is in good condition (IE: clean internal filter screen) a cold start shouldn't bog the engine but for a moment or two. But all engines need a warm-up period, and I highly recommend you let your engine get up to temperature before getting throttle-happy. YES, adjusting your fuel metering lever will change the pop-off pressure. Unless you have the proper tool(s) to set the lever and pop-off pressure, I would "highly" recommend you leave well enough alone. This is the most critical adjustment on a carb. If you get your fuel metering out of whack, it will NEVER take a clean tune no matter how much you mess with the high/low needles.

Good tuning practice applies to all diaphragm carbs, so if you have a Zama, Tillotson, DelOrto, Walbro, and etc, the tune up method is the same.

ANYTIME your engine makes a sudden change in performance, gets to be hard starting, or needs a big needle adjustment (high or low) to fly... YOU HAVE A PROBLEM. It's time to clean & service the carb.

[mfuess]

Bob,

Here is some techno-info for you: The "ideal" air/fuel ratio for a gasoline internal combustion engine is 14:1. In other words, your engine must run at the burn rate 14 pounds of AIR per pound of Gasoline, to provide optimum performance.

[bob_nj]

Thanks alot for the reply. I've been reading and digesting your suggestions for the last few days and can't wait to get out and try it. It's raining here today (07/04) so it may not happen until the weekend.I do have a pop off tester, fulcrum arm gauge, and a spring kit. I've been looking at some of the other tools available from Walbro and would like to invest is them as I am a tinkerer and don't want to leave a problem go because I don't have the tools to fix it.The tool I'm thinking about is this kit -> http://tewarehouse.com/W500-500 My carb is a WG. This kit doesn't list that model as being one the kit applies to.I was wanting it to properly pull the welch plug when the secondary filter needs attention.Do you know if the kit will service the WG?Is the WG still around, or has it been superceded by another/better carb?Thanks again_bob

[mfuess]

Bob,

That tool kit will work for your WG. I think I'll get one too! I make my own carb tools to fit a specific application and it's time-consuming. I generally don't remove the small filter screen (below the brass welch plug). I have found that a good back-flush will get it clean. RAINING? We are on our 11th day of non-stop rain!

[bob_nj]

Wash your car, it'll rain for sure.

I'll go online today and look for a bargain on some tools.
Do you have a favorite vendor for your carb tools?

[JimC-MD]

	Quote: Originally Posted by mfuess
	Bob, Here is some techno-info for you: The "ideal" air/fuel ratio for a gasoline internal combustion engine is 14:1. In other words, your engine must run at the burn rate 14 pounds of AIR per pound of Gasoline, to provide optimum performance.

Stoichiometry is actually 14.7:1 or it can be expressed as Lambda 1.0. All this means is that the equation is balanced so that if a theoretical perfect burn takes place, all the air and all the fuel in the engine are consumed and the byproducts are CO2 and H20. The number of each type of molecule is in balance so everyone has a dance partner. This is the most critical for proper catalyst operation so that the feedgass out of the engine is able to be finished off by the catalyst. That is because a perfect burn does not exist in real application. Since we are not dealing with those types of systems on models, perfect stoich is not as much of an issue. We are usually looking for maximum power. That is typically at around Lambda .9 or so and that is a "richer" mixture. Even computer controlled cars as a general rule go into "power enrichment operation" when load demand is high to maximize power output. Then they settle back into more precise control. Going for that last little bit of leaning can reduce maximum power. If the oil would not damage the sensors on my gas bench, it could be interesting to see what the actual mixture is on a two stroke tuned the way you describe. My guess it that setting the high side where max rpm is achieved would reveal a mixture a little richer than stoichiometry. Something in the 12.5-13.5:1 or Lambda .85 to .9.

Not countering anything you have written Mark. Just hoping to help people see that over leaning an engine for the desired operation are losing power and driving temperatures up too.

Now if they ever try to make us install catalytic converters on these things......

[bob_nj]

I mentioned in a previous post that my carb is a WGA-7, and was wondering if it's still available. According to this Walbro site listing -> http://wem.walbro.com/walbro/component2.asp?component=&CategoryName=&Series=HD& partnum=HD-2-1&GroupName=&FamilyName==

WGA-7-1CarburetorNo longer available

It is not available, and does not have a supercede number.
Do any of the gurus out there know what to use in place of the WGA-7?
How about a carb kit for it for the same reasons?

Take Care
Bob

[mfuess]

Bob,

What is the displacement of your engine? Both the WT & HDA series offer carbs from 20 to 100cc.

[bob_nj]

3W 140I'm just wondering if the mounting dimesnsions are the same, and if all of the holes will line up?

[Phil N. DaBlank]

Billa.. I've had a couple of DA 50's (great engines), and each time when the bogging began after starting and large needle changes were needed, the carb screens were clogged. One time, the large screen and the small screen under the brass plug were both dirty. After cleaning, both engines ran great again.
Just curious and in case I missed it, you said your friend flew a whole session with the DA running perfectly. Did you mean 1 flight or 1 day. The reason I'm asking is, one day my 50 ran great for a few flights and then started to bog. Looked at the large screen in the carb and it had clear gel(stuff) clogging it. I talked to MFuess about it and he said my fuel probably had moisture in it. Cleaned the screen, fuel tank, and threw out that fuel. Runs perfectly. Bottom line, most cases for me have been the screens in the carbs.

[bob_nj]

I dod get to order my Walbro tool kit yesterday.Should be here in about a week.Can't wait!