Am having some issues with with my DA50, am running a 22x10 prop with 32:1 poulan oil weed eater, my idle is running between 1500 - 1700. Sometimes I can even get it lower and reliable. About 3/4 done on the second gallon of breakin.

Transitioning from idle to full throttle there is barely any hesitation and am happy with it, at full throttle with the cowl off am keeping an eye on the fuel line for any signs of air bubbles, at first there was, but that was the fuel tank not being secured enough, so fixed the issue.

However at 3/4 to full throttle whilst flying, the engines has the following symptom, it's like a coughing or a misfire, but the engine does not die. It sounds like a burble but not like a burble.

A ground check revels no isssues whatsoever, only in the air.

I just got of the phone from DA, they said to lean out the engine more, the engine could be rich.

I had the needle set at 1 7/8 on the low and 1 5/8 on the high. Or was it the othr way round. anyways it was set the right way as per the manual, after speaking with DA they said there is a revision to the needle setting, which I need to readjust next weekend.

2 Turns out on the High, and 1 3/4 on the low.

Also note that reading my spark plug, showed that there were alot of carbon deposits, as from my experience tunning jetskis, carbon deposits could be related to bad 2 stroke oil quality or a rich issue.

Wonder if that's reallu applicable.

Anyone else had the same issue ?

No two engines of the same type run with the same needle settings at the same place at the same time. Period!!

ALL engines need to have the needles set to the elevation, the temperature, the humidity, and the prop. Always.

The manufacturer settings and manual notes are for starting points only, and not the "gospel" positions that they should always be at. It just can't work that way.

I don't mean for this to sound harsh, I really don't, but you will have to play with things until you find the right settings for YOUR engine. There are many, many others that could stand a little enlightenment in this area, so hopefully your post will help them, too.

BTW, a few small air bubbles are nothing to worry about.

Pat

what he said......



and don't fret too much until you get to the 5 gallon range.....

silver Oh I definetly agree about the engines never being alike and I do understand the factory settings are always a starting point, been tunning pwc carbs mikuni triple carbs for a number of years now with eci units and big bore's , it's just that my experience with gas engine is some what limited not as much as pwc carbs, however the basic is there carb needles low and high tach reading spark plug reading and all. I wonder if they use an pop setting in their carbs.

I am going to have to try what DA suggested about tunning the engine the right way, well the person I spoke to on the phone with, and how he tunes his da's.

If I recall correctly.

Set everything at default, to get the engine started, warm it up.

1- Get it to idle smooth
2- Transition to half throttle if no hesitation go on to 3/4 and lean the engine out a little at a time, you should hear the engine pick up in rpm, if not drop accordingly.
3- If it drops, way to lean, back of a a little on the h needle.
What you want is to hear the peak rpm and then back off a little.

Am also going to tach the cylinder and see what am getting when I fiddle with the needle.

BTW am at sea level.

I do it a little differently since the Walbro carbs do not have a mid range needle.

I set the idle up to about 2500-3000 rpm. The prop size has no relevance. Tweak the low needle to attain the maximum rpm possible at that idle setting. Now go to the high needle after running the engine up to max rpm. Peak the high needle to max rpm, then past just enough to hear the rpm start to fall off. Back off the needle to the rich side to just short of the peak rpm. Check the low to high and back transition. If it's good, then go fly and make minor needle adjustments as the engine breaks in. After it's broken in you may need to adjust the needles avery 6 months or so, or if you make some changes in flying sites that vary more than 1,200 feet (+/-) in elevation.

Dually noted

I agree with the above and would like to add One other item you might want to try.
If the atmospheric vent is receiving any positive pressure try running a line off of that to a less pressurized area. The only reason I say this is that you mentioned it was fine on the ground but when in the air you have the problem. Sometimes it can be as simple as the needles and other times it can be a "true" pressure problem.

I can almost guarantee you RTK hit it right on the head. It sounds like it is richening up a tad. Not a burble quite as you said. There is a simply fix. I know Gene at Troy Built Models sells a little port cover. It is just a set of spacers to get a thin piece of carbon over the atmospheric vent. All it does is block swirling air from hitting the port. The port is not blocked, but swirling air can not hit it and "confuse" it.

I can promise you if you get the needles perfect on the ground and it still does it in the air, that is it. This is all provided it is NOT a needle issue. Try tweaking the needles like DA says.

Let us know how it comes out,

Norman Ross Jr.

Okay, will take a look at that also. Here are the pics of the build just for your information. http://www.rcuniverse.com/forum/m_15..._2/key_/tm.htm

RTK what do you mean run a line off??? I did not understand.

I made a vent hole for the carb to breath since the spacing between the firewall and the carb opening was very close,

Today I popped over to the local Hobby club was asking some questions in regards to the problem one did say he closed his Firewall port hole completely and that solved the problem.

Before I do attempt any firewall modifications I will retune the carb needles as mentioned above, RTK would you be kind enough to explain what you mean by running a line off ? and if all else fails I will seal the firewall again and see.

The DA50 uses a Walbro carb. On the carb there is a plate that covers the diaphram. On that plate there is a small hole. Sometimes that hole needs to have the air coming to it deflected to prevent pressurizing the diaphram. Never, never cover this hole up in a manner than can block it completely. Sometimes a line needs to run from the cover to a low pressure area in the fuse. All a matter of trial and error.

shesha--Making a vent hole is always a good idea if the carb is to close to the firewall.

The vent line should come off of the diaphragm side of the carb, you can make your own or buy an after market. What happens is the diaphragm reacts to atmospheric pressure and venturi pressure letting in the amout of fuel the engine needs. If you have a positive pressure situation the diaphragm is pushed down opening the metering needle causing extra fuel to be pumped into the engine when it is not required. (causing rich condition) If you have a negative pressure just the opposite will happen. This is why sometimes on the ground your engine will run fine and in the air you have problems.
Here is a picture of an after market plate, off of the nipple you would run a line to "somewhere" where there is a constant pressure.

Let me know if I have made myself clear.

Great minds think alike We must have been typing at the same time.

Diaphram pressurisation okay got it. Yeah that makes sense it's the same logic that happens to a pwc carb when doing a dive undewater causes the engine to richen up, cause of pressure build up in the shell thus affecting the siphoning action of the carb resulting in the carb to get flooded and engine shutdown. okay cool.

Okay am going to hold the idea of porting that hole with a nipple or is that a nible... for a while till I make sure it aint a needle issue but thanks for the feedback silver anr rtk much apprieciated.

You are welcome and I think I can say that for both of us.

okay problem solved it was the needle setting that were not right, as per the manual, after consulting DA they were reset t 13/4 on low and 2 on high then leaned them out. The more gallons I am getting into the plane the more the low needle is getting rich, so going to close it at the next gallon, its on it's third gallon and the engine is sweet, idle coming more and more reliable.