I have an almost new 3w-100. I flew it the other day and the problem is: I tune it on the ground and it runs awesome, great idle, transision, power, everything. But in the air it will barely keep running. It even died on me in flight. I've adjusted the needles all over the place with the same symptons. Great on the ground, bad in the air. I have soldered a vent line to the diaphram cover with a vent line ran into the fuse, but it didnt help.
Whats going on here???

eraser
does it present rich or lean symptoms in the air?

It acts like it goes very rich from idle to 1/2 stick, then cleans out at full throttle.

eraser---I have a 3w with a similar, but not to your extent, problem. I did the line from the diaphragm thin with no success, in fact made it worse. I could not find an area in my plane that was not pressurized.
What I ended up doing was making a box about 1"x1" out of balsa. Then you put the the diaphragm vent line into it. I made sure mine was pretty air tight. Problem solved.
It is worth a try and costs next to nothing

RTK
That sounds like its worth a try. Mine runs perfect on the ground, so it must be a pressure thing when the plane gets airborne. There is alot of air blowing through the fuse.

do you have an exit hole in the fuse someplace so it won't pressure up?

I did, but it still did not help. I even made a louver to help create a low pressure zone at the exit area.

That engine has one of the fussiest carbs you can find. It likes to be adjusted for every flight. The tube RTK is talking about plays a large part in the performance. Even if the tube ends up 4 feet long, try to locate a dead air location in the fuse.

I never had to tune mine once it broke in, one thing I always do with the old style carb blocks is take it apart and use some RTV to seal up any imperfections, try that and get a "Intake manifold" from Aircraft International, they work great!!
Tom

I did the same. RTVed everything, made sure the carb block was not warped etc. I'm going to try RTKs box method next. If that doesnt work, maybe get a walbo carb for it???

Three solutions:

1 > Invest in the 3W air horn - best $30 you can spend, run the vent line to the carb or just behind the firewall.
2> Make sure you are not "catching" air in your fuselage - if needed, open up a vent hole in the covering (easy to build with some leftover stringer stock) The trick is to not have presure build up in the fuselage which can effect the metering of the carb. If you run cans, you don't have to worry about this as you should have a large airflow through the fuselage
3> Take apart the entire carb base and reed block assembly and HONDABOND it back together. Don't use Loctite, and don't use RTV. Hondabond is the best sealant money can buy (its $15 a tube at a Honda dealer). Be very careful not to get the sealant in the pulse pressure hole or anywhere on the reeds. BE VERY CAREFUL NOT TO OVERTIGHTEN the Ryton block... its easy to distort it which will cause vacuum and/or fuel leaks. A new Ryton block is like $50 too... so handle it with care.

The Tillotsen carbs are FAR SUPERIOR to the walbros. They are the reason 3W engines have a better midrange and fantastic transition. They are picky to tune, and some of them do come from the factory with inherent problems but once you take the time to get them right... they stay right. I prefer them over the walbros but there are times they test my patience.

Don't waste your time building boxes, or running 4' tubes. It really is not necessary and by doing so you really are covering up a problem and adding weight. By installing the air horn, re-sealing the Ryton block and venting the fuselage you will eliminate all problems. Needle tuning on this carb is also very critical. I have seen some 3W newbies battle the needle settings for dozens of flights before finally getting it right.

While it is true the DA, BME, ZDZ, etc does not need this level of detail (or BS as some call it) those engines all have their quirks as well. I think the 3W 100 series, the 106 in particular is one of the best engines ever made.

DP

DP---
I tried everything you mentioned and a few more tricks, no go. The Dead Air BOX was the only fix I found, believe me I ended up with more holes in the bottom of my fuse than you could shake a stick at.
As for the superiority of the Till carb,,,,,,,,,,

Desert Pig
Are you talking about the carb snorkel? There is a ton of air blowing through the fuse, so thats not the problem. I have a 3w-75 with a rear carb, and it was very east to tune

Ok
I tried the balsa box thing and it did not work. Just mounted the 90 degree intake horn and will try it this weekend. If that does not work, I don't know what to do? What would be the correct Walbro replacement to fit the 3w-100?
Getting very FRUSTRATED

An SDC80 will work, but might not fix the problem...[8D]

wow i hope the horn does the trick

Desert pig,gas won't eat hondabond?I han'nt had much luck w/518!