I have a 3w 106cs with about ten gallons through it. I have the metal reed block holder update installed and am running it with 3w Canisters(this made little to no difference). I have an untuneable midrange burble. It doesn't seem to matter to what extreme I go too on the top and bottom end I can't seem to get it to smooth out. From about 1/4 throttle to 3/4 throttle it stumbles along and then once you get past 3/4 throttle the power comes on hard. Not too much fun when your flying 3d right on the deck. Running the bottom lean makes not difference to the midrange and same for the top end. I love the top end of this engine but if I can't get the mid to settle down I'm going to use it as a paper weight. I've been running two strokes for years of all kinds without any real issues until this engine. I have a rebuild kit for the carb that I'm going to install this weekend. Any suggestions would be appreciated.
cheers,
Richard...

Go back to those cannisters again and play with the header length. I think you'll find they did indeed make a difference.

Before you turn it inot a paper weight, consider I might like to have a paperweight of similar appearence I'll pay the postage.

Pat, if you don't take it I will If you can, try putting a set of bolt on mufflers to rule out the canisters. My 106 has the best mid-range of any gasser I have ever had, but I am running bolt on mufflers.

I wish I had a set of bolt on mufflers to try. We have major noise bylaws at our field so I can't really go that route. I don't have a lot of room to change my header length. which direction do you think is going to make the most difference? That almost makes sense though it's behaving like i'm running tuned pipes. reminds me of the dirt bike days. Not much power till it comes on the pipe?

How long are the pipes? Probably close to the 10-12" area for better middles.

Jon,

You already have my 106, you can't have this one BTW, I'm soon to be putting that Ultimate together and I'd like to converse with you about the way you had the electronics in it.

Is the metal reed block cast metal looking or all cnc machined. There were 2 versions and the cast metal one is the one that worked for me (I had both).

Well the only thing better than one 106 is two 106's That is too bad that you can't put some mufflers on it to try but I can see how that would be tough. I have the first cnc milled spacer on my and it runs very smooth so either one should work. I does sound like more of a canister issue though. You should have a very linear and powerful low end on that engine when it is set up well.
Pat,
You can call me anytime if you want to chat about the Ultimate. If you don't have my number, pm me and I will send it to you.

Roger that.

Hey guys .. I got a brand new in the box 3W 106iB2 AI series blue heads, with the bolt on SS mufflers and accessories. I'll sell mine for $995. Too lazy to take pics and post it in the marketplace I guess ....

refresh my memory again on where you measure from and too for the correct header length. If memory serves me right Mine is just under 12 inches from where the header bolts on to the engine to the joint. I'll have to re- measure and confirm that. The opening in the fuse where the pipe comes out is pretty tight. I think I could go shorter but would have to cut the headers and to go longer I would have to cut new holes in the fuse.

Middle of the drop to the end of the header. You'll likely end up shorter. Run down to the local truck tractor parts store and pick up a foot of high temp heater hose. Use that as a long slide coupling that can be used to adjust header length for longer or shorter. You'll need to cut some off the headers to go shorter. Pick up some screw type pipe clamps while you're there.

thanks for the suggestions. I'll go down and grab some of that this week and try it out. I sure hope it helps.

well it turns out that my header length is about eight inches measuring from the middle of the drop. If I go to 10 to 12 inches the outlets on my exhaust is right above my landing gear. Just to confirm again do you measure from half way around the bend to the end of the header or once you have the header coupled to the exhaust measure to where the canister opens up to its full diameter. I can't even run it to test it the way it is right now.

You should measure the full header pipe length to where it meets the beginning of the can where it starts to increase diameter. I made a boo boo and provided the wrong method earlier. A lot of planes have tunnels for cans. That didn't mean they had the tunnels and engine mounting locations that would permit effective use of them.

Just an FYI, the prop used will have quite an impact on pipe/can performance.

While you'e working with the above, check for leaks around the reed block and carb base. It possible there's an issue there that's contributing to the problem. The 106 is a very good engine when all is as it should be. I seriously doubt there's anything mechanical causing the problem. It can only be carb and pipe related.

the plane is an aeroworks extra 300 and the prop is a mejzlik 28x10. I rebuilt the carb today all the old seals looked good though. I'm going to have go and remeasure again hopefully it works out.

Is there any easy way to check for leaks or just look for residue. Everything looks nice and clean.

I went through this same thing last summer when I corrected mine. That's why I mentioned the 2 different reed blocks earlier. The first metal one did nothing for me (CNC'd). The cast one they produce now fixed it. Used Threebond 1211 to seal everything from the crankcase to the reed block and reed block to the carb mounting plate. Even the carb plate to the carb. My plate is still warped but I made my own gaskets and that sealant I mentioned is the hot ticket. I've worked as a mechanic for 25 years and that stuff has held up better to gasoline than any other product I have ever used. You probably do not have enough run time to see any leakage? You could slightly pressurize the engine w/the carb off and use soapy water. I run mine on a stand and use CRC throttle body cleaner. When it finds the air leak the running engine will dramatically slow down. I do this at idle and use extreme caution, I would not advise it though. Much easier on a single or rear mounted carb.

Did you buy this engine new? Mine was slightly used and the previous owner mentioned they could never get it tuned right to get the serious burble out of it, and to not lean it out anymore (even though the plugs were black and fouled). Gave me a good deal on it and when fixed it now runs great.

Good luck,
Jon

I have the cast reed block housing. I bought the engine new and just figured that it was going to get better as I broke it in. That was 11 gallons ago now. I'll try and find some of the Threebond 1211. Is that exactly what it's called? I noticed that there is quite a bit of blowback coming out of the carb as well.

Threebond is the company name. 1211 is the product name. Do a search on it to find a supplier near you.

My money is on an air (vacuum) leak. Get it fixed and you will be able to lean out the low end and it will accelerate properly. Are your plugs black and fouled?

Interesting thread. I have a 3W106 that runs perfectly .. but a 3W80XI single that has all the problems listed in this thread. I have been pursuing troubleshooting method around air leaks using the red locktite stuff that AI recommends .. and have also noted a lot of carb blowback .. that piqued my interest .. is that connected to the air leak or something else? I was thinking it was an indication of improper functioning of the reed valves...

Dave

A reed remaining open will contribute to blow back. Most all of our engines have some amount of blowback.

My reeds seem to be in good shape definantly not broken anyways. I guess you can never really tell until you change them.

As for the threebond 1211 it doesn't seem to be too readily available it Canada. I did some reading and I found that guys are using High Tak Gasket Sealant from the company Loctite. It`s made to be used with gaskets and it doesn`t go hard. I think I`ll give that a try and see if I can eliminate air leaks.

You could also pull all the carb and reed mounting parts and straight edge (metal architects scale) all the flange surfaces. Do the same on the engine. Look for any cracks or deformities around all the screw bosses. This has been an issue with 3w plastic reed blocks where screws have been tightened without uniformity. The plastic reed blocks also manage to continue compressing at the screw bosses over time, typically with one or more ending up set tighter than another, creating later leaks.

well I've rebuilt my carb now with no change. I checked all the surfaces for deformaties everything looks nice and straight. I used hi tack sealant on all the joints between the engine and the carb and it's running exactly the same. I'm still waiting on an exact header length before I cut mine shorter. I noticed on 3W's site that they measure from the beginning of the header where it bolts to the engine to the end of the header at the coupler. They don't have specs for the 106 anymore but for the 110 the length is 6.69 - 8.26 inches. I'm sure that it's probably similar I'm just waiting to find out.

Header lengths are also dependant on prop loads. Different props require different header lengths. You will have to wait for someone flying the same engine/plane/prop combo to have the header length delivered to you unless ou do the math. Even then it's only close.

In the meantime borrow some mufflers to see if the problem goes away. It will require driving to another flying field or course but at least you have an answer.