What would be the correct Walbro carb for a 3W-100? I'm not making friends with the Tolitson carb.

I have 5 years experience with the Tillotson carb on a 3W 100 (and there are hundreds more of us here on RCU). I don't know the answer to your question about the Walbro equivalent, but if you describe your issues with the Tillotson, we may be able to help.

What he said...Or buy an SDC80 for about $75, it works well on ALL 80 to 100cc engines...

Well, I'm not totally sure it is a carb problem. The motor is just not dependable. It runs great, has plenty of power, but it just dies once in awhile in flight for what seems like random reasons. The last time in a hover at 30 ft. and killed my airplane. Some days it runs, some days it doesn't.
I have the snorkel on it, as well as baffeling. One guy told me it could be the carb is getting too hot because the muffler is about a 1/4 inch from it. Any suggestions????

3W ignitions are notorious for quiting when they get a little warm, make sure there is adequate space below the ignition and good ventilation around it.

The Tillotson on the 3W engines really likes to be adjusted. Both between and DURING flights if you want to maintain a proper mixture and/or power level. Go with what RCIGN suggested. The company I work for uses hundreds of 3w engines, and ALL are reliably equipped with Walbro carbs for a reason.

Eraser - I fought with my 3W 100 for most of the past 6 months. I fly almost weekly and some days I'd have good experience, and some days i'd get random quitting of the engine. I chased the needle valves all over the place. Most experts say that when the engine quits during transition from idle to full, the idle NV is set too lean. Or that when it quits at full throttle it may be too lean, etc. All of this is probably true, but I found another cause. My ignition had intermittent failure. Finally, it got to the point that it would only run on one cylinder. This was obvious as the engine had no power and one cylinder was cold even after running a few minutes. I swapped the spark plug leads and moved the problem from one cylinder to the other. So definietly it is the ignition. So I buy another ignition and all of my problems are solved. The engine runs as good as new. I'm pretty sure the ignition was causing most of my problems over the past 6 months. Thankfully it finally quit in a way that forced me to buy another one. I have a dozen or more flights since replacing the ignition and it has never quit since. If you can afford to buy another ignition, I'd try this before buying another carb. Or if you can borrow someones ignition, try that approach.

By the way, I've had 4 ignitions in 5 years. the first two quit in a way that was easily diagnosed -- a hard failure. The third one is the one that messed me up for 6 months. The fourth one has been running for a few weeks now with no problem. The first 2 ignitions were from 3w. the next two I got from DA. (the DA and 3W ignitions are interchangeable). I understand that C&H has an ignition for the 3W now also.

So the muffler being so close to the carb is not an issue???

eraser, I have never had any reason to believe that this was an issue. I use the johnson mufflers and they are very close to the carb. One thing I have improved over the years is the baffling to force the incoming air through the fins. This is very low-cost and can't hurt anything. For the first couple of years I did not use any baffling. I have seen others do the same. But it gets hot here in st louis and I think the baffling helps out a little.

Another thing to check: every year or two I have to remove the cans from the engine and "de-carbon" the insides of the combustion chamber. This is a relatively easy repair and can make a world of difference in all around running if you have a lot of hours on the engine. Once the rings had so much carbon on them that they were effectively stuck in the grooves. Each cylinder comes off with just four bolts. You can leave the engine on the plane (remove the cowl), and pull the cans off. Clean the inside real good (I use a paint remover) and if the rings are stuck on the pistons, remove them and clean them. The cans slip back over the pistons and rings quite easily. You just compress the rings with your fingers as you guide the cans back on to the piston. The bottom of the cans are bevelled to help slip these back on. I put in new spark plugs at this time also.

I'm not sure why this carbon develops, but some will say too rich running, too much oil or too hot running. perhaps it is normal to some degree for a 2C engine.

I never had to adjust my 100 after it got broke in. The general consensus is that the Tillotson's are better carbs, just a PITA to get right. Look for an ignition issue. Muffler close to the carb is not a problem. I de-carboned my 100 by "cooking" the cylinders and pistons in straight Prestone anti-freeze in a crock pot for 24 hours, works great!!!!

Tom

The engine only has about 12 hours on it, so I dont think carbon is an issue. It was baffled, so ignition huh????
I'm kind of afraid to put it in a new plane after my last experience.

Suit yourself, but I've witnessed some rather extreme improvements in performance and reliability by changing carbs and ignitions. Everything I've experienced has been fully substantiated using some very high end real time telemetry.

Guys:

You have me a little spooked about the 3W engines. Will be buying a 50-75 in the next month or so for 3-d. Looking at 3W 75 hard as they offer a number of engines from 50 to 100 and I am prone to go with good old German quality. There is not much weight difference brom the 50 to the 75. Lately, I have to add lead to the nose of the latest generation of birds to get proper CG, so whats the big deal of a DA-BME-3W weight issue ? I am looking for the best reliable quality in a engine so you don't have to send the thing back. My ZDZ 40 has been running for 3 years without a burp. Almost cry when I see a great bird die from a burp close to the ground. Is this a Ford-Chevy thing, or is there a clear winner out there?

You really can't go wrong with any of the top manufacturers.
I have found that a lot of the new ARF's are being built to accommodate these lighter engines, and lighter flies better.

Rmenke
This 100 is the only motor I have had problems with. I own a 3w-75 that has performed flawless for over a year now, and it just keeps getting stronger. This is the rear carb version, with the new style ignition. I'm turning 26x8s.

Silversurfer
So a sdc-80, and what kind of ignition should I get????????

I will answer for Silversurfer since it might be awhile until he does. "CH"

Thanks, Ralph. That's precisely what I would have said. I was able to access the internet this morning and got lucky and was also able to access RCU.

BTW, we map our fuel mass down to a tenth of a kilogram using the Walbro carbs. Can't do that with the Tillotson's due to erratic fuel and air flows.

My last post was in error. I used the wrong decimal point. We map to 1/100th of a kg, not 1/10. And only if we're using a Walbro.

I have used the tillison and the Walbro carbs for the past 9 years on my 3w engines. I find no difference in adjusting the engine for perfect performance. I find though that the tillison is a much better carb and actually will provide faster and smoother throttle responce. There is no problem with the heat coming off your mufflers going into your carb. There are thousands of 3w 100-106 engines out there running the same way yours is with no problems. I'm pointing fingers but usually when there is a problem its user error. You may have a case of a bad ignition so I would take the advice of the other guys here and see about getting a new one. Call up Bobby at Cactus Aviation and talk with him. You might still be under warrenty and end up getting a new one at no cost. But switching to a Walbro carb will not solve any problems.
Garrett Morrison

Thanks Garrett
Yeah, ignition sounds like the probable cause, and you are right the 3w-100 seems to have better throttle response than my DA-100 (I might be dreaming, but it might be more powerful too).
Someone said that the DA ignition is a direct, bolt on replacement. I could try the ignition off of my DA and see if it solves my problem????

The DA ignition and the 3W ignition that I have (several years old) are interchangeable. They use the same pick-up technology (coil, not hall-effect sensor). So you can swap the ignition module, but leave the pickup sensor in place. You may have to solder on a different connector between the sensor and the module, I can't remember for sure.

12,000 flight hours on this one and we obviously haven't learned a thing. Then again, we fly more than 15 minutes at a time.

It's been awhile, but as I recall we had to re-time the engines for the DA ignition when we tossed the 3W unit on another platform.