Billl,
I've finally surrendered!
I bought a 50SB about 2 years ago and just installed it in an airplane at the end of last year.
It has always been a bear to start. I've cranked on that damn thing until my right arm looks like Arnold's.
Flipping it 200-300 times while alternately choking it was not uncommon. Nothing helped. Squirting raw gas into the carb doesn't seem to have any effect. All of a sudden it would fire up and run...maybe on the 20th flip...maybe on the 300th...maybe more.
At first, when it did start, it ran pretty good...but then things started going south. I'd adjust the mixture settings on the ground so it ran fine, but after about 2 minutes of flying it would start sagging in the air. I've alternated between Zinger 20 X 8 and 20 X 10 props, but that's not the issue.
I'd re-adjust, and it would do the same thing.
I took the Walbro HDA carb apart and found some resin-like material in it. I thought this was a Eureka moment and my problems were over. The engine ran much better...for awhile.
It was still very hard to start and my body was looking unbalanced...huge biceps and forearm on my right arm.
Soon the engine returned to its old ways...sagging after the initial tune up.
Starting was still unbelievably hard. It was so bad, the boys on the flight line would cheer whenever the engine would "pop". If it actually started, there was wild celebration. Remarks such as "boat anchor" , "dud", and "POS" were not uncommon.
But, I'm a determined guy and was determined to fix the problem. After all, so many guys on RCU claim it's easy to start...2-3 flips at the most!
I changed all of the fuel lines, rebuilt the tank, checked the Bakelite extension for cracks, cleaned and re-gapped the plug, tore down the Walbro carb again.
It continued to start hard and now I could barely keep it tuned.
Pretty soon it wouldn't even run...only short bursts after choking it for 20 flips or so.
I ordered a rebuild kit and read everything on the internet about the HDA series carb. I meticulously rebuilt the carb and checked every orifice. Lo and Hi speed set at 3/4 and 1 3/8 respectively.
Nothing! Still only short bursts.
I've tried everything. Even the lengthy list of profanity I learned in the military didn't help.
I flipped it for the last time on Sunday. I'm done messing with it.

Now you guys are going to get it back...please give me an address and name to send it to.
If it comes back with a note, "no problem, starts fine, runs good" I'm going to join a monastery and quit flying.

Bob Wilson

We'll be glad to check your engine to see what the difficulty may be. Here's how to send it to us:

http://www.rcuniverse.com/forum/m_1154083/tm.htm