I am having the same problem with two G26's.

Engine #1 was mounted in a H9 Taylorcraft. I was going to fly this airplane last Sunday. I checked the RPM and it was turning 7200 with a 18/6 zinger. Using my fish scale I was getting 10.1 pounds of thrust. Throttle response was good. I started my takeoff roll and the airplane lifted and at the same time the engine started to slow down. I was too slow in taking action and lowering the nose and it stalled on me. That part was my fault. No damage to the engine or wings. Fuse will need major repair.

Engine #2 mounted in a Ultra Stk 120. Checked the RPM and it was turning 8000 on a 16/8 prop. My fish scale was showing 10.4 pounds of thrust. It looked and sounded good so I put it the air. Same thing, the engine started to sag and slow down. This time I got the nose down came back around to land. The 120 was very slow but no problem with the landing.

I am at a loss on these two engines. I have checked everything I can think off. The choke butterfly sticks out in air and I wonder if this could change the airflow going in the carb. No sign of overheating on either engine. I have two G23,s and I have never had any problem with them.

Thanks in advance for any help.
Tom

Could be a vent problem, when you start to get airflow over it, it may be creating a vacuum in the tank instead of pressure.

It is possible, though a lot less likely, that your engines are too lean and are leaning out in the air.

Air flowing over the intake of the carb causes the mixture to change. Get a velocity stack from Horizon, Great Planes, or Carr precision. 1st try it towards the wind but you may have to turn it slightly for best results.

It does sound like your going lean for some reason?

Good luck

Jim

Check out the BME website and click on the manual section. It discusses exactly what w8ye said.

http://www.bmeengine.com/

Radar:

Did you try to fly with the velocity stack that came with the engine??..Seems to me as if the engine was too lean for your first flights..what are trying to do to resolve the problem....Just mounted one ( G-26) in my Gee Bee Y..thanx

Radar,your problem is the new intake block the carb is mounted on.It gives you a direct shot at the carb but it turns the carb so that the diaphram is compressed as you gain airspeed and it leans the engine and dies.There is a hole in the plate over the diaphram which lets the air in and causes the problem you are having.I sold a Giant stinger to a friend of mind and he installed the new block on his and had the same problem.You can put a deflector on by just using a lite peice of metal that has a 45 degree bend and drill two holes in it to match the screws in the plate on the carb or go back to the old intake block and change the throttle location which would be more work.There are also problems with the inserts in the new block,they have a tendency to turn inside of the block.If you install the plate it will solve your problem.

Atmospheric pressure pushing on the diaphragm opens the inlet needle, allowing fuel to enter the carb. Pressure higher than atmospheric makes the engine run RICH..the plate keeps air from pushing on the diaphragm...

Thanks for your input on the problem with my engines. I am going to try each of your suggestions.

I will let you know how things turn out.

Thanks
Tom

Rcign1,what I thought happened was it leaned out because it would do just as the 26's above are doing.It seems to me that if it keeps the diaphram compressed so that it cannot pump, would it not cause it to lean out.I know once I suggested to him to put the deflector on the problem went away and it had to be leaned out.Good luck and happy flying.

There are two diaphragms, one opens the inlet needle and the other, on the back side, is the pump..As long as the engine is running there is always fuel in the chamber under the inlet needle diaphragm..Excess pressure, more than atmospheric, makes it act funny..Most engines don't have the hole facing forward so the problem isn't there...Putting a shield over the hole in the cover is a good idea, another way to do it is to solder a tube in the hole and run a line into the firewall to dead air in the fuselage, as many do with 3W engines..ALL the ideas are good and worth a try...
The big carbs on the G26 act a little funny, when too rich they make the engine die fast, just like being lean...Sometimes going back to the beginning and re tuning both needles will fix the problem..I first saw this with the first G26, and the others I sold worked the same...

Today I was able to go to the flying field and fly my Ultra Stk with one of my G26's. The first thing I did to the engine was block off the vent hole from air pressure using 600 MPH tape. This is good stuff. The next thing I installed a velocity stack. Also tweaked the needles a little.

I will have to say this made a huge difference in the performance of this engine. It took off and I think it would have gone vertical. The Stk was very fast and had outstanding vertical. I was able to hover for about ten seconds. I believe it would hover very well with someone on the sticks that knew how.

I am very happy with this engine now. I would like to thank each of you for your ideas on how to solve my problem.

Tom

Radar:

Glad to see you problem was resloved...now where do you get the 600mph tape???....Brand name?

Don't completey seal the hole, the carb needs atmospheric pressure to work..Just keep air from being forced into the hole....

Jimmy: A friend of mine with a major airline gave me the 600 MPH speed tape. I don't know if it can be bought on the open market. It has been around for many years.

RCIGN1: The speed tape is a little stiff, so I made something like a tent over the vent hole. It worked great and the air pressure did not seem to bother it. The G26 sure does a great job with the Ultra Stk 120.

Thanks
Tom

I don't remember the speed rating- but I used to use a 5 mil aluminum tape that had around 60 ounce/inches of adhesion and a temp range from freezing to 325 degrees.

Does that sound like your tape? If it does you can buy it at aircraft parts supply houses. taped many a cessna fairing back on with it.

If you're getting 10 lbs thrust you're shortchanging yourself..A G26 with an 18-6 Mejzlik will pull at least 17 lbs on a spring scale..Been there, converted many, they all work the same, 8200 rpm with the stock muffler and a Mejzlik 18-6.....Try it, you'll like the extra 6 or so lbs extra thrust....

All,

I ran the G26 RC Ingnition converted for me for the first time in the air yesterday. WOW! On the ground, just before the maiden flight, it was turning 8550 with an APC 17x8 prop. Sweet little engine! I'll have to try the Mejzlik 18x6 next.