I agree that the GMS is a great engine and is well priced. It starts better than any engine I gave ever owned and certainly delivers power, I dont think thats an issue. What we are trying to do is address the running consistancy which seems overly sensitive to the aircraft orientation (compared to other motors) and results in lean running and unexpected engine cuts.

Some manufacturing quality issues have been found, such as leaking carb interface, needle seals and now the fuel inlet hole lineup. From f/b, it appears GMS are addressing at least the hole lineup. Hopefully the other issues will be addressed too as I believe they do contribute to the overal running consistancy to a greater or lesser extent based on other factors such as tank placement , % nitro etc.

With the mods I have done to date, the biggest improvement was made by moving the tank closer to the carb. That is not to say the other mods did not make an improvement and im glad I did them. The one thing I have not tried, and I belive will make a significant improvement is increasing the muffler backpressure. It appears that before moving the tank previously, the pressure was insufficient to raise the fuel the 8 inches or so required without excessive decrease in flow. Ive eliminated fuel restictions with the mods, so it follows that the insufficient pressure must be the culprit. I am talking about leaning out at full throttle between the horizontal and vertical atiitudes here, so I dont *think* part throttle carburation is the issue here.

Others may have other issues, I can only comment on my findings here, hope it helps!

I am now happy with the running with the mods so am ready to flight test. My next step would be to insert a baffle or different silencer to increase the muffle pressure. (im using the dull finned one). But maybe not required now. It would have allowed the tank to be placed more rearward, at the loss of a few hundred rpm.

Wayne, I drilled the exhast to 2mm right at the beggining (see my detailed post) and it made no difference. I dont think air has a problem flowing through a 1.5mm hole, fuel however does seem to!

Captn, I use a perry pump in my 1.60Fx equipped 1/4 scale lazer, I cant seem to justify (in my head at least!) spending on one for a GMS in a spad type plane!!

Will hopefull get some test flying in this w/e, good luck to you all!
R.
Mark