My ST 2500 idles well, and has a strong top end, however, when I try to go around after making an approach, or touch & go, I punch the throttle and it quits.

Please help. - Jim

Great handle GEEBEE Jim: I was experiencing a similar problem with the ST 2300. After reconstruction of landing gear support in my Sukhoi, the tank position was altered, sitting lower than the previous setup. This caused a vacuum in the fuel feeding line. After readjusting the tank position, the engine no longer stalled during throttle ups. Hope this is helpful.

Usually, the engine quitting on rapid throttle-up can be traced to a too-rich midrange. On the S2500, this is caused by a too-rich idle mixture. You're likely idling the engine too slowly, and this affects the midrange. You'll need to lean the idle mixture a bit and bring the RPM at idle up a bit to compensate.

Please see the carb setting instructions that are on a sticky post at the top of this forum.

Thanks Bax; I flew my ST 2500 in my Spitfire again this mornin. Yes, it is capable of idling at a very low RPM, and I did learn this. If I advance the throttle slowly, it will be OK, and will not die. However, when I punch the throttle forward from idle, it dies immediately.
Does this tell you anything more ? Also, What Prop should I be using on a 15 lb airplane, and what kind of RPM can I expect with it ? I'm using Cool Power 10% nitro, with 3 oz. of castor added, bringing the oil to about 19%. Top end and idle seems to love this fuel. Overall, it's a great running engine on this fuel, just quits when punched ? I'd like to stay with this blend to remain compatable with my other engines.

> Jim

Hello Jim, I have a 2500 on a 22 pound 4star 120 and it is using a 18x9 prop that seems to be the max for this engine as it truly does not like to wind up but does pu;ll a larger prop. I have all of the big tigres up to the 6000 and I do like the 2500. I have switched to the OS 7d carb on some and on others the stock carb works fine. Why? I do not know and I suspect that no one does as I see so many differant ways that it is very confusing.. I disagree with Bax as my 2500 loves a rich idle and if I lean it then it does exactly what your's does Quits on advancing a throttle. I have mine where it smokes all the time on full throttle and it ticks over on idle and advances like a electric motor.
On my 3000's (I have 3) the suggestion is to use a cline or iron bay regulator with crank pressure as they love fuel withthe tigre carb. If you use muffler as a source the pressure is to low and flow of fuel is low. With crank pressure you get 12 PSI and the regulator drops it to 11/2 PSI and the flow is perfect, when you shut the engine off all flow stops so it is great for an inverted install. I understand that6 the chinese tigre carns are better but have not tried any so cannot state for sure but I have done all of the above and since I know what a low slow and dead engine can do to a plane, I insist on dead reliable engines and this is what makes my tigres reliable. I like the 2500 better than the 2300 or the 2000 but it is not as powerful as the 3250 which figures and the 3250 is my favorite.

We normally prop the engine for mid- to high-7,000's. Any prop that turns that RPM on the ground and flies the model well is the "correct" propeller. We normally run a 16 x 8 to an 18 x 6 prop. The 18-inch prop is just about the largest you can use. The fuel you're using is OK.

One thing you didn't mention was whether you increased the idle RPM and then reset the carb. The engine can idle as low as 1,800-2,000 RPM, but that's much too low for good overall throttle handling. We usually set idle RPM around 2,200-2,300 RPM.

Bax: Thanks for verifying that my 19% oil content fuel is OK. It runs smokey, but it runs good. It likes the 16 x 8 best, yow ! it's turning 8600 ! but it's smooth, smokey and reliable. I can now punch it without it sagging. The Fox Miracle plug helped too.

Thanks a bunch.

> Jim