Hi Bill,
hope you can offer some advice on a problem I'm having with my S-2500. Now this engine is fitted with an OS 7D carby so will understand if you don't want to offer advice on it but hope you might know what my problem is.

1. The engine is having a lot of trouble starting, unusual for the big ST engines. Once it is running it idles nicely

2, It will not transition past about 1/2 throttle. When you do advance the throttle it is like somebody just cut the fuel right off on it and it dies. If you bring the throttle right back it then will pick up and run at the lower throttle setting.

I have replaced the needle valve and O-ring, o-ring on base of carb, flushed the carby out, replaced all fuel lines and pressure tested for leaks. All ok.

We did adjust the idle mix on the carb to where I could run it at full throttle but it was not very reliable at all and if the throttle was slammed forward it would die.

Next issue: Parts. I'm having trouble getting a piston and liner for this engine, Tower do not have them. any thoughts where i can get them?

SUPG4170 22042115 CYL SLEEVE S2500


SUPG5275 22202201 PISTON S2500

Anyway hope you can shed some light on this for me.
thanks in advance.

cheers
Peter

If the engine will run nicely once it's started, then the problem with starting usually isn't due to an internal problem, though it may be a bit low on compression that gets better once the engine's had a chance to warm up.

To properly-set the carburetor...any carburetor, we start with a too-rich idle mixture, richen the high-speed needle, and start the engine at part throttle. We then get the full-throttle mixture properly-set. Only then do we retard the throttle and work on the idle mixture.

What fuel are you using? If the engine's starting to wear out, going to a higher-oil content fuel may help.

As far as parts are concerned, we'd not know where you might be able to locate any. The engine's been out of production since 1998, and parts for it are generally not available. You may be able to locate parts through an internet RC swap-shop site, or auction site. Perhaps checking the model magazines for ads from hobby retailers who collect parts for engine collectors may help.

thanks Bill,

pretty much what I'm trying to do. I use a 12% coolpower mix, no nitro. Normally this type of engine is a 10% mix.

Have located all the parts for a rebuild now except for the piston. The piston looks quite ok in fact, no scoring just carbon build up around it's centre.

thanks
cheers
Peter

If the piston's clean of scoring, it should be OK, if the ring groove's not been worn to oversize. Just use fine steel wool to scrub the carbon off of the top of the piston. We use a grade known as "0000" (also called "four-ought" here). Hot water with regular dish detergent is all you need. Rinse with water as hot as you can stand with your bare hands, shake off, and let air dry. Oil it to reassemble into the engine.

Hi Bill,
thanks mate, the piston has the carbon on top as well as around the middle. I did manage to track down a new piston in the UK and have all the other parts coming from the US.

thanks for your help.

cheers
Peter