I decided to ask this here, as I'm fairly sure this is engine related now. I have an RS4 evo 3. It ran fine when I got it, then I crashed it, which messed up the throttle lever arm, unbeknowsnt to me. I never could get the engine setting right in it, because I didn't realize the carb arm was loose and constantly moving. So, I thought I messed up the engine. I got a new HPI 18 SS engine for it. I never could get that engine to run right unless I put the carb from the stock T-15 on it(I bought a replacement for it after I bought the new motor.) Even then, the only way I could get it to run right is to remove the pressure return line from it. If I left it hooked up, it would run too rich, and I'd have to turn the mixture screw almost all the way in to get it to rev, then it was tricky to start. I eventually left the line off all the time because no matter what I did, the only way the engine would run right was if I left the return line off. I replaced everything remotely related. Fuel tank, both fuel lines, carbs. I checked for vacum leaks, none. I messed with the throttle linkages, and trims on the radio. I have even replaced the muffler with a stock for the RS4 Evo muffler because I broke the tip at one point. LIke I said, I eventually just left the line off. Last week, I decided to order a new engine for the car. I think I messed up the threads in the head, losing compression, because even with the line off, the car wasn't as fast.

Today I replaced the engine with the new one, an O.S. 18 CVRX. I got it all bolted in, tried to start it, and just about killed myself doing so. That sucker wouldn't start with the pull start. I then swapped the rotostart back plate from the old engine to make it easier. I finally got it started, but the thing would not keep running unless I turned the mixture screw in, which I did not want to do since it's a new motor. I had the return line hooked up at this time, thinking I would be able to have everything working correctly. When I couldn't get it to stay running unless I cranked the mixture screw in, I said screw it, and removed the line. VIOLA!!!!!! The idle shot way up. I had to turn the mixture screw out to where the manufacturer specs say to set it.

It must be because the larger engines need a larger muffler, because they are too restrictive for the larger motors. I've never seen anyone talk about this, and anyone I've asked was dumbfounded. Does anyone know?!?!?!?!?! I'm now going to buy a new muffler from O.S. in the hopes this will fix the problem.


Anyone??!?!?!