Unfortunately, many bear the misconception that SH engines run very hot and thus wear out faster. The truth is that these are incredibly powerful and reliable engines. In fact, they are currently the largest exporters of RC on road, off road and competition engines in Asia, displacing the previously popular Toki and Team Infinity branded engines. However, to the inexperienced hobbyist, they may experience overheating problems with their SH engine. This is because the factory needle settings may be incorrect. Apparently, the default needle settings for the SH .21 and .28 engines are 4.75 turns out for HSN and 3 turns out for LSN – both from a fully closed position. My SH engine arrived with a very lean LSN setting. Consequently, I experienced problems starting the engine, as well as difficulty getting the engine to idle. If I did not adjust the trim or hold the throttle, the engine would shut off. I did a check on the exhaust and found that the fumes were grey or transparent and did not splutter unburnt fuel. The engine also hit temps of over 270 f. I proceeded to richen LSN in gradual increments and I hit the right tune after richening about .45 turn. I just finished my 5th tank and temperature does not exceed 225 f, like any other big brand engine described in RC car engine break in instructions found online. If you own a SH engine that is running hot, do try the tips I described in this post. If you have a question or feedback on SH engines, do leave me a comment on this post. Cheers!
Brushless & Nitro RC Cars Trucks | HPI | Traxxas 
Thinking about putting the sh .21 in my 1/8 truggy. Do you think its powerful enough for this application? Thanx
if you’re talking about the cheap SH 21 3 port pullstart engine, it would be underpowered. even if you really lean out the engine to get a top temperature of 130 degrees celsius, which should give peak power, it’s still underpowered. those are rated only at 2.1 hp. whereas, some of their non pullstart comp engines like the pt 2009 or pt 2010 produce 2.5-2.8hp. that’s sufficient.
Hi not sure if your still keeping track of this post as its over a year old
I have the motor in my redcat aftershock 3.5 and what you described is whats going on with my truck
I took it to a local hobby shop and they told me it was a bad motor as they turned out the HSN 4 1/2 and the LSN 3
are you saying if I richen it up even more it should take care of the problem
as the truck runs great for 1/2 a tank then it heats up and will not start or run till it cools down and repeats the above all over
If I sound inexperienced please forgive me as I am just that
Thank you and I look forward to some input from you
Paul
i realised the problem is air leak. I’ve trashed all my BSD and Redcat cars. after i’ve done some serious driving and racing with “proper” cars like the kyoshos and hot bodies, the redcat/bsd durability doesn’t hold up.
your engine is fine. look at this video on how to detect air leaks: http://www.youtube.com/watch?v=tZ3WcPoa1DY
and look at this video on how to seal it: http://www.youtube.com/watch?v=rncdYL-PBL4