SAVAGEJIM
Posts: 6309
Joined: 7/6/2005
From: Torchy the Fiery Fast RC Turtl, USA
Status: offline
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Your right. Even when over revving, the engine did not detonate.
When I broke the engine in, I used the cheap-o HPI polished exhauset and HPI header. I ran the the engine in on the HPI exhaust for about half a gallon. I then transplanted my THS in-line exhaust for big block engines onto my D28M. During this time, I never had any problems with any sort of over revving. The engine presented no problems whatsoever and I probably heat cycled the D28M for at least 10 cycles. Once broken in, the engine ran great and held a tune for excellent performance.
It idled perfectly and I never had any problems during start up and warm up with the HPI or THS exhaust systems. I changed the HPI exhaust system for the THS in-line and my D28M picked up in performance a little, I think because this pipe is designed to provide its resonance at higher RPMs. The engine kept its tune easily (of course, after re-tuning for the THS system) and never once had any problems with over revving.
I know I've run at least one gallon of Rocket Science through the D28M equipped with the THS exhaust, so I am thinking it might be my 3rd gallon that I resorted to Blue Thunder when my store sold out of RS. Even on Blue Thunder, all I had to do was retune a little (Blue Thunder is very high in oil content) but my D28M still performed like a champ.
I cannot remember how far I got into that gallon of Blue Thunder, maybe a quart or a third. That is when I noticed the plug glow element looking unusual and blueish, but not really showing signs of richness or lean mixtures, but it looked like it was beginning to foul. I decied to be proactive and chunck that plug and get some fresh plugs, McCoy long plugs, one of each temp range rating.
Upon installing a McCoy hot, my D28M started up immediately, but warmed up too quickly, and then began to over rev. I richened to compensate, but the over revving failed to correct. Then I switched to the McCoy medium, and the engine started up immediately again, but again warmed up too quickly and began to over rev at idle. Then I resorted to the McCoy cold and the same issue.
To try to compensate further, I turned the idle screw to the point that the carb was open very very little, probably 0.01mm (yes, one one hundreth of a milimeter) and the engine would barely even run since it was air starved at idle. I would have to pull the trigger ever so slightly to open the carb more to get the engine to stay running while I tuned some more, and tuning in this manner was an absolute pain.
I dismounted the engine, and particularly the carb, tore it down, installed fresh o-rings, and resealed everything. The carb components are prestine, even to this day, so no malfunctions can be credited to the carb.
After doing about $50 more of work on my Savage and D28M(brand new fuel lines, brand new tank, brand new air filter system, etc.), I searched all the articles concerning STS engines I downloaded and I found some old posts in which others before me mentioned about using short plugs on the D28M. I therefore went back to the store and bought some more OS shorts, reinstalled them, and the overrevving disappeard.
During the overreving ordeal, I too thought it was a tuning issue, but no engine (NovaRossi or whatever), no matter how tune picky it is, would behave in this manner. I just about tried every tuning practice save for adding more shims under the head. I never took off any shims, but I considered buying more shims to help reduce compression ratio in hopes to retard and therfore slow the over revving.
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RE: STS 28 a Deep Look (56k murder) - 
