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Old 04-01-2019, 10:43 AM
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Hello guys, i have HPI Trophy Truggy 4.6 which i haven't been using for 6 years or so. Eventually i wanted to run it once again so i disassembled the engine. Cleaned all the parts, piston, sleeve, crankshaft, bearings, carburetor... But the problem here is when i was trying to take the sleeve out, i scratched it a lil bit. My friend's father who is auto-repairer fixed it by grinding it gently. Then we oiled the parts and assembled back. I tried to start the engine with my 6 years old fuel. Which i succeeded it on rich carb settings. The problem here is i can't get a performance. Engine's performance is like %50 or sth. I tried to tune and at some point the performance was like %80-85 which is not too bad for me but it didn't last long. (like %50-60 of the fuel tank) And every tank, at the end of the tank car reaches almost the %90-100 performance. But only at the end of the tank. I bought a new fuel and it is %25, i was using %20 before.

So what might be the problem, first i thought i damaged the engine but i saw a satisfying performance for a bit even with the 6 years old fuel. And as i said car reaches almost the top speed at the and of the tank while the engine is about to die.
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Old 04-03-2019, 11:30 AM
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Its probly a tuning problem look up factory settings and start from there. always wait till the engine is completely warm before tuning.
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Old 04-03-2019, 01:02 PM
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Thanks will try my best and does tuning make that much difference at performance?
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Old 04-04-2019, 01:40 PM
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Tuning makes all the difference in performance. With that said your 6yr old fuel is most likely shot.
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Old 04-04-2019, 01:50 PM
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Did you scratch the inside or outside of the sleeve? Taking a grinder to the inside of the sleeve would probably do more harm than good. If on the outside of the sleeve lightly knock any but off with emery cloth and most likely no harm done.
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Old 04-04-2019, 03:27 PM
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I actually scratched the inside. While i was trying to take the sleeve out, i put screwdriver in to the hole (intake hole on the sleeve) and then i pushed it with piston but i should have used plastic material instead of a screwdriver so it damaged a bit.(btw sleeve was stucked due to 6yo dried oil) The scratch was hard to feel by hand but the piston couldn't move easily.
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Old 04-04-2019, 03:43 PM
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When removing a sleeve put a zip tie in the exhuast port and rotate the flywheel so the piston hits the zip tie and in turn pushes the sleeve up..

The piston is not suppose to go in and out of the sleeve freely.. Nitro engines require a pinch. The pinch is what gives the engine compression. If the piston goes full stroke freely in the sleeve of a nitro engine the engine is done. When it loses its pinch you either have to re pinch the sleeve, replace piston and sleeve or replace the entire engine..
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Old 04-04-2019, 03:55 PM
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As i mentioned before i am not curtain if the engine is done or not. At some point the performance was satisfying for a limited short time. And at the end of the tank, like at the last drops of the fuel, performance raises. I am not sure, i will try to tune bit more and then if i can't manage to fix it i am gonna take it to the expert and if the engine is done i'm gonna consider to replace it. HPI Trophy is the best Truggy for me and i don't want to waste this car.
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Old 04-04-2019, 03:57 PM
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Can carb cause this kind of a problem?
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Old 04-04-2019, 04:34 PM
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I realize that, I was just explaining pinch..

The reason your engine performance improved at the end of the tank is because it was extra lean. To a point a engine that's to lean will improve performance, however it gets to hot and that shortens the engine life..

Nitro fuel has a short lifespan, less than gas' especially if the bottle has been open.. Even if you squeeze as much air out as you can before putting the lid back on (which you should do) the nitro will absorb the moisture in the air.. If it was me I would get some fresh fuel and try that first and foremost.. There is like a billion tuning videos on YouTube.. Look for ones by the likes of Adam Drake, JQ, or any other pro racer that actually know what they are doing and are not just someone that has a nitro engine, camera and a YouTube channel that probably knows less than you..
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Old 04-04-2019, 05:40 PM
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Originally Posted by Frenzi3d View Post
As i mentioned before i am not curtain if the engine is done or not. At some point the performance was satisfying for a limited short time. And at the end of the tank, like at the last drops of the fuel, performance raises. I am not sure, i will try to tune bit more and then if i can't manage to fix it i am gonna take it to the expert and if the engine is done i'm gonna consider to replace it. HPI Trophy is the best Truggy for me and i don't want to waste this car.
All is not lost. Run whar YOU like, thats the most important part... I learned a lot of things the hard way, and you really never stop learning..

The fact that you had your engine running is a good sign. Your tune is probably realitivly close or it most likely wouldn't start.. I'm really thinking your biggest problem is old fuel.. Think of it as having 6 yr old gas blended with ethanol sitting in your garage and you decide to mow.. Mowers don't like ethanol blended fuel in the first place, however ethanol really soaks up moisture. The mower probably won't start, if by some chance it does it will run like crap.

Even with squezzing as much air out of the bottle as possible before putting the lid on I still toss out any open bottle of nitro when I put car up for the winter.. The less nitro in the bottle is just more air for the fuel to absorb the moisture..

Once while pulling a sleeve I had one that was really tight. Putting a zip tie in the exhuast port and rotating the flywheel didnt work. I got it out by heating the sides of the engine block as I tried the zip tie technique. Doing it that way the aluminum will heat up and expand faster than the sleeve.
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Old 04-05-2019, 08:50 AM
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As i said before i bought a new fuel and tried with that too. But i tried just the half of the tank i couldn't observe any difference yet. But as i said just the half of the fuel tank. I am kinda busy these days, i will try to tune it with new fuel as soon as i have time.
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