• Welcome to RCTalk! 🚀

    Join the #1 RC community where hobbyists connect, share, and get expert advice on RC cars, trucks, boats, drones, and more!

    • ✓ Friendly & passionate RC enthusiasts
    • ✓ RC tips & troubleshooting
    • ✓ Buy, sell & trade RC gear
    • ✓ Share builds & upgrades

Loosing power.. Why?

This site may earn a commission from merchant affiliate
links, including eBay, Amazon, and others.
R

rrrunner

RCTalk Rookie
Messages
17
Reaction score
0
Points
0
RC Driving Style
i've been using os tr pt engine since the past 10 mths. the moment i start the engine until the temp is about 100-120c, it begins to lose compression(when i pull full throttle, it doesn't accelerate as fast as it was. somehow, the top speed is superb. Do you guys think my engine has worn out? Or is it just a tuning problem? i couldn't get it richer cause it will drastically loose power.. Opinion guys...
 
I would agree with Rolex. I had issues like that and all I did was just lean out the LSN and from then on it took off at the snap of the throttle. It works great on short track turns and short straights where you want that quick acceleration in short distances.
 
I always make sure to rtv the top of the carb and the backplate to seal any air leaks. Gotta let it dry for 24 hours to make sure it cures right. Check that head to make sure that the head screws are snug but don't overtighten. Is your plug in straight? All these things can cause havoc on tuning and starting.

Good luck

Jon
 
One thing nobody asked is how much fuel do you have through this engein? It might be tome for a rebuild.
 
vbgagnon said:
One thing nobody asked is how much fuel do you have through this engein? It might be tome for a rebuild.
Click to expand...

Not likely, since he says it is superb at WOT. This sounds like a simple adjustment on the LSN.
 
With engines I've had, they will run well at WOT, but not idle worth a crap when I loose quite a bit of pinch. It progressivly gets worse as it warms up as well.

Just my .02.
 
You have a point, Olds. Less time to lose compression at high RPMs. It's just that I haven't kept an engine long enough to need a pinch or a rebuild.
 
thanks for the reply guys.. just to make sure, LSN is the screw in front of the engine which is connected to the throttle right? i'm new in this hobby and i have a bad experience on tuning the engine. When i first bought it, it was tuned by the lhs guy, it was good but after i tried to tune it myself (misdiagnose, i didn't realise the carb screw has loosen up) i can't get it right since then.. i'm trying to learn and do this myself. Also thanks for the reminder jon2, i'll make sure there's no leak..
 
Yes, normally (depending on engine maker and carb design), you have 2 "needles" and one set screw. The set screw with the spring you can see on it is normally for setting your idle. It's normally a small screw that is screwed into the side of the carb body itself. The high speed needle (HSN) is normally sticking up where the fuel line connects to the carb and the low speed needle (LSN) is either in the center of the shaft the throttle arm is connected on or (OS 21 RG) it's on the opposing side of the throttle arm.

Also, on most engines I've come accross, the basic settings are:
HSN - 4 turns out from screwing it in all the way
LSN - Flush with where it screws in
IDLE - while looking down the throat of the carb, you set it so you can see a 1-2mm gap.

Good luck.
 
id say a combination of tuning needs to addressed i would start to turn your lsn in in 1/16-1/8 increments,then when you get it to clear up a bit then do it to the hsn moniter your temp then go from the if it gets to hot the richen her up a bit ,but make sure you only make one change at a time and take your time..
 
Here are the basics that should make any healthy engine run right.

Put the nose of the truck against something firm so it can't get away from you. If you have an EZ start, keep it running while moving your LSN one way or the other till it starts to run.
Adjust your LSN and idle screw till it idles well and will run up to half throttle. (get it to running temp before you finalize any settings) Running temp at idle shouldn't be more than 200-215 or so. When it idles properly, throttle it to half and see if it stalls or bogs down. If it stalls, it's too lean. If it bogs, it's too rich.
Now go to full throttle. This is when you adjust your HSN. Same thing. If it bogs, it's too rich, stalls, it's too lean.
When it seems to be running good, pinch the fuel line. It should speed up slightly and then stall within 3 - 4 seconds. If it stops quickly, your LSN is too lean. If it takes longer, the LSN is too rich.
Drive it for a while and then take a temp check to make sure it's at the proper temp. If it's too hot, richen the HSN.
You will have to make small adjustments on the HSN almost daily to compensate for outside temperature and humidity.

By the way, the factory settings are for break in, or a starting point if you really messed things up. Once an engine is broken in, don't expect it to run right by going to those settings.
 
Since the top speed is good, do i have to re-tune the hsn and the idle screw as i tune the lsn? what are the symptoms of a 'worn of' engine? thanks for the guide and effort to help me guys.. today is saturday and i'm going to run the engine on the track. i'll get back to u guys.
 
No. If the top speed is good, and the temp is good, leave it alone. Both needles serve their own purpose. The HSN only needs to be tweaked a bit for temperature and humidity changes.
 
When you can turn the flywheel over with a finger with a glowplug in and the engine is cold, it's probably about dead. Also, inconsistent tuning, overheating a lot can be either a sympton of bad tuning or an engine on it's way out.

Basically, the piston and sleeve get worn over time or due to incorrect tuning. When the compression is gone when the engine is cold, it only gets worse when the engine warms up since the sleeve expands.
 
i can turn the flywheel, but it's hard. anyway, i've read from an article about possibilities of leakage. when i do the test i can see it's not airtight (near the carb o ring and carb screw head). So i seal it with silicon, like they suggested.. Could this be the reason of my problem?
 
Yes, it could be. It sounds like it's messing up the tune on you as it warms up, but air leaks are funny like that. Most times it causes overheating and erratic running. Like it will idle fine one minute and die the next.

If your going to seal up the carb neck, you might as well pull the backplate, clean it, and seal it up as well. I do the carb and backplate on any new engine when I buy it just to avoid having leaks down the line. Doing it first has served me well.
 
Thanks olds97 lss... i did not seal it permanently. Just to make it air tight. i've got another problem. The carb neck came out from its place when i pull the throttle, so i adjusted my controller so it doesn't pull more than needed.. but i think, the screw(which keep the carb neck in place) keeps loosen up, i'm afraid i might over tighten it which will damage the thread. so i tighten it just enough(i think). is there any way/tips to make sure that the carb neck could not come out? i dont think of sealing it permanently cause i might want to open it for some purpose in future.Thanks for ur help....
 
Are you talking about where the carb sits on the engine? If the screw is plastic put some superglue on it, and if its metal put some locktite and this should fix your problems.
 
If your actually talking about the throttle barrol, then I don't know, tighten it. If your talking about the carb neck where it goes into the crank case, again, tighten it. It shouldn't move at all. If either is loose, your going to have problems. If threads are stripped and you can't tighten it, your going to have problems. Vibrations will make it rattle apart. Sealing it with the silicone is like using putty to fill a crack. It doesn't really "bond" to the surfaces enough to compensate for a stripped screw.
 

RC Builds

Back
Top