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Old 05-07-2005, 06:06 PM   #1
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Default Motor Help Wanted!

Ok guys if I could get some good advise here fill me in on the missing link. I have a Rex P5 motor that when it starts off it is fat on the bottom end and fine on top end, but after 3 or four minutes of racing the low end leans out into a bog and the top end stays the same. Now I know that after time it will run leaner the more you run and get the motor hotter. I noticed that when it was running that I would get some air bubbles in the fuel lines when it was running so I am thinking there is maybe an air leak somewhere. What are some good or how to methods to check for air leaks in the motor, tank and lines? Anybody have a good link to a tutorial on this subject? Thanks!
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Old 05-07-2005, 10:09 PM   #2
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As for air leaks, just replace your fuel line if you're worried about it. And you got to tune it with the engine at running temps. It takes a bit to get it up that high. Like the 3 or 4 minutes you say. That's what you need to tune the motor for, that stage of running. Then start it up early and warm it up by using your finger on the servo if you have to.

To test the tank, take it out first. Put fuel lines on both the pickup and exhaust hole. Put it in sink full of water. Plug the carb line, and blow into the pressure line. If it bubbles it's got a leak.

Air leaks from the motor will make you have to retune all the time, and the temps will fluctuate all over the place.

Most common leaks on the motor are at the backplate, under the carb, and around the banjo fitting (fuel nipple). You can take all those off and put some orange rtr (sensor safe) on those parts. It works wonders for sealing motors. Just a small amount is all it takes.

If your high end stays the same and your temps don't spike you probably don't have an air leak. More likely you just need to tune the motor when it's warmed up.

Last edited by jbrow1; 05-07-2005 at 10:15 PM.
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Old 05-08-2005, 07:37 AM   #3
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Found a link to a website which was very informative.
http://www.misbehavin-rc.com/links/links-articles.asp
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Old 05-08-2005, 08:41 PM   #4
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as for spotting air leaks....

they are probably my #1 most frustrating problem in nitro. If i suspect an air leak, as i suspect you may, I first wrap zip ties (tiny ones) around all of fuel line connectors (at the barb) and rub a little permatex around the fitting the fuel line connects to. if I still have the problem, i replace the fuel lines, then the fuel tank. replacing the whole shebang will cost maybe $20 for everything, and its worth saving yourself the headache. just smart small. zip tie the fuel line barbs, permatex the tank, and if all else fails replace the fuel lines, and then the tank.
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Old 05-08-2005, 10:23 PM   #5
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To check for air leaks on the motor just use some motor spray or carb spray with a hose on it. Just a small squirt on a suspect area will tell you quick if its leaking air. It will either die or rev slightly.
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Old 05-09-2005, 09:45 PM   #6
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I know that the fuel lines and tank aren't leaking because I just pulled out my rtr motor that came with the buggy and it runs fine and I have also tested everything in the pressure line. There is a new bearing in the front part of the crank shaft (it was replaced as part of mabe a thought) but now I am starting to think that the piston and sleeve in the motor are starting to go bad (motor has almost 5 gallons through it). Anybody know the factory needled settings for the three needle carb that comes with the REX P5?
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Old 05-09-2005, 09:55 PM   #7
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5 gallons the motor is defianatly shot
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