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Old 10-03-2007, 08:41 PM   #1
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Default Engine Tuning

Need some help from you Nitro experts. If the engine revs up really high and stays there for a few seconds or so, is the low speed to lean or to rich? Engine has great top end but takes about 20 or so seconds to drop back down to a normal idle level. I'm running 1.1 springs with carbon shoes. It's a Vega .21 7 port engine. PLEASE HELP!
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Old 10-03-2007, 08:57 PM   #2
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sounds like the bottom is to lean...
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Old 10-03-2007, 10:08 PM   #3
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seems lean to me too. try this method. keep it idling and then squeeze the fuel line to stop the engine. If the engine revs up very fast and then it dies within 2-3secs, the engine is lean.
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Old 10-03-2007, 11:08 PM   #4
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seems lean to me too. try this method. keep it idling and then squeeze the fuel line to stop the engine. If the engine revs up very fast and then it dies within 2-3secs, the engine is lean.
Thats the same test me and my buddy do on or motors and that seems to work the best
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Old 10-04-2007, 07:10 AM   #5
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That's what my first thought was too. I'll keep fattening her up and see how that works. I know the needle was practically all the way in when I opened the box so I'll turn it out some more. Thanks Guys.
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Old 10-04-2007, 08:36 AM   #6
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seems lean to me too. try this method. keep it idling and then squeeze the fuel line to stop the engine. If the engine revs up very fast and then it dies within 2-3secs, the engine is lean.
this is an excellent lean checker for the low end needle! i also use this method. very telling test!.
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Old 10-04-2007, 09:00 AM   #7
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When you say it revs up for a few seconds, are you saying that after a few seconds the idle will drop?
EDIT: Nevermind I reread your post and I see the idle eventually drops. I'm going to go against the grain here and say that I think your too rich on the lsn and the idle screw set too hight to compensate for the overly rich bottom.

Get your car out and run it around to get the engine warmed up (200+). Assuming you have your hsn is set, I'll usually just throw it back on the starter box or car stand and rev it a bit to "clear it out". Now WOT to rev it (don't hold it or go crazy and blow your motor) then nail the brake and listen to the motor. If the idle stays high and then slowly drops, lean your lsn (you'll probably have to lower your idle after you lean it). If you do this and your idle drops when you hit the brake and slowly raises, the you need to richen your lsn. Your goal is to get it to almost immediately return to the same idle as before you did the wot. When done you may need to adjust your idle screw. This is how I've always done it and it works great for me. Once I do this I rarely have to touch the lsn, usually just the hsn.

Last edited by g26er; 10-04-2007 at 09:51 AM.
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Old 10-04-2007, 10:11 AM   #8
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I'll try both methods and see how it works. I'll try the pinch test first though and see where it leads me. If that doesn't work I'll to the lean out and see how that works. It takes it a while to come back down, maybe 10-15 seconds from high RPM's. I'll let you know which method worked the best. Thanks again all.
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Old 10-04-2007, 03:01 PM   #9
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Originally Posted by stiffler297 View Post
Need some help from you Nitro experts. If the engine revs up really high and stays there for a few seconds or so, is the low speed to lean or to rich? Engine has great top end but takes about 20 or so seconds to drop back down to a normal idle level. I'm running 1.1 springs with carbon shoes. It's a Vega .21 7 port engine. PLEASE HELP!
If your vehicle come to a stop and take 20 seconds or so to drop down to a normal idle level, the low end needle might be just a bit rich and your idle might be set at higher than it needs to be. I would try set the idle lower and lean out the low end needle just a bit until you obtain the idle speed with no variation in rpm for 15-20 seconds. On the other hand, if you vehicle come to a stop and then the rpm go up as you engine is idling, the low end needle is too lean.
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Old 10-04-2007, 05:50 PM   #10
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.21 engine tuning 101 ;
do the pinch test about 2-3 inches from the carb fuel intake , should take about 3 seconds for the engine to idle up if the low needle is set properly . adjust the idle as low as it will allow you to and still stay running after reving out the engine and it comes back down to idle . after you get the perfect tune richen up the lsn 2 hours and idle up about 1/4 turn to stop engine from flaming when race conditions are applied . when adjusting the high speed , start off very rich but runnable , lean out to desired temp and feel , watch for good smoking for at least 6 feet and pay attention to the engine , if it starts to lose power on the bottom , you either have the wrong clutch/pipe combo or if there is no smoke it is a lean bog (dangerous) stop running it on the track , bring it in and richen the low speed at least 6 hours and the high needle at least 3 hours and start over .REMEMBER WHEN TUNING : FUEL MAKES POWER , NOT AIR !!!!!!
happy tuning bro ,
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Old 10-04-2007, 06:49 PM   #11
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I've never had so many problems with an engine before. I did all the tests, pinch test, smoke test, temp test and everything was cool, then I when to do a couple of passes and it would bog like a lean bog. So I gave it a 1 hour rich on the high speed and then there was no power at the top. So I then reversed it to no avail. Is there anyone in the socal area that might be going to Revelation on Sunday that could help me out with this? It sounds really blubbery when you hit the throttle so I gave it a little leaner on the HSN. Then it would get a really bad lean bog midrange. I'm utterly confused with this motor. I practically richened the lsn till the needle came out. I'm getting desparate here. This isn't my first engine either, I've had several picco motors, jammin motors and a few rtr motors and this on just doesn't want to tune. I'm using a JP-1 pipe at the moment so I might need a different pipe combo but I'd hate to buy a new pipe after spending good hard earned money on this one. Please help!
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Old 10-04-2007, 09:55 PM   #12
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check your clutch set up. What clutch are you running??

if a spring is broke or a shoe is stuck it can cause the motor to sound like it is lean bogging.
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Old 10-04-2007, 09:57 PM   #13
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houston...wow...good tips bud!!!!
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Old 10-05-2007, 02:54 AM   #14
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Bottom end is too rich and your idle is too high trying to compensate for it,like another member suggested.The motor is running on the unburnt fuel left in the crankcase.
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Old 10-05-2007, 03:10 AM   #15
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