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Old 08-27-2009, 05:02 PM   #1
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Default Need some help - idling engine issue

I am trying to break in my engine and I don't know what to do.

This is my first engine break in and I am relatively new to the scene in general - so please don't assume:

a) I know what I am doing
b) I might have tried something obvious

If you have an idea please post it here. If I've tried it - I'll tell you - if not I'll try it.

I have the HS needle flush with the housing. I have richened the LS needle to try and make sure I do no damage to the engine. I have set the idling needle so there is roughly 1 - 1.5 mm gap.

The engine starts fine and idles ok for a few seconds. However, very shortly thereafter it starts to rev and will continue to do so until I do one of two things:

1) Hit the brake on the radio
2) Shut it down.

To the best of my ability to determine the throttle/brake linkage is correct. I closely watch the servo and linkage arms when I hit the brake and I don't see any "releasing". In fact the throttle arm and the bulb it attaches to don't seem to move at all when I hit the brake (the spring compresses, but the arm doesn't open or close the slide at all).

As long as I keep the brake held, the engine seems to idle OK. Within a few seconds of releasing it, the engines start to rev pretty high again.

I have been told it may be an air leak and will test that out tonight. I wanted to see if anyone else had some thoughts.

Thanks a lot in advance.
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Old 08-27-2009, 05:10 PM   #2
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Well, to be honest it just sounds like you need to lower your idle.

Edit: When you release the brake, watch the linkage to see if it pulls the carb open a bit. I know I had this problem once. I would release from the brakes and it would pull the carb open and give it a high idle. Just try to lower your idle via the screw on the engine. You could have a air leak, but test the easiest stuff first and start to narrow it down.
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Old 08-27-2009, 06:00 PM   #3
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Originally Posted by ace921000 View Post
Well, to be honest it just sounds like you need to lower your idle.

Edit: When you release the brake, watch the linkage to see if it pulls the carb open a bit. I know I had this problem once. I would release from the brakes and it would pull the carb open and give it a high idle. Just try to lower your idle via the screw on the engine. You could have a air leak, but test the easiest stuff first and start to narrow it down.
I just took the carb insert out of the carberator and noticed that the slide gap was bigger than I thought. It looked like 1.0mm with the insert in, but now appears to be ~2.5mm without the carb insert. Could this account for my behaviour?
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Old 08-27-2009, 06:19 PM   #4
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Yes, you may also need to adjust your linkages...Close the idle to 1 mm with no insert and then make sure your servo is closing the carb slide all the way back to idle, sometimes it holds it open but its a simple adjustment of the coller, or the rod..
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Old 08-27-2009, 06:30 PM   #5
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Well I have some more information. I tightened the carb slider to about 1mm without the carb insert.

This significantly improved the problem. The idle was able to last 15-20 secs before it revved up, but it definitely still revved up.

Also I took the air filter off so I could see whether or not the slider moved. As the engine revved up, the slider did not move. As I hit the brake the slider did not move - so I doubt it is a side affect of my throttle/brake linkage.

Are there other possibilities that could account for this problem other than an air leak?

If it is an air leak, could it be between the manifold and the engine or the manifold and the pipe?
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Old 08-27-2009, 07:15 PM   #6
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You may want to try putting a rubber band or hair band sround the carb so that it stays shut when you let off the throttle
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Old 08-27-2009, 07:32 PM   #7
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Richen your low speed till the idle comes down. Turn little by little to be nervous by the engine reving and turn it a bunch all at once.
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Old 08-27-2009, 08:12 PM   #8
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You may want to try putting a rubber band or hair band sround the carb so that it stays shut when you let off the throttle
I will definitely do that for a fail safe, but I doubt this is the problem since the slider isn't moving at all when the engine revs or when it returns to a normal idle.
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Old 08-27-2009, 08:14 PM   #9
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Richen your low speed till the idle comes down.
Can I change the HS or LS needle when the engine is running or do I need to shut it off before changing the needle settings? Either way - I will try this tomorrow - to late to start the engine now.

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Richen your low speed till the idle comes down. Turn little by little to be nervous by the engine reving and turn it a bunch all at once.
I'm sorry - I need to up my dosage of mind altering drugs to follow this

Can you try again please?
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Old 08-27-2009, 08:15 PM   #10
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Yea your right. Have you tested the engine for an airleak yet? Maybe you can lower your idle enough and tune it to the airleak. Try picking an idle you like then turn it down so that whne it revs up, it goes to the idle you want. Or just fix the air leak, if there is one.
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Old 08-27-2009, 11:26 PM   #11
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If your engine revs like mad and the idle gap is set at 1mm then you either have an air leak (major something like a front bearing seal leaking) or your low speed needle is to lean starving the motor for fuel at idle.

No drugs required
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Old 08-28-2009, 11:43 AM   #12
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sounds like your low speed needle is too lean. it makes sense. you prime your engine before you start it and it runs fine for like 10 seconds or so. then all that fuel that you used to prim has been burned up and now the engine is starving for fuel. richen the low speed needle 2 hours at a time.
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Old 08-28-2009, 06:13 PM   #13
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Quote:
Originally Posted by ace921000 View Post
sounds like your low speed needle is too lean. it makes sense. you prime your engine before you start it and it runs fine for like 10 seconds or so. then all that fuel that you used to prim has been burned up and now the engine is starving for fuel. richen the low speed needle 2 hours at a time.
+1 on this. I had the same problem the first time I tried running a nitro. Breaking it in will have it's own set of tuning nuances, but once you have the motor broken in, and are tuning for performance, you should always tune in this order.... HSN, LSN, HSN again (if needed), idle screw.

One more thing...go buy yourself a temp gun. $26 at Home Depot for the blue Ryobi (the one that takes a 9V, not the $70 rechargeable one). It's REALLY good to have for making sure your engine is in the correct temp range during break in, and a useful tool to aid in tuning once you're up and running.
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