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All Forums >> RC Cars, Buggies, Trucks, Tanks and more >> RC Monster Trucks >> HPI Monster Truck Forum >> High revs after letting of gas.
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High revs after letting of gas. - 5/13/2008 3:25:52 PM   
Hordsak


 

Posts: 507
Joined: 5/31/2007
From: Maple Ridge, BC, CANADA
Status: offline 		I'm done breaking in my LRP engine. I was out bashing today, and I noticed that after I accelerate hard, and then let my finger off the throttle, the revs seem to get high pitched for a few seconds and then settle down. Is my low speed too lean?

< Message edited by Hordsak -- 5/13/2008 3:27:38 PM >
       Post #: 1

RE: High revs after letting of gas. - 5/13/2008 3:31:51 PM   
supertib


 

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From: , MB, CANADA
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quote:

ORIGINAL: Hordsak

I'm done breaking in my LRP engine. I was out bashing today, and I noticed that after I accelerate hard, and then let my finger off the throttle, the revs seem to get high pitched for a few seconds and then settle down. Is my low speed too lean?



LSN too lean or you have an mild airleak somewhere.....most common cause of airleaks is aftermarket fuel filters....... if you have a fuel filter remove it asap then re-test....... fuel filters can cause huge tuning issues..

(in reply to Hordsak)
       Post #: 2

RE: High revs after letting of gas. - 5/13/2008 3:33:39 PM   
Argess



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Joined: 1/12/2006
From: Pleasantville, NS, CANADA
Status: offline 		Sounds like your HSN is too lean. After you let off the throttle, it takes a second until the LSN can richen the mixture properly. Try richening your HSN.

(in reply to supertib)
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RE: High revs after letting of gas. - 5/13/2008 8:56:01 PM   
beer=food


 

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From: hervey bay, AUSTRALIA
Status: offline 		Its more likely the bottom end needle if its doing it after you finish WOT, richen it, still does it, airleak is likely.If its blue smoked and ok at WOT , chech it out, the bottom end needle.

(in reply to Argess)
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RE: High revs after letting of gas. - 5/13/2008 9:47:04 PM   
Argess



Posts: 367
Joined: 1/12/2006
From: Pleasantville, NS, CANADA
Status: offline 		well.....he said the revs are high for a few seconds, then it settles down. If the LSN was too lean, it wouldn't settle down. It could if the LSN was too rich, but it that case, he'd hardly notice the momentary leaning. So...I stand by my guess.....LOL......richen your HSN a bit.

(in reply to beer=food)
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RE: High revs after letting of gas. - 5/13/2008 9:58:07 PM   
NitroVenom



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From: North Babylon, NY, USA
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quote:

ORIGINAL: Argess

well.....he said the revs are high for a few seconds, then it settles down. If the LSN was too lean, it wouldn't settle down. It could if the LSN was too rich, but it that case, he'd hardly notice the momentary leaning. So...I stand by my guess.....LOL......richen your HSN a bit.


Play this video from 2:35.. The bottom end is too lean...

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(in reply to Argess)
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RE: High revs after letting of gas. - 5/13/2008 10:29:35 PM   
Argess



Posts: 367
Joined: 1/12/2006
From: Pleasantville, NS, CANADA
Status: offline 		Yes, but that "too lean" part of the video isn't what he is describing. He says the idle is momentarily high (1-2 seconds), then drops.

In order for the idle to drop after the 1-2 seconds, the LSN must be either rich enough to sustain a good idle, or too rich and the engine rpms will drop over time, so it can't be too lean. It could be OK, or too rich.

If it is too rich, the idle will slowly decrease in rpms over a much longer time....like 10 to 20 seconds. But he hasn't said about long idling.

If you run your HSN too lean, and the LSN set properly, or even a bit too rich, and you let off WOT, the engine will drop to a high idle for a tiny bit before the LSN can adjust the fuel delivery to the proper idle.

Anyway....it's hard to tell what his exact situation is without hearing it.

ps: hey...someone else help me with this please!......I being out-numbered.....LOL

(in reply to NitroVenom)
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RE: High revs after letting of gas. - 5/13/2008 10:34:07 PM   
BudBud


 

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Joined: 12/21/2006
From: Salina, KS, USA
Status: online 		I think that is pretty common, especially on a newer engine with tight pinch. You get the cylinder and block good and hot and when you come off of that high speed scream, it has a little heat to disperse. For that few seconds it is way too hot in the hole, it is suffering a lean condition. I have have tried to tune it out of several newer engines and it seems like you are fighting yourself. BB

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RE: High revs after letting of gas. - 5/13/2008 11:51:04 PM   
NitroVenom



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From: North Babylon, NY, USA
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quote:

ORIGINAL: Argess

Yes, but that "too lean" part of the video isn't what he is describing. He says the idle is momentarily high (1-2 seconds), then drops.

In order for the idle to drop after the 1-2 seconds, the LSN must be either rich enough to sustain a good idle, or too rich and the engine rpms will drop over time, so it can't be too lean. It could be OK, or too rich.

If it is too rich, the idle will slowly decrease in rpms over a much longer time....like 10 to 20 seconds. But he hasn't said about long idling.

If you run your HSN too lean, and the LSN set properly, or even a bit too rich, and you let off WOT, the engine will drop to a high idle for a tiny bit before the LSN can adjust the fuel delivery to the proper idle.

Anyway....it's hard to tell what his exact situation is without hearing it.

ps: hey...someone else help me with this please!......I being out-numbered.....LOL


See now this is were I kind of agree with you, but on some parts I don't. Now the LSN is what is controls the low end tuning correct? Well if you come from a high speed pass, or hard acceloration, it will drop back from what the HSN controls, to the what the LSN contols. Now if the LSN is lean, the truck will have a high idle. So once the truck goes from a high speed pass, it will be lean and also idle high as it decelorates.

Now if it was rich, it would just idle kinda low as soon as you lett off the throttle. Watch the whole vid and they show you what a Rich lLSN looks like while running.

LOL not trying to out-number you.

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RE: High revs after letting of gas. - 5/14/2008 3:53:32 AM   
Skinner1


 

Posts: 96
Joined: 10/13/2007
From: Maple Ridge, BC, CANADA
Status: offline 		I have about 2 gallons thru my stock savx rtr motor and it does the same thing as yours hordsak

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RE: High revs after letting of gas. - 5/14/2008 5:47:49 AM   
carldav



Posts: 391
Joined: 9/26/2006
From: Oakland Gardens, NY, USA
Status: offline 		I believe the LSN is lean. If you were able to tune the HSN correctly, I would suggest to flush the LSN needle and work from there turning 1/12 increments, then make sure the carb gap is 1-2mm open.

Do some high-speed passes and observe if it still revs high after releasing the throttle.


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RE: High revs after letting of gas. - 5/14/2008 7:14:53 AM   
supertib


 

Posts: 3147
Joined: 3/30/2004
From: , MB, CANADA
Status: online 		high idle off a high speed pass is a lean LSN..if the HSN was lean the motor would cut out on the high speed pass.... When your closing the throttle off a high speed pass the motor still needs fuel, so if the LSN is a touch too lean the motor will run on for a second or so.... a motor with a slightly lean LSN can still load up down low, especially if your using a cooler plug... if the LSN is ultra lean then the motor would of course high idle and never settle down......

But as I say inline fuel filters are a huge cause of airleaks...unless you seal the fuel filter there is a good chance its leaking... I never run inline fuel filters and usually the first sign of tuning issues I advise people to remove the fuel filters.....

(in reply to carldav)
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RE: High revs after letting of gas. - 5/14/2008 12:13:13 PM   
Argess



Posts: 367
Joined: 1/12/2006
From: Pleasantville, NS, CANADA
Status: offline 		LOL........so many thoughts, and all could be right, or all could be wrong, or a combination of problems may exist.

Anyway......Bud-Bud seems to have it ......too much heat after a high speed run....why?......HSN too lean. As he also says, it can be difficult to tune out. So maybe I've only ever masked the problem with my tuning technique.

LSN could be richened to cure problem as well, but then you may find a sluggish launch.

And don't forget, the LSN setting is somewhat affected by the HSN (thought I'd throw that in there to complicate matters).

Regardless, if his vehicle didn't do it before, and it does now, something is too lean (and probably for that particular day and it won't occur again for a while....LOL).

From the amount of attention and controversy this post has acheived (which is a typical question, I think) it would be nice if Hordsak posts his findings.

(in reply to supertib)
       Post #: 13

RE: High revs after letting of gas. - 5/14/2008 1:08:23 PM   
supertib


 

Posts: 3147
Joined: 3/30/2004
From: , MB, CANADA
Status: online
quote:

ORIGINAL: Argess

LOL........so many thoughts, and all could be right, or all could be wrong, or a combination of problems may exist.

Anyway......Bud-Bud seems to have it ......too much heat after a high speed run....why?......HSN too lean. As he also says, it can be difficult to tune out. So maybe I've only ever masked the problem with my tuning technique.

LSN could be richened to cure problem as well, but then you may find a sluggish launch.

And don't forget, the LSN setting is somewhat affected by the HSN (thought I'd throw that in there to complicate matters).

Regardless, if his vehicle didn't do it before, and it does now, something is too lean (and probably for that particular day and it won't occur again for a while....LOL).

From the amount of attention and controversy this post has acheived (which is a typical question, I think) it would be nice if Hordsak posts his findings.



Dude its the LSN lean, not the HSN...........trust me !!!!!! please seriously just trust me on this, don't argue, just go with me on this............. LSN lean+high idle off highspeed pass.....

And of course the HSN affects the LSN.. how else could it work ?

If HSN was lean the motor would act up at WOT..if the problem exists when you let off the throttle then its the LSN as the throttle is now closed..... Of course richening the HSN will also solve this issue as richening the HSN will also richen the LSN....... But if the HSN was lean you would see symptoms of it when the engine is at WOT, not when you let off the throttle........this is not rocket science at all ...please quite complicating a simple LSN issue...

< Message edited by supertib -- 5/14/2008 1:12:52 PM >

(in reply to Argess)
       Post #: 14

RE: High revs after letting of gas. - 5/14/2008 1:28:00 PM