Releasing throttle at high speeds kills engine

[ShaDoWShah]

Hey guys, I recently bought a Thunder Tiger EB4 S3 1/8th nitro off-road buggy. Went through the break-in process. Now working on getting better tuning.
Anyhow, If I'm running it at high speeds and release the throttle all together (or hit the brakes) the engine dies. It seems to idle fine though, but the idle screw is indeed quite open. I'm guessing its about 2mm wide. The low end tuning seems not too off, good power off the line.

Any suggestions as to what this might be?

 

[Childresshunt]

Set it in front of you turn on your electronics take your air filter off and put the break on if the gap closes you will need to turn it in but from the sound of what you have going thats not the deal. If your running wot and its cutting out thats usually a lean hsn

 

[ShaDoWShah]

Hitting the brakes at low speeds does not cut the engine out.
Neither does driving at WOT cut out the engine. Suddenly releasing the engine, whilst running at WOT, cuts it.

 

[andydrew39219]

Hitting the brakes at low speeds does not cut the engine out.
Neither does driving at WOT cut out the engine. Suddenly releasing the engine, whilst running at WOT, cuts it.

Yeah, when you go WOT and let off the throttle and it dies, that means the HSN is probably too lean. The LSN doesn't have enough time to kick in and get a better fuel mixture so it stalls. and a 2mm idle gap is pretty big. I bet it varies a little per engine but I think it should be in the 1mm range.

 

[Childresshunt]

From a stop what does it do till it hits wot and does it continue going at wot

 

[ShaDoWShah]

From a stop what does it do till it hits wot and does it continue going at wot

It seems to accelerate fine....very very slight hesitation to pick up speed. By asking if it continues going at WOT, if you mean does the speed remain constant, yes it does. If you release the throttle slowly it doesn't quit, but a sudden release causes the engine to quit. Even if the speed is not all the way to WOT, just a higher speed, and you relase the throttle or brake suddenly, it quits.

 

[Childresshunt]

i meant does it stay constant once it reaches top. and if you let off and it dies i would richen up 1/8th of a turn and see if anything changes.

 

[ShaDoWShah]

i meant does it stay constant once it reaches top. and if you let off and it dies i would richen up 1/8th of a turn and see if anything changes.

Ill definitely give it a try and see what happens.
Thank you.

 

[2revo1maxx]

You need to set the idle gap at 1mm or it'll never be right. I would say the hsn is good or maybe a little bit lean right now, but you need to fine tune the idle and lsn right now.
The easiest way to tune the hsn is to slowly richen it up until you notice a loss of power, then slowly lean it back in to good performance.

 

[ShaDoWShah]

You need to set the idle gap at 1mm or it'll never be right. I would say the hsn is good or maybe a little bit lean right now, but you need to fine tune the idle and lsn right now.
The easiest way to tune the hsn is to slowly richen it up until you notice a loss of power, then slowly lean it back in to good performance.

So before anything I should close the idle a bit and THEN work on tuning the low and high end?? What effect would that immediately have on the low end settings??

---------- Post added at 3:44 PM ---------- Previous post was at 3:37 PM ----------

Would it help if I posted a video??

---------- Post added at 3:45 PM ---------- Previous post was at 3:44 PM ----------

Would it help if I posted a video??

 

[Childresshunt]

videos are always helpful

 

[2revo1maxx]

Nitro engines are supposed to have a 1mm or less idle gap. Read these two write-ups:

https://www.rcnitrotalk.com/forum/showthread.php?t=76808

https://www.rcnitrotalk.com/forum/showthread.php?t=94326

 

[badboy2]

the idle gap should only be enough for a sharpened tip of a pencil to go thru..thats how i do it.

 

[andydrew39219]

the idle gap should only be enough for a sharpened tip of a pencil to go thru..thats how i do it.

Sounds about right, I use the paperclip trick. Just make sure you don't get any graphite in your carb

You ever get it going shadow? Tuning is honestly really difficult and I'm willing to bet tuning a new engine his harder than tuning a fully broken in engine. I almost gave up on nitro at one point because of tuning. It took me a quite a few tries to get my .15 pro going, and I certainly did some damage. The top of my piston looks burnt....oops

Still runs strong as ever though.

 

[ShaDoWShah]

Sounds about right, I use the paperclip trick. Just make sure you don't get any graphite in your carb

You ever get it going shadow? Tuning is honestly really difficult and I'm willing to bet tuning a new engine his harder than tuning a fully broken in engine. I almost gave up on nitro at one point because of tuning. It took me a quite a few tries to get my .15 pro going, and I certainly did some damage. The top of my piston looks burnt....oops

Still runs strong as ever though.

You and the rest of the guys were right about it being too lean. I ran it at WOT and it started bogging down, engine was starving. I havent had the chance to tune it and run it again, but initial run suggests it was too lean. Hopefully richening out the HSN will solve most of the issue. Might have to lean out the LSN after I richen out the HSN to keep acceleration, does that sound about right?

 

[andydrew39219]

You and the rest of the guys were right about it being too lean. I ran it at WOT and it started bogging down, engine was starving. I havent had the chance to tune it and run it again, but initial run suggests it was too lean. Hopefully richening out the HSN will solve most of the issue. Might have to lean out the LSN after I richen out the HSN to keep acceleration, does that sound about right?

Personally, I would richen both needles 1 hour. Check performance and go from there. To determine what you should do with the lsn, use the pinch test.

If you pinch your fuel line it should rev up then die within 3-5 seconds then it means your lsn is set.
If it dies before the 3-5 seconds then your too lean.
If it dies after the 3-5 seconds then your too rich.

 

[Childresshunt]

as long as it idles and takes off dont worry about the lsn until you get the hsn tuned. id just richen the hsn first

 

[olds97_lss]

I have a feeling that once you richen the high, your going to have a hard time idling anyway. You have such a wide idle gap that your low end must be pretty rich, which is somewhat compensating for your lean HSN.

 

[ShaDoWShah]

I have a feeling that once you richen the high, your going to have a hard time idling anyway. You have such a wide idle gap that your low end must be pretty rich, which is somewhat compensating for your lean HSN.

I dropped the idle down, its actually just about or under 1mm....
From there on, when I richen the HSN out, what will the effect on the LSN be immediately??

---------- Post added at 2:24 PM ---------- Previous post was at 2:21 PM ----------

Personally, I would richen both needles 1 hour. Check performance and go from there. To determine what you should do with the lsn, use the pinch test.

If you pinch your fuel line it should rev up then die within 3-5 seconds then it means your lsn is set.
If it dies before the 3-5 seconds then your too lean.
If it dies after the 3-5 seconds then your too rich.

Why do you think I should richen out the LSN as well??
You were right about the HSN, and as a beginner, I wish to understand the reasons behind your diagnoses.

 

[Childresshunt]

If you would like to understand how to tune search on google how to tune nitro engine. and just browse threw a few sites and do some reading trust me its worth it. I'm by far not an expert on tuning but when i first got into nitro i read as much as i could about tuning nitro motors and I've never really had a problem with it

---------- Post added at 4:11 PM ---------- Previous post was at 4:10 PM ----------

or well shall i say if you would like to better understand tuning and the reasons behind the pinch test but remember the pinch test is just a ball park setting it will still take some fine tuning