Just CAN'T tune my engine

[echelon6]

Hi all, been a while since I asked questions here, but seems like I'm in need of advice again as I'm out of ideas and at my wits end

My rig is a wholly stock hpi rs4 evo3+ with the stock engine Nitrostar T3.0

Firstly I can't seem to get it tuned no matter what

The problem is during some high speed runs (1/2 throttle or more), SOMETIMES it bogs down when I put 1/2 to WOT throttle (quite uncommon occurrence, but is guaranteed to happen). What I mean by bog down is that the engine's tone suddenly becomes a low pitched sound, and sputters, before stalling.

There is good amount of smoke coming out of the car during acceleration, and less smoke when the car is already running fast (maybe because of the wind, cos its already moving quite fast) so from this, I assume it is a HSN rich bog.

So I've tried leaning the HSN, but I'm at the point where if I lean the HSN any more, the idle becomes too high the clutch engages. OK so then I should richen the LSN to prevent this, right? But if I richen the LSN any more than my current point, the car will bog on acceleration.

So I'm trapped in a box as you can see

Here's some more info:
Idle temp: 200-220 (shell on)
High speed runs: 250-260 (shell on)
(temps above appear OK to me)

Pinch test: 2 seconds, revs up and then dies, so LSN seems OK.

I've considered the possibility that my high-speed run stalls may be caused by a Lean bog, in which case I should richen the HSN. But if I do this, it will bog on acceleration from stationary (in which case I should lean the LSN, which DOES help this, but the idle would be too fast and clutch engages). With a rich HSN, I've never had the opportunity to go high speed and see whether the WOT-bog still happens, because it always bogs down on initial acceleration.

PLEASE COMMENT, much appreciated!



My second, much simpler problem is probably easily fixable. My engine is easy as hell to start when cold, but impossible to start once warm. Could it be vapor-lock? I doubt it, I tried rubbing alcohol on the carb to accelerate cooling until it was room-temperature (while piston was still very clearly very hot) and it still won't start.

As the rotostart is spinning the hot engine, I hear signs of life, i.e. the knocking sounds which tells me there is some combustion going on, but the engine just wont fire up.

OK so it might be pre-ignition? hot engine = fuel igniting too early = can't start? Maybe. I did recently change to the OS 8 med-hot glowplug, but the stock glowplug was cold-med. Could this be the problem?

Thanks for your input

 

[brentmorl]

first one id look for a air leak second one junk the motor or re sleeve it sounds like a forsure sighn the motor is wore out ...gets warmed up sleeve expands no compression

 

[echelon6]

Backplate and Carb have been sealed. Fuel tank primer seal is relatively new so I doubt its too leaky.

Engine is only 2 litres old (that's slightly over half a gallon to you yanks )

 

[harshybar]

I have a t-maxx and I am ahving the same exact problem.

 

[jack_mcgill]

my nitro star t-15 had the same problem........ i yanked it out put an o.s instead and since then its a charm....

 

[LouisianaSwampbug]

So I've tried leaning the HSN, but I'm at the point where if I lean the HSN any more, the idle becomes too high the clutch engages. OK so then I should richen the LSN to prevent this, right? But if I richen the LSN any more than my current point, the car will bog on acceleration.

Hope I didnt miss read this, but you are adjusting the HSN it should not affect the idle. Are you sure you are not getting the two mixed up???

LSN will affect "low speed" or Idle. As you lean out the LSN you should hear a change in rpm until it becomes to lean and dies. Pinch test is good in this case.

HSN is adjusted to help with WOT. As you lean it out you will gain rpm.

Remember to watch temps and turn in small amounts. Your LSN is only used while at idle.

One thing that is overlooked is that fuel can puddle in crank case and this will cause a rich condition until it clears out. So its a good idea before making any adjustment to rev engine a few times to clear fuel. Then start making adjustments. Hope this helps.

Tim

 

[echelon6]

So you would think

My HSN definitely affects idle. If I lean it out any more than current, idle will increase and clutch engages.

I'm aware of the puddling effect and it's very pronounced in my engine

Today I spent a good hour analysing my engine and tuning it and I've reached a compromise where it won't bog down on WOT anymore, but everytime it idles a while, the 'puddle' grows and if I try to accelerate from stop after the idle period (e.g. after refueling / putting on shell etc), it would stall. To combat this I have to lift up my rig and very very slowly accelerate for about 2 seconds to burn the 'puddle' away, then the car runs perfectly.

Oh well I guess I'm satisfied, but the experience of running a poopy engine definitely has taught me heaps about engine tuning. I'll run my engine this way until its time is up, then I'll get something more user friendly like an OS mill

 

[jack_mcgill]

Hope I didnt miss read this, but you are adjusting the HSN it should not affect the idle. Are you sure you are not getting the two mixed up???

the hsn leans the overall fuel intake.. so yeah, at a point it can start affecting your idle .. especially on an engine hard to tune like that one

 

[LouisianaSwampbug]

the hsn leans the overall fuel intake.. so yeah, at a point it can start affecting your idle .. especially on an engine hard to tune like that one

I never have heard nor experienced the HSN effecting idle. From my experiences the HSN is not even used during idle. It does not come into play until the carb is opened. But stranger things have happened. I do agree that the HSN to lean can cause the engine to hang on high idle after WOT but not at idle. Sounds like the LSN is set to rich. It could be fuel is boiling in carb or if fuel filter is to close to head it could boil before going to carb causing vapor problem.

Tim

 

[echelon6]

I'm satisfeid with the way it runs right now, will be testing it out later today. I'll report back if something else goes wrong. Thanks

 

[chuck3]

try using the tuning flow chart I'm sure youve looked at it already, but if not try it. I've even seen masters of nitro tuning refer to this chart now and then.

as for some of the problems I've read, have you sealed your mill? checked for airleaks in any of the lines? the glance i did of your first post points my nose to an airleak.

and your HSN should not affect idle unless your jsut that far out of tune. HSN= 1/2 throttle and up, LSN 1/2 throttle and down. I suggest starting whith factory settings to get your bearings on your tune.

EDIT: After reading the entire thread, I see youve sealed your mill. I still smell an airleak so Id check to make sure all of your lines are good, also get rid of that primer. even though its relatively new it still can leak. look at brand new mills for instance, a good chuck of them leak strait out of the box.

 

[echelon6]

Haha the primer... I'm addicted to the convenience of pushing a button to prime the engine

 

[qaart]

i got the traxxas 3.3 if i hit 3/4 throttle it just dies and can't get it tuned where it wont do that its frustrating