Hpi savage 21 tuning help

[Rcguy]

So I got my savage running today but can't seem to get it tuned for the life of me. What happening is when I thing I get a good tune and take it for a lap it seems to lose the tune any help.

 

[ohsnap]

I get a good tune and take it for a lap it seems to lose the tune any help.

In a previous thread on what I assume is the same Savage and engine you wrote...
"...it turns out that the oring on the carb was bad and it was way to rich"

If it "won't keep a tune" my first guess would be an air leak - possibly old o-rings or a poorly sealed backplate.
Maybe a piston and cylinder that's lived their lives and now have lost compression.
I've seen engines that will start, but once they warm up, they are for all intents and purposes spent and useless - and can't keep a tune.

Other questions:
1. Is this engine the original HPI .21 (3.5) BB engine or something else?
2. Are you saying that one or two laps and the engines performance dies?
3. What temperature is it reaching?
4. New fuel - old fuel?
5. Does this engine still exhibit adequate compression?
6. Which o-ring(s) have you replaced?
7. Which needle or needles have you adjusted?
8. What are the current settings of:
8A - The HSN
8B - The Mid-range needle
8C - The low peed needle

 

[Rcguy]

This is the original engine, the engine is freshly rebuilt just now through break in it has brand new 20% in it after a couple laps it like bogs down and dies I replaced the base oring on the carb and the tune RN is 3 1/4 mid range 2 3/4 lsn and 2 1/2 hsn

 

[ohsnap]

the tune RN is 3 1/4 mid range 2 3/4 lsn and 2 1/2 hsn

According the booklet that came with my .21 BB, your settings are within HPI's recommended range.
Factory preset:
HSN 3 1/2 turns out from fully closed
LSN 3 1/2 turns out from fully closed
Midrange 3 1/4 turns out from fully closed

After break-in:
HSN 2 1/2 to 3 turns out from fully closed depending upon blah blah blah...
LSN 2 1/2 to 3 turns out from fully closed depending upon blah blah blah...
Midrange "It is recommended that you do not adjust the midrange adjustment screw."

Note 1 - I've never altered the LSN from factory settings on a stock .21BB.
Note 2 - I can't find it right now, but I've read (as a rule of thumb) that the LSN and mid-range needles should be moved in unison to one another. Meaning, if the LSN is screwed in, the mid-range is supposed to be turned out the same amount. Which by inference of note 1, means that I've never changed the mid-range adjustment on a stock .21BB.
Given my personal experience, I would reset the LSN to 3 1/2 turns out and run a test.
You got nothing to lose.
See note 3 for specific LSN adjustment guidance

I would not discount a dried out o-ring on one of the needles needing to be replaced (back to a bad seal / air leak), although I would try the above test first.

I would also not discount damaged needles. For example, over tightening the LSN into the midrange could damage either or both needles. but that would be my long-shot odds to have occurred.

Note 3 - Under the LSN guidance it says this.
"With the engine idling, accelerate to full throttle.
If the engine emits a heavy amount of smoke and bogs (hesitates) before accelerating or shuts off, the needle setting is too rich (too much fuel). Turn the LSN clockwise in 1/8 turn increments to lean out the fuel/air mixture. Continue to adjust the needle in 1/8 increments until the acceleration is smooth.

If the engine shutters or shuts down before full throttle acceleration and little or no smoke is visible from the exhaust pipe, the needle setting is too lean. Turn the LSN counterclockwise in 1/8 turn increments to richen the fuel/air mixture. Continue to adjust the needle in 1/8 increments until the acceleration is smooth."

Hope this helps.

 

[Rcguy]

I think it is a high possibility that there is an air leak because sometimes it wants to hang at idle thank you for your input I just want to get this fixed before it blows up from a wrong tune

 

[Vinni]

So I got my savage running today but can't seem to get it tuned for the life of me. What happening is when I thing I get a good tune and take it for a lap it seems to lose the tune any help.

Cud b air leak from the tank lid mate looks n closed but not sealing props add same fing n rather than replace it i ziptie it shut quick test jus undo exhaust n carb fuel line block 1 off n blow into other c if air tite ? Gotta b summat small if engines add rebuild n check exhaust coupler n gasket fo small rips n holes the check carb neck n backplate hope you get it sorted pal let us no

 

[Rcguy]

Its the oring at the base of the carb again so it think I'm just going to buy OEM

 

[ohsnap]

HPI no longer sells just those two O-rings (part number 1469)
I believe that their size is 10x12x1.0mm

Either of these two parts kits can supply them for you.
HPI's website lists both as being in stock in their warehouse and available for distribution.
#1435 - O-ring complete set for the Nitro Star 21BB
#1450 - O-ring complete set for the Nitro Star .25

The engine blocks for the Nitro Star 21BB and the Nitro Star .25 share the same dimensions.
I have what must be an early production Nitro Star .25 where the side of the casting proclaims that it's a "3.5" (.21) instead of stating that it's a "4.1" (.25).