Ambient temperature effects on the HSN mixture setting

[KnightAzul]

Hi,

After a 3 week break from the RC car, I got my A into gear and took her down for a run.

To my surprise she took a long time start and also I had to richen the HSN needle (1.75 to 2.25) to get her running well (she was bogging down on full throttle and sometimes with the engine cutting out). This was a little odd since with this HSN needle setting (1.75) everything was running ok before, 3 weeks ago, with no bogging down.

The only changes were:
1. Ambient temperature was hotter this time by around 10 degrees. However, would it be true to say that the hotter it is outside, the richer the fuel mixture should be - I would have said with my limited knowledge just the opposite!
2. Changed the fuel brand, however they both were 16% nitro-methane mix. There was no reference to the lube content on either can.
3. Changed the glowplug. This was a like-for-like change. However the one used before towards the end was badly fouled.

Actually thinking about it, that it alot of changes! However that basic question here is: would it be true to say that the hotter it is outside, the richer the fuel mixture should be, or is there no rule of thumb regarding outside temp and the relative HSN setting.

Any ideas?
KnightAzul

 

[lykan]

When changing fuel brands I have noticed (the one time I changed) I had to completely re-tune my engine.

I went from a No-name brand to Trinity Horespower. The improvement in how the engine runs was well worth it. I did however have to spend time re-working the needles.

I had to richen the HSN needle (1.75 to 2.25) to get her running

Do you mean you had to richen it up by 1/2 turn? If so, that small of an adjustment could definetaly be due to fuel brands. If you don't think it's the fuel, here's some ideas..


I has been 3 weeks since you ran it. Is it possible that;

You were running lean, but didn't notice?

You left a little bit of fuel in the tank, and you had a bit of unnoticed sludge in the bottom? (it looks just like fuel but has consistancy of jello). This would make it a pain to start, and require a re-tune.

Because it ha been sittin you developed an air leak? maybe the O-rings in the carb dryed out?

Maybe your new glow plug hasn't seated all the way?

 

[gutterboy]

I dont think 10 degress would matter to much, I was leaning towards the fuel being left in the tank like lykan said.

 

[KnightAzul]

It is quite possible that a little bit of fuel was left in the tank. I understand why this would make it hard to start, but after 3 tanks why would this still have an effect?

>Because it ha been sittin you developed an air leak? maybe the >O-rings in the carb dryed out?

Anything that I can do to stop this happening?

Thanks,
KnightAzul

 

[nitro zombie]

Originally posted by KnightAzul
[B However that basic question here is: would it be true to say that the hotter it is outside, the richer the fuel mixture should be, or is there no rule of thumb regarding outside temp and the relative HSN setting.

Any ideas?
KnightAzul [/B]

I’m pretty sure that you want to set your needles richer when it is colder. Cold air is denser and therefor has more available o2 to burn requiring richer settings to keep from forcing a lean condition. Somebody correct me if this is wrong.

 

[SkyMaxx]

Colder outside air temps means denser air and thus a richer setting (per my school of thought). Others would argue differently.