Help with needle settings

[Nitrolizer]

Ok, here is a problem I usally have on all my nitro-racing engines (boats & cars).

When I'm tuning in the needles, I usally set the high-speed needle first. It may take a few testruns to find the best setting, but no problems so far.

Then it's time for the idle-needle. I usally make sure to start with a setting that is sure to be too rich, rather than being too lean. Then I just lean it until the throttle response (from idle to full throttle) gets quick and stable. But here is the problem:

Usally, I can run on mid to high-throttle, then go to idle for just a second, and if I then crank it again there is an instant response. BUT.... If I let my model run on idle for a litte longer (let's say 15 secs or more), then when I suddenly crank it the respons is very slow, and I can hear the engine running in "4-cycle" for just half a sec or so, just before it goes back into normal 2-cycling and revs up to its peak.

My questions:

1. Why does this happen only when I let the engine run on idle for a longer time, and not when running in idle for just a second before I rev it up again?

2. Can this be fixed with the idle-needle? If I set the idle-needle too lean, my engines most often get unstable when running on idle. If I then richen it a little, I get stable idling but the problem I described above occurs instead (slower reving after idling for a longer period of time).

I have this problem on all my boat and car engines, basically. Old as new.

By the way, I'm usally running 25% nitro with 15-20% oil (the oil mixing usally differs a bit depending on where I buy the fuel).

Any suggestions? I'm sure most of you have experienced this yourself. Anyone who has managed to get the needle just perfect, without experiencing any of these problems? Or do you usally just tune it for secure idling as a first priority, and then try to not run in idle for too long (as a way of avoiding slow throttle responses)?

All suggestions are appreciated. Thanks.

 

[Terry Keeley]

Ok, here is a problem I usally have on all my nitro-racing engines (boats & cars).
When I'm tuning in the needles, I usally set the high-speed needle first. It may take a few testruns to find the best setting, but no problems so far.

Then it's time for the idle-needle. I usally make sure to start with a setting that is sure to be too rich, rather than being too lean. Then I just lean it until the throttle response (from idle to full throttle) gets quick and stable. But here is the problem:

Usally, I can run on mid to high-throttle, then go to idle for just a second, and if I then crank it again there is an instant response. BUT.... If I let my model run on idle for a litte longer (let's say 15 secs or more), then when I suddenly crank it the respons is very slow, and I can hear the engine running in "4-cycle" for just half a sec or so, just before it goes back into normal 2-cycling and revs up to its peak.

My questions:

1. Why does this happen only when I let the engine run on idle for a longer time, and not when running in idle for just a second before I rev it up again?

2. Can this be fixed with the idle-needle? If I set the idle-needle too lean, my engines most often get unstable when running on idle. If I then richen it a little, I get stable idling but the problem I described above occurs instead (slower reving after idling for a longer period of time).

I have this problem on all my boat and car engines, basically. Old as new.

By the way, I'm usally running 25% nitro with 15-20% oil (the oil mixing usally differs a bit depending on where I buy the fuel).

Any suggestions? I'm sure most of you have experienced this yourself. Anyone who has managed to get the needle just perfect, without experiencing any of these problems? Or do you usally just tune it for secure idling as a first priority, and then try to not run in idle for too long (as a way of avoiding slow throttle responses)?

All suggestions are appreciated. Thanks.

May be the motor is cooling off too much, how 'bout a hotter plug?

What size motor? What plugs you runnning? :blink:

 

[Ray Sametz]

Nitrolizer, I think it's just the nature of the beast, idle too long and the pipe loads up with fuel. Hit it and it takes a few seconds to clean out. Shorter idle, less loading of the pipe, quicker response. Lean the low end down too much and she will die trying to idle. Some carbs have a very fine line on adjusting the low end. May take a while to find the sweet spot or happy medium. Ray B) B)

 

[Nitrolizer]

Thanks both for your replies.

May be the motor is cooling off too much, how 'bout a hotter plug?
What size motor? What plugs you runnning? :blink:

Hmm... Maybe a hotter plug could be worth a try, I actually never thought of that When I buy plugs, I usally just buy what is recommended for 25% nitro which is medium-cold or something like that. I am not experimenting with plugs very often, mostly I just stick to the recommended ones.

But you think a hotter plug can solve this problem? What if I run with a plug that is too hot, what will happen then?

As for my boat engines, I have an O.S. Max 21 (3.5cc) outboarder on my TS2 boat and an OPS 67 (11 cc) on my mono-hull boat. I have the same problems on both, and also on most of my cars that I've had.