Idle Screw VS LSN

[josegarcia8578]

Hi all,

I need a concept explainer. 2hy would you use the idle screw to control the idle? Instead wouldn't you just use the LSN?

When is it right to control RPM with idle screw?

 

[cbaker65]

Hi all,

I need a concept explainer. 2hy would you use the idle screw to control the idle? Instead wouldn't you just use the LSN?

When is it right to control RPM with idle screw?

The idle set screw is very important ,its function is to not allow the barrel of the carb. to close off ,
at idle or at braking with the transmitter!

Some people will alter this setting when they are tuning ,then they go back an re-set it to lower or raise
the idle!

 

[josegarcia8578]

@cbaker65 thanks for that explanation. That makes sense. What about the gap though? When should I adjust the gap? Instead of the LSN to increase idle?

 

[cbaker65]

@cbaker65 thanks for that explanation. That makes sense. What about the gap though? When should I adjust the gap? Instead of the LSN to increase idle?

The gap could vary ,but is usually set at 1mm for a base setting or about the thickness of a paper clip wire!

The Lsn. is only function is for fuel supply at idle an the transition from idle to WOT.

Usually the Lsn. ,if its not set too good ,your engine will die ,or wont start .an will also die at throttling!

Usually if an engine pings when your running at full WOT conditions ,it is too lean at the Hsn. setting!

I run my engines on the rich side a little ,an engine does not have to be perfectly tune ,just as long as
you dont run it too lean!

 

[josegarcia8578]

Currently, engine idles fine, I have to open the trim a little bit to get the engine warmed up. This is the idle after warmed up, before runnning a WOT:

Throttle response is great, and WOT is fine as well. But sometimes dies when breaks applied after WOT when I stop to idle. My dile carb gap is set to 0.5mm should I increase this @cbaker65?

Thanks for the help!

 

[cbaker65]

Currently, engine idles fine, I have to open the trim a little bit to get the engine warmed up. This is the idle after warmed up, before runnning a WOT:

Throttle response is great, and WOT is fine as well. But sometimes dies when breaks applied after WOT when I stop to idle. My dile carb gap is set to 0.5mm should I increase this @cbaker65?

Thanks for the help!

That's what the idle screw is for ,it should be called set screw ,because its function is to not allow the carb. barrel to close off
when braking or at idle!

If the engine dies when you brake ,then that set screw needs to be turned in so the barrel remains open to allow some
air flow!

The transmitter trim has nothing to do with or preventing the barrel to close off ,the transmitter will still kill the engine
when you brake if the idle set screw is not set!

 

[josegarcia8578]

Okay, I'll set the screw to have a 1.0m gap. If this rises the idle RPM should I richen the LSN a tad? Or leave it (if you think my current idle is too slow)

 

[cbaker65]

Okay, I'll set the screw to have a 1.0m gap. If this rises the idle RPM should I richen the LSN a tad? Or leave it (if you think my current idle is too slow)

The gap does not have to be a perfect ,as long as the engine idles with out the truck creeping forward!

If you have to almost close that gap ,then you may have to richen the Lsn, ,but only about an 1/8 of a turn at a time ,
it sounds like your not to far off on the tune ,if the engine idles an runs good with out over heating ,then you already
have a descent bashing tune with out killing your engine ,you should also see a little trail of smoke when you run!

Monitor the heat on the engine ,if you don't have a heat gauge ,you can put a little spit on the head ,
if it sizzles off on contact ,then its too hot ,the Hsn. is too lean ,an again ,only make 1/8 turn increments!

A tune also vary's in different locations & altitudes!

 

[josegarcia8578]

Thanks @cbaker65. I'm honestly happy with the tune, I just need to adjust it slightly so that it wot shut off after WOT run. It seems like a ile set crew adjustment is needed. I have a temp gun and a thermocouple I am using!

 

[cbaker65]

Thanks @cbaker65. I'm honestly happy with the tune, I just need to adjust it slightly so that it wot shut off after WOT run. It seems like a ile set crew adjustment is needed. I have a temp gun and a thermocouple I am using!

In my opinion ,if your engine idles & runs good at full WOT with out getting too hot ,then your good!

As long as the engine runs consistant temps with some trail of smoke from the pipe ,then you dont have nothing
to worry about!

My engines still run good after 10 years with out having a perfect tune ,my glo-plugs are even old!....

 

[cbaker65]

In my opinion ,if your engine idles & runs good at full WOT with out getting too hot ,then your good!

As long as the engine runs consistant temps with some trail of smoke from the pipe ,then you dont have nothing
to worry about!

My engines still run good after 10 years with out having a perfect tune ,my glo-plugs are even old!....

There is a very fine line between a perfect tune an a blown engine!

 

[josegarcia8578]

@Cbaxter26 : Understood. I do like the tune I have right now. It just dies after WOT, not necessarily with breaks, just when idle drops due to idle. I'll increase the idle set screw.

If I open the carb gap, this will increase RPM. Can I check the LSN with the pinch test after this? If anything, opening the gap will allow me to run richer at bottom end correct?

 

[cbaker65]

@Cbaxter26 : Understood. I do like the tune I have right now. It just dies after WOT, not necessarily with breaks, just when idle drops due to idle. I'll increase the idle set screw.

If I open the carb gap, this will increase RPM. Can I check the LSN with the pinch test after this? If anything, opening the gap will allow me to run richer at bottom end correct?

Yes ,if you richen the Lsn up ,it should calm the engine down a little from a high rev!

 

[josegarcia8578]

@cbaker65 The high speed needle is performing well, but I need to check to see if it's slightly rich as per d3mon, this can also cause my engine to die after a WOT run, when returning to idle.

 

[josegarcia8578]

If my HSN is as good as it get's, I will open the gap a little bit. What would happen if I do find that the HSN is a little on the rich side, but still performs and only shuts off when going straight to an idle? Can I leave the HSN alone and just open the gap a little bit so it does not die/bog when going straight to idle?

or would it be best to just lean out the HSN more?

 

[cbaker65]

After running full WOT ,an you return to just sitting to idle ,how long does it take for the engine to die ,an also ,
does it seem to clear up if you hit the throttle?
If so ,then your engine could be loading up with fuel!

 

[josegarcia8578]

I have to wait a few more hours for the loctite to fully cure and then I will go out again and answer your questions. I did notice yesterday though that the the engine was turning on fine until I flipped it and it turned off immediately. Maybe my high end is rich. I opened up the carb using trim to get it started again.

 

[cbaker65]

I have to wait a few more hours for the loctite to fully cure and then I will go out again and answer your questions. I did notice yesterday though that the the engine was turning on fine until I flipped it and it turned off immediately. Maybe my high end is rich. I opened up the carb using trim to get it started again.

That might also be the gap on your carb. barrel if you have to open it up by trim on the trans.!

 

[josegarcia8578]

I believe I did not have trim at that time. I was only using trim to start it/warm it up.

 

[cbaker65]

I believe I did not have trim at that time. I was only using trim to start it/warm it up.

I would open & set the gap first at 1mm ,an then warm the engine up ,reset the Lsn!

Usually when it starts to rev with gap set for idle ,then its too lean ,a little richer will calm the engine
rev down with the gap on the carb barrel set at idle!