Fixing high idle which drops after a blip of throttle !

[robbie1]

Hi all,

I've been tweaking away on a couple of my buggy/ car and both have this problem.

I've been following how to tune guide and getting it there but it's just this high idle which drops when I blip the throttle. Is the Lsn to rich ?

I have set the idle gap to 1.5mm so that's good.

I had to lean the Lsn a bit as engine died after removing glow starter. ( checked plug was good )

I have leaned the hsn a bit and getting temps after WOT to 200f - 220f.

So all seems ok. Is it just find tuning now to sort this problem ?

[UltimateRC]

Sounds like the LSN is rich. Try leaning it out a little more If it dies on a blip of throttle it could be getting too much fuel

[Deafty]

+1 LSn too rich,.

also it is likely your idle gap is too wide. It is possible for the engine to idle speed to appear normal when in actual fact the idle gap is too wide and the rich LSN is loading it up with fuel of which only some can be burnt.

Pinch fuel tube 1-2cm back from carb inlet. It should eventually only rev up 500 rpm or so.

Higher the revs indicates wide idle gap.

Little to no revs indicates to small idle gap. (usually also coupled with too lean LSN)

Heres a quote from the "tuning Bible"

Dont confuse this with standard pinch test.

2. Set the idle air gap and the initial LSN setting using the " MassiveMods 7 second Pinch Test"

The first and most important step is to ensure the idle gap is set correctly.

Because the LSN is directly connected to the throttle slide, getting the idle air gap set properly, so the throttle slide and LSN are correctly positioned before you start tuning is paramount.

Fill the fuel tank and start the motor. Let it warm up for 30 seconds on the starter box - no more.

If the motor will not idle pinch the fuel line to listen where the idle gap is set to, lean the low speed needle 1/8 of a turn at a time until the motor idles without stalling.

Now, fully pinch off the fuel line 1 to 2 cm back from the fuel nipple.

What you are looking for is a slow and steady rise in revs (only 500 rpm or so), which will indicate the idle air gap is correct.

If the revs rise high or "chirp up" quite high, this indicates the idle air gap is too wide.

Decrease the idle air gap a little at a time until you get the slow steady rise previously mentioned.

2a. Initial setting of the Low Speed Needle

Now that the Idle Gap is correctly positioned you can adjust the low speed needle so the motor will die from fuel starvation after 7 seconds when you pinch off the fuel line.

The length of time it takes the motor to die reveals how rich or lean the bottom end is.

If the motor dies at say 4 seconds that means its too lean , you need to richen the bottom end. If it takes 10 seconds for the motor to die, you must lean the bottom end.

7 seconds is the time we want to achieve for a basic tune on the motor.

NB: The idle air gap and 7 second pinch test procedures outlined above need to be carried out before the motor gets too warm - otherwise higher crankcase temperatures will not allow the correct results to be achieved. You need to be able to conclude this procedure in about 2 to 3 minutes. Once you get the hang of it you can do it in less than a minute.

Now we have the idle air gap set correctly, and the low speed needle close to where we want it, run a full tank of fuel through to warm the motor and saturate the chassis with engine heat. Depending on the chassis this can take up to 3 consecutive tanks.

You must always fine tune a motor when it is hot - this is very important.

Heres a link to the whole article Towards end of 1st post

Edited October 25, 2012 by Deafty

[robbie1]

Thanks very much. A great answer, I will get it sorted. Thanks again !!!!

[Deafty]

YW

[robbie1]

Hi all,

I've been following post on how to set them up. I got one of the cars working good to this, but the other one is a bit more of a pain. I set the carb gap to a 1mm gap using a 1mm thick pin. But on starting the buggy the idle runs to high. Just wanting to check if I should be tweaking the Lsn or hsn. I assume with a 1mm gap on the carb that the reason for high idle is the Lsn or hsn setting. ?

[Deafty]

Um,. did you read my previous post..?

Carb gap setting of 1mm is a guidline. There is no way that by measuring this exactly your engine will idle perfectly. Its impossible. If for LSN or HSn are adjusted the tune is adjusted and this naturally effects the idle too. (though may not be as noticeable).

If it idles too high, adjust the idle screw. What does it sound like when you pinch the fuel line?

Is it a high idle or is the clutch enaging too early?