Whilst the gasket on the engine could be brand new theres no guarantee the exhaust and other exhaust gasket are.

It's sounds like an air leak, and until recently i didn't realise how critical the exhaust gaskets are to a stable tune.

Check this link http://www.rctech.net/forum/nitro-of...ing-bible.html one of the first issues it discusses is carb imbalance which if you have no linkage problems it will probably help you resolve the idle issues.

oooooooooooooh yes... very often overlooked $1 item that prevents proper engine tune... I learnt it the hard way... :nod:

for now don't mind all the people telling you it's an air leak, no sense in dissassembling things when it's most likely what Joe said the LSN is just too rich and the idle gap too large. Although the only thing I would stay away from that he said is adjusting the MRN. Very few people are good enough tuners to utilize the mid range, just leave it where the factory had it (flush around 2:00). You can most likely correct your issue with just the idle screw and LSN. I would say 50% of the people at the track running nitro have a double idle of some sort, especially on Vspecs because they still get around the track just fine with a rich LSN. Some engines with a rich LSN just don't run good an force you to find an optimal tun, Vspecs will stay running even when they are way off, which is why some people love them.

Just a heads up though, if the LSN is rich enough to cause this problem, your HSN may be too lean once you get it fixed, so re-check that. If the LSN and idle adjustments don't fix it, then look possibly into gaskets, and areas that could cause a leak, sure it's possible just a lot easier to start with just one screwdriver.

Brandon,
the problem with not touching the MRN is that like you said "leave it at factory at 2 oclock" well every new engine I've seen the factory setting is different. when the carbs are manufactured they use a "power tap" to thread the carbs and the stating point is always different, so each carb is different. I usually set mine at 3-1/4 turn from bottomed (11o'clock), and it's within a couple hours of tuned. dont be afraid of the MRN, it really helps get them dialed in perfect if you understand how it works with the LSN.

check your fuel line and tank for leaks to. My mill wasn't idleing down like normal on jumps other day, found out my tank lid wouldn't seal all the way. May not be theissue, but it is easy to check and rule out.

check fuel tank, replace fuel line, check/replace pipe gaskets, return needles to factory settings and before you re tune, READ THE TUNING BIBLE.

I have too... from an air leak in the bottom of the case that cracked. Not sure if this is a problem on the new ones or not... but it is worth checking IF you don't find anything else causing it.

sounds like the low end is too lean. try getting the motor up to temp, and back low end out until it stops. Does not sound like a air leak to me, but a tuning issue. Air leak should affect the whole motor including the high end. But you said the high end runs out fine?

also try going back to the factory settings and see if it stops then

Im with Joe and Brandon. Rich LSN and too big of an idle gap. OS engines are set like this from the factory so you run plenty of fuel through them when new and they wont stall constantly but as it breaks in the idle starts to climb because its not so hard to rotate the engine.

Whats happening is the idle gap is too large so coming off the high end it stays at high idle until it starts to load up then the idle comes down.

Set the idle gap to about 0.5mm then lean the LSN out. This should get you back in the ballpark. Then make sure the HSN isnt too lean which is common when the LSN is too rich because when the LSN is rich the temps come down significantly which usually leads people to lean the HSN out too much.

With the help of all of you I have gotten the high rev down to 6 seconds before perfect idle and on the pinch test it dies at about 6 seconds. Buggy runs great now but i am going to replace the tank again just to make sure that is not causing a problem. Should the engine idle down right away or does it normally take a few seconds? I still think there is a problem some where but for now I will keep trying to fine tune.

keep leaning the lsn.. the closer you get to perfect, the shorter the 2 stage will be. you should be able to eliminate the 2 stage completely if you spend the time fine tuning as i explained.. good luck!

Can you explain what you did to bring the revs down?

Two possible conditions were:

• LSN too lean
• Idle gap too big and LSN too rich

It should idle down pretty quick in a perfect race tune. More casual or false tune settings will take longer.

Not saying you were wrong, I understand how needles work. No offense to the guy asking the question, but someone who has to ask why an engine doesn't idle down, doesn't need to be messing with a MRN. There's no reason with the factory setting that an OS carb won't achieve good idle. That's all. I ran plenty of VSpecs in my day and all of them came to idle just fine with factory settings on the mid range.

It would be like a doctor telling someone to go get a medicine decribed by all the scientific names of the ingredients, instead of saying, "go get tylenol".