Great thread...after 2 years playing with these little engines I finally get it

Help me out here I think I'm experiencing what in this article is called lean bog. I notice it after about 5-6 minutes of running. My engine is the alpha lutz worlds edition I was coming off the track about 240. I've richened up the hsn as per the article says, coming off about 210 and it still lean bogs when getting low on fuel. I don't wanna richen anymore I'll start losing performance and temps will lower I'd like to be able to run it at 240 for racing. What can I do to rectify this issues is it possibly something else causing the issue??

This is the onroad forum but I will give it a shot. Have you replaced the fuel tank? it could be the lid on the tank is not properly sealing causing a lean bog when the tank gets low.


Pass you soon...

Where on the track is it bogging?

Could also be that the engine is old, when they start to wear out they will run good for a few minutes then loose performance.

Hi guys, I just watched this video

https://www.youtube.com/watch?v=rUBCDQHDb3g

and what this guys states near the end of the video that the idle should come down after 1o seconds and the settle. From what I am hearing when the car stops it idles up then down and then down again.
other guys say that after stopping the idle should go down instantly and stay consistent.

Is this guys wrong?

Yes he's completely wrong. If your idle hangs after a WOT run and then drops its because you're too lean on the HSN. If you're car drops to normal idle and then begins to idle up after that then your LSN is too lean. Any time your idle hangs or goes up on its own you're too lean on the top end or bottom end. If you're car idles down normally then up and down again like you said then you need to be checking for air leaks in your fuel system, carb and engine. I suspect your have a bad fuel tank cap seal. With a proper tune your engine should immediately drop to idle after WOT and stay there. After about 10 seconds it should start to blubber and richen up then almost die. At no time should your idle increase or hang on its own.

Thanks for the response that video was confusing me

I wouldn't say he is completely wrong!! Those guys are factory Reds and Kyosho team and a very very quick driver with lots of top end results.

There are two trains of thought relating to engine setup. The method in the video is the 2 stage idle technique and has its merits however the method described by RoketRdr is also valid.

My preference is the 2-stage as I find the engine generally has more punch out of corners and is better (cleaner?) off the line. The engine is also more reliable and less likely to stop in the event of a crash leading to the car being upside down while the marshal gets to you.

As I said both have merits and this is why you've heard different folk recommend a different thing. I see more engines setup by the 2 stage idle method than anything else.

To say Elliot's mechanic is wrong however is absolutely not the case.

Having said that they are discussing offroad engines!! Now we can talk about onroad setup which is slightly different.

Here we do look for the engine to drop to idle quickly but the size of the engine also matters. For example a.12 engine will have a tenancy for the idle to run on after WOT on the straight for example. This is normal as long as it returns to idle within around 2-3 seconds. The bigger engines shouldn't run on however.

Good evening, I'm having a problem tuning the Picco .21 otto engine. It idles good but when I give it gas it stays at a high idle for about 5 to 10 seconds and then it will come back down. It seems like it stays at a high rev for too long.

Is there a tunning bible for 1/8 on road clutches?

https://youtu.be/aYNzdzQnlzY

Open the HSN 1/4 and run another laps and see how long the idle will be high until it drops again. If does not make any difference you might be having the self turning HSN syndrome which happens quite frequently in (.21 and above) engines when the HSN seat is worn out or the o'rings are square (too old). When this condition happens although you might always set the needle right, after running the engine high revs the HSN starts closing spontaneously due to very high vibration frequency and leaning the engine overall fuel flow and makes you think the LSN is wrong. If you want to know if you have a self turning HSN just mark the needle position with a pen marker and run feel laps. if the needle is moving even a bit, replace either the o'rings or the whole needle seat. The best way to test this is set the carburetor to the factory settings or any settings you remember the engine will be rich enough to start easily and check the engine behavior from cold to hot and see if the HSN will turn. This is one of the reasons most airplanes have a ratchet on the HSN, it is easy to do small increments and also prevents the needle to turn spontaneously under high vibration.

Tuning question too. My XRD GT 0.21 (15 litres old) running in an 1/8 GT is running reasonable but.....Today it was quite hot (27 Celsius) so I leaned ithe HSN 1 hour or so. When I start my run the idle is pretty good but after I've run for about 10 laps the idle is like very high and stays high. After let say 10 seconds I blip full throttle and then it goes down to normal. Its not the slide of the carb. My thought was the idle screw is to high and after I blip full throttle the crankcase fills up and due to the "richness" the idle goes down. More or less the same behaviour as a rich LSN.

Any advice here?

regards

In addition: If i lower the idle screw I lower the LSN also if I'm not mistaking. The air gap gets smaller but the needle is also closer to the jet.........right?

Running a Nova P5 - probably on 3/4 of a gallon.

Is it possible to run the idle gap too small disguising a lean bottom end? I was getting a lean bog on the LSN when opening the throttle. Car would hesitate then take off. The idle wasn't racing high or pinging but richening the LSN took this bog away. I then had to raise the idle slightly.

running carbon shoes with 1.0 springs.

Thanks
Rob