Its only the first liter or so (1/4 gallon) which needs a light throttlefinger. After that you set the HSN just a little richer than the perfect tune, and run it for the next gallon or so :) That setting are perfect for practise and you are not wasting your fuel

Yes, you will have metal pinch in our engines for the first 1.5-2 gallons... until the pinch is gone you will not see full power or runtime, we see 2+ mins of runtime gain from the first tanks to the end of metal pinch. You can race it sure, I race mine after about 4-5 tanks, I keep a close eye on it and run the HSN slightly rich. Fully seating the piston wont happen quickly. Some engines metal pinch is completely gone after .5 gallons. Some take longer, but they also have incredible seal/compression for a very long time also ;):D Id rather have an engine hold strong compression for 5+ gallons than go away after a couple

note: metal pinch and compression are completely different, in a perfect world you want 0% leakdown, builds compression immediately after the piston covers the exhaust port and 0% pinch (unwanted heat and drag) to have the perfect engine.

Pinch is something you only feel when the engine is cold. You will never know how it is in operating condition, even when you directly take off the engine from the track, stop it and feel it you will feel different becaust the short idle and stopping did already cool down the piston.

Mostly an engine is runned in after an half of gallon but can become really loose after one or even more gallon and will get some hundreds of rpm's extra.

NOT being argumentative as you really know your stuff...... but almost every tuning article I've seen says to do HSN first.

Reason is that HSN is the 'master control' and if you lean the HSN it also leans the LSN a bit - the LSN is only the fine control for the bottom 1/4 of throttle opening.
If you get the LSN right, and then change the HSN, you will have altered your LSN setting a bit.

I would say get HSN right, then LSN using the pinch test (and 10sec idle followed by punching it off the line will help).

Not saying you are wrong, but why do you advocate the opposite to most tuning guides?

Nova base engines tune from the bottom first. You leave the top a bit rich, get the bottom tuned in then retune the top. OS engines tune top first then bottom, so it all depends opn the engine you run, and how the way it works for you!

Hmmm... I am about to get an RB so may have to rethink my tuning process huh?

BUt can anyone explain why? I thought on all carbies the HSN controls fuel flow and the LSN just finetunes to lower end mix - so adjusting the HSN has to affect the LSN ??? :confused:

I have a RB here, I tuned the HSN first and the engine runs A1. I always tuned my engines (RB, Nova, LRP, OS, Reedy, Picco,...) by adjusting the HSN first.

If you get the bottom end close to where the final setting will be it makes tuning the top easier. Reason is if the bottom is set real rich you have to burn off the excess fuel in the crankcase before you get a feel for the top needle. Every time you let off the throttle you put extra fuel in the crankcase. You will have to tweek the bottom again afterwords because of the fuel flow interaction but overall the tuning process should be easier.
And it does not matter what brand it is, they all act this way.

Ahhhhh bentgear that makes sense. I was assuming they were talking about adjusting the LSN to be 100% perfect, then do the HSN 100% perfect and not touch the LSN again.

I still think all motors tune HSN first .... but as you said the LSN needs to be in the ballpark to avoid it loading up with fuel when you back off on the throttle.

I hope this clears some things up for you Mark.

Original post from Ron of Werks Racing:

The one thing that people need to remember when trying to tune or trying to understand how they should be tuning an engine is how the two needles affect the engines performance. This is key! Sooo...

Always remember that the idle stop screw is there so that you can simply set a minimum amount of air that flows into the engine. This is important because it is the basic starting point that you are going to tune off of. Think of it like a house. In order to build a house you have to lay down a foundation first, this foundation for your engine is the air gap set with the idle stop screw. Just like the house example, if you have a messed up foundation you are going to have nothing but problems building the house!

Then you have your HS needle. The HS needle dictates overall fuel delivery, so the fuel passes through the HS needle first then on to the LS needle. Using an example of the garden hose with a nozzle on the end connected to your water faucet. The HS needle is the water faucet. If you think about it, if your water faucet is closed, it does not matter how far you open the nozzle on the end of the hose because their ain' t no water coming through it lol. So using the HS needle if your HS needle is too lean it does not matter how much you mess with the LS needle their ain't no fuel flowing through it! This is why I always say that you need to set the HS needle to flush, this is just like having the tap half ways open.

You need to have fuel flowing through the HS needle so that you can adjust the LS needle (the nozzle on the hose) properly. This is the starting point from which to tune. Now when you are tuning the thing to remember with the HS needle is that while it affects the overall fuel delivery, you are basically adjusting it to affect your performance from throttle half open to throttle wide open. So when driving (or tuning the engine on the box) keep this in mind! The only thing that you have to remember is that because the HS affects the overall fuel delivery if you lean the HS needle you are also leaning the LS needle by default.

Using the water hose example again if you have the faucet and the nozzle adjusted so that your water goes 2 feet and you then close the faucet a bit (just like closing aka leaning the HS a bit), your water will not go so far. So to compensate for your closing the faucet (leaning the HS) you are going to have to open the nozzle a little bit (richen the LS) so that more water flows through it and it again goes the 2 feet. This is exactly how the needles on your carburetor works! If you have your idle set, you have your engine performing ok but you lean the HS a bit, it will lean your LS and you will notice this because the idle also will go up.

Next step is talking about the LS and I will get into that in the next installment of engine tuning 101 by Ron if you guys find this type of information helpful?

Yes agrees with what I said and everything I've read, bar Tony's post :D

you cannot "tune" LSN first - you get it close enough, then the tuning starts...... get HSN 100% sweet, then tune LSN with pinch and punch test

Maybe this clears things up. It is a drawing of the needles in the carburator.

As the 2 needles ar a serial connection you must understand the HSN is affecting the LSN but the LSN is not affecting the HSN.
Thats why the HSN is set first and can be corrected in small steps when the LSN is setted.