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Engine Tuning For Performance

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Joined: 12 Oct 2005
Posts: 127

PostPosted: Thu Oct 13, 2005 6:51 am    Post subject: Engine Tuning For Performance Reply with quote

This was originally written for the Hyper 8/ Picco engines but generally works with any engine.
Well I imagine you are at the fine tuning point now. So set the car on a starter box or block.

Set the HSN to about 2 turns out. To adjust the LSN, rev the engine up 2-3 times quickly to clean it out, then let it settle down to semi high idle. Immediatly pinch the fuel line near the carb and hold it. Count how many seconds it takes for the engine to rev up and die. Ideally it should take about 5-6 seconds and the engine should rev up smoothly and steady and shut off cleanly. If it revs up almost instantly when you pinch the fuel line then it's too lean. Richen it up a turn and try again. It it takes longer than 6 seconds and it surges near the end and struggles to die then it's too rich. Lean it a and try again. You want it a bit on the rich side for the next part but not over rich.

Now find a long straight smooth streach of road. Run the car easy back and forth a for a couple minuets to get it warmed up. Then make a high speed pass at full throttle. It should be real rich and have low performance. Make 2 passes and bring it in. Lean the HSN about 1/8th turn. Make a couple more warm up passes and then make 2 full throttle passes. The engine may or may not show improvement for the first 2-3 adjustments.
Be patient and go slowly. Keep repeating making a couple warmup passes and then 2 high speed passes and leaning the HSN only. Don't change anything else.

At some point the engine should begin to show a marked increase in lowend accelleration and top end performance at the same time. Pay very close attention to how then engine sounds at top speed and how fast it seems to be going. Keep leaning the HSN a little at a time untill you don't notice any improvement in the top speed or the engine begins to 'stumble' at full throttle. As soon as you reach the engines peak then richen up the HSN about 1/4 turn.

Now go back to the box/block and readjust the LSN again so that it runs for about 5-6 seconds with the fuel line pinched off.

Long post and it will take some time to do all this. If you're still with me at this point your engine should be pretty much at it's ideal tuning curve. If it does not perform well at this point you have a carb or fuel problem.

A follow up to tuning. Caution, some people have found that when they bottom the LSN too far it gets stuck in the MSN and changes the MSN setting.
Although it doesn't say so it's a very big no-no. You've found out already that when you bottom the LSN what you are bottoming it out into is the inside of the so called MSN. Again this is not a needle. It's what's calle the "spraybar". When you set the LSN all the way it binds inside the spraybar and then turns it along with the LSN. Also, if you have bottomed the LSN hard enough to bind it in the end of the spray bar tip then you probably have flared the end of the spray bar and damaged it.

For the typical 8p carb at 2 turns out you are still about a 1/4 turn too rich. Again we've noticed that the stock carb is extreamly sensitive to changes and 1/4 turn is a whole bunch. You are correct on the 360 being one full turn but it's easier and more popular to imagine the end of the needle housings as a clock face. When you make an adjustment go by "hours". ie, one full turn is 12 hours. 1/2 full turn is 6 hours and 1/4 turn is 3 hours. On the stock carb 2 hours either way when near perfect will cause the engine to change about 50-60 degrees in temp and affect accelleration a lot. Go easy.

Contributed by Jim Newman
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