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Tuning Woes

Old 08-16-2022, 03:28 PM
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Default Tuning Woes

How come an engine wants to run either too rich or too lean. Its a Novarossi carb Ive heard they are very sensitive with the needles but still.
If I turn 1/48 of a turn even it affects the tune way too much. Almost impossible to get a sweet spot. I guess Ill just switch to an OS carb which
definitely tune easier. Is there an advantage to running a Nova carb over an OS carb?
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Old 08-16-2022, 03:39 PM
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I wonder where people get the idea a OSMAX carb is the best, Novarossi carbs are very good. An engine can be very sensitive on its tuning if the compression is too high, check if the amount of headshims is right.
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Old 08-19-2022, 11:18 AM
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I wouldnt switch carbs . Just make sure everything is legit, good seals, tank, fuel line,no leaks on the motor, etc.

I find that most my novas tune very different than an OS. I found that my novas were much more lean on the bottom than an OS.

But no matter. Start with rich needles, warm the engine, get the top set first, get the bottom clean, adjust idle accordingly.
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Old 08-19-2022, 12:39 PM
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Originally Posted by Roelof View Post
I wonder where people get the idea a OSMAX carb is the best, Novarossi carbs are very good. An engine can be very sensitive on its tuning if the compression is too high, check if the amount of headshims is right.
I agree Nova carbs are great but in my experience, OS are even easier. I would put OS carbs #1 followed very closely by Nova then post 2008 or so Picco with everything else trailing way behind.

Of course tuning isn't always about the carb (and this is for OP, not you Roelof. You know all this already). OS tends to be a little more conservative in port timings than Nova which gives them a broader tuning window. So no matter what carb is on it, it's going to a more user friendly experience. Thus the excellent reputation of OS carbs
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Old 08-23-2022, 09:37 PM
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There are several variables. fuel, plug, tank pressure, pipe and header.
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Old 09-08-2022, 03:19 AM
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Originally Posted by wingracer View Post
I agree Nova carbs are great but in my experience, OS are even easier. I would put OS carbs #1 followed very closely by Nova then post 2008 or so Picco with everything else trailing way behind.

Of course tuning isn't always about the carb (and this is for OP, not you Roelof. You know all this already). OS tends to be a little more conservative in port timings than Nova which gives them a broader tuning window. So no matter what carb is on it, it's going to a more user friendly experience. Thus the excellent reputation of OS carbs
hmmm-conservative in port timing? thought they were more aggressive as most say.... so OS crank timing is aggressive? not ports?
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Old 09-08-2022, 04:40 AM
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Originally Posted by sn47som1 View Post
hmmm-conservative in port timing? thought they were more aggressive as most say.... so OS crank timing is aggressive? not ports?
You will know if you keep track on the timings. I do as far as possible (what people send me to break in) OS has a very decent port timing and no extreme crank timing compared with most current (modified) engines.
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Old 10-21-2022, 10:27 PM
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Originally Posted by Roelof View Post
You will know if you keep track on the timings. I do as far as possible (what people send me to break in) OS has a very decent port timing and no extreme crank timing compared with most current (modified) engines.
So modifying an OS (crank) would give an awesome engine
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Old 10-22-2022, 03:48 AM
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Originally Posted by sn47som1 View Post
So modifying an OS (crank) would give an awesome engine
Depends which crank you have but yes, there is room.
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Old 10-22-2022, 07:02 AM
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I start with factory stock carb settings and leave it alone.
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Old 10-27-2022, 01:23 AM
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Originally Posted by 1995 Monster T View Post
I start with factory stock carb settings and leave it alone.
But then you'd be running it way too rich and down on power
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Old 10-27-2022, 09:14 AM
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Originally Posted by sn47som1 View Post
But then you'd be running it way too rich and down on power
Once you get the low set then you can adjust the high? Putting on a different carb on a engine changes the settings.
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Old 10-27-2022, 09:21 AM
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Something I learned for someone who knows these engines very well, is that Italian engines can be very sensitive to needle adjustments. Compared to OS, they need to have their setting just right or they tend to not run as well. I recently switched to OS from Reds and I find that tuning OS is much easier. And if you havenít already, try changing your glow plug and making sure you have no air leaks. Make sure your bearings are good too. Hope this helps.

thereís also this
"the engine tuning bible"
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Old 10-27-2022, 09:56 AM
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Just to add, a bad air filter can change a tune. Dirty filters or a filter with the wrong oil or too much oil can also have an effect.
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Old 10-27-2022, 10:07 AM
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Tuning of an engine is an art but if you are experienced with it, it is just a piece of cake with any engine and any carburettor.
And when an experienced person can not tune the engine right then there is something wrong.

Things that make an engine hard to tune:

1) dirt in the carburettor or exhaust. It happens that a piece of torn off silicone fuel hose or exhaust rubber goes inside the exhaust and floating around in front of the holes inside.
2) broken or cracked O-ring of the carburettor, common problem no one checks.
3) wrong timings of ports/crankshaft. Should not be a thing with an out of the box engine but people w/o knowledge grinding on an engine can cause that. But yes, some high timed engines out of the box can have a small perfect tuning window.
4) play on bearing, rod and/or worn P/S set
5) lose head screws
6) forgot the copper ring with standard plugs, it happens more than you think.....
7) Wrong combination plug, head clearance and nitro percentage. These 3 factors do set the ignition timing. When the timing is too soon the tuning window can become too small.
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