sn47som1

iTrader: (8)

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?

Roelof

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.

jpz_67

iTrader: (56)

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.

wingracer

iTrader: (24)

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

token

There are several variables. fuel, plug, tank pressure, pipe and header.

sn47som1

iTrader: (8)

hmmm-conservative in port timing? thought they were more aggressive as most say.... so OS crank timing is aggressive? not ports?

Roelof

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.

sn47som1

iTrader: (8)

So modifying an OS (crank) would give an awesome engine

Roelof

Depends which crank you have but yes, there is room.

1995 Monster T

I start with factory stock carb settings and leave it alone.

sn47som1

iTrader: (8)

But then you'd be running it way too rich and down on power

1995 Monster T

Once you get the low set then you can adjust the high? Putting on a different carb on a engine changes the settings.

Medic29358

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 haven’t already, try changing your glow plug and making sure you have no air leaks. Make sure your bearings are good too. Hope this helps.

there’s also this
"the engine tuning bible"

Pharcyed

iTrader: (18)

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.

Roelof

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.