Timing/Carb jet size question

[lemming303]

So I have been reading and watching shows and trying to teach myself about working on engines and obviously I keep coming up with lots of questions. I am starting to understand how timing works, but now I have a bigger question.

I read that you get the best timing by advancing until you hit the highest RPM, then backing off 4 to 5 degrees. However this only works if you have the correct jet size. So how do you know if you have the correct size? How do you determine the correct jet size? Sorry if this is a basic question, I am still learning all of this stuff.

[Moparal]

I used to go with the smoothest idle and not highest rpm.. When doing iit by ear. Then I would go for a performance test ride a few times with a 1/2 wrench on hand.    I have found in some ways that if you go up more than 3 or 4 jet sizes from stock setting, a bigger carb is required.  Just my way of doing thing by the fly

[Chryco Psycho]

jetting is tough to determine , you can go by plug color & get close but with all the crap they add to fuels now you can still be way off , I have seen clean white plugs that looked lean but tested rich on the dyno & hp improved when we leaned it out , you really need a sniffer in the exhaust / O2 sensor to get it right , you can also feel the difference , if it is to rich the response will become less crisp as you increase jet size , same the other way if it is too lean the response will suffer & start to stumble as you lean out

[moper]

This question is a great reason why it's not the right way to set timing utilizing rpm or vacuum to determine the timing. You get the timing curve set with a light, and then set up the carb. Then if you want or need to you tweak the timing by testing at the track or on a dyno toget the best results. Carb does not affect timing settings. Timing does affect carb settings.

[lemming303]

OK. That makes sense. All this stuff can be confusing sometimes.