360 timing

Wow! I thought in an earlier post the max was 45*. Do I remember it wrong, or has something changed? In any case,doing the math; 51-20=31* in the distributor.Thats too much. No, thats; WAY too much.But the better news is that the rate of advance is in the ballpark....Just to double-check; Thats with no vacuum advance.
-First,the tools; You will need a tachometer,a vacuum guage and a timing lite, and a pen/paper. So heres what I would do.Lets see what the engine likes for idle timing. With the engine off, loosen the dist. hold down screw so that with a little effort, the dist can be moved.Hook up the vacuum guage to an intake manifold source.Hook up your timing lite.Next,with the trans in Park,start the engine and let it warm up.Now, I assume since you supplied the 900 rpm number, that the engine idles there. Thats good.Is the idle speed stable? If you lightly blip the throttle, does it return to idle nicely? If yes and yes,then we can continue.If no, we will have to address that first. Assuming yesses,watch the vacuum guage for a bit. Is the needle jumping around, or drifting lazily up and down, or pretty much hanging around one point? If its jumping around, find a small clamp and pinch the hose lightely until it stabilizes.Blip the throttle a couple of times to be sure it still indicates properly.It must move fairly freely, just not jumpy.If it drifts around we will need to adjust the idle mixture screws. If its stable, we can proceed. So, write down exactly what the V-guage is saying( to the nearest 1/2* or even 1/4*) and the /associated rpm with it and the associated advance degrees. Next, advance the dist. 2 degrees per the lite. Did the rpm go up or down?Next put the rpm back to where it was before the advance was added. For the test to be meaningful the rpm has to remain consistently the same. Then again read the V-guage. Write all the numbers down,again. Now we analyze the results.Is the second vacuum number higher or lower than the first? If higher add 2 more degrees and repeat the rpm and V-guage readings.Keep doing this until the V-guage readings no longer increase. But if the V-guage results from the first test went lower, then take the 2* out that you put in there, plus 2*more.Again, keep taking out by 2s until you find the highest vacuum reading.Ok thats part one.(Now I dont normally, go through all the trouble of writing this stuff down.But Im asking you to, so that if you get lost, you can always return to the beginning. And also, you will be able to see the how things work out. Usually I just pull on the can until the rpm stops rising, then put the idle speed back, then repeat. The highest idle will usually be the point of highest vacuum.This is a shortcut.Same results.However, if the idle timing gets to be too high, the hot-start sometimes suffers, as the starter may have trouble, experiencing "kick-back", and possible failure.)
-Now, re-evaluate the idle quality and stability just like we did in the beginning. Is the V-guage needle stable? When you blip the throttle, does the rpm return nicely to the same vacuum reading? Does the engine sound happy?I realize this is a subjective question, but answer as best as you can. What is the new idle timing number? Theres a real good chance that the original 20* was close. Thats part 2 done.
-Now,climb in the saddle,and jam on the brakes, and put it into first gear.What happens? Rpm still stable? Idle quality still good? If yesses, Shift it from 1st to Neutral and back, several times. All good? Ok with brakes still jammed on, and trans in 1st, just feed it a bit of throttle, and back off.Still good? Ok, next blip it a bit. Dont go crazy, just a little blip.Still good? If at any time, the engine stumbles,coughs,hesitates or just generally isnt happy, we will have to pursue, and remedy that. Ok end part 3,done.Well almost, put it back into Park.
-At this point we have determined what the engine likes for idle timing. Do not drive it this way.Now I will await your report back.
-If at any time,you think that the idle mixture isnt right,or the needle starts to drift around, or you just want to fool with it, heres the procedure.First you need to know which carb-screws to mess with. IIRC you said you had a Carter on there,right? Ok first the mixture screws; Air cleaner probably off, standing in front of the rad, looking at the joint line where the carb meets the intake manifold, behind the T-stat housing.Pointing at you will be two screws with flat slots in them.They have little springs on them, visible just under the screwheads. They are referred to, in order of popularity, as; mixture screws,or idle screws,or idle mixture screws, or A/F screws,or pilot screws, or low speed screws, or pilot air screws........The list goes on.Ok next, you probably already know which screw controls the curb idle speed. Those are the only 3 screws we are going to monkey with.The mixture screws are always treated the same.So, engine off. We need to be sure the mixture screws are currently both adjusted the same.You will need to gently screw them in(cw), until they LIGHTLY bottom, counting the turns as you go.If they werent the same,return them to the starting point and make them so.Next, with trans in park, start the engine and warm it up.Next,increase the idle SPEED to about 2000ish rpm.Then screw each mixture screw in(cw) 1/2 turn.As you do this, observe the idle speed.If the speed went down, then put the screws back where you found them, and then turn them out(ccw) 1/2 turn each, again observing the idle speed. What we want is to find the highest rpm that the screws can produce.Generally this will fall between 1.5 and 3 turns out from lightly seated.If it doesnt, and the timing is close,and there are no intake leaks, then we will have to pursue the reason.Next, if the engine temp is ok, increase the idle speed to 2500ish, and repeat the adjusting procedure.Hopefully the results will be the same. Finally return the idle speed to where you started, and observe the idle stability and quality, both in Park and 1st.If all goes well, it will be right on.Thats usually all there is to it.