My set up. SFT cam. 259/266. Timing all in by 1500. Stick car. Here’s the issue that I have been fighting for several years. My car is a street/strip car. When cruising just off idle, between 1300-2000rpm, I’m getting a “buck”, not a miss, a buck. If I give it a bit more gas, It’s as smooth as you can ask for. Full throttle is also perfect. It’ s Just the frickin’ buck that has me stumped. IFR’s. .035”. HSAB’s. .033”. LSAB’s .073”. PV is a 4.5. Idle is 950 rpm. Oh, Victor intake with RPM heads. Suggestions??
What first and axle gear ratios do you have? Why is the timing “all in” by 1500??? That’s not a good way to do it IMO.
Two other questions. What ignition are you using and how did you come up with a 4.5 power valve?
. Timing is all out for throttle response. Gear ratio is 4:56. Power valve was determined by idle best vacuum (8hg) then divide by two. 4.5 got me close so I used it. Ignition is Digital MSD.
Never set power valve opening by idle vacuum. It’s DEAD WRONG. It’s been wrong since day one and it gets repeated over and over. Check your idle vacuum at CRUISE and then start at two numbers lower than your cruise vacuum. That’s where you start tuning power valve opening.
Also, you need to fix your timing curve. In fact, that needs to be corrected first. With those light springs you loose control of the weights and the timing will be bouncing all over ever time you touch the throttle.
You might think you have better throttle response with basically no timing curve, but you don’t. What happens under a load is far different than what happens under a load.
That bucking is telling you that you have issues. With a 4.56 gear you should be able to creep along at walking speed and not buck.
Between your timing curve and that late opening power valve you are confusing the engine. BTW, when you correct PV timing it will make other changes necessary on your carb tune up. You will probably end up rich on transition. You’ll have to deal with that.
