Re: Carb Tuning
Posted: Sun Oct 07, 2018 9:22 pm
So when you are driving along steady speed, at cruise at a speed high enough to be on the pri main jets, what is the AFR?
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18-20" Hg. It was a stock '66 220 HP 289. The difference in advance curve for your engine vs. a stock (non smog) engine is sporty cam timing needs more timing at idle and below 1500 RPM. The stock engine timed at 6 initial instead of 18 and the primary spring let it advance from 6 degrees at 600 or 700 to 18 or so at 1500. Sporty and radical cams simply need more initial, but the curve above 2000 will be similar to a mild cam stock engine. Engines almost always want the same advance curve in the power band, usually adding 1-1/2 to 2 degrees per 1000 RPM from the torque peak up to the power peak and beyond. Some engine want more, some less, but they nearly all run better with a full RPM range curve than locked timing. Besides optimizing advance for best torque and power, when the advance mechanism does not hit a mechanical stop the weight and spring mechanism acts as a pendulous absorber and isolate the timing trigger from engine torsional noise.
Did you put a timing light on it after you added the 2 turns to check the amount of advance added? 2 turns is a significant change in timing advance on the canisters I've messed with.BobbyB wrote: ↑Tue Oct 23, 2018 8:00 am Between hurricanes and cold weather, I have not driven the car in over a week. The last change I made was to give the crane adjustable vacuum advance 2 turns clockwise to increase total vacuum advance. The change seems to have made it even better at cruise. I reduced the idle speed in park from about 1050 rpm to 1000 rpm. Afr gauge shows 12.5 in park.
Hope to take it for a spin in the next day or two, weather permitting.
Is there any reason not to add some stabil to the gas now since I doubt I will buy more before spring?
I use the blue cam alot, really aids in tip in. I've seen that a couple times and seems to be inconsistent geometry in the arms, it never cause me an issue to have it bottom out(maybe Tuner or Mark can chime in if it's a problem). You can always take some lift off the cam with a file or whatnot.GRTfast wrote: ↑Mon Oct 29, 2018 10:07 am Figured this is a decent spot to ask this question. I've been getting my primary accel pump (30cc) dialed in on my 850 double pumper. I have it working great, no hesitation on tip in, smooth gentle acceleration, or stabbing it (street big block chevy).
The combo it likes is a blue cam on the 2 hole with a 0.032 discharge nozzle. The problem is, the blue cam has so much lift that at wide open throttle, the nut on the adjuster screw is lifting off of the pump arm (the lever is traveling further than the throw of the pump). If I adjust so this doesn't happen, there is about 1/8th of an inch of free play in the pump actuation lever, which obviously doesn't. It seems to me that this is unavoidable with the blue pump cam because of the amount of lift it has. I see a few videos and tutorials that say to make sure you have .010 to .015 clearance between the pump arm and the screw at wide open throttle, but I can't achieve this without the aforementioned setting that causes a ton of free play prior to engagement. In short, it seems that a "correct" adjustment isn't possible with the blue cam. What am I missing?
Yes Mark put annular boosters in the carb for me, and helped me get the jetting and stuff right, he’s great. The before and after was a seat of the pants difference, which is significant.In-Tech wrote: ↑Mon Oct 29, 2018 10:12 amI use the blue cam alot, really aids in tip in. I've seen that a couple times and seems to be inconsistent geometry in the arms, it never cause me an issue to have it bottom out(maybe Tuner or Mark can chime in if it's a problem). You can always take some lift off the cam with a file or whatnot.GRTfast wrote: ↑Mon Oct 29, 2018 10:07 am Figured this is a decent spot to ask this question. I've been getting my primary accel pump (30cc) dialed in on my 850 double pumper. I have it working great, no hesitation on tip in, smooth gentle acceleration, or stabbing it (street big block chevy).
The combo it likes is a blue cam on the 2 hole with a 0.032 discharge nozzle. The problem is, the blue cam has so much lift that at wide open throttle, the nut on the adjuster screw is lifting off of the pump arm (the lever is traveling further than the throw of the pump). If I adjust so this doesn't happen, there is about 1/8th of an inch of free play in the pump actuation lever, which obviously doesn't. It seems to me that this is unavoidable with the blue pump cam because of the amount of lift it has. I see a few videos and tutorials that say to make sure you have .010 to .015 clearance between the pump arm and the screw at wide open throttle, but I can't achieve this without the aforementioned setting that causes a ton of free play prior to engagement. In short, it seems that a "correct" adjustment isn't possible with the blue cam. What am I missing?
I can get it to not bottom if I change the screw position, but then it doesn't actuate immediately when I start moving the throttle. I think the solution is going to involve reducing the lift of the cam.In-Tech wrote: ↑Mon Oct 29, 2018 10:51 am You know what, now that I think about it I didn't let those cars go, bottoming out, as it dawned on me that it might fubar the spring. It's been a while, did I change the screw position or file, I'll think about it and post back if I remember and nobody else has replied. Nice car btw.