So I've been tuning in my truck after the cam swap and I noticed crusing in 2nd around 1500 rpm I get this surging feeling. Kind of like tapping the gas real fast. Is that normal with a bigger cam or something in the carb or timing? It didn't do it before the cam swap so it's something new. I hate to keep bugging you guys but everyone I know doesn't know what a carb is.
That's what a big cam does, makes it run rough at low rpm. could be a lean surge, could be a rich surge, my guess is lean. but I don't know everything about the engine, carb, timing, etc.
I agree Is it a Holley carb.? Double check for vacuum leak, put a vacuum gauge on and check to see if you have the right power valve. What engine do you have and cam did you install?
The bigger the cam, the less vacuum signal at the metering point. In this case I'd richen the off-idle circuit. What carb do you have?
Engine is a 1970351w with 70 heads 10-1comp ratio. Stealth dual plane intake Timing set at 12btc Carb is quick fuel 600 double pumper Vacuum is pulling 9-10 but fluctuates with the idle. Cam is an xe262 RPM Range: 1300 to 5600 - Valve Timing: 0.006 - Lobe separation (degrees): 110 - Intake Centerline (degrees): 106 - Valve Lash: Hydraulic - Duration: Intake 262/Exhaust 270 - Duration @ .050" Lift: Intake 218/Exhaust 224 - Valve Lift: Intake 0.493/Exhaust 0.5 - Lobe Lift: Intake 0.309/Exhaust 0.313 Is degreeded straight up and has a rougher idle than I thought it would If I let it idle for a few minutes and the rev it it its rough the first time like it's loading up at idle. Overall I'm pretty happy with the cam. The bottom end feels good and pulls up to 5500. Torque curve feels pretty flat but I don't like the surge and would like to tune it out if I can.
When your Harley Davidson motorcycle experienced surge problems,they could ALWAYS be remedied by fattening or enriching the low speed circuit.
Is this an automatic or a stick. My 63 340 horse corvette never saw anything below 2500-3000 around town , course it was a stick with 4,56 gears. you guys are way too easy on these things. A little rpm don't hurt em at all, right Jim? Seemed smooth to me. Sometimes it is not an engine problem, sometimes it's a right foot problem. Lippy
Even though that's a pretty "small" cam , you're still asking the engine to operate in an rpm range the cams not happy with , the short answer is to downshift & keep the revs up where it's happy..... the long answer is an air/fuel meter & the ability to modify all the circuits in the carb [idle/transition/main] , there's no simple answer & unless you can find someone w/extensive carb tuning experience , just downshift .. dave
I agree it's not that big over all but the cam that came out was .442/.450 so it makes the engine much different. But my electric choke maybe messing with me. I am going to try and reset it today even though it's 80+ degrees and see if that changes anything.
So I've tried it with the advance unhooked and it's the same maybe a little worse with the stumble. It's more like it's loading up or a miss. It's fine when accelerating and is only an issue at cruse.
Yeah it's stumbling at any rpm when it's not under a load now. Won't hardly start either. I'm going to pull the carb and look for junk in it.
The carb is only 2 years old but it sits for 6 months a year and this ****py ethanol gas has probably made it nasty. I need to start filling a 55 gallon drum from the gas station 20 miles up the road that sells pure gas.
Well I found trash in the carb and a vacuum advance with a hole in it. I love reman stuff that's junk from the start
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