dialing my 318 in finally!

[zinser72]

I recently got my 318 on the road, heres my combo in detail or skip to the bottom paragraph for the short version:

Engine:
'72 318, .030 over, kb167's zero decked, scat i-beam rods, forged crank, fully ported EQ heads with 2.02 intakes, voodoo hyd roller cam (.535IN/.550EX 231IN/239EX dur @ .050) 10.1 static compression, roller rockers, 978 dual springs, msd street fire box with electronic ignition, rpm air gap intake and, a holley 750 double pumper with proform main body and billet metering blocks with 4 corner idle adjustment.

Carb setup:
mains 73, secondaries 82, power valve is 4.5 in/hg, primary air screws are 1 7/8 turns out, sec are 1 out. secondary jets are on standoffs, primary throttle plates are drilled about 3/32" one hole in each. primary bowl level is 2/3 up sight glass and secondary level is halfway.

Timing:
18* initial, mech curve starts to ramp up at about 2500 and hits 36* all in at 3800.

i wanted to hook up the vacuum advance but when i put a gauge on the ported vacuum port in the side of the metering block it stayed at 0 while driving around. direct vacuum gave me these numbers: idle 12", cruise 15", and coasting (4spd) 20"

shouldnt ported vacuum be active while your driving but be zero at idle? im confused. i just want to get the vacuum advance working to improve its manners and it also seems a little lean which i think is weird. i havent even got on it hard yet because it feels like its bogging and i dont want to cause any issues. Any input at all is greatly appreciated, thanks in advance! :thumblef:

 

[67Dart273]

I'd say we need a photo of your carb. Maybe you have the wrong port. The other possibility is that either the metering block/ body has a plug or a flaw, or even a bad gasket.

You are right, a ported vacuum fitting SHOULD bring up vacuum as you drive around. You should also be able to bring up RPM to a "high cruise" setting, hold the throttle there and observe vacuum

 

[zinser72]

thanks for the quick response! thats the reassurance i needed before taking it apart to look, ill see if i can get a picture up. if it worked i circled what i think is the ported vacuum in green. the blue tip sticking out from under the bowlis the plug on the direct port that i got readings from

 

[zinser72]

also i just took it for a ride and i eased down on the gas past the hesitation (2-3k) and it popped so i let off right away. it sounded like it backfired out the carb. the plugs look a little lean. maybe whatever is blocking that port is also causing an issue with the carb?? im open to any suggestions

 

[crackedback]

ignition curve is too slow. It should be ALL IN where it just starts to feed in with your set up. I'd be looking for lighter springs.

 

[zinser72]

will that cause the pop as well? how early is too early to be all in? i will look into that as well, i might even have the springs i need laying around

 

[OldmanRick]

We're really taking some "fine" tuning issues here. A lot of your numbers look decent, especially as far as the vacuum with that cam. I'm wondering how lean you are on the primary side with the drilled plates...That could be a issue, especially at the 1.7/8 A/F adjustment and still acting lean. I'd prefer the float levels a little lower, but a lean condition can also require the higher adjustment. My personal liking would be a primary PV in the 8.5" range from the info you've given. I may disagree a little with "cracked" as far as the timing curve, considering you seem to have a pretty high compression ratio. As far as the vac advance, i'd get it running right without that first, and then try to add it later in the tune.

 

[zinser72]

4.5 to 8.5 is a big jump! what does that do exactly? its cheap and easy to try i just like to understand what i'm doing as well...doesn't it temporarily "increase" the main jet size when accelerating? i don't have much experience...only 19 but trying to catch up with you guys! the knowledge base in this site it amazing! thanks again guys

 

[swinger340]

I had a 340 that was popping as the secondaries started to open. Fattened up the secondary jets and it went rite away. 72 P 84 S with a 6.5 PV

 

[zinser72]

i will keep that in mind as well! right now my plan is to take it apart today and track down why the ported vacuum is plugged. maybe thats contributing to other problems. then i will try a bigger PV and upping the secondaries. its just hard for me to believe i need to throw all this fuel at a 318!

 

[OldmanRick]

I may disagree a little with "cracked" as far as the timing curve, considering you seem to have a pretty high compression ratio.

After rereading the thread this morning, i need to backtrack just a little on the above statement. I like the numbers as far as it should be able to run good with the one's you used, but the curve itself could be brought in a little earlier.......Maybe starting and totaling approx. 1000rpm's sooner.

As far as the power valve, it allows leaner metering during the idle and cruise operation, and then allows a full fuel load during heavy acceleration. The general consensus is to use a opening rate with 1/2 of the idle vacuum produced. I personally prefer a little tighter spread on moderately cammed/vacuum combinations. Just keep in mind, it's either open or shut, and as long as the majority of your driving, except heavy throttle, keeps it above that vacuum level, a higher opening wont be a issue. It basically just lets you get to power enrichment with less throttle opening.

There is another member here dialing in his carb that has a proform body, and i'm coming to realize the jetting requirements tend to be a little different because of air bleed sizes, so i shouldn't comment on specific jet numbers.

One last thought. If you do change the timing, do that first and then proceed with the carb adjustments. And, i'd lower your float adjustments to just a trickle at the site plugs before really fine tuning the carb.

 

[moper]

I think I'd first look at the power valve. If you're pulling 12 at idle (is it a 4sp or auto?) then you need a much higher valve than 4.5. I'b install at least an 8.5, then drive around with a vacuum gage taped to the window so you can watch what the vacuum level does and when. Popping sounds to me like too lean on tip in - the accelerator pump covers the movemnt of the arm as the throttle is moving, but the PV needs to enrigh when the pump flow stops.

 

[1970Duster]

I know this doesn't help but that's the exact same cam I have in my 340 lol. How do you like it (minus the vacuum problems).

 

[zinser72]

that will be my next step, it is a 4 spd. i spent today changing advance springs and fixing another issue that came up with the car. i got the curve to be 18* initial and be all in 36* at 3200 rpm. carb is next but it already runs a little better. thanks guys! i wouldve never though PV is the first change. ill give it a try and report back

 

[zinser72]

well i havent really USED it but so far so good. has a good sound to it and not too radical, im very happy with it in my combo

 

[zinser72]

so i swapped out the power valve for a 8.5 and while i had it apart i investigated the lack of ported vacuum and it seems the proform main body doesnt have it. where do i go from here?

i have been researching it and it sounds like the main body can be drilled for ported vacuum, has anyone heard of or done this themselves?