Camshaft Guru; Tell me where to start with jets
 

Apparently, I cannot ask a short question. Even if I did, someone would ask for more info, so, I will just include all I know about this one. Looking for a good starting point on jets and power valve sizes.

I have been asked to get another 302 running good. Guess I did too good a job on the last one, and he referred a friend to me. Because I don't work on cars for a living, I just tell these guys I will track the parts, let them reimburse me and then ask for a donation to our Museum project. Works out well for everybody so far.

Here is what I am working on.

Original 302 motor that supposedly had only 20k miles on it. Suspicious why it would need rebuilt, but it was. Don't know if it was bored, and if so, how much. Don't know the quench. Don't know if they kept compression at or near 11:1. I wish I had more info, but here is all I have.

Still 302 crank, so 3 inch stroke.
Early angle plug iron heads installed.
Hooker Super Comp headers running through a repop chambered exhaust (I know, what a waste... but it isn't my car, so it wasn't my decison).
Factory Z/28 high rise.
Original (not to this car, but correct) 4053 carb jetted 68/76 and stock power valves.
Had a generic points distributor. Put it in my distributor machine and didn't reach full advance until about 4k rpm. I installed the correct guts (532 cam) and recurved it to get full advance in about 2900 rpm. Limited the full advance, so I can run a bit more initial. The vac cannister (stamped 201) did not start moving until 13 inches of vac, and did not fully engage until almost 16. Swapped it out for a B28 can that fully engages at 8 inches.

The carb was leaking something fierce both internally and externally. Ran so bad, I trailered the car here. Good thing. Checked the oil and it was two quarts high with tons of fuel in the oil. Drained the oil overnight, installed new filter and oil. It ran so poorly, I was afraid it had a bad cyl. But, compression test showed all of them to be 130# and all were withing 2#. I changed the plugs. As you can imagine, they were all black. All were gapped close to .060 which isn't going to work with points. I gapped the new plugs at .035.

Since this carb is not original to the car, I have another really nice DZ carb that I am going to install. I test ran it on the last Z I worked on (waiting for his original carb to come back from Eric... which by the way happened at lightning speed) and it ran perfectly. No leaks, great idle, etc. But, that engine was bone stock except for headers.

Other than the angle plug heads, and the headers, the other major mod is a mechanical roller camshaft.

Here is a link to the specs. http://www.compcams.com/Company/CC/c...?csid=305&sb=2

Says it has a rough idle.

Doesn't look that radical. Much higher lift than the 30 30 cam or the LT-1 cam, but duration seems to be close.

Finally.... here is my question. If you were installing this carb, what jets and power valve sizes would you start with? I am thinking 72 / 76 with 6.5.

I know the first question is: what vac do I get at idle? I don't know. Ran to crappy and leaked too much gas to get a reading. I realize I may have to pull the carb back off and change jets or pv after I get it running, just looking for a good place to start. On a bone stock 302 Eric recommends "6.5 primary and 8.5 secondary, 72 primary jets (68 was OEM, too lean) and 76 secondary". Just wondering if this cam is radical enough to deviate from that.

Thanks for any help. If I post up another long question, maybe I will get Dave to re-write if for me to make it more entertaining.

72/76 jets is a great place to start...are you starting this on an engine dyno or in a car?

6.5 Power valve will also be a good start. What is or was the vacuum on the 302? Since your

running super comps...you will need to be a tad richer in the jetting on the primary. 02

censor will help with zeroing in your jet setting. Not an expert like Eric but had to go through

same issue with my 302. Big cam/low vacuum {6.5} at idle so it was a 3.5 for me. Cross ram

was even harder to get right but you have to keep trying.

Dave
67 Nova Boy

Car ran so crappy and carb leaked so much fuel that I didn't even get a vac reading. If I had, it would be easy to figure power valve. Unless someone with experience with this camshaft has another suggestion, will start with 72 /76 and 6.5. After I get it running, I can check vac and go from there.

I have 72/76 jets setup for my Z, but use two 6.5 power valves. Was told to go with this setup by a hot rodder day two type guy. Don't know if it's good or bad, seems to work, but do get some surging issues. Might go back and try 6.5/8.5 setup this coming summer.

DITTO NovaBoy and Mr. Nickey Nova. Nothing trick about a Holley. It comes pretty much ready to go except for maybe a jet change or minor adjustments.

Correct Sammy...Holley comes with allot of backround testing and they are ready to use with

factory settings and go from there.

Dave
67 Nova Boy

Yep, Pete always tells me that.

holley questions...
 

I would check with Eric Jackson for help with Holley carbs..nobody better.

-wilma

Agree. Eric sent me an email. What a great resource.

I set them up here for various applications. What you have shouldn't be difficult to start with. You can subtract at least 10 degrees duration from the solid cam right off the bat so that camshaft really isn't all that big. The tighter LSA might make it choppy compared to 115 on a DZ cam, but it will shorten up and bring in the torque curve a bit sooner and feel stronger.

I run a similar flat tappet solid in our DZ, with 112 LSA, with other specs close to the 30/30, but with more lift and tight lash. Basically a cheater cam. I also run Hooker Super Comps. Everything else about ours is stock OEM issue with a true 11:1 compression.

I find the stock DZ intakes like a stagger jetting in the carb. Mine made a pinch more HP. The way the runners are designed prefers more jet on the driver side. Before I'd worry about that I'd concentrate on a basic setup and make sure everything is okay.

72/76 jetting is perfectly fine and should perform well enough to get things going. As far as power valves, a common misconception on them is that they have to be lower than the vacuum reading at idle or they'll flood the engine. Doesn't work that way. Fuel is only pulled through the power valve circuit when the throttle blades are exposing the transition slot and pulling fuel through the jets, only then does the power valve circuit become active. They do not work at idle. It's very important to make sure initially that your throttle blades aren't exposing more than about 1/8" of the transition slots both front and rear. Much more than that and you will be pulling fuel through the jets (and power valves if engine vacuum is low enough) and have a very rich condition at idle, and also makes your mixture screws inoperative.

If the car doesn't idle properly like this there could be one of a couple things going on. One may be that you need to create a small vacuum leak by drilling a pair of very small holes in the throttle blades so they can be closed properly. The other issue that I find most common these days, if trying to run this on 10-15% ethanol mixed gas is that the idle circuit may not be rich enough. 10% ethanol stoich is 14:1, not 14.7:1, and will sometimes act a little funky trying to run a very lean mixture with inconsistent idle. Almost every carb I do I have to richen the idle circuit to compensate. On our DZ I had to drill the idle feed restrictors for more idle fuel. I'll have to check but I think I ended up .002 or .003" larger. Every engine is a little different here and I use a wideband to dial things in combined with what the engine is telling me it's happy with and best drivability.

Getting back to the power valves, that cam you're using, if you have a true 11:1 compression, and the cam was installed at a proper ICL, the engine shouldn't have much trouble making at least 12 inches of vacuum at sea level. Mine makes 10" at 5,000 ft elevation and 13 inches at sea level. I'd stick with the 6.5 power valves until you get some driving in. What I find with too low of a power valve in most cases is tip in stumble because the PV circuit is delayed too much, and no amount of squirter tuning will get rid of it. You might be able to bandaid it and cover most of it up, but the PV is the real cure and will also help mid range throttle transitions. My engine still likes 6.5 PV's in it front and rear. Even trying 4.5's creates an off idle stumble.

I found with mine, I stagger jet the driver side up 2 sizes to compensate for the runner design of the DZ intake. I'm at 5,000 ft, and routinely drive the car to sea level so I make a compromise on mine so I don't have to keep fiddling with it. I run 70/72 front and 76/78 rear with the 6.5 PV's. Along with the idle circuit fattened slightly (we run strictly 91 pump gas) Throttle response is crisp and quick. With the wide band up here where we routinely see DA numbers near 8,000 ft in the summer, it cruises around town between 12.5 to 13:1 AFR. Idle is right at 13.8:1 AFR, and WOT hovers around 12.4:1. Wife drives it daily, plugs stay nice and clean, the engine seems to like it, and it knocks down 14 mpg around town and 17 mpg highway with an M-20 and 3.55's. When we drive down to sea level, the AFR's lean out about a full point, and it runs fantastic so I find no need to constantly tinker with it, I just live with it being ever so slightly rich up here on the mountain.
That's with Hooker super comps and a complete Pypes 2 1/2" transverse muffler system. Hope that helps a bit. More questions you can PM me or email if you wish. [email protected]
Larry

On the distributor, that looks pretty good and close to how I set them up here. On our DZ the only difference is I have my curve coming in a tad quicker at 2400 rpm and it likes 36 degrees total, with 18 initial. I also run a B28 vacuum canister with a simple modification on mine welding the slot to limit 10 degrees at the crank. I found mine likes the additional timing at idle so I run mine off manifold vacuum. I switched back and forth for a while between ported and manifold. Mileage was better around town, and idle was smoother with manifold vacuum so that's where I leave it. I'm still running points in it and Autolite plugs gapped at .035

X33rs


" What I find with too low of a power valve in most cases is tip in stumble because the PV circuit is delayed too much, and no amount of squirter tuning will get rid of it. You might be able to bandaid it and cover most of it up, but the PV is the real cure and will also help mid range throttle transitions. My engine still likes 6.5 PV's in it front and rear. Even trying 4.5's creates an off idle stumble."


I've had this issue which was caused as you state by too low # power valve. I chased this issue for months, years ago. Very informative post... Thanks Larry!

Camshaft Guru; Tell me where to start with jets
 

Lynn: My biggest concern is the 2 Quarts fuel dilution of the oil, that's a lot of fuel! Check your fuel pump, they've been known to fail and dump fuel into the oil from the fuel pump mounting area of the block. As for jets, I'd stick with 72 in the primary side until you get the engine to idle correctly, possibly reduce the secondary side to 72 in the future. New Camshaft specs are not too radical for a DZ engine as the original cam specs are .485 lift on both intake & exhaust sides with 254 degrees duration at . 050 lift. with a 114 degree lobe separation to allow better idle for emissions and 50 state usage. The newer cam is 236 degree duration at .050 lift, 18 degrees less. Disassemble the carb and clean with a bucket type carb cleaner, later using spray cleaner through carb metering block passages and air bleed and passages in the main body. Reassemble carb making sure to use correct metering block gaskets (most kits have 2 different style gaskets). Stay with the factory power valve values until you get the carb to idle smooth enough to obtain vacuum readings with a good working vacuum gauge. Adjust power valves to be between 1 to 1 1/2 inches below vacuum reading at idle in neutral. Always use NEW power valves unless you have a tester to insure that the power valve diaphragm wasn't damaged due to backfire as the original carbs did not have a check ball to prevent backfire damage. Ignition timing seems to be fine as is. Always use full intake manifold or carb baseplate vacuum advance hookup to canister on distributor, stay away from ported vacuum. Good luck, keep us updated on the progress. Don.

Something else you can do Lynn that I check with all Holley carbs here is flatness with the metering blocks.

I noticed you mentioned a large internal fuel leak. If you already checked the obvious (blown PV, transition slots not overly exposed, or dirt in needle and seat) and you're still having a serious flood issue, I find a warped metering block often a cause, especially on these 50 year old carbs. Meter blocks that aren't sealing properly cause all kinds of wonky idle issues and internal fuel leaks.

Holley used to make a tool to bend the meter blocks back into place. Yes sounds crazy but this was a problem even back in the day. I have one of these tools in a box somewhere I haven't found since I've moved but it's just as easy to chuck it in a vice.

What happens over years of cranking on the float bowl screws is that it draws in the corners of the meter blocks. If you run a straight edge across the block you'll find a lot of them bowed in the center. You can carefully chuck it in a vice in such a way to apply pressure and gently bow the meter block in the other direction, and let it rest for a few minutes. It's okay if it now bows slightly the other direction. It will push and seal in the center of the gasket better, and saves some of these hard to find meter blocks.

I also run a straight edge across the face of the carb, and often find the corners of the carb pulled out from the bowl screws. I lightly run a fine file across the face until I see the file contacts the entire surface, then clean and blow out all passages as necessary. I find this is most often the cure for old carbs that most people removed long ago for poor running problems they could never figure out.
Hope that helps.

I agree, two qts of fuel most likely came from the fuel pump leak into the block. If that much fuel had come from the carb, the cylinders would be washed and the car would be burning oil due to piston ring wear.


Lynn keep an eye on the fuel in the oil issue....

I will do so, but this carb was dumping gas in huge volumes, both internally and externally. You could barely keep the thing running. And, I am pretty sure the rings were washed out, as it had started smoking pretty good. After changing the oil and putting the new carb on it, I took it for a drive, and after about 4 miles it quit smoking. Checked the oil when I got back and it is clean and fuel free.

Put 11 gallons of 100ll. Runs awesome.

Thanks to all for the input. Especially the info on staggered jetting. I had heard about it, but didn't know which side got the increased jet size. Didn't get that involved on this one, as it ran so well, I didn't want to mess with it as it was running so well. Giant improvement. Eric told me to just put the carb on the way it was. I did, and was really happy with how it ran. Slightly lumpy idle at 950. Just enough to remind you it has a cam. Doesn't run that much different than the last stock 302 I worked over.

And yes, I used a "T" fitting in line on the choke pull off for vac source to the B28 can.

I set initial at 12 degrees. Mechical is 26 for a total of 38. May be too much for pump gas, but runs great on the aviation fuel. Limited the vac advance to 10 degrees and it idles great there.

After setting the timing, all I had to do was adjust idle speed and mixture screws.

if the carb has been sitting or has not been freshened up the needle and seat assemblies are probably leaking- not a sticking float- but fuel leaking past the 'o' ring on the needle assy. this will cause very rich condition that is hard to find.

Good to hear and some great Holley info. :burnout:

Oil is already black, which could just be a result of so much fuel getting in there from the carb. But, because this car will be residing over an hour away from me, I decided to change the fuel pump. This car does have the original engine, but has a few mods, so assembly line correc isn't an issue. The last few mechanical Chevy pumps I got put out way too much pressure. What is a good pump to buy that will only give me about 5 to 7 psi? Last one I checked pressure on was 11 psi.

I know I asked this before, but couldn't find the thread. Fuel pump will need the outlet fitting in the correct position to accomodate the 3 piece fuel line.