Camshaft Guru; Tell me where to start with jets

[x33rs]

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

[Steve Shauger]

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!

[Flying Undertaker]

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.

[x33rs]

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.

[Steve Shauger]

Originally Posted by Flying Undertaker

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. Don.

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....

[Lynn]

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.

[L78racer]

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.

[Mr70]

Good to hear and some great Holley info.

[Lynn]

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.